ZOONOMIA; OR THE LAWS OF ORGANIC LIFE. ZOONOMIA; OR THE LAWS OF ORGANIC LIFE. VOL. I. By ERASMUS DARWIN, M.D. F.R.S. AUTHOR OF THE BOTANIC GARDEN. Principiò cœlum, ac terras, camposque liquentes, Lucentemque globum lunæ, titaniaque astra, Spiritus intus alit, totamque infusa per artus Mens agitat molem, et magno se corpore miscet. VIRG. Æn. vi. Earth, on whose lap a thousand nations tread, And Ocean, brooding his prolific bed, Night's changeful orb, blue pole, and silvery zones, Where other worlds encircle other suns, One Mind inhabits, one diffusive Soul Wields the large limbs, and mingles with the whole. NEW-YORK: Printed by T. & J. SWORDS, Printers to the Faculty of Physic of Columbia College, No. 99 Pearl-Street. — 1796.— DEDICATION. TO the candid and ingenious Members of the College of Physicians, of the Royal Philosophi- cal Society, of the two Universities, and to all those who study the Operations of the Mind as a Science, or who practise Medicine as a Pro- fession, the subsequent Work is, With great respect, Inscribed by THE AUTHOR. DERBY, May 1, 1794. CONTENTS. PREFACE to the American Edition. Lines to Erasmus Darwin. Author's Preface. Sect. I. Of Motion. II. Explanations and Definitions. III. The Motions of the Retina demonstrated by Experiments. IV. Laws of Animal Causation. V. Of the four Faculties or Motions of the Sen- sorium. VI. Of the four Classes of Fibrous Motions. VII. Of Irritative Motions. VIII. Of Sensitive Motions. IX. Of Voluntary Motions. X. Of Associate Motions. XI. Additional Observations on the Sensorial Powers. XII. Of Stimulus, Sensorial Exertion, and Fibrous Contraction. XIII. Of Vegetable Animation. XIV. Of the Production of Ideas. XV. Of the Classes of Ideas. XVI. Of Instinct. XVII. The Catenation of Animal Motions. XVIII. Of Sleep. XIX. Of Reverie. XX. Of Vertigo. XXI. Of Drunkenness. XXII. Of Propensity to Motion. Repetition, Imi- tation. XXIII. Of the Circulatory System. XXIV. Of the Secretion of Saliva, and of Tears. And of the Lacrymal Sack. SECT. viii CONTENTS. Sect. XXV. Of the Stomach and Intestines. XXVI. Of the Capillary Glands, and of the Mem- branes. XXVII. Of Hœmorrhages. XXVIII. The Paralysis of the Lacteals. XXIX. The Retrograde Motions of the Abserbent Vessels. XXX. The Paralysis of the Liver. XXXI. Of Temperaments. XXXII. Diseases of Irritation. XXXIII. - of Sensation. XXXIV. - of Volition. XXXV. - of Association. XXXVI. The Periods of Diseases. XXXVII. Of Digestion, Secretion, Nutrition. XXXVIII. Of the Oxygenation of the Blood in the Lungs and Placenta. XXXIX. Of Generation. XL. Of Ocular Spectra. PREFACE PREFACE TO THE AMERICAN EDITION. IN the progress of observation and experiment in physics, within a few years, such a number of new and important facts have been brought to light, that many philosophers have believed the people of the pre- sent day were possessed of a, great deal more know- ledge than the moderns of the three last centuries, or their ancient predecessors. This opinion, in particular, has been deemed well founded, and true in its respect to medicine, which, at this time, is not only considered susceptible of new ex- positions and interpretations, but of being greatly im- proved and enlarged, both in theory and practice. And although among those who think thus are reck- oned most of the original and clear-sighted geniuses of our time, yet there are not wanting some, and those men of talents and reputation too, who are in the ha- bit of thinking, if the ancients knew not quite as much as ourselves, yet their writings contain the leading hints, or great outlines of almost every thing discover- able, either directly expressed, or signified in allegori- cal terms. This literary superstition has been carried a great way; and if it had stopped at declaring the Iliad the best of possible poems, or the Phillipics the most finished of the rhetorical productions, I should not at this time have troubled myself to contradict it. But when these enthusiastic admirers of antiquity declare, that, in matters of science as well as of letters, the subjects of enquiry have been exhausted two thousand years ago, a and x PREFACE TO THE and that no idea can be started which is not an imita- tion of something, that a Greek or a Roman, or some body else, had thought before, I own I am a little dis- posed to believe their assertions are grounded neither in truth nor in the nature of things. For why must we resort to the PLATONIST, STOICS, and PERIPATE- TICS, for doctrines which the ACADEMY, the PORCH, and the LYCEUM never knew? These remarks are made in consequence of an opi- nion propagated and believed by some, that a certain method of reasoning upon medical subjects, and of practicing physic, introduced now of late, as many be- lieve, which is already pretty well established, and ac quiring rapidly more and more adherents, is in fact but a revival and new-modelling of the opinions and pro cedure of the METHODIC SECT, founded by ASCLE- PIADES, the cotemporary of MITHRIDATES and CRASSUS. In order to know whether this opinion is well found- ed, I shall enquire what the philosophy of the Metho- dic Sect was. Its founder, ASCLEPIADES, adopted that philoso- phy, whose foundation had been laid by ANAXAGO- RAS, EMPEDOCLES, and HERACLITUS, and which was afterwards wrought up into the Atomic System, by LEUCIPPUS, and DEMOCRITUS, of the Eleatic Sect, who, rejecting all metaphysical explanations of the causes of things, undertook the interpreting nature, from the laws of matter and motion. This was af- terwards commented upon, enlarged, and adorned by EPICURES, so as to form, what was afterwards called the Epicurean Philosophy. What the details of this are, may be seen in DIOGENES LAERTIUS, in BRUCKER, and his translator ENFIELD, as well as in the poem of LUCRETIUS, who has confessedly attempted a poetical display of these very doctrines. A general view, comprising a mere sketch of the system of this Avτoδιδαητoς as far as connected with the present subject, is xi AMERICAN EDITION. is all I shall offer here. An Epicurean would explain himself thus :—" It is clear, from the changes which natural bodies undergo, that there is a perpetual for mation and destruction of them going on; there must then exist matter of which these things are formed, and into which they are resolved; and hence proceeds the conclusion which is the ground-work of the system, that a thing can neither be made out of nothing, nor reduced to nothing. ' Nullam rem e nihilo gigni divi- nitus unquam’ The universe, therefore, as to its con- stituent atoms or particles, was always as it is at pre- sent; and consequently matter is eternal. The work- man cannot perform any thing without materials; and these self-existent materials, in the decay and renova- tion they undergo, account for the phenomena of na- ture and of art. If things were created out of nothing, then every kind should proceed from each, and the greatest irregularity ensue; men should be produced in the sea, fifties on the land, and cattle in the clouds; generation would be useless, and food unnecessary: if they returned to nothing, then, in the course of past ages, through waste, consumption, and loss, much must have vanished to non-existence, and have been completely annihilated. But neither of these suppositions is true, since, out of the wreck or ruin of one being or exist- ence, nature, we know, without an act of creation or annihilation, can work up the old materials into a new fabric. " All existences in nature are referable to two kinds, 1. Bodies; and, 2. The inane, or void in which they exist. " Our senses satisfy us of the existence of bodies, as also do their actions passions, and resisting powers; par- ticularly as they operate upon each other, and upon our touch: " Tangere enim et tangi nisi corpus nulla potest res." " From the existence and motion of bodies is in- ferred the existence of space; and the effect of bodies operating upon each other is denominated "an event;" and xii PREFACE TO THE and if there was not a void there would not be a possibility of motion; for if a plenum existed, then every portion of space being closely impacted and wedged with solidity, the most uniform rest and dead stillness would pervade the whole of nature. " As to bodies, they either consist of elementary atoms, or of substances formed from these; and these primordial particles, notwithstanding some appearances to the contrary, are simple, solid, and indivisible. " Sunt Igitur solida, ac sine inani corpora prima." " All these atoms possess the same general proper ties, and do not differ from each other in any essential respect. Though, from their different operations up- on the senses, is inferred a difference among them as to size, shape, and heaviness. Their figures, in parti- cular, are varied in an endless manner, so as to take on every mechanical form; but in all these cases they are still infrangible and incapable of farther division. " Each atom contains, within itself, an active energy, or internal force, by which it is either constantly in motion, or making an effort to move; and this is de- nominated gravity. These atoms, impelled by gravity through void space in curvilinear courses, strike against each other, exercise repelling powers, and produce vi- bration or agitation; and as this gravitating power is essential to matter, it can never be inactive, but must be always at work, and has been so from eternity. “ Every compound body, being made up of indivi- dual atoms, therefore possesses the united energy of them all, which energy is the sole agent in nature; but by reason of their different figures, their varied magni- tudes, and particular situations, it is variously modifi- ed; as when the atoms are hooked or rough, motion will be retarded among them, and be facilitated when they are round and smooth, as in the principles of fire and animation. Bodies thus being composed of atoms, derive their actions from the energy inherent in and proceeding from these atoms. “ All xiii AMERICAN EDITION. " All alterations happening in bodies, whether in Their shape, hardness, sweetness, &c. are ascribable to the change taking place in the arrangement, disposi- tion, &c. of the constituent particles; and thus poro- sity, transparency, elasticity. malleability, &c. are to be accounted for in the same way. Gravity being an essential property of matter, all corpuscules, and all bodies formed of them, must be heavy. " Thus, from these properties of bodies, their sever- al combinations and mechanical operations, arise other more complex phenomena, referable however to the principle of motion, such as the heating of bodies from the influx of soft, round and smooth particles; the cool- ing of them, from the ingress of atoms of opposite and ir- regular figures; even sensations, both of the pleasureable and painful kinds, motion, rest, and time itself, are con- tingences to bodies. In short, the whole phenomena of the production, growth, nutrition, decline, and dissolution of bodies, is to be ascribed to an alteration of arrangement in the particles, and to their addition or substraction. " Minerals, plants, and animals were thus produced in the beginning, according to these mechanical laws of matter and motion, and so was the world they compose and inhabit. They continue to propagate their kinds in regular ways, because nature has become accustom- ed, by habit, to produce them in an order so uniform as to look like design. The eye, however, was not made for seeing, nor the ear for hearing; but having been accidentally formed in such a way as to answer these purposes, the sentient principle within, which is co-ex- istent it with the organization, finding them fit for the purposes of sight and hearing, makes use of them ac- cordingly. " Sensation, proceeding from the arrangement and texture of particles, is to be ascribed to their peculiar magnitude, shape, combination, &c. so that instead of being an original property of matter, it is, in fact, only an xiv PREFACE TO THE an occasional quality. Death is the privation of sensa- tion, in consequence of the separation of the sentient principle from the body: and this sentient principle, when a man dies, is decompounded into its simple atoms, loses its sensitive powers, and goes into other forms and combinations. The foul, in this respect, re- sembling the eye, which is no longer capable of per- forming its functions than the connection of its or- ganized texture with the body lasts." What ASCLEPIADES did, was to apply the princi- ples of the Epicurean Philosophy to medicine, and this he did with much ingenuity and acuteness. Building upon that hypothesis, he supposed the human body composed of Epicurus' ultimate atoms, which, by their figure, proximity, and arrangement, enabled it to per- form its functions; and in a particular manner, that health consisted in the symmetry and permeability of certain passages through the firm parts, which he called pores; and the closing up, or obstruction of these, consti- tuted disease. He imagined the fluids to be formed of particles, varying in figure and size, and thus making all the varieties of them, from the thickest blood to the most attenuated animal spirits. And when these fluids moved freely through their pores, the body was sound; but when they were too narrow, so as to pro- duce stagnations, or so oblique as not to be readily passable, then indisposition ensued. Such were the leading principles of ASCLEPIADES, and he had many followers, among whom THEMISON of LAODICEA was the most eminent. He rejected most of the subtle and laboured reasonings of his master, and, declaring such minute investigations were useless, affirmed, without defending to particulars, and bur- thening himself with details, a physician need only make himself acquainted with the general principles of dis- eases. These, he said, all belonged to two classes. 1. Those proceeding from laxity; and, 2. Such as were caused by stricture. All that was necessary to be done, therefore, xv AMERICAN EDITION. therefore, was to ascertain to which class any given. disease belonged; and then, if to the former, to pre- scribe astringent; if to the latter, relaxing remedies. The regular and systematic plan which THEMISON and his numerous followers adopted in their practice, differing very widely from the conjectural and uncertain mode of other physicians, caused them to be called METHODISTS; and they are to this day known in his- tory by the name of the METHODIC SECT. While THEMISON was reflecting upon his system, and endea- vouring to advance it to maturity, he died, and the un- finished work was taken up and completed by his fol- lower THESSALUS. He lived in the time of NERO; and having rejected, as frivolous, all the opinions of his predecessors, he declaimed, with vehemence and fury, against the physicians of all ages, and offered to instruct a beginner in the art of medicine in the short duration of six months. He, with a degree of arrogance and impudence, of which, as no parallel is known to have existed in ancient times, it can only be found in the history of modern quackery, took upon himself the appellation of ialpovixiV, or the conqueror of physi- cians. After THESSALUS the sect began to decline and dwindle, and although SORANUS, JULIAN, and MOSCHION retarded for a while its downfall, yet it was totally absorbed and lost in the Galenic Doctrines which followed. Thus, from an examination of the Methodic System, it is evident the explanation of every thing in the ani- mal economy is attempted upon PRINCIPLES OF ME- CHANISM only. The first notice of any thing else requisite to give life, and regulate its functions, seems to have occurred to HIPPOCRATES, the cotemporary of DEMOCRITUS and LEUCIPPUS. The to 6»op^» of this sagacious ob- server, as the interpretation of the word imports, ob- viously means an exciting power in animals: and the effects xvi PREFACE TO THE effects of animation resulting from this, imperfectly known, and badly explained, doubtless give rise, ac- cording to the opinion and judgment of the different writers, to the Nature of SYDENHAM,* the Aura Vi- talis of VAN HELMONT, † the Vis natura Medicatrix of GAUBIUS, ‡ the Anima Medica of STAHL and NICHOS,§ and the learned and curious treatise, enti- tled Impetum Faciens, of KAAUW BOERHAAVE. ‖ And here it is worthy of remark, that from HIP- POCRATES to BROWN, all writers entertain the opi- nion of a principle or power within, existing as the cause of life, as appears by the active signification of all their terms; whereas the idea of the Brunonians is, that the organized animal solid possesses no internal energy, and would always remain inactive, unless excited by stimuli from without; they therefore speak of the vi- tal capacity in the passive voice, as susceptible of being acted upon. HERMAN BOERHAAVE, in his account of the dis- eases of a lax and of a rigid fibre, seems again to relapse into the mechanical consideration of these things; but HALLER, by his numerous and luminous experiments on sensibility and irritability, led the way to a right mode of pursuing and understanding such enquiries. The attention of Hoffman had been turned to the consideration of the nervous system, as influencing dis- eases, more particular than any other person; and from his writings were probably taken the hints which ter- minated in CULLEN'S doctrine of Excitement and Col- lapse, in his Physiological Tract; ¶ enlarged afterwards, and * Opera Passim. † Equidem sciant Spiritum esse al'quem illud impetum faciens Hippocrates, vitæ ciavum manu sua tenens (Ort. Medicin. p. 724.) ‡ Who quotes Hippocrates lor the idea (Sect. 649.) couched under the term of auloxplsia. § Animam esse Gubernatricem, &c. &c. Oratio de anima Modica. passim. ‖ Lug. Batav. Luchtman's, 1745. (Chap. 2.) ¶ Institutes of Medicine, § 126 to 135. " From what has been now said of the excitement and collapse of the brain, it will ap- xvii AMERICAN EDITON. and applied to practice, in his chapter on vesaniæ, (First Lines, § 1544. and seq.) as well as the observa- tions in his letter on the recovery of persons drowned: (p. 4.) " Though the circulation of the blood is necessary to the support of life, the living state of animals does not consist in that alone, but especially depends upon a certain condition of the nerves and muscular fibres, by which they are sensible and irritable, and upon which the action of the heart itself depends," &c. And also the remarks on the effect of stimuli in keeping up the action and energy of the brain* at all times, in his treatise upon the materia medica. JOHN HUNTER had been speculating too on this subject. In his experiments on animals, with respect to their power of producing heat, he has brought curious and important facts to view: though his reasoning on them is in some instances inconclusive and exceptiona- ble, in others quite unphilosophical. This enquiry was intended as a counterpart to the experiments of BLAG- DEN and his associates in the heated chamber, on the power of the human body to produce cold in high temperatures. He ascribes a great deal, throughout his performance, to the stimulant action of cold, and to the exhaustion of the whole of the powers of life in freezing animals, by their efforts to produce heat; he even ascribes the attempt of his poor victim, the dor- mouse, to get out of the vessel in which he was to be frozen to death, to the rousing of animal action by cold! He seems to take little notice of the vital organs, the fire-place whence the constitution receives its warmth; nor regard much the condition of the respiratory func- tion in any of the creatures he operated upon, nor the pain they endured, and the changes in their economy consequent upon it. The experiments on the egg, b frog, pear that we suppose life, as far as it is corporal, to consist in the ex- citement of the nervous system, and especially of the brain, which unites the different parts, and forms them into a whole." § 136. * Materia Medica, p. 67, &c. xviii PREFACE TO THE frog, eel and snail, may be as well explained on the idea of the increased susceptibility of impression, pro- duced by the subduction of stimuli, and by an extra- ordinary exertion of the respiratory organs causing a greater evolution of heat, as upon the author's hypo- thesis, which may be summoned up in this general conclusion; that cold produces its effect in suspending the voluntary actions, by acting as a sedative to a cer- tain point; beyond which it seems to act as a stimulant, exciting the animal powers to exert themselves for self- preservation. It will be evident to him who reflects on what has been related, that the EPICUREAN SECTARIES en- tertained no other than mechanical notions concerning the production, actions, and changes of bodies; and that HIPPOCRATES and his followers, though consi- derably more advanced towards the truth, had gone no farther than to observe solitary and individual facts, ar- range these into detached sentences, or insulated apho- risms, sometimes intirely true, and some containing only a mixture of truth; or frame strange and whimsical hypotheses, by aid of which, as general principles, they attempted to explain things; and the most forward of them seems to have done little more than trace the cor- poreal functions, by partial induction, to the aic-e^pa*, x*Go*nto> or COMMON SENSORY. Such was the condition of medical science, until nearly twenty years ago, when, in that very place where spasm, reaction, and vis medicatrix natur æ were flourish- ing in full vigour, under the assiduous cultivation of CULLEN, they were nipped and cropped in the blossom, and nearly eradicated as noxious, by the improv- ing hand of BROWN. From the intimate acquaints ance which BROWN, or BRUNO, as he called himself, had with the published writings, and probably with the private opinions of CULLEN; from his academic habits, his erudition and knowledge of every thing passing at the University of Edinburgh, he must have xix AMERICAN EDITION. have had great opportunities, as well of learning all that was printed in physic, as of studying the de- fects, and detecting the weakness of that professor's doctrines. He told the writer of this preface, that he ventured one day to talk to CULLEN on the incom- prehensible ideas of atony and spasm existing in the same vessels of the body at the same time, and thereby provoked him to manifest signs of impatience and dis- pleasure. A coolness took place immediately, which increased at last, by successive and mutual aggrava- tions, to rooted aversion and deep opposition. And to this irritated state of BROWN'S mind, indignant with a sense of unbecoming treatment, is to be ascrib- ed no small portion of that resolution and energy with which he laboured out a System of Medical Philoso- phy, which, though not free from errors, borrows, however, none from CULLEN. On the publication and contents of the first edition of the Elementa Medicinæ of this author I shall be a little particular, on account of the scarcity of the work, and of the gratification it may afford to an enquiring mind to learn the progress of useful discoveries. It was published in 1780, and was dedicated to Sir JOHN ELLIOT; but this dedication was withheld from the second edition. After stating his twenty years labour in learning and teaching physic, he observes, it was not until the fourth lustrum that some dawning of light broke in upon him. The opinion that in the phlegmasiæ of nosologists, local affection was not the cause of pyrexia, but, on the contrary, a symptom consequent upon a previous general excitement of the whole constitution, appears to have been early adopted by him; and from his own personal sufferings in erysipelas, cynanche tonsillaris, catarrh, and synocha, and from his perusal of what ever had been written by MORGAGNI, TRILLER, and other candid authors on these subjects, and on pneu monia, he was confident his idea was right. He xx PREFACE TO THE He, at this time, proposed the doctrine of cold pre- disposing the body to be operated upon in a powerful manner, and to a morbid degree, by subsequent heat; which, indeed, may be regarded as one of the most important practical truths in medicine. He calls in question the propriety of forming opi- nions of the nature of diseases by their symptoms mere- ly, and boldly adopts the method of judging from the "lædentia and juvantia." He offers well-founded criticism on nosological ar- rangement, and shews wherein, through want of dis- tinction between universal and local diseases, a number of these had been chilled wrong. On examining the phlogistic exanthemata he con- tends, that in mealies and scarlet fever, as well as in small-pox, the general indication of cure is to dimi- nish the inflammatory diathesis, without the least re- gard to the particular nature of the contagion, or the stage of eruption; but these are carefully to be distin- guished from the plague, and other eruptive diseases of a totally opposite character: and that without at- tending to the peculiarity of the respiration, or the pre- cise nature of the morbific cause, the certain things to be attended to are, How far the diseased condition de- viates from health; and in what degree the living body approximates towards death. The exanthematous symptoms in the two classes of complaints, varying in each, their form only, and not their nature. Having proceeded thus far, he declares that diseases of the same type or class are to be relieved, or cured, by the same mode of treatment; and that the volumes of diagnostics, and the endless distinctions of nosology, in spite of the authority of even BAGLIVI and SY- DENHAM, when opposed to clear reason and matter of fact, ought to be disregarded. He expresses his apprehensions too, left the infinite distinction of diseases should lead to a mode of practice equally diversified, and have a very baneful effect upon materia medica and prescriptions. In xxi AMERICAN EDITION. In his remarks upon predisposition to bad health, he avers that no person ever suddenly became sick, but that gradually a predisposition was created by the agen- cy of the exciting powers, and out of this predisposi- tion grew the disease. Of this he gives examples in the phlogistic exanthemata, wherein he says, a high degree of excitement produces the disease, a lower pre- disposition, and a still lower health: the means, there- fore, conducive to the latter of these he thinks so sim- ple, that the use of the common nosology is intirely superseded. Proceeding upon this plan, he distinguishes local from universal ailments; both of which are confusedly classed together, in the different nosological arrange- ments. This led him to an examination of hemorrhagy, which, if attended in the beginning with phlogistic diathefis, he thought always became eventually asthe- nic, and in this enquiry it was that he was induced to call in question the existence of plethora, as a cause of hemorrhagy, and to reject altogether the notion of a vis medicatrix naturae as an agent in the animal system. This first edition of the Elementa is an unfinished work, and comprehends the details of his doctrine no farther than sthenic form of diseases. Among these he there ranks hemorrhagy, especially menorrhagia, hæmorhois, epistaxis, and apoplexy; an arrangement which he afterward considered wrong, and altered ac- cordingly in the following editions, by placing them all in the asthenic class. Such, he tells us, was the train of ideas passing in his mind as he reflected upon the animal economy; and upon these considerations did he judge himself war ranted in undertaking an explanation of the subject, different in many respects from any thing done before him. He declares, throughout the whole, he never de- scends beneath his dignity to animadvert upon particu- lar xxii PREFACE TO THE lar persons; though in certain cases, where almost im- plicit faith and idolatrous reverence had been given to certain authors, he has freely attacked and refuted their opinions. He apologizes for the plainness of stile and manner with which the performance is written, espe- cially, since to avoid the contagion of opinion, he had read no medical book for five whole years, and had scarcely consulted the monuments of ancient elegance for twenty. There is a great deal of animation and force in his argument against plethora, from the ninety-fourth to the ninety-eighth section, which he concludes with this challenge: " Si sit quod ad hoc respondeas, re- sponde STAHLI aut jube JUNCKERUM." In the hundred and fourth section he opposes, in de- cided terms, the tonic or astringent operation of cold, particularly as causing constriction of the skin; and repeats the same in several places, (§ 180—182) de- nying that it acts as a stimulant. In his reasoning against lentor in the fluids as a cause of disease, he breaks out into the following spirited exclamation: " Quam inselix ea pathologia est! cujus perpetuum principium, quod universis comprehensis. partibus convenire, universas illustrare, et explicare debet, ne uni quidem convenit, unam illustrat, unam explicat, contra omnibus repugnat, omnes obscurat, et consundit;" and, rejecting the pathology of the fluids, declares, that cool water, pure air, wine, and Peruvian bark resist putrifaction in no other way than by keeping up excitement. In his remarks upon spasm, he endeavours to shew that it cannot be a cause of disease, either of the sthe- nic or asthenic kind, and ought, of course, to be re- jected from both, as should also what has been called the reaction of the system, in fever. In the course of his animated argument, he asks if, toward the end of the eighteenth century, " quis, opinionem meram, nullâ rationis, nulla veri vel tenuissimâ umbrâ commenda- tam, xxiii AMERICAN EDITION. tam, solidissimis argumentis, item ipsi tuendæ aditibitis compertam salsam, post vanam omnifalfæ logicæ genere desensionem, pro re verâ et certâ oblatum iri crederet " He is every where opposed to that classification and arrangement of diseases which has so much obtained of late, and closes this work with the words, " Noso- logia delenda." He published a second edition in the year 1784, and added thereto the asthenic class of diseases. Taught, by experience and observation, in the dif- ferent forms of the gout and asthma, of the benefit of stimulant remedies, he had no hesitation to consider them among the effects of Weakness; as were likewise fevers strictly so called (febres) both intermittent and continued, and all the kinds of hemorrhagy, &c. In short, the consideration of the diseases not belonging to the sthenic class, convinced him they must be re- ferred to the asthenic; such were all spasmodic or con- vulsive ailments, dyspepsia, and other the like affec tions of the alimentary canal, and the greater part of the maladies of children. In this performance too, he contends against the advocates for sedatives. Opium, he declares, has a sti- mulant operation; colds or catarrhs are produced by heat succeeding to cold, and not vice versa; and ex- tends his laws of animation to the vegetable creation. In short, he concluded there was in the medullary nervous matter, and muscular solid of living bodies, which have been generally called the nervous system, a property by which they could be affected by outward agents, as well as by their own functions, in such a way as to produce the phenomena peculiar to the liv- ing state. This capacity of being acted upon is term- ed excitability, and the agents are all denominated stimulants, while the effect produced by the operation of stimulants upon excitability is called excitement. Excitement is terminated in two ways. 1. By the exhaustion of excitability, through the violence or con- tinuance xxiv PREFACE TO THE tinuance of stimulus, which is called indirect debility; 2. By the accumulation of excitability, through defi- cient stimulus, which is termed direct debility. Be- tween the two extremes of indirect and direct debility are experienced both health and diseases of the sthenic kind, or those febrile complaints (pyrexiæ,) accom- panied with what has been called phlogistic diathesis, wherein, though the excitement considerably exceeds the healthy rate, still it does not reach the limits of indirect debility. Stimuli lose their efficacy after long and frequent ap- plication; but even then the excitability, exhausted in relation to one stimulus, is capable of being acted upon by another. Therefore, the waste of excitability, after exhaustion of one stimulus after another, is very hard to be re- paired, by reason of the difficulty of access to fresh stimuli to work upon the languishing excitability; which, by being applied strong at first, and gradually weakened afterwards, answers the purpose; and also the superabundant excitability left by subduction of, one stimulus after another, produces such an excitable condition of the system, that much nicety is requisite to wear it gradually away by application of very weak stimuli at first, and by degrees stronger and stronger, until the accustomed ones can be comfortably borne. Recording to the Brunonian Doctrine diseases appear under various modifications, as exhibited in the table below. Thus they may be, 1. Universal, such as primarily affect the whole constitution, as fevers, &c. 2. Local, where, from limited morbid affection, a particular part labours, without disordering the intire habit; as trifling wounds, phlegmons, &c. 3. Loco-universal, when, from a local affection, the whole body is eventually brought into a diseased condition; as in lues originating from chancre, small-pox from inoculation, &c. 4. Universo- xxv AMERICAN EDITION. 4. Universo-local; as if after a general ailment any particular part or organ is affected in a secondary way; as the eruptions of exanthematous pyrexiæ, syphilitic blotches, &c. And each of these forms of diseases must consist either in, 1. Direct debility; as in scurvy, hunger, cold, &c. 2. Sthenic diathesis; as in pleurisy, other forms of synocha, &c. 3. Indirect debility; as in old age, intoxication, fa- tigue, &c. 4. Direct debility added to indirect; as in gout very often, and in many diseases of advanced life. 5. Indirect debility added to direct; as in over-feed- ing a famished person, &c. in most diseases of infants and young persons. Let now the candid reader compare this view with the opinions of the old Methodists, and say, whe- ther it be a mere revival of the practice of THEMISON and THESSALUS? Surely they who have asserted it was, can never be supposed to have given themselves the trouble to examine. Yet, with all this novelty about it, Brown's doc- trine wants precision. It proceeds not far enough be- yond general principles, which, by reason of their ab- stract or speculative nature, have not been found closely enough applicable to the subjects of pathology and physiology—He takes for granted, for instance, that the nervous system is always one and the same excitable thing. He says scarcely any thing accurate on the different qualities of the blood and circulating fluids, and of the secretions; and gives nothing very minute concerning the mighty influence of the respiratory and digestive processes upon the animal œconomy. He passes over entirely the chemical composition of our food and drink, of our inhalations and excretions, of the gases we breathe and the remedies we swallow: in short, he has left not a sentence on the composition or the na- c ture xxvi PREFACE TO THE ture of bone, muscle, vessel, fat, lymph, or gluten, nor how variously these are affected by disease, nor in what their healthy differs from their morbid state, nor by what means the alterations they undergo are brought about. These, and other omissions and defects in the BRU- NONIAN SYSTEM, called for amendment; and this was to be begun by attending to the varying condition of the living solid, and the concomitant state of the fluids. The establishment of the new nomenclature of chemistry in France, in 1787, may be considered as forming a new epoch in science. Since the publica- tion of that invaluable performance, language has been adapted with greater accuracy to the expression of ideas, and philosophical investigation conducted with superior advantage and success. LAVOISIER, in his Elements of Chemistry, has attempted the ex- planation of the putrefactive, as well as the fermenta- tive process in the organized forms of animals and of plants, upon the modern principles; and, in a natural and convincing manner, has proceeded a great way beyond any one who undertook the explanation be- fore. SPALLAZANI indeed, in his Experiments on the Concoction of Food in the Stomach, and CRAW- FORD, in his Application of the Principles of Com- bustion to the Function of the Lungs in breathing, had given excellent specimens of this mode of reason- ing on physiological subjects. Great progress has been made since in detecting the nature and properties of the atmosphere, the gases and æriform fluids; and the right knowledge of these derived from experiment and observation, has furnished the means of expound- ing many of the animal functions, in a plain and happy manner. We do not merely know, as Priestley and Scheele did, that there is a gaseous production, pure air, ne- cessary to the preservation and continuance of animal life; xxvii AMERICAN EDITION. life; but we think we know it is a compound sub- stance, and what its compound ingredients are; we believe we can make and unmake it artificially, and that nature is doing so incessantly: we think the term " dephlogisticated air" not accurately nor logically ap- plied; but, judging from its tendency to produce sourness when combined with other bodies, we call the basis of it " the acidifying principle," and the combination of that base with light and caloric, or the matter of heat, " oxygene gas or air." From noting the operation of this oxygene, or prin- ciple of souring, upon various bodies, we imagine we know the composition of acids, and have made out a considerable list of acidifiable bases; so that the forma- tion of fixed air from oxygene and carbone, or char- coal, of nitrous acid from it and azote, of vitriolic acid from the same and sulphur, and phosphoric acid from its union with phosphorus, seem to be well esta- blished truths. We imagine that a certain other class of bodies capable of combining with oxygene, but not to the point of acidity, forms thereby half-acids or oxydes, and that thus the calces of metals, animal blood and secretions, as well as the farinaceous, gum- my, and mucilaginous parts of plants, are formed. We think the composition of water is understood, and instead of being an elementary body, as was for- merly believed, that it is, in fact, but the oxyde of hydrogen, or a combination of this latter substance with the principle of acidity, but not to the souring point. It is considered also, that more is known concern- ing the composition of the irritable fibre, of the adi- pose matter, and of the bones: and that the effects produced upon the circulated fluids by breathing, and through them upon the solids of the animal body in health, and the alterations too that the liquid and firm parts undergo by impeding, vitiating, or obstructing that function, in ordinary cases, as well as in gravid females, xxviii PREFACE TO THE females, are now better comprehended than they used to be. Inasmuch, that, after the great light thrown upon this subject by GOODWIN, GIRTANNER has been enabled to dress up the Brunonian System in the more recent fashion, and BEDDOES, to supply and adorn it with almost all that was wanting to make it additionally engaging and attractive. Submersion, consumption, scurvy, stone, catarrh, obesity, dropsy, and fever, have already received great elucidation, both in theory and practice, from the application of che- mical principles; and we may reasonably hope, that before many more years elapse, better and more cor- rect ideas will be entertained of many articles of the materia medica, and of their manner of operating; that a new medical nomenclature (than which nothing in science is more wanting) will be made out; and that, from the ascertained condition of the body, and the known composition and operation of remedies, physi- cians may prescribe fairly for the actual state of the constitution, and the removal of the present malady, without being milled, as too often happens at present, by specious words, and idle or deceitful names. But, notwithstanding the many and beautiful ap- plications of chemical principles to the explanation of the animal functions, we are not to imagine every thing in life susceptible of chemical interpretation. What it is that enables the atoms composing a muscle to cohere, and the muscle to contract and perform great exertions of strength, we know not; but this we know very well, that we can never form a muscle by synthesis, or the putting together, in any artificial form, those substances which appear, from analysis, to constitute a muscle. There is something in animated existence, which eludes our most active researches, and which defies submission to either mechanical or chemical laws. With respect to chemical modes of reasoning upon these subjects, it is observable, that they apply, with their greatest extent and accuracy, to xxix AMERICAN EDITION. to such parts of the body as have the lowest degrees of animation, as the teeth, bones, fat, and, generally speaking, the circulated and secreted fluids; while the qualities of muscular fibres, by which they become contractile, and of nervous expansions, whereby they take on sensation, with the whole of the functions arising from irritability and sensibility, are referable to other and different laws. The investigation of these Laws of Organic Life is attempted by our learned and very ingenious author in the following work. The Zoonomia, therefore, though not exempt from fanciful and visionary doc- trines, presents considerations of the first importance, both to the speculative philosopher and the practical physician; to him who contemplates the operations of mind as a science, or to him that attends to the cor- poreal functions as an artist. How far Dr. Darwin has succeeded, and how much still remains to be done on this subject, it may not perhaps be easy to say, espe- cially since his second volume has not yet reached us; but I have no hesitation, from a consideration of the present work, to recommend it warmly to the perusal of students, and especially of beginners, whose unbi- ased minds will receive and comprehend its interesting contents, with less difficulty than those already occu- pied by pre-conceptions and prejudices. SAMUEL L. MITCHILL, Plandome, June 20, 1796. TO ERASMUS DARWIN, ON HIS WORK ENTITLED ZOONOMIA. By DEWHURST BILSBORROW. HAIL to the Bard! who sung, from Chaos hurl'd How suns and planets form'd the whirling world; How sphere on sphere Earth's hidden strata bend, And caves of rock her central fires defend; Where gems new-born their twinkling eyes unfold, 5 And young ores shoot in arborescent gold. How the fair Flower, by Zephyr woo'd, unfurls Its panting leaves, and waves its azure curls; Or spreads, in gay undress, its lucid form, To meet the sun, and shuts it to the storm; 10 While in green veins impassion'd eddies move, And Beauty kindles into life and love. How the first embryon-fibre, sphere, or cube, Lives in new forms,—a line,—a ring,—a tube; Closed in the womb with limbs unfinish'd laves, 15 Sips with rude mouth the salutary waves; Seeks round its cell the sanguine streams that pass, And drinks, with crimson gills, the vital gas; Weaves with soft threads the blue meandering vein, The heart's red concave, and the silver brain; 20 Leads the long nerve, expands the impatient sense, And clothes in silken skin the nascent Ens. Erewhile, emerging from its liquid bed, It lifts in gelid air its nodding head; The light's first dawn with trembling eye-lid hails, 25 With lungs untaught arrests the balmy gales; Tries its new tongue in tones unknown, and hears The strange vibrations with unpractised ears; Seeks with spread hands the bosom's velvet orbs, With closing lips the milky fount absorbs; 30 And, xxxii TO ERASMUS DARWIN. And, as compress'd the dulcet streams distil, Drinks warmth and fragrance from the living rill; Eyes with mute rapture every waving line, Prints with adoring kiss the Paphian shrine, And learns ere long the perfect form confess'd, 35 Ideal Beauty from its mother's breast. Now in strong lines, with bolder tints design'd, You sketch ideas, and pourtray the mind; Teach how fine atoms of impinging light To ceaseless change the visual sense excite; 40 While the bright lens collects the rays, that swerve, And bends their focus on the moving nerve: How thoughts to thoughts are link'd with viewless chains, Tribes leading tribes, and trains pursuing trains; With shadowy trident how Volition guides, 45 Surge after surge, his intellectual tides; Or, Queen of Sleep, Imagination roves With frantic Sorrows, or delirious Loves. Go on, O FRIEND! explore with eagle-eye, Where wrapp'd in night retiring causes lie; 50 Trace their slight bands, their secret haunts betray, And give new wonders to the beam of day; Till, link by link with step aspiring trod, You climb from NATURE to the throne of GOD. -So saw the Patriarch with admiring eyes 55 From earth to heaven a golden ladder rise; Involved in clouds the mystic scale ascends, And brutes and angels crowd the distant ends. Trin. Col. Cambridge, Jan. 1, 1794. REFERENCES TO THE WORK. Botanic Garden, Part I. Line 18. Sect. XVI. 2. and XXXVIII. Line 1 Canto I l. 105.- 26 - XVI. 4. - 3 -IV. l. 402. -30 -XVI. 4. -4 -I. I.140. -36. - XVI.6. -5 -III. I.401. -38 -III. and VII. -8-IV. I. 452. -43 -X. -9-I. 1. 14. -44 -XVIII. 17. -45- XVII. 3. 7. Zoonomia. -47-XVIII. 8. -50- XXXIX. 4. 8. -12. Sect. XIII. - 51 - XXXIX. the Motto, -13 -XXXIX.4.1. -54 -XXXIX. 8. PREFACE. THE purport of the following pages is an endeavour to re- duce the facts belonging to ANIMAL LIFE into classes, or- ders, genera, and species; and, by comparing them with each other, to unravel the theory of diseases. It happened, perhaps unfortunately for the inquirers into the knowledge of diseases, that other sciences had received improvement previous to their own; whence, instead of comparing the properties belonging to animated nature with each other, they, idly ingenious, busied themselves in attempting to explain the laws of life by those of mechanism and chemistry; they considered the body as an hy- draulic machine, and the fluids as passing through a series of chemical changes, forgetting that animation was its essential characteristic. The great CREATOR of all things has infinitely diversified the works of his hands, but has at the same time stamped a cer- tain similitude on the features of nature, that demonstrates to us, that the whole is one family of one parent. On this simi- litude is founded all rational analogy which, so long as it is I concerned in comparing the essential properties of bodies, leads us to many and important discoveries; but when with licentious activity it links together objects, otherwise discordant, by some fanciful similitude, it may indeed collect: ornaments for wit and poetry, but philosophy and truth recoil from its combinations. The want of a theory, deduced from such strict analogy, to conduct the practice of medicine, is lamented by its professors; for, as a great number of unconnected facts are difficult to be acquired, and to be reasoned from, the art of medicine is in many instances less efficacious under the direction of its wisest practitioners; and by that busy crowd, who either boldly wade in darkness, or are led into endless error by the glare of false theory, it is daily practised to the destruction of thousands; add to this the unceasing injury which accrues to the public by the perpetual advertisements of pretended nostrums; the minds of the indolent become superstitiously fearful of diseases, which B they 2 PREFACE. they do not labour under; and thus become the daily prey of some crafty empyric. A theory founded upon nature, that should bind together the scattered facts of medical knowledge, and, converge into one point of view the laws of organic life, would thus on many accounts contribute to the interest of society. It would capa- citate men of moderate abilities to practise the art of healing with real advantage to the public; it would enable every one of literary acquirements to distinguish the genuine disciples of me dicine from those of boastful effrontery, or of wily address; and would teach mankind in some important situations the knowledge of themselves. There are some modern practitioners who declaim against medical theory in general, not considering that to think is to theorize; and that no one can direct a method of cure to a per- son labouring under disease without thinking, that is, without theorizing; and happy therefore is the patient, whose physician possesses the best theory. The words idea, perception, sensation, recollection, sug- gestion, and association, are each of them used in this treatise in a more limited sense than in the writers of metaphysic. The author was in doubt, whether he should rather have substituted new words instead of them; but was at length of opinion, that new definitions of words already in use would be less burthensome to the memory of the reader. A great part of this work has lain by the writer above twenty years, as some of his friends can testify: he had hoped by frequent revision to have made it worthy the acceptance of die public; this however his other perpetual occupations have in part prevented, and may continue to prevent, as long as he may be capable of reviling it; he therefore begs of the candid reader to accept of it in its present state, and to excuse any inaccuracies of expression, or of conclusion, into which the intricacy of his subject, the general imperfection of lan- guage, or the frailty he has in common with other men, may have betrayed him; and from which he has not the vanity to believe this treatise to be exempt. ZOONOMIA ZOONOMIA. SECT. I. OF MOTION. THE WHOLE OF NATURE may be supposed to consist of two essences or substances; one of which may be termed spirit, and the other matter. The former of these possesses the power to commence or produce motion, and the latter to receive and communicate it. So that motion, considered as a cause, imme- diately precedes every effect; and, considered as an effect, it immediately succeeds every cause. THE MOTION OF MATTER may be divided into two kinds, primary and secondary. The secondary motions are those which are given to or received from other matter in motion. Their laws have been successfully investigated by philosophers in their treatises on mechanic powers. These motions are dis- tinguished by this circumstance, that the velocity multiplied into the quantity of matter of the body acted upon, is equal to the velocity multiplied into the quantity of matter of the acting body. The primary motions of matter may be divided into three classes, those belonging to gravitation, to chemistry, and to life; and each class has its peculiar laws. Though these three classes include the motions of solid, liquid, and aerial bodies; there is nevertheless a fourth division of motions; I mean those of the supposed ethereal fluids of magnetism, electricity, heat, and light; whose properties are not so well investigated as to be classed with sufficient accuracy. 1st. The gravitating motions include the annual and diurnal rotation of the earth and planets, the flux and reflux of the ocean, the descent of heavy bodies, and other phænomena of gravitation. The unparalleled sagacity of the great NEWTON has deduced the laws of this class of motions from the simple prnciple of the general attraction of matter. These motions are distinguished by their tendency to or from the centers of the sun or planets. 2d. The chemical class of motions includes all the various appearances of chemistry. Many of the facts, which belong to 4 DEFINITIONS. SECT. II. 1. to these branches of science, are nicely ascertained, and ele- gantly classed; but their laws have not yet been developed from such simple principles as those above-mentioned; though it is probable, that they depend on the specific attractions belong- ing to the particles of bodies, or to the difference of the quan- tity of attraction belonging to the sides and angles of those par- ticles. The chemical motions are distinguished by their being generally attended with an evident decomposition or new com- bination of the active materials, 3d. The third class includes all the motions of the animal and vegetable world; as well those of the vessels, which cir- culate their juices, and of the muscles, which perform their locomotion, as those of the organs of sense, which constitute their ideas. This last class of motion is the subject of the following pages, which, though conscious of their many imperfections I hope may give some pleasure to the patient reader, and contri- bute something to the knowledge and to the cure of diseases. SECT. II. 1. EXPLANATIONS AND DEFINITIONS. 1. Outline of the animal economy.—II. 1. Of the sensorium. 2. Of the brain and nervous medulla. 3. A nerve, 4. A Muscular fibre. 5. The immediate organs of sense. 6 The external organs of sense. 7. An idea or sensual motion. 8. Perception 9. Sensation. 10. Recollection and sug- gestion. 11. Habit, causation, association, catenation. 12. Reflex ideas. 13. Stimulus defined. As some explanation, and definitions will be necessary In the prosecution of the work, the reader is trouble with them in this place, and is intreated to keep them, in his mind as he proceeds, and to take them for granted till an apt opportunity occurs to evince their truth; to which I shall premise a very short outline of the animal economy. I.-1. THE nervous system has its origin from the brain, and is distributed to every part of the body. Those nerves, which serve the senses, principally arise from that part of the brain, which is lodged in the head; and those, which serve the purposes of muscular motion, principally arise from that part of 5 SECT. II. 1. DEFINITIONS. of the brain, which is lodged in the neck and back, and which is erroneously called the spinal marrow. The ultimate fibrils of these nerves terminate in the immediate organs of sense and muscular fibres, and if a ligature be put on any part of their passage from the head or spine, all motion and perception cease in the parts beneath the ligature. 2. The longitudinal muscular fibres compose the locomotive muscles, whole contractions move the bones of the limbs and trunk, to which their extremities are attached. The annular or spiral muscular fibres compose the vascular muscles, which constitute the intestinal canal, the arteries, veins, glands, and absorbent vessels. 3. The immediate organs of sense, as the retina of the eye, probably consist of moving fibrils, with a power of contraction similar to that of the larger muscles above described. 4. The cellular membrane consists of cells, which resemble those of a sponge, communicating with each other, and con- necting together all the other parts of the body. 5. The arterial system consists of the aortal and die pulmo- nary artery, which are attended through their whole course with their correspondent veins. The pulmonary artery re- ceives the blood from the right chamber of the heart, and car- ries it to the minute extensive ramifications of the lungs, where it is exposed to the action of the air on a surface equal to that of the whole external skin, through the thin moist coats of those vessels, which are spread on the air-cells, which constitute the minute terminal ramifications of the wind-pipe. Here the blood changes its colour from a dark red to a bright scarlet. It is then collected by the branches of the pulmonary vein, and conveyed to the left chamber of the heart. 6. The aorta is another large artery, which receives the blood from the left chamber of the heart, after it has been thus aerated in the lungs, and conveys it by ascending and descending branches to every other part of the system: the extremities of this artery terminate either in glands, as the salivary glands, la- chrymal glands, &c. or in capillary vessels, which are probably less involuted glands; in these some fluid, as saliva, tears, per- spiration, are separated from the blood; and the remainder of the blood is absorbed or drank up by branches of viens correspon- dent to the branches of die artery; which are furnished with valves to prevent its return; and is thus carried back, after having again changed its colour to a dark red, to the right chamber of the heart. The circulation of the blood in the liver differs from this general system; for the veins which drink up the refluent blood from those arteries, which are spread on the bowels 6 DEFINITIONS. SECT. II. 2. bowels and mesentery, unite into a trunk in the liver, and form a kind of artery, which is branched into the whole substance of the liver, and is called the vena portarum; and from which the bile is separated by the numerous hepatic glands, which constitute that viscus. 7. The glands may be divided into three systems, the con- voluted glands, such as those above described, which separate bile, tears, saliva, &c. Secondly, the glands without convo- lution, as the capillary vessels, which unite the terminations of the arteries and veins, and separate both the mucus, which lubricates the cellular membrane, and the perspirable matter, which preserves the skin moist and flexible. And thirdly, the whole absorbent system, consisting of the lacteals, which open their mouths in the stomach and intestines, and of the lym- phatics, which open their mouths on the external surface of the body, and on the internal linings of the cells of the cellular membrane, and other cavities of the body. These lacteal and lymphatic vessels are furnished with nu- merous valves to prevent the return of the fluids, which they absorb, and terminate in glands, called lymphatic glands, and may hence be considered as long necks or mouths belonging to these glands. To these they convey the chyle and mucus, with a part of the perspirable matter, and atmospheric moisture; all which, after having passed through these glands, and having suffered some change in them, are carried forward into the blood, and supply perpetual nourishment to the system, or re- place its hourly waste. 8. The stomach and intestinal canal have a constant vermi- cular motion, which carries forward their contents, after the lacteals have drank up the chyle from them; and which is ex- cited into action by the stimulus of the aliment we swallow, but which becomes occasionally inverted or retrograde, as in vomit- ing, and in the iliac passion. II. 1. The word sensorium in the following pages is designed to express not only the medullary part of the brain, spinal mar- row, nerves, organs of sense, and of the muscles; but also at the same time that living principle, or spirit of animation, which resides throughout the body, without being cognizable to our senses, except by its effects. The changes which occasionally take place in the sensorium, as during die exertions of volition, or the sensations of pleasure or pain, are termed sensorial mo- tions. 2. The similarity of the texture of the brain to that of the pancreas, and some other glands of the body, has induced the inquirers into this subject to believe, that a fluid, perhaps much more 7 SECT. II. 2. DEFINITIONS. more subtile than the electric aura, is separated from the blood by that organ for the purposes of motion and sensation. When we recollect, that the electric fluid itself is actually accumu- lated and given out voluntarily by the torpedo and the gymno- tus electricus, that an electric shock will frequently stimulate into motion a paralytic limb, and lastly, that it needs no per- ceptible tubes to convey it, this opinion seems not without pro- bability; and the singular figure of the brain and nervous sys- tem seems well adapted to distribute it over every part of the body. For the medullary substance of the brain not only occupies the cavities of the head and spine, but passes along the innu- merable ramifications of the nerves to the various muscles and organs of sense. In these it lays aside its coverings, and is in- termixed with the slender fibres, which constitute those muscles and organs of sense. Thus all these distant ramifications of the sensorium are united at one of their extremities, that is, in the head and spine; and thus these central parts of the censori- um constitute a communication between all the organs of sense and muscles. 3. A nerve is a continuation of the medullary substance of the brain from the head or spine towards the other parts of the body, wrapped in its proper membrane. 4. The muscular fibres are moving organs intermixed with that medullary substance which is continued along the nerves, as mentioned above. They are indued with the power of con- traction, and are again elongated either by antagonist muscles, by circulating fluids, or by elastic ligaments. So the muscles on the one side of the fore-arm bend the fingers by means of their tendons, and those on the other side of the fore-arm ex- tend them again. The arteries are distended by the circulating blood; and in the necks of quadrupeds there is a strong elastic ligament, which assists the muscles, which elevate the head, to keep it in its horizontal position, and to raise it alter it has been depressed. 5. The immediate organs of sense consist in like manner of moving fibres enveloped in the medullary substance above men- tioned; and are erroneously supposed to be limply an expansi- on of the nervous medulla, as the retina of the eye, and the rete mucosum of the skin, which are the immediate organs of vision, and of touch. Hence, when we speak of the contrac- tions of the fibrous parts of the body, we shall mean both the contractions of the muscles, and those of the immediate organs of sense. These fibrous motions are thus distinguished from the sensorial motions above mentioned. 6. The 8 DEFINITIONS. SECT. II. 2. 6. The external organs of sense are the coverings of the immediate organs of sense, and are mechanically adapted for the reception or transmission of peculiar bodies, or of their qualities, as the cornea and humours of the eye, the tympanum of the ear, the cuticle of the fingers and tongue. 7. The word idea has various meanings in the writers of metaphysic: it is here used simply for those notions of external things, which our organs of sense bring us acquainted with originally; and is defined a contraction, or motion, or con- figuration, of the fibres, which constitute the immediate or- gan of sense; which will be explained at large in another part of the work. Synonymous with the word idea, we shall sometimes use the work sensual motion, in contradistinction to mus- cular motion. 8. The word perception includes both the action of the or- gan of sense in consequence of the impact of external objects, and our attention to that action; that is, it expresses both the motion of the organ of sense, or idea, and the pain or pleasure that succeeds or accompanies it. 9. The pleasure or pain which necessarily accompanies all those perceptions or ideas which we attend to, either gradually subsides, or is succeeded by other fibrous motions. In the lat- ter case it is termed sensation, as explained in Sect. V. 2, and VI. 2.—The reader is intreated to keep this in his mind, that through all this treatise the word sensation is used to express pleasure or pain only in its active state, by whatever means it is introduced into the system, without any reference to the sti- mulation of external objects. 10. The vulgar use of the word memory is too unlimited for our purpose: those ideas which we voluntarily recall are here termed ideas of recollection, as when we will to repeat the alphabet backwards. And those ideas which are suggested to us by preceding ideas, are here termed ideas of suggestion, as whilst we repeat the alphabet in the usual order; when by habits previously acquired B is suggested by A, and C by B, without any effort of deliberation. 11. The word association properly signifies a society or con- vention of things in some respects similar to each other. We never say in common language, that the effect is associated with the cause, though they necessarily accompany or succeed each other. Thus the contractions of our muscles and of organs sense may be said to be associated with irritations, or with volition, or with sensation; because they are caused by them, as mentioned in Sea. IV. When fibrous contractions suc- ceed other fibrous contractions, the connection is termed asso- ciation; 9 SECT. III. MOTIONS OF THE RETINA. ciation; when fibrous contractions succeed sensorial motions, the connection is termed causation; when fibrous and sensorial motions reciprocally introduce each other in progressive trains or tribes, it is termed catenation of animal motions. All these connections are said to be produced by habit; that is, by fre- quent repetition. 12. It may be proper to observe, that by the unavoidable idiom of our language the ideas of perception, of recollection, or of imagination, in the plural number signify the ideas be longing to perception, to recollection, or to imagination; whilst the idea of perception, of recollection, or of imagina- tion, in the singular number is used for what is termed "a re- flex idea of any of those operations of the sensorium." 13. By the word stimulus is not only meant the application of external bodies to our organs of sense and muscular fibres, which excites into action the sensorial power termed irritation; but also pleasure or pain, when they excite into action the sen- sorial power termed sensation; and desire or aversion, when they excite into action the power of volition; and lastly, the fibrous contractions which precede association; as is further explained in Sect. XII. 2. 1. SECT. III. THE MOTIONS OF THE RETINA DEMONSTRATED BY EXPERIMENTS. I. Of animal motions and of ideas. II. The fibrous structure of the retina. III. The activity of the retina in vision. 1. Rays of light have no momentum. 2. Objects long viewed be come fainter. 3. Spectra of black objects become lumi- nous. 4. Varying spectra from gyration. 5. From long in- spection of various colours. IV. Motions of the organs of sense constitute ideas. I. Light from pressing the eye- ball, and found from the pulsation of the caroted artery. 2. Ideas in sleep mistaken for perceptions. 3. Ideas of ima- gination produce pain and sickness like sensations. 4. When the organ of sense is destroyed, the ideas belonging to that sense perish. V. Analogy between muscular motions and sensual motions, or ideas. 1. They are both originally excited by irritations. 2. And associated together in the same manner. 3. Both act in nearly the same times. 4. Are alike strengthened or fatigued by exercise. 5. Are alike painful from inflammation. 6. Are alike benumbed by com- C pression. 10 MOTIONS OF THE RETINA. SECT.III. 1. pression. 7. Are alike liable to paralysis. 8. To convulsion. 9. To the influence of old age. VI. Objections answered. 1. Why we cannot invent new ideas. 2. If idea resemble external objects. 3. Of the imagined sensation in an am- putated limb. 4. Abstract ideas. VII. What are ideas, if they are not animal motions. BEFORE the great variety of animal motions can be duly arranged into natural classes and orders, it is necessary to smooth the way to this yet unconquered field of science, by removing some obstacles which thwart our passage. I. To demonstrate that the retina and other immediate organs of sense possess a power of motion, and that these motions constitute our ideas, according to the fifth and seventh of the preceding assertions, claims our first attention. Animal motions are distinguished from the communicated motions, mentioned in the first section, as they have no mecha- nical proportion to their cause; for the goad of a spur on the skin of a horse shall induce him to move a load of hay. They differ from the gravitating motions there mentioned, as they are exerted with equal facility in all directions; and they differ from the chemical class of motions, because no apparent de- compositions or new combinations are produced in the moving materials. Hence, when we say animal motion is excited by irritation, we do not mean that the motion bears any proportion to the mechanical impulse of the stimulus; nor that it is affected by the general gravitation of the two bodies; nor by their chemical properties; but solely, that certain animal fibres are excited into action by something external to the moving organ. In this sense the stimulus of the blood produces the contrac- tions of the heart; and the substances we take into our stomach and bowels irritate them to perform their necessary functions. The rays of light excite the retina into animal motion by their stimulus; at the same time that those rays of light themselves are physically converged to a focus by the inactive humours of the eye. The vibrations of the air irritate the auditory nerve into animal action; while it is probable that the tympanum of the ear at the same time undergoes a mechanical vibration. To render this circumstance more easy to be comprehended, motion may be defined to be a variation of figure; for the whole universe may be considered as one thing possessing a cer- tain figure; the motions of any of its parts are a variation of this figure of the whole: this definition of motion will be fur- ther explained in Sect. XIV. 2. 2. on the production of ideas. Now, PLATE I 11 SECT. III. 1. MOTIONS OF THE RETINA. Now, the motions of an organ of sense are a succession of configurations of that organ; these configurations succeed each other quicker or flower; and whatever configuration of this organ of sense, that is, whatever portion of the motion of it is, or has usually been, attended to, constitutes an idea. Hence the configuration is hot to be considered as an effect of the mo- tion of the organ, but rather as a part or temporary termination of it; and that, whether a pause succeeds it, or a new configu- ration immediately takes place. Thus, when a succession of moving objects are presented to our view, the ideas of trumpets, horns, lords and ladies, trains and canopies, are configurations, that is, parts or links of the successive motions of the organ of vision. These motions, or configurations of the organs of sense, differ from the sensorial motions to be described hereafter, as they appear to be simply contractions of the fibrous extremi- ties of those organs, and in that respect exactly resemble the motions or contractions of the larger muscles, as appears from the following experiment: --- Place a circular piece of red silk, about an inch in diameter, on a sheet of white paper, in a strong light, as in Plate I.—look for a minute on this area, or till the eye becomes somewhat fatigued and then, gently closing your eyes, and shading them with your hand, a circular green area of the same apparent diameter becomes visible in the closed eye. This green area is the colour reverse to the red area, which had been previously inspected, as explained in experiments on ocu- lar spectra at the end of the work, and in Botanical Garden, P.I. additional note, No. I. -Hence it appears, that a part of the retina, which had been fatigued by contraction in one di- rection, relieves itself by exerting the antagonist fibres and pro- ducing a contraction in an opposite direction, as is common in the exertions of our muscles. Thus, when we are tired with long action of our arms in direction, as in holding a bridle, on a journey, we occasionally throw them into an opposite position to relieve the fatigued muscles. Mr. Locke has defined an idea to be "whatever present to the mind;" but this would include the exertions of volition, and the sensations of pleasure and pain, as well as those opera- tions of our system, which acquaint us with external objects; and is therefore too unlimited for our purpose. Mr. Locke seems to have fallen into a further error, by conceiving that the mind could form a general or abstract idea by its own operation, which was the copy of no particular perception; as of a triangle in genera], that was neither acute, obtuse, nor right angled. The ingenious Dr. Berkley and Mr. Hume have demonstrated, that 12 MOTIONS OF THE RETINA. SECT. III. 2. 3. that such general ideas have no existence in nature, not even in the mind of their celebrated inventor. We shall therefore take for granted at present, that our recollection or imagination of external objects consists of a partial repetition of the percep- tions which were excited by those external objects at the time we became acquainted with them; and that our reflex ideas of the operations of our minds are partial repetitions of those operations. II. The following article evinces that the organ of vision consists of a fibrous part as well as of the nervous medulla, like other white muscles; and hence, as it resembles the muscu- lar parts of the body in its structure, we may conclude, that it must resemble them in possessing a power of being excited into animal motion.—The subsequent experiments on the optic nerve, and on the colours remaining in the eye, are copied from a paper on ocular spectra, published in the 76th volume of the Philos. Trans. by Dr. R. Darwin of Shrewsbury, which, as I shall have frequent occasion to refer to, is reprinted in this work, Sect. XL. The retina of an ox's eye was suspended in a glass of warm water, and forcibly torn in a few places; the edges of these parts appeared jagged and hairy, and did not con- tract and become smooth like simple mucus, when it is distended till it breaks, which evinced that it consisted of fibres. This fibrous construction because still more distinct to the sight by adding some caustic alkali to the water; as the adhering mucus was first eroded, and the hair-like fibres remained floating in the vessel. Nor does the degree of transparency of the retina invalidate this evidence of its fibrous structure, since Leeuwen- hoek has shewn, that the chrystaline humour itself consists of fibres. Arc. Nat. V. I. 70. Hence it appears, that as the muscles consist of larger fibres, intermixed with a smaller quantity of nervous medulla, the organ of vision consists of a greater quantity of nervous medul- la, intermixed with smaller fibres. It is probable that the loco- motive muscles of microscopic animals may have greater tenuity than those of the retina; and there is reason to conclude, from analogy, that the other immediate organs of sense, as the portio mollis of the auditory nerve, and the rete mucosum of the skin, possess a similarity of structure with the retina, and a similar power of being excited into animal motion. III. The subsequent articles shew, that neither mechanical impressions, nor chemical combinations of light, but that the animal activity of the retina constitutes vision. 1. Much has been conjectured, by philosophers, about the momentum of the rays of light: to subject this to experiment, a very PLATE II. 13 SECT. III. 3. MOTIONS OF THE RETINA. a very light horizontal balance was constructed by Mr. Michel, with about an inch square of thin leaf-copper impended at each end of it, as described in Dr. Priestley's History of Light and Colours. The focus of a very large convex mirror was thrown by Dr. Powel, in his lectures on experimental philosophy, in my presence, on one wing of this delicate balance, and it re- ceded from the light; thrown on the other wing, it approached towards the light, and this repeatedly; so that no sensible im- pulse could be observed, but what might well be ascribed to the ascent of heated air. Whence it is reasonable to conclude, that the light of the day must be much too weak, in its dilute state, to make any mechanical impression on so tenacious a substance as the retina of the eye.—Add to this, that as the retina is nearly transpa- rent, it could therefore make less resistance to the mechanical impulse of light; which, according to the observations related by Mr. Melvil, in the Edinburgh Literary Essays, only com- municates heat, and should therefore only communicate mo- mentum, where it is obstructed, reflected, or refracted.— From whence also may be collected the final cause of this de- gree of transparency of the retina, viz. least by the focus of stronger lights, heat and pain should have been produced in the retina, instead of that stimulus which excites it into ani- mal motion. 2. On looking long on an area of scarlet silk of about an inch in diameter laid, on white paper, as in Plate I. the scarlet colour becomes fainter, till at length it entirely vanishes, though the eye is kept uniformly and steadily upon it. Now, if the change or motion of the retina was a mechanical im- pression, or a chemical tinge of coloured light, the perception would every minute become stronger and stronger,—whereas in this experiment it becomes every instant weaker and weaker. The same circumstance obtains in the continued application of found, or of sapid bodies, or of odorous ones, or of tangi- ble ones, to their adapted organs of sense. Thus, when a circular coin, as a shilling, is pressed on the palm of the hand, the sense of touch is mechanically com- pressed; but it is the stimulus of this pressure that excites the organ of touch into animal action, which constitutes the per- ception of hardness and of figure: for in some minutes the perception ceases, though the mechanical pressure of the ob- ject remains. 3. Make with ink on. white paper a very black spot about half an inch in diameter, with a tail about an inch in length, so as to resemble a tadpole, as in Plate II.; look stedfastly D for 14 MOTIONS OF THE RETINA. SECT. III. 3 for a minute on the center of this spot, and on moving the eye a little, the figure of the tadpole will be seen on the white part of the paper; which figure of the tadpole will appear more luminous than the other part of the white paper; which can only be explained by supposing that part of the retina, on which the tadpole was delineated, to have become more sensible to light than the other parts of it, which were expos- ed to the white paper; and not from any idea of mechanical impression or chemical combination of light with the retina. 4. When any one turns round rapidly, till he becomes diz- zy, and falls upon the ground, the spectra of the ambient ob- jects continue to present themselves in rotation, and he seems to behold the objects still in motion. Now if these spectra were impressions on a passive organ, they either must conti- nue as they were received last, or not continue at all. 5. Place a piece of red silk, about an inch in diameter, on a sheet of white paper, in a strong light, as in Plate I. ; look stea- dily upon it, from the distance of about half a yard, for a minute; then closing your eye-lids, cover them with your hands and handkerchief, and a green spectrum will be seen in your eyes, resembling, in form, the piece of red silk. After some seconds of time the spectrum will disappear, and in a few more seconds will re-appear; and thus alternately three or four times, if the experiment be well made, till at length it vanishes entirely. 6. Place a circular piece of white paper, about four inches in diameter, in the sunshine; cover the center of this with a circular piece of black silk, about three inches in diameter; and the center of the black silk with a circle of pink silk, about two inches in diameter; and the center of the pink silk, with a circle of yellow silk, about one inch in diameter; and the center of this with a circle of blue silk, about half an inch m diameter; make a small spot with ink in the center of the blue silk, as in Plate III. ; look steadily for a minute on this central spot, and then closing your eyes, and applying your hand at about an inch distance before them, so as to prevent too much or too little light from passing through the eye-lids, and you will see the most beautiful circles of colours that imagina- tion can conceive; which are most resembled by the colours occasioned by pouring a drop or two of oil on a still take in a bright day. But these circular irises of colours are not only different from the colour of the silks above-mentioned, but are at the same perpetually changing as long as they exist. From all these experiments it appears, that these spectra in the eye are not owing to the mechanical impulse of light im- pressed PLATE III 15 SECT. III. 4. MOTIONS OF THE RETINA. pressed on the retina; nor to its chemical combination with that organ; nor to the absorption and emission of light, as is supposed, perhaps erroneously, to take place in calcined shells and other phosphorescent bodies, after having been exposed to the light: for in all these cases the spectra in the eye should ei- ther remain of the same colour, or gradually decay, when the object is withdraw; and neither their evanescence during the presence of their object, as in the second experiment, nor their change from dark to luminous, as in the third experiment, nor their rotation, as in the fourth experiment, nor the alternate presence and evanescence of them, as in the fifth experiment, nor the perpetual change of colours of them, as in the last experiment, could exist. IV. The subsequent articles (new, that these animal motions, or configurations of our organs of sense, constitute our ideas. 1. If any one in the dark presses the ball of his eye, by ap- plying his finger to the external corner of it, a luminous ap- pearance is observed; and by a small stroke on the eye great flashes of fire are perceived. (Newton's Optics.) So that, when the arteries, that are near the auditory nerve, make stronger pulsations than usual, as in some fevers, an undulating sound is excited in the cars. Hence it is not the presence of the light and sound, but the motions of the organ, that are immediately necessary to constitute the perception or idea of light and sound. 2. During the time of sleep, or in delirium, the ideas of imagination are mistaken for the perceptions of external ob- jects; whence it appears, that these ideas of imagination are no other than a reiteration of those motions of the organs of sense, which were originally excited by the stimulus of external ob- jects: and in our waking hours the simple ideas, that we call up by recollection or by imagination, as the colour of red, or the smell of a rose, are exact resemblances of the same simple ideas from perception; and in consequence must be a repetition of those very motions. 2. The disagreeable sensation called the tooth-edge is origi- nally excited by the painful jarring of the teeth in biting the edge of the glass, or porcelain cup, in which our food was given us in our infancy, as is further explained in the Section XVI. 10, on Instinct.—This disagreeable sensation is after- ward excitable not only by a repetition of the sound, that was then produced, but by imagination alone, as I have my- self frequently experienced; in, this case the idea of biting a china cup, when I imagine it very distinctly, or when I see another person bite a cup or glass, excites an actual pain in the 16 MOTIONS OF THE RETINA SECT. III. 4. the nerves of my teeh. So that this idea and pain seem to be nothing more than the reiterated motions of those nerves, that were formerly so disagreeably affected. Other ideas that are excited by imagination or recollection in many instances produce similar effects on the constitution, as our perceptions had formerly produced, and are therefore undoubtedly a repetition of the same motions. A story which the celebrated Baron Van Swieton relates of himself is to this purpose. He was present when the putrid carcase of a dead dog exploded with prodigious stench; and some years after- wards, accidentally riding along the same road, he was thrown; into the same sickness and vomiting by the idea of the stench, as he had before experienced from the perception of it. 4. Where the organ of sense is totally destroyed, the ideas which were received by that organ seem to perish along with it, as well as the power of perception. Of this a satisfactory instance has fallen under my observation. A gentleman about sixty years of age had been totally deaf for near thirty years: he appeared to be a man of good understanding, and amused himself with reading, and by conversing either by the use of the pen, or by signs made with his fingers, to represent letters. I observed that he had so far forgot the pronunciation of the language, that when he attempted to speak, none of his word had distinct articulation, though his relations could sometimes understand his meaning. But, which is much to the point, he assured me, that in his dreams he always imagined that peo- ple conversed with him by signs or writing, and never that he heard any one speak to him. From hence it appears, that with the perceptions of founds he has also lost the ideas of them; though the organs of speech still retain somewhat of their usual habits of articulation. This observation may throw some light on the medical treat- ment of deaf people; as it may be learnt from their dreams whether the auditory nerve be paralytic, or their deafness be owing to some defect of the external organ. It rarely happens that the immediate organ of vision is per- fectly destroyed. The most frequent causes of blindness are occasioned by defects of the external organ, as in cataracts and obfuscations of the cornea. But I have had the opportu- nity of converting with two men, who had been some years blind; one of them had a complete gutta serena, and the other had lost the whole substance of his eyes. They both told me that they did not remember to have ever dreamt of visible ob- jects, since the total loss of their sight. V. Another method of discovering that our ideas are ani- mal 17 SECT. III. 5. MOTIONS OF THE RETINA. mal motions of the organs of sense, is from considering the great analogy they bear to the motions of the larger muscles of the body. In the following articles it will appear that they are originally excited into action by the irritation of external objects like our muscles; are associated together like our mus- cular motions; act in similar time with them; are fatigued by continual exertion like them; and that the organs of sense are subject to inflammation, numbness, palsey, convulsion, and the defects of old age, in the same manner as the muscular fibres. 1. All our perceptions or ideas of external objects are universally allowed to have been originally excited by the stimu- lus of those external objects; and it will be shewn in a suc- ceding season, that it is probable that all our muscular mo- tions, as well those that are become voluntary as those of the heart and glandular system, were originally in like manner excited by the stimulus of something external to the organ of motion. 2. Our ideas are also associated together after their produc- tion precisely in the same manner as our muscular motions which will likewise be fully explained in the succeeding season. 3. The time taken up in performing an idea is likewise much the same as that taken up in performing a muscular mo- tion. A musician can press the keys of an harpsichord with his fingers in the order of a tune he has been accustomed to play, in as little time as he can run over those notes in his mind. So we many times in an hour cover our eye-balls with our eye-lids without perceiving that we are in the dark; hence the perception or idea of light is not changed for that of dark- ness in so small a time as the twinkling of an eye; so that in this case the muscular motion of the eye-lid is performed quicker than the perception of light can be changed for that of darkness.—So if a fire-stick be whirled round in the dark, a luminous circle appears to the observer; if it be whirled somewhat flower, this circle becomes interrupted in one part; and then the time taken up in such a revolution of the stick is the same that the observer uses in changing his ideas: thus the δολιχοςχοτον ενχος of Homer, the long shadow of the flying ja- velin, is elegantly designed to give us an idea of its velocity, and not of its length. 4. The fatigue that follows a continued attention of the mind to one object is relieved by changing the subject of our thoughts; as the continued movement of one limb is relieved by moving another in its stead. Whereas a due exercise of the faculties of the mind strengthens and improves those facul- ties, 18 MOTIONS OF THE RETINA. SECT. III 5. ties, whether of imagination or recollection; as the exercise of our limbs in dancing or fencing increases the strength and agility of the muscles thus employed. 5. If the muscles of any limb are inflamed, they do not move without pain; so when the retina is inflamed, its mo- tions also are painful. Hence light is as intolerable in this kind of ophthalmia, as the pressure is to the finger in the pa- ronychia. In this disease the patients frequently dream of having their eyes painfully dazzled; hence the idea of strong light is painful as well as the reality. The first of these facts evinces that our perceptions are motions of the organs of sense; and the latter, that our imagination, are also motions of the same organs. 6. The organs of sense, like the moving muscles, are lia- ble to become benumbed, or less sensible, from compression. Thus, if any person on a light day looks on a white wall, he may perceive the ramifications of the optic artery, at every pulsation of it, represented by darker branches on the white wall; which is evidently owing to its compressing the retina. during the diastole of the artery. Savage Nosolog. 7. The organs of sense and the moving muscles are alike liable to be affected with palsy, as in the gutta serena, and in some cases of deafness; and one side of the face has sometimes lost its power of sensation, but retained its power of motion; other parts of the body have lost their motions, but retained their sensation, as in the common hemiplegia; and in other instances both these powers have perished together. 8. In some convulsive diseases a delirium or insanity super- venes, and the convulsions cease; and conversely the convul- sions shall supervene, and the delirium cease. —Of this I have been a witness many times in a day in the paroxysms of violent epilepsies which evinces that one kind of delirium is a convul- sion of the organs of sense, and that our ideas are the motions of these organs: the subsequent cases will illustrate this ob- servation. Miss G —, a fair young lady, with light eyes and hair, was seized with most violent convulsions of her limbs, with outrageous hiccough, and most vehement efforts to vomit: af- ter near an hour was elapsed this tragedy ceased, and a calm talkative delirium supervened for about another hour; and these relieved each other at intervals during the greatest part of three or four days. After having carefully considered this disease, I thought the convulsions of her ideas less dangerous than those of her muscles; and having in vain attempted to make any opiate continue in her stomach, an ounce of lauda- num 19 SECT. III. 5. MOTIONS OF THE RETINA. num was rubbed along the spine of her back, and a dram of it was used as an enema; by this medicine a kind of drunken delirium was continued many hours; and when it ceased the convulsions did not return; and the lady continued Well many years, except some slighter relapses, which were relieved in the same manner. Miss H---, an accomplished young lady, with light eyes and hair, was seized with convulsions of her limbs, with hic- cough, and efforts to vomit, more violent than words can ex- press; these continued near an hour, and were succeeded with a cataleptic spasm of one arm, with the hand applied to her head; and after about twenty minutes these spasms ceased, and a talkative reverie supervened for near another hour, from which no violence, which it was proper to use, could awaken her. These periods of convulsions, first of the mus- cles, and then of the ideas, returned twice a day for several weeks; and were at length removed by great doses of opium, after a great variety of other medicines and applications had been in vain experienced. This lady was subject to frequent relapses, once or twice a year, for many years, and was as frequently relieved by the same method. Miss W---, an elegant young lady, with black eyes and hair, had sometimes a violent pain of her side, at other times a most painful strangury, which were every day succeeded by de- lirium ; which gave a temporary relief to the painful spasms. After the Vain exhibition of variety of medicines and applica- tions by different physicians, for more than a twelvemonth, die was directed to take some doses of opium, which were gradually increased, by which a drunken delirium was kept up for a day or two, and the pains prevented from returning. A flesh diet, with a little wine or beer, instead of the low regimen she had previously used, in a few weeks completely established her health; which, except a few relapses, has continued for many years. 9. Lastly, as we advance in life all the parts of the body become more rigid, and are rendered less susceptible of new habits of motion, though they retain those that were before established. This is sensibly observed by those who apply themselves late in life to music, fencing, or any of the me- chanic arts. In the same manner may elderly people retain the ideas they had learned early in life, but find great diffi- culty in acquiring new trains of memory; insomuch that in extreme old age we frequently see a forgetfulness of the busi- ness of yesterday, and at the same time a circumstantial re- membrance of the amusements of their youth; till at length E the 20 MOTIONS OF THE RETINA. SECT. III. 6. the ideas of recollection and activity of the body gradually cease together,—such is the condition of humanity! —and nothing remains but the vital motions and sensations. VI. 1. In opposition to this doctrine of the production of our ideas, it may be asked, if some of our ideas, like other animal motions, are voluntary, why can we not invent new ones, that have not been received by perception? The answer will be better understood after having perused the suc- cecding section, where it will be explained, that the muscular motions likewise are originally excited by the stimulus of bo- dies external to the moving organ; and that the will has only the power of repeating the motions thus excited. 2. Another objector may ask, Can he motion of an organ of sense resemble an odour or a colour? To which I can only answer, that it has not been demonstrated that any of our ideas resemble the objects that excite them; it has generally been believed that they do not; but this shall be discussed at large in Sect. XIV. 3. There is another objection that at first view would seem less easy to surmount. After the amputation of a foot or a finger, it has frequently happened, that an injury being offered to the stump of the amputated limb, whether from cold air, too great pressure, or other accidents, the patient has complained of a sensation of pain in the foot or finger that was cut off. Does not this evince that all our ideas are excited in the brain, and not in the organs of sense? This objection is answered by observing, that our ideas of the shape, place, and solidity of our limbs, are acquired by our organs of touch and of light, which are situated in our fingers and eyes, and not by any sensations in the limb itself. In this case the pain or sensation which formerly has arisen in the foot or toes, and been propagated along the nerves to the central part of the sensorium, was at the same time accom- panied with a visible idea of the shape and place, and with a tangible idea of the solidity of the affected limb: now, when these nerves are afterwards affected by any injury done to the remaining stump with a similar degree or kind of pain, the ideas of the shape, place, or solidity of the lost limb, return by as- sociation; as these ideas belong to the organs of sight and touch, on which they were first excited. 4. If you wonder what organs of sense can be excited into motion, when you call up the ideas of wisdom or benevo- lence, which Mr. Locke has termed abstracted ideas; I ask you by what organs of sense you first became acquainted with these ideas? And the answer will be reciprocal; for it is certain 21 SECT. IV. ANIMAL CAUSATION. certain that all our ideas were originally acquired by our or- gans of sense; for whatever excites our perception must be external to the organ that perceives it, and we have no other inlets to knowledge but by our perceptions; as will be fur- ther explained in Section XIV. and XV. on the Productions and Classes of Ideas. VII. If our recollection or imagination be not a repetition of animal movements, I ask, in my turn, What is it? You tell me it consists of images or pictures of things. Where is this extensive canvass hung up? or where are the numerous receptacles in which those are deposited? or to what else in the animal system have they any similitude? That pleating picture of objects represented in miniature on the retina of the eye, seems to have given rise to this illu- sive oratory! It was forgot that this representation belongs ra- ther to the laws of light, than to those of life; and may with equal elegance be seen in the camera obscura as in the eye; and that the picture vanishes for ever, when the object is withdrawn. SECT. IV. LAWS OF ANIMAL CAUSATION. I. The fibres, which constitute the muscles and organs of sense, possess a power of contraction. The circumstances attending the exertion of this power of CONTRACTION con- stitute the laws of animal motion; as the circumstances at tending the exertion of the power of ATTRACTION consti- tute the laws of motion of inanimate matter. II. The spirit of animation is the immediate cause of the contraction of animal fibres; it resides in the brain and nerves, and is liable to general or partial diminution or accumulation. III. The stimulus of bodies external to the moving organ is the remote cause of the original contractions of animal fibres. IV. A certain quantity of stimulus produces irritation, which is an exertion of the spirit of animation exciting the fibres into contraction. V. A certain quantity of contraction of animal fibres, if it be perceived at all, produces pleasure; a greater or less quantity of contraction, if it be perceived at all, produces pain; these constitute sensation. VI. A certain quantity of sensation produces desire or a- version; these constitute volition. VII. All animal motions which have occurred at the same time, or in immediate succession, become so connected, that when 22 SENSORIAL FACULTIES. SECT. V. when one of them is reproduced, the other has a tendency to accompany or succeed it. When fibrous contractions suc- ceed or accompany other fibrous contractions, the connec- tion is termed association; when fibrous contractions succeed sensorial motions, the connection is termed causation; when fibrous and sensorial motions reciprocally introduce each other, it is termed catenation of animal motions. All these connec- tions are said to be produced by habit, that is, by frequent re- petition. These laws of animal causation will be evinced by numerous facts, which occur in our daily exertions; and will afterwards be employed to explain the more recondite phæ- nomena of the production, growth, diseases, and decay of the animal system. SECT. V. OF THE FOUR FACULTIES OR MOTIONS OF THE SENSORIUM. 1. Four sensorial powers. 2. Irritation, sensation, volition, association defined. 3. Sensorial motions distinguished from fibrous motions. I. THE spirit of animation has four different modes of ac- tion; or, in other words, the animal sensorium possesses four different faculties, which are occasionally exerted, and cause all the contractions of the fibrous parts of the body. These are the faculty of causing fibrous contractions in convenience of the irritations excited by external bodies, in consequence of the sensations of pleasure or pain, in consequence of volition, and in consequence of the associations of fibrous contractions with other fibrous contractions, which precede or accompany them. These four faculties of the sensorium during their inactive state are termed irritability, sensibility, voluntarity, and asso- ciability; in their active state they are termed as above, irri- tation, sensation, volition, association. 2. IRRITATION is an exertion or change of some extreme part of the sensorium residing in the muscles or organs of sense, in consequence of the appulses of external bodies. SENSATION is an exertion or change of the central parts of the sensorium, or of the whole of it, beginning at some of those extreme parts of it, which reside in the muscles or organs of sense. VOLITION is an exertion or change of the central parts of the sensorium, or of the whole of it, terminating in some of those extreme parts of it, which reside in the muscles or organs of sense. ASSOCIATION 23 SECT. VI. 1. SENSORIAL FACULTIES. ASSOCIATION is an exertion or change of some extreme part of the sensorium residing in the muscles or organs of sense, in consequence of some antecedent or attendant fibrous contractions. 3. These four faculties of the animal sensorium may, at the time of their exertions, be termed motions, without impropriety of language; for we cannot pass from a state of insensibility or inaction, to a state of sensibility or of exertion, without some change of the sensorium, and every change includes motion. We shall therefore sometimes terra the above described facul- ties sensorial motions, to distinguish them from fibrous mo- tions; which latter expression includes the motions of the muscles and organs of sense. The active motions of the fibres, whether those of the muscles or organs of sense, are probably simple contractions; the fibres being again elongated by antagonist muscles, by cir- culating fluids, or sometimes by elastic ligaments, as in the necks of quadrupeds. The sensorial motions, which consti- tute the sensations of pleasure or pain, and which constitute volition, and which cause the fibrous contractions in conse- quence of irritation or of association, are not here supposed to be fluctuations or refluctuations of the spirit of animation; nor are they supposed to be vibrations or revibrations, nor condensations or equilibrations of it; but to be changes or motions of it peculiar to life. SECT. VI. OF THE FOUR CLASSES OF FIBROUS MOTIONS. I. Origin of fibrous contractions. II. Distribution of them into four classes, irritative motions, sensitive motions, voluntary motions, and associate motions, defined. I. ALL the fibrous contractions of animal bodies originate from the sensorium, and resolve themselves into four classes, cor- respondent with the four powers or motions of the sensorium above described, and from which they have their causation. 1. These fibrous contractions were originally caused by the irritations excited by objects, which are external to the moving organ. As the pulsations of the heart are owing to the irritations excited by the stimulus of the blood; and the ideas of perception are owing to the irritations excited by external bodies. 2. But as painful or pleasureable sensations frequently ac- companied those irritations, by habit these fibrous contractions became causeable by the sensations, and the irritations ceased to 24 FIBROUS CONTRACTIONS. SECT. VI. 2. to be necessary to their production. As the secretion of tears in grief is caused by the sensation of pain; and the ideas of ima- gination, as in dreams or delirium, are excited by the pleasure or pain with which they were formerly accompanied. 3. But as the efforts of the will frequently accompanied these painful or pleasureable sensations, by habit the fibrous contrac- tions became causeable by volition; and both the irritations and sensations ceased to be necessary to their production. As the deliberate locomotions of the body, and the ideas of recollection, as when we will to repeat the alphabet backwards. 4. But as many of these fibrous contractions frequently ac- companied other fibrous contractions, by habit they became causeable by their associations with them; and the irritations, sensations, and volition, ceased to be necessary to their produc- tion. As the actions of the muscles of the lower limbs in fenc- ing are associated with those of the arms; and the ideas of sug- gestion are associated with other ideas, which precede or ac- company them; as in repeating carelessly the alphabet in its usual order after having began it. II. We shall give the following names to these four classes, of fibrous motions, and subjoin their definitions. 1. Irritative motions. That exertion or change of the sen- sorium, which is caused by the appulses of external bodies, either simply subsides, or is succeeded by sensation, or it produces fibrous motions; it is termed irritation, and irritative motions are those contractions of the muscular fibres, or of the organs of sense, that are immediately consequent to this exertion or change of the sensorium. 2. Sensitive motions. - That exertion or change of the sen- sorium, which constitutes pleasure or pain, either simply sub- sides, or is succeeded by volition, or it produces fibrous motions; it is termed sensation, and the sensitive motions are those con- tractions of the muscular fibres, or of the organs of sense, that are immediately consequent to this exertion or change of the sensorium. 3. Voluntary motions. That exertion or change of the sensorium, which constitutes desire or aversion, either simply subsides, or is succeeded by fibrous motions; it is then termed volition, and voluntary motions are those contractions of the muscular fibres or of the organs of sense, that are immediately consequent to this exertion or change of the sensorium. 4. Associate motions. That exertion or change of the sen- sorium, which accompanies fibrous motions, either simply sub- sides, or is succeeded by sensation or volition, or it produces other fibrous motions; it is then termed association, and the associate 25 SECT. VII. 1. IRRITATIVE MOTIONS. associate motions are those contractions of the muscular fibres, or of the organs of sense, that are immediately consequent to this exertion or change of the sensorium. SECT. VII. OF IRRITATIVE MOTIONS. I. 1. Some muscular motions are excited by perpetual irrita- tions. 2. Others more frequently by sensations. 3. Others by volition. Case of involuntary stretches in paralytic limbs. 4. Some sensual motions are excited by perpetual irritations. 5. Others more frequently by sensation or volition. II. 1. Muscular motions, excited by perpetual irritations, occasionally become obedient to sensation and to volition. 2. And the sensual motions. III. 1. Other muscular motions are associated with the irri- tative ones. 2. And other ideas with irritative ones. Of letters, language, hieroglyphics. Irritative ideas exist without our attention to them. I. 1 . MANY of our muscular motions are excited by per petual irritations, as those of the heart and arterial system by the circumfluent blood. Many other of them are excited by inter- mittent irritations, as those of the stomach and bowels by the aliment we swallow; of the bile-ducts by the bile; of the kid- neys, pancreas, and many other glands, by the peculiar fluids they separate from the blood ; and those of the lacteal and other absorbent vessels by the chyle, lymph, and moisture of the atmosphere. These motions are accelerated or retarded, as their correspondent irritations are increased or diminished, without our attention or consciousness, in the same manner as the various secretions of fruit, gum, resin, wax, and honey, are produced in the vegetable world, and as the juices of the earth and the moisture of the atmosphere are absorbed by their roots and foliage. 2. Other muscular motions, that are most frequently con- nected with our sensations, as those of the sphincters of the bladder and anus, and the musculi erectores penis, were ori- ginally excited into motion by irritation, for young children make water, and have other evacuations without attention to these circumstances; " et primis etiam ab incunabulis tendun- ter sæpius puerorum penes, amore nondum expergefacto." So the nipples of young women are liable to become turgid by irritation, 26 IRRITATIVE MOTIONS. SECT. VII. 1. irritation, long before they are in a situation to be excited by the pleasure of giving milk to the lips of a child. 3. The contractions of the larger muscles of our bodies, that are most frequently connected with volition, were origi- nally excited into action by internal irritations; as appears from the stretching or yawning of all animals after long sleep. In the beginning of some fevers this irritation of the muscles produces perpetual stretching and yawning; in other periods of fever an universal restlessness arises from the same cause, the patient changing the attitude of his body every minute. The repeated struggles of the fœtus in the uterus must be ow- ing to this internal irritation: for the fœtus can have no other inducement to move its limbs but the tœdium or irksomeness of a continued posture. The following case evinces, that the motions of stretching the limbs after a continued attitude are not always owing to the power of the will. Mr. Dean, a mason, of Austry in Leicestershire, had the spine of the third vertebra of the back inlarged; in some weeks his lower extremities became feeble, and at length quite paralytic: neither the pain of blisters, the heat of fomentations, nor the utmost efforts of the will could produce the least motion in these limbs; yet twice or thrice a day, for many months, his feet, legs, and thighs were affect- ed, for many minutes, with forcible stretchings, attended with the sensation of fatigue; and he at length recovered the use of his limbs, though the spine continued protuberant. The same circumstance is frequently seen in a less degree in the common hemiplagia; and when this happens, I have believed repeated and strong shocks of electricity to have been of great advantage. 4. In like manner the various organs of sense are originally excited into motion by various external stimuli adapted to this purpose, which motions are termed perceptions or ideas; and many of these motions, during our waking hours, are excited by perpetual irritation, as those of the organs of hearing and of touch. The former by the constant low indistinct noises that murmur around us, and the latter by the weight of our bodies on the parts which support them; and by the unceasing varia- tions of the heat, moisture, and pressure of the atmosphere; and these sensual motions, precisely as the muscular ones above men- tioned, obey their correspondent irritations without our atten- tion or consciousness. 5. Other classes of our ideas are more frequently excited by our sensations of pleasure or pain, and others by volition: but that these have all been originally excited by stimuli from ex- ternal 27 SECT. VII. 2. 3. IRRITATIVE MOTIONS. ternal objects, and only vary in their combinations or separa- tions, has been fully evinced by Mr. Locke; and are by him termed the ideas of perception, in contradistinction to those which he calls the ideas of reflection. II. 1. These muscular motions, that are excited by perpe- tual irritation, are nevertheless occasionally excitable by the sensations of pleasure or pain, or by volition, as appears by the palpitation of the heart from fear, the increased secretion of saliva at the fight of agreeable food, and the glow on the skin of those who are ashamed. There is an instance told in the Philosophical Transactions, of a man, who could for a time stop the motion of the heart when he pleased; and Mr. D. has often told me, he could so far increase the peristaltic motion of his bowels by voluntary efforts, as to produce an evacuation by stool at any time in half an hour. 2. In like manner the sensual motions, or ideas, that are excited by perpetual irritation, are nevertheless occasionally excitable by sensation or volition; as in the night, when we listen under the influence of fear, or from voluntary attention, the motions excited in the organ of hearing by the whisper- ing of the air in our room, the pulsation of our own arteries, or the faint beating of a distant watch, become objects of perception. III. 1. Innumerable trains or tribes of other motions are associated with these muscular motions, which are excited by irritation; as by the stimulus of the blood in the right cham- ber of the heart, the lungs are induced to expand themselves; and the pectoral and intercostal muscles, and the diaphragm, act at the same time by their associations with them. And when the pharinx is irritated by agreeable food, the muscles of deglutition are brought into action by association. Thus when a greater light falls on the eye, the iris is brought into action without our attention; and the ciliary process, when the focus is formed before or behind the retina, by their asso- ciations with the increased irritative motions of the organ of vision. Many common actions of life are produced in a similar manner. If a fly settle on my forehead, whilst I am intent on ray present occupation, I dislodge it with my finger without ex- citing my attention or breaking the train of my ideas. 2. In like manner the irritative ideas suggest to us many other trains or tribes of ideas that are associated with them. On this kind of connection, language, letters, hieroglyphics, and every kind of symbol, depend. The symbols themselves produce irritative ideas, or sensual motions, which we do not attend to; and other ideas, that are succeeded by sensation, F are 28 SENSITIVE MOTIONS. SECT. VIII. 1. are excited by their association with them. And as these irri- tative ideas make up a part of the chain of our waking thoughts, introducing other ideas that engage out attention, though themselves are unattended to, we find it very difficult to investigate by what steps many of our hourly trains of ideas gain their admittance. It may appear paradoxical, that ideas can exist, and not be attended to; but all our perceptions are ideas excited by irri- tation, and succeeded by sensation. Now, when these ideas, excited by irritation, give us neither pleasure nor pain, we cease to attend to them. Thus whilst I am walking through that grove before my window, I do not run against the trees or the benches, though my thoughts are strenuously exerted on some other object. This leads us to a distinct knowledge of irrita- tive ideas; for the idea of the tree or bench, which I avoid, exists on my retina, and induces, by association, the action of certain locomotive muscles; though neither itself, nor the actions of those muscles, engage my attention. Thus, whilst we are conversing on this subject, the tone, note, and articulation of every individual word forms its cor- respondent irritative idea on the organ of hearing; but we only attend to the associated ideas, that are attached by habit to these irritative ones, and are succeeded by sensation: thus; when we read the words "PRINTING-PRESS," we do not attend to the shape, size, or existence of the letters which compose these words, though each of them excites a corres- pondent irritative motion of our organ of vision; but they introduce by association our idea of the most useful of modern inventions; the capacious reservoir of human knowledge, whole branching streams diffuse sciences, arts, and morality, through all nations and all ages. SECT. VIII. OF SENSITIVE MOTIONS. I. 1. Sensitive muscular motions were originally excised into action by irritation. 2. And sensitive sensual motions, ideas of imagination, dreams. II. I. Sensitive muscular motions are occasionally obedient to volition. 2. And sensitive sensual motions. III. 1. Other muscular mo- tions are associated with the sensitive ones. 2. And other sensual motions. I. 1. MANY of the motions of our muscles, that are ex- cited into action by irritation, are at the same time accompa- nied 29 SECT. VIII. 2. SENSITIVE MOTIONS. nied with painful or pleasurable sensations; and at length be- come by habit causable by the sensations. Thus the motions of the sphincters of the bladder and anus were originally ex- cited into action by irritation: for young children give no at- tention to these evacuations; but as soon as they become sen- sible of the inconvenience of obeying these irritations, they suffer the water or excrement to accumulate, till it disagreea- bly affects them; and the action of those spincters is then in consequence of this disagreeable sensation. So the secretion of the saliva, which in young children is copiously produced by irritation, and drops from their mouths, is frequently at- tended with the agreeable sensation produced by the mastication of tasteful food; till at length the fight of such food to a hun- gry person excites into action these salival glands; as is seen in the slavering of hungry dogs. The motions of thole muscles, which are affected by las- civious ideas, and those which are exerted in smiling, weep- ing, darting from fear, and winking at the approach of dan- ger to the eye, and at times the actions of every large muscle of the body, become causable by our sensations. And all these motions are performed with strength and velocity in pro- portion to the energy of the sensation that excites them, and the quantity of sensorial power. 2. Many of the motions of our organs of sense, or ideas, that were originally excited into action by irritation, become in like manner more frequently causable by our sensations of pleasure or pain. These motions are then termed the ideas oi imagination, and make up all the scenery and transactions of our dreams. Thus, when any painful or pleasurable sensations possess us, as of love, anger, fear; whether in our sleep or waking hours, the ideas, that have been formerly excited by the objects of these sensations, now vividly recur before us by their connection with the sesensations themselves. So the fair smiling virgin, that excited your love by her presence, whenever that sensation recurs, rises before you in imagination; and that with all the pleasing circumstances that had before engaged your attention. And in sleep, when you dream under the influ- ence of fear, all the robbers, fires, and precipices, that you for- merly have seen or heard of, arise before you with terrible viva- city. All these sensual motions, like the muscular ones above mentioned, are performed with strength and velocity in propor- tion to the energy of the sensation of pleasure or pain which excites them, and the quantity of sensorial power. II. 1. Many of these muscular motions above described, that are most frequently excited by our sensations, are nevertheless occasionally 30 VOLUNTARY MOTIONS. SECT. IX. occasionally causable by volition; for we can smile or frown spontaneously, can make water before the quantity or acrimony of the urine produces a disagreeable sensation, and can volun- tarily masticate a nauseous drug, or swallow a bitter draught, though our sensation would strongly dissuade us. 2. In like manner the sensual motions, or ideas, that are most frequently excited by our sensations, are nevertheless occasion- ally causable by volition, as we can spontaneously call up our last night's dream before us, tracing it industriously, step by step, through all its variety of scenery and transaction; or can volun- tarily examine or repeat the ideas that have been excited by our disgust or admiration. III. 1. Innumerable trains or tribes of motions are associated with these sensitive muscular motions above mentioned; as when a drop of water failing into, the wind-pipe disagreeably affects the air-vessels of the lungs, they are excited into violent action; and with these sensitive motions are associated the actions of the pectoral and intercostal muscles, and the diaphragm; till by their united and repeated succussions, the drop is returned through the larinx. The same occurs when any thing disagreeably affects the nostrils or the stomach, or the uterus: variety of muscles are excited by association into forcible action, not to be suppressed by the utmost efforts of the will; as in sneezing, vomiting, and parturition. 2. In like manner with these sensitive sensual motions, or ideas of imagination, are associated many other trains or tribes of ideas, which by some writers of metaphysics have been classed under the terms of resemblance, causation, and contiguity; and will be more fully treated of hereafter. SECT. IX. OF VOLUNTARY MOTIONS. I. 1. Voluntary muscular motions are originally excited by irritations. 2. And voluntary ideas. Of reason. II. 1. Voluntary muscular motions are occasionally causable by sensations. 2. And voluntary ideas. III. I. Voluntary, muscular motions are occasionally obedient to irritations. 2. And voluntary ideas. IV. I. Voluntary muscular mo- tions are associated with other muscular motions. 2. And voluntary ideas. WHEN pleasure or pain affect the animal of its system, many motions, both muscular and sensual, are brought into ac- tion; as was shown in the preceding section, and were called sensitive 31 SECT. IX. 1. VOLUNTARY MOTIONS. sensitive motions. The general tendency of these motions is to arrest and to possess the pleasure, or to dislodge or avoid the pain: but if this cannot immediately be accomplished, desire or aversion are produced, and the motions in consequence of this new faculty of the sensorium are called voluntary. I. 1. Those muscles of the body that are attached to bones, have in general their principal connection with volition; as, I move my pen or raise my body. These motions were origi- nally excited by irritation, as was explained in the section on that subject; afterwards the sensations of pleasure or pain, that accompanied the motions thus excited, induced a repeti- tion of them; and at length many of them were voluntarily practised, in succession or in combination, for the common pur- poses of life, as in learning to walk, or to speak; and are performed with strength and velocity in proportion to the energy of the volition that excites them, and the quantity of sensorial power. 2. Another great class of voluntary motions consists of the ideas of recollection. We will to repeat a certain train of ideas, as of the alphabet backwards; and if any ideas, that do not belong to this intended train, intrude themselves by other connections, we will to reject them, and voluntarily persist in the determined train. So at my approach to a house which I have but once visited, and that at the distance of ma- ny months, I will to recollect the names of the numerous fa- mily I expect to see there, and I do recollect them. On this voluntary recollection of ideas our faculty of rea- son depends, as it enables us to acquire an idea of the dissi- militude of any two ideas, Thus if you voluntarily produce the idea of a right-angled-triangle, and then of a square; and after having excited these ideas repeatedly, you excite the idea of their difference, which is that of another right-angled-tri- angle inverted over the former; you are said to reason upon this subject, or to compare your ideas. These ideas of recollection, like the muscular motions a- bove mentioned, were originally excited by the irritation of external bodies, and were termed ideas of perception: after- wards the pleasure or pain, that accompanied these motions, induced a repetition of them in the absence of the external bo- dy, by which they were first excited: and then they were termed ideas of imagination. At length they became volun- tarily practised, in succession or in combination, for the com- mon purposes of life; as when we male ourselves masters of the history of mankind, or of the sciences they have investi- gated; and are then called ideas of recollection; and are per- formed 32 VOLUNTARY MOTIONS. SECT. IX. formed with strength and velocity in proportion to the energy of the volition that excites them, and the quantity of sensorial power. II. 1. The muscular motions above described, that are most frequently obedient to the will, are nevertheless occa- sionally causable by painful or pleasurable sensation, as in the starting from fear, and the contraction of the calf of the leg in the cramp. 2. In like manner the sensual motions, or ideas, that are most frequently connected with volition, are nevertheless oc- casionally causable by painful or pleasurable sensation. As the histories of men, or the description of places, which we have voluntarily taken pains to remember, sometimes occur to us in our dreams. III. 1. The muscular motions that are generally subservi- ent to volition, are also occasionally causable by irritation, as in stretching the limbs after sleep, and yawning. In this man- ner a contraction of the arm is produced by passing the elec- tric fluid from the Leyden phial along its muscles; and that even though the limb is paralytic. The hidden motion of the arm produces a disagreeable sensation in the joint, but the muscles seem to be brought into action simply by irritation. 2. The ideas, that are generally subservient to the will, are in like manner occasionally excited by irritation; as when we view again an object, we have before well studied, and often re- collected. IV. 1. Innumerable trains or tribes of motions are associated with these voluntary muscular motions above mentioned; as when I will to extend my arm to a distant object, some other muscles are brought into action, and preserve the balance of my body. And when I wish to perform any steady exertion, as in threading a needle, or chopping with an ax, the pectoral muscles are at the same time brought into action to preserve the trunk of the body motionless, and we cease to respire for a time. 2. In like manner the voluntary sensual motions, or ideas, of recollection, are associated with many other trains or tribes of ideas. As when I voluntarily recollect a Gothic window, that I saw some time ago, the whole front of the cathedral occurs to me at the same time. SECT. 33 SECT. X. 1. ASSOCIATE MOTIONS. SECT. X. OF ASSOCIATE MOTIONS. I. 1. Many muscular motions, excited by irritations in trains or tribes, become associated. 2. And many ideas. II. 1. Many sensitive muscular motions become associated. 2. And many sensitive ideas. III. 1. Many voluntary mus- cular motions become associated. 2. And then become obe- dient to sensation or irritation. 3. And many voluntary ideas become associated. ALL the fibrous motions, whether muscular or sensual, which are frequently brought into action together, either in combined tribes, or in successive trains, become so connected by habit, that when one of them is re-produced, the others have a tendency to succeed or accompany it. I. 1. Many of our muscular motions were originally excited in successive trains, as the contractions of the auricles and of the ventricles of the heart; and others in combined tribes, as the various divisions of the muscles which compose the calf of the leg, which were originally irritated into synchronous action by the tædium or irksomeness of a continued posture. By fre- quent repetitions these motions acquire associations, which continue during our lives, and even after the destruction of the greatest part of the sensorium; for the heart of a viper or frog will continue to pulsate long after it is taken from the body, and when it has entirely ceased to move, if any part of it is goaded with a pin, the whole heart will again renew its pulsations. This kind of connection we shall term irritative association, to distinguish it from sensitive and voluntary asso- ciations. 2. In like manner many of our ideas are originally excited in tribes; as all the objects of light, after we become so well acquainted with the laws of vision as to distinguish figure and distance as well as colour; or in trains, as while we pass along, the objects that surround us. The tribes thus received by irritation become associated by habit, and have been termed complex ideas, by the writers of metaphysics, as this book, or that orange. The trains have received no par- ticular name; but these are alike associations of ideas, and fre- quently continue during our lives. So the taste of a pine- apple, though we eat it blindfold, recalls the colour and shape of it; and we can scarcely think on solidity without a figure. II. 1. By the various efforts of our sensations to acquire or avoid their objects, many muscles are daily brought into successive 34 ASSOCIATE MOTIONS. SECT. X. 3. successive or synchronous actions; these become associated by habit, and are then excited together with great facility, and in many instances gain indissoluble connections. So the play of puppies and kittens is a representation of their mode of fighting, or of taking their prey; and the motions of the mus- cles necessary for those purposes, become associated by habit, and gain a great adroitness of action by these early repeti- tions: so the motions of the abdominal muscles, which were originally brought into concurrent action with the protrusive motion of the rectum or bladder by sensation, become so con- joined with them by habit, that they not only easily obey these sensations occasioned by the stimulus of the excrement and urine, but are brought into violent and unrestrainable ac- tion in the stranguary and tenesmus. This kind of connec- tion we shall term sensitive association. 2. So many of our ideas, that have been excited together or in succession by our sensations, gain synchronous or successive associations, that are sometimes indissoluble but with life. Hence the idea of an inhuman or dishonourable action perpe- tually calls up before us the idea of the wretch that was guilty of it. And hence those unconquerable antipathies are formed, which some people have to the fight of peculiar kinds of food, of which in their infancy they have eaten to excess or by constraint. III. 1. In learning any mechanic art, as music, dancing, or the use of the sword, we teach many of our muscles to act together or in succession, by repeated voluntary efforts; which by habit become formed into tribes or trains of association, and serve all our purposes with great facility, and in some in- stances acquire an indissoluble union. These motions are gradually formed into a habit of acting together by a multi- tude of repetitions, whilst they are yet separately causable by the will, as is evident from the long time that is taken up by children in learning to walk and to speak; and is experi- enced by every one when he first attempts to skate upon the ice or to swim; these we shall term voluntary associations. 2. All these muscular movements, when they are thus asso- ciated into tribes or trains, become afterwards not only obedi- ent to volition, but to the sensations and irritations; and the same movement composes a part of many different tribes or trains of motion. Thus a single muscle, when it acts in con- sort with its neighbours, on one side, assists to move the limb in one direction; and in another, when it acts with those in its neighbourhood on the other side; and in other directions, when it acts separately or jointly with those that lie immedi- ately 35 SCT. X. 3. ASSOCIATE MOTIONS. ately under or above it; and all these with equal facility after their associations have been well established. The facility with which each muscle changes from one as- sociated tribe to another, and that either backwards or for wards, is well observable in the muscles of the arm in moving the windlass of an air-pump; and the slowness of those muscu- lar movements, that have not been associated by habit, may be experienced by any one, who shall attempt to saw the air quick perpendicularly with one hand, and horizontally with the other at the same time. 3. In learning every kind of science, we voluntarily associate many tribes and trains of ideas, which afterwards are ready for all the purposes, either of volition, sensation, or irritation; and in some instances acquire indissoluble habits of acting to- gether, so as to affect our reasoning and influence our actions. Hence the necessity of a good education. These associate ideas are gradually formed into habits of acting together by frequent repetition, while they are yet separately obedient to the will; as is evident from the difficulty we experience in gaining so exact an idea of the front of St. Paul's church, as to be able to delineate it with accuracy, or in re- collecting a poem of a few pages. And these ideas, thus associated into tribes, not only make up the parts of the trains of volition, sensation, and irritation; but the same idea composes a part of many different tribes and trains of ideas. So the simple idea of whiteness composes a part of the complex idea of snow, milk, ivory; and the complex idea of the letter A composes a part of the several associated trains of ideas, that make up the variety of words, in which this letter enters. The numerous trains of these associated ideas are divided by Mr. Hume into three classes, which he has termed contiguity, causation, and resemblance. Nor should we wonder to find them thus connected together, since it is the business of our lives to dispose them into these three classes; and we become valuable to ourselves and our friends, as we succeed in it. Those who have combined an extensive class of ideas by the contiguity of time or place, are men learned in the history of mankind, and of the sciences they have cultivated. Those who have connected a great class of ideas of resemblances, possess the source of the ornaments of poetry and oratory, and of all rational analogy. While those who have connected great classes of ideas of causation, are furnished with the powers of producing effects. These are the men of active wis- G dom, 36 SENSORIAL ACTIONS. SECT. XL. r. dom, who lead armies to victory, and kingdoms to prosperity, or discover and improve the sciences, which meliorate and adorn the condition of humanity. SECT. XI ADDITIONAL OBSERVATIONS ON THE SENSORIAL POWERS. I. Stimulation is of various kinds, adapted to the organs of sense, to the muscles, to hollow membranes and glands. Some objects irritate our senses by repeated impulses. II. 1. Sensation and volition.frequently affect the whole sen- sorium. 2. Emotions, passions, appetites. 3. Origin of desire and aversion. Criterion of voluntary actions, dif- ference of brutes and men. 4. Sensibility and voluntari- ty. III. Associations formed before nativity; irritative motions mistaken for associated ones. Irritation. I. THE various organs of sense require various kinds of stimulation to excite them into action; the particles of light penetrate the cornea and humours of the eye, and then irritate the naked retina; sapid particles, dissolved or diffused in water or saliva, and odorous ones, mixed or combined with the air, irritate the extremities of the nerves of taste and smell; which either penetrate or are expanded on the membranes of the tongue and nostrils; the auditor; nerves are stimulated by the vibrations of the atmosphere, communicated by means of the tympanum and of the fluid, whether of air or of water, behind it; and the nerves of touch by the hardness of surrounding bodies, though the cuticle is interposed between these bodies and the medulla of the nerve. As the nerves of the senses have each their appropriated ob- jects, which stimulate them into activity; so the muscular fibres, which are the terminations of other lets of nerves, have their peculiar objects, which excite them into action; the lon- gitudinal muscles are stimulated into contraction by extension whence the stretching or pendiculation after a long continued posture, during which they have been kept in a state of exten- sion; and the hollow muscles are excited into action by disten- sion, as those of the rectum and bladder are induced to protrude their contents from their sense of the distention, rather than of the acrimony of those contents. There 37 SECT. XI. 2. SENSORIAL ACTIONS. There are other objects adapted to stimulate the nerves, which terminate in a variety of membranes, and those especial- ly which form the terminations of canals; thus the prepara- tions of mercury particularly affects the salivary glands, ipe- cacuanha affects the sphincter of the anus, cantharides that of the bladder, and lastly, every gland of the body appears to be induced with a kind of taste, by which it selects or forms each its peculiar fluid from the blood, and by which it is irritated into activity. Many of these external properties of bodies, which stimu- late our organs of sense, do not seem to affect this by a single impulse, but by repeated impulses; as the nerve of the ear is probably not excitable by a single vibration of air, nor the optic nerve by a single particle of light; which circumstance produces some analogy between those two senses, at the same time the solidity of bodies is perceived by a single application of a solid body to the nerves of touch, and that even through the cuticle; and we are probably possessed of a peculiar sense to distinguish the nice degrees of heat and cold. The senses of touch and of hearing acquaint us with the me- chanical impact and vibration of bodies; those of smell and taste seem to acquaint us with some of their chemical properties; while the sense of vision and of heat acquaint us with the ex- istence of their peculiar fluids. Sensation and Volition. II. Many motions are produced by pleasure or pain, and that even in contradiction to the power of volition, as in laugh- ing or in the stranguary; but as no name has been given to pleasure or pain, at the time it is exerted so as to cause fibrous motions, we have used the term sensation for this purpose; and mean it to bear the same analogy to pleasure and pain, that the word volition does to desire and aversion. 1. It was mentioned in the fifth Section, that what we have termed sensation is a motion of the central parts, or of the whole sensorium, beginning at some of the extremities of it. This appears, first, because our pains and pleasures are always caused by our ideas or muscular motions, which are the mo- tions of the extremities of the sensorium. And, secondly, be- cause the sensation of pleasure or pain frequently continues some time after the ideas or muscular motions which excited it have ceased: for we often feel a glow of pleasure from an agreeable reverie, for many minutes after the ideas, that were the subject of it, have escaped our memory; and frequently ex- perience 38 SENSORIAL ACTIONS, SECT. XI. 2. perience a dejection of spirits, without being able to assign the cause of it but by much recollection. When the sensorial faculty of desire or aversion is exerted so as to cause fibrous motions, it is termed volition; which is said in Sect. V. to be a motion of the central parts or of the whole sensorium, terminating in some of the extremities of it. This appears, first, because our defiles and aversions always terminate in recollecting and comparing our ideas, or in exert- ing our muscles; which are the motions of the extremities of the sensorium. And, secondly, because desire or aversion be- gins, and frequently continues for a time in the. central parts of the sensorium, before it is peculiarly exerted at the extremities of it; for we sometimes feel desire or aversion without imme- diately knowing their objects, and in consequence without im- mediately exerting any of our muscular or sensual motions to attain them: as in the beginning of the passion of love, and perhaps of hunger, or in the ennui of indolent people. Though sensation and volition begin or terminate at the extremities or central parts of the sensorium, yet the whole of it is frequently influenced by the exertion of these faculties, as appears from their effects on the external habit; for the whole skin is reddened by shame, and an universal trembling is pro- duced by fear: and every muscle of the body is agitated in angry people by the desire of revenge. There is another very curious circumstance, which shews that sensation and volition are movements of the sensorium in contrary directions; that is, that volition begins at the central parts of it, and proceeds to the extremities; and that sensation begins at the extremities, and proceeds to the central parts: I mean, that these two sensorial faculties cannot be strongly ex- erted at the same time; for when we exert our volition strongly, we do not attend to pleasure or pain; and conversely, when we are strongly affected with the sensation of pleasure or pain, we use no volition—As will be further explained in Section XVIII. on deep, and Section XXXIV. on volition. 2. All our emotions and passions seem to arise out of the exertions of these two faculties of the animal sensorium. Pride, hope, joy, are the names of particular pleasures: shame, des- pair, sorrow, are the names of particular pains: and love, am- bition, avarice, of particular desires: hatred, disgust, fear, anx- iety, of particular aversions. Whilst the passion of anger in- cludes the pain from a recent injury, and the aversion to the adversary that occasioned it. And companion is the pain we experience at the sight of misery, and the desire of relieving it. There 39 SECT. XI. 2. SENSORIAL ACTIONS. There is another tribe of desires, which are commonly termed appetites, and are the immediate consequences of the absence of some irritative motions. Those which arise from defect of in- ternal irritations, have proper names conferred upon them, as hunger, thirst, lust, and the desire of air when our respiration is impaired by noxious vapours; and of warmth when we are exposed to too great a degree of cold. But those, whose sti- muli ate external to the body, are named from the objects which are by nature constituted to excite them; these desires originate from our past experience of the pleasurable sensations they occasion, as the smell of an hyacinth, or the taste of a pine-apple. Whence it appears, that our pleasures and pains are at least as various and as numerous as our irritations; and that our de- sires and aversions must be as numerous as our pleasures and pains. And that as sensation is here used as a general term for our numerous pleasures and pains, when they produce the contractions of our fibres; so volition is the general name for our desires and aversions, when they produce fibrous contrac- tions. Thus, when a motion of the central parts, or of the whole sensorium, terminates in the exertion of our muscles, it is generally called voluntary action; when it terminates in the exertion of our ideas, it is termed recollection, reason- ing, determining. 3. As the sensations of pleasure and pain are originally in- troduced by the irritations of external objects, so our desires and aversions are originally introduced by those sensations; for when the objects of our pleasures or pains are at a distance, and we cannot instantaneously possess the one, or avoid the other, then desire or aversion is produced, and a voluntary ex- ertion of our ideas or muscles succeeds. The pain of hunger excites you to look out for food; the tree that shades you presents its odoriferous fruit before your eyes; you approach, pluck, and eat. The various movements of walking to the tree, gathering the fruit, and masticating it, are associated motions introduced by their connection with sensation; but if, from the uncom- mon height of the tree, the fruit be inaccessible, and you are prevented from quickly possessing the intended pleasure, desire is produced. The consequence of this desire is, first, a deli- beration about the means to gain the object of pleasure in pro- cess of time, as it cannot be procured immediately; and, second- ly, the muscular action necessary for this purpose. You voluntarily call up all your ideas of causation, that are 40 SENSORIAL ACTIONS. SECT. XI. 3. are related to the effect you desire, and voluntarily examine and compare them, and at length determine whether to ascend the tree, or to gather stones from the neighbouring brook, is easier to practise, or more promising of success; and finally, you gather the stones, and repeatedly fling them to dislodge the fruit. Hence, then, we gain a criterion to distinguish voluntary acts or thoughts from those caused by sensation. As the former are always employed about die means to acquire pleasurable objects, or the means to avoid painful ones; while the latter are employed in the possession of those which are already in our power. Hence the activity of this power of volition produces the great difference between the human and the brute creation: The ideas and the actions of brutes are almost perpetually em- ployed about their present pleasures or their present pains; and, except in the few instances which are mentioned in Section XVI. on instinct, they seldom busy themselves about the means of procuring future bliss, or of avoiding future misery; so that the acquiring of languages, the making of tools, and labouring for money, which are all only the means to procure pleasures, and the praying to the Deity, as another means to procure hap- piness, are characteristic of human nature. 4. As there are many diseases produced by the quantity of the sensation of pain or pleasure being too great or too little; so are there diseases produced by the susceptibility of the constitu- tion to motions causable by these sensations being too dull or too vivid. This susceptibility of the system to sensitive motion is termed sensibility, to distinguish it from sensation, which is the actual existence or exertion of pain or pleasure. Other classes of diseases are owing to the excessive promp- titude or sluggishness of the constitution to voluntary exertions, as well as to the quantity of desire or of aversion. This sus- ceptibility of the system to voluntary motions is termed volun- tarity, to distinguish it from volition, which is the exertion of desire or aversion: these diseases will be treated of at length in the progress of the work. Association. III. 1. It is not easy to assign a cause, why those animal movements that have once occurred in succession, or in com- bination, should afterwards have a tendency to succeed or ac- company each other. It is a property of animation, and distin- guishes this order of being from the other productions of nature. When 41 SECT. XII. OF STIMULUS AND EXERTION. When a child first wrote the word man, it was distinguish- ed in his mind into three letters, and those letters into many parts of letters; but by repeated use the word man becomes to his hand in writing it, as to his organs of speech in pronounc- ing it, but one movement without any deliberation, or sensa- tion, or irritation, interposed between the parts of it. And as many separate motions of our muscles thus become united, and form, as it were, one motion; so each separate motion before such union, may be conceived to consist of many parts or spa- ces moved through; and perhaps even the individual fibres of our muscles have thus gradually been brought to act in con- cert, which habits began to be acquired as early as the very formation of the moving organs, long before the nativity of the animal; as explained in Section XVI. 2. on instinct. 2. There are many motions of the body, belonging to the irritative class, which might, by a hasty observer, be mistaken for associated ones; as the peristaltic motion of the stomach and intestines, and the contractions of the heart and arteries, might be supposed to be associated with the irritative motions of their nerves of sense, rather than to be excited by the irritation of their muscular fibres, by the distention, acrimony, or momen- tum of the blood. So the distention or elongation of muscles by objects external to them, irritates them into contraction, though the cuticle or other parts may intervene between the stimulating body and the contracting muscle. Thus a horse voids his excrement when its weight or bulk irritates the rec- tum or sphincter ani. The motion of these muscles act from the irritation of distention, when he excludes his excrement; but the muscles of the abdomen and diaphragm are brought into motion by association with those of the sphincter and rectum. SECT. XII. OF STIMULUS, SENSORIAL EXERTION, AND FI- BROUS CONTRACTION. I. Of fibrous contraction. 1. Two particles of a fibre cannot approach without the intervention of something, as in mag- netism, electricity, elasticity. Spirit of life is not electric ether. Galvani's experiments. 2. Contraction of a fibre. 3. Relaxation succeeds. 4. Successive contractions, with intervals. Quick pulse from debility, from paucity of blood. leak contractions performed in less time, and with shorter intervals. 42 OF STIMULUS AND EXERTION. SECT. XII. intervals. 5. Last situation of the fibres continues after contraction. 6. Contraction greater than usual induces pleasure or pain. 7. Mobility of the fibres uniform. Quantity of sensorial power fluctuates. Constitutes exci- tability. II. Of sensorial exertion. 1. Animal motion in- cludes stimulus, sensorial power, and contract the fibres. The sensorial faculties act separately or conjointly. Sti- mulus of four kinds. Strength and weakness defined. Sensorial power perpetually exhausted and renewed. Weakness from defect of stimulus. From defect of senso- rial power, the direct and indirect debility of Dr. Brown. Why we become warm in Buxton bath after a time, and see well after a time in a darkish room. Fibres may act violently, or with their whole force, and yet feebly. Great exertion in inflammation explained. Great muscular force of some insane people. 2. Occasional accumulation of sensorial power in muscles subject to constant stimulus. In animals sleeping in winter. In eggs, seeds, schirrous tu- mours, tendons, bones. 3. Great exertion introduces pleasure or pain. Inflammation. Libration of the sys- tem between torpor and activity. Fever-fits. 4. Desire and aversion introduced. Excess of volition cures fevers. III. Of repeated stimulus. 1. A stimulus repeated too fre- quently loses effect. As opium, wine, grief. Hence old age. Opium and aloes in small doses. 2. A stimulus not repeated too frequently does not lose effect. Perpetual movement of the vital organs. 3. A stimulus repeated at uniform times produces greater effect. Irritation com- bined with association. 4. A stimulus repeated frequently and uniformly may be withdrawn, and the action of the organ will continue. Hence the bark cures agues,, and strengthens weak constitutions. 5. Defect of stimulus re- peated at certain intervals causes fever-fits. 6. Stimu- lus long applied ceases to act a second time. 7. If a sti- mulus excites sensation in an organ not usually excited into sensation, inflammation is produced. IV. Of stimu- lus greater than natural. 1. A stimulus greater than na- tural diminishes the quantity of sensorial power in gene- ral. 2. In particular organs. 3. Induces the organ in- to spasmodic actions. 4. Induces the antagonist fibres in- to action. 5. Induces the organ into convulsive or fixed spasms. 6. Produces paralysis of the organ. V. Of sti- mulus less than natural. 1. Stimulus less than natural occasions accumulation of sensorial power in general. 2. In 43 SECT. XII. 1. OF STIMULUS AND EXERTION. In particular organs, flushing of the face in a frosty morn- ing. In fibres subject to perpetual stimulus only. Quantity of sensorial power inversely as the stimulus. 3. Induces pain. As of cold, hunger, head-ach. 4. Induces more feeble and frequent contraction. As in low fevers. Which are frequently owing to deficiency of sensorial power rather than to deficiency of stimulus. 5. Inverts successive trains of motion. Inverts ideas. 6. Induces paralysis and death. VI. Cure of increased exertion. I. Natural cure of exhaustion of sensorial power. 2. Decrease the irritations. Vanesection. Cold. Absti- nence. 3. Prevent the previous cold fit. Opium. Bark. Warmth. Anger. Surprise. 4. Excite some other part of the system. Opium and warm bath relieve pains both from defect and from exceess of stimulus. 5. First in- crease the stimulus above, and then decrease it beneath the natural quantity. VII. Cure of decreased exertion. 1. Natural cure by accumulation of sensorial power. Ague-fits. Syncope. 2. Increase the stimulation, by wine, opium, given so as not to intoxicate. Cheerful ideas. 3. Change the kinds of stimulus. 4. Stimulate the associated organs. Blisters of use in heart-burn, and cold extremities. 5. Decrease the stimulation for a time, cold bath. 6. Decrease the stimulation below natural, and then increase it above natural. Bark after emetics. Opium after vanesection. Practice of Sydenham in chlo- rosis. 7. Prevent unnecessary expenditure of sensorial power. Decumbent posture, silence, darkness. Pulse quickened by rising out of bed. 8. To the greatest degree of quiescence apply the least stimulus. Otherwise para- lysis or inflammation of the organ ensues. Gin, wine, blisters, destroy by too great stimulation in fevers with de- bility. Intoxication in the slightest degree succeeded by debility. Golden rule for determining the best degree of stimulus in low fevers. Another golden rule for deter- mining the quantity of spirit which those who are debili- taded by drinking it may safely omit. I. Of fibrous Contraction. 1. IF two particles of iron lie near each other, without mo- tion, and afterwards approach each other, it is reasonable to conclude that something besides the iron particles is the cause of their approximation; this invisible something is termed magnetism. In the same manner, if the particles which com- pose an animal muscle do not touch each other in the relaxed H state 44 OF STIMULUS AND EXERTION. SECT. XII. r. state of the muscle, and are brought into contact during the contraction of the muscle; it is reasonable to conclude that some other agent is the cause of this new approximation. For nothing can act where it does not exist; for to act includes to exist; and therefore the particles of the muscular fibre (which in its state of relaxation are supposed not to touch) cannot affect each other without the influence of some inter- mediate agent; this agent is here termed the spirit of animation, or sensorial power, but may with equal propriety be termed the power which causes contraction; or may be called by any other name, which the reader may choose to affix to it. The contraction of a muscular fibre may be compared to the following electric experiment, which is here mentioned; not as a philosophical analogy, but as an illustration or simile to facilitate the conception of a difficult subject. Let twenty very small Leyden phials, properly coated, be hung in a row by line silk threads, at a small distance from each other; let the in- ternal charge of one phial be positive, and of the other nega- tive, alternately: if a communication be made from the internal surface of the first to the external surface of the last in the row, they will all of them instantly approach each other, and thus shorten a line that might connect them like a muscular fibre. See Botanic Garden, p. i. Canto I. 1. 202, note on Gymnotus. The attractions of electricity or of magnetism do not apply philosophically to the illustration of the contraction of animal fibres, since the force of those attractions increases in some proportion inversely as the distance; but in muscular motion there appears no difference, in velocity or strength, during the beginning or end of the contraction, but what may be clearly ascribed to the varying mechanic advantage in the approxima- tion of one bone to another. Nor can muscular motion be assimilated, with greater plausability, to the attraction of cohe- sion or elasticity; for in bending a steel spring, as a small sword, a less force is required to bend it the first inch than the second; and the second than the third; the particles of steel on the con- vex side of the bent spring endeavouring to restore themselves more powerfully the further they are drawn from each other. See Botanic Garden, p. 1. addit. note XVIII. I am aware that this may be explained another way, by sup- posing the elasticity of the spring to depend more on the com- pression of the particles on the concave side, than on the exten- sion of them on the convex side; and by supposing the elasticity of the elastic gum to depend more on the resistance to the late- ral compression of its particles, than to the longitudinal exten- sion of them. Nevertheless, in muscular contraction, as above observed, 45 SECT. XII. 1. OF STIMULUS AND EXERTION. observed, there appears no difference in the velocity or force of it at its commencement or termination; from whence we must conclude, that animal contraction is governed by laws of its own, and not by those of mechanics, chemistry, magnetism, or electricity. On these accounts I do not think the experiments conclusive, which were lately published by Galvani, Volta, and others, to shew a similitude between the spirit of animation, which contracts the muscular fibres, and the electric fluid; since the electric fluid may act only as a more potent stimulus, exciting the muscular fibres into action, and not by supplying them with a new quantity of the spirit of life. Thus, in a recent hemi- plegia, I have frequently observed, when the patient yawned and stretched himself, that the paralytic limbs moved also, though they were totally disobedient to the will. And when he was electrified, by passing shocks from the affected hand to the af- fected foot, a motion of the paralytic limbs was also produced. Now, as in the act of yawning the muscles of the paralytic limbs were excited into action by the stimulus of the irksomeness of a continued posture, and not by an additional quantity of the of life; so we may conclude, that the passage of the elec- tric fluid, which produced a similar effect, acted only as a sti- mulus, and not by supplying any addition of sensorial power. If, nevertheless, this theory should ever become established, a stimulus must be called an eductor of vital ether; which stimu- lus may consist of sensation or volition, as in the electric eel, as well as in the appulses of external bodies; and, by drawing off the charges of vital fluid, may occasion the contraction or motions of the muscular fibres and organs of sense. 2. The immediate effect of the action of the spirit of anima- tion, or sensorial power, on the fibrous parts of the body, whe- ther it acts in the mode of irritation, sensation, volition, or as- sociation, is a contraction of the animal fibre, according to the second law of animal causation. Sect. IV. Thus the sti- mulus of the blood induces the contraction of the heart; the agreeable taste of a strawberry produces the contraction of the muscles of deglutition; the effort of the will contracts the muscles which move the limbs in walking; and, by associ- ation, other muscles of the trunk are brought into contraction to preserve the balance of the body. The fibrous extremities of the organs of sense have been shewn, by the ocular spectra in Sect. III. to suffer similar contraction by each of the above modes of excitation; and by their configurations to constitute our ideas. 3. After animal fibres have for some time been excited into contraction, 46 OF STIMULUS AND EXERTION. SECT. XII. 1. contraction, a relaxation succeeds, even though the exciting cause continues to act. In respect to the irritative motions this is exemplified in the peristaltic contractions of the bow- els; which cease and are renewed alternately, though the sti- mulus of the aliment continues to be uniformly applied; in the sensitive motions, as in strangury, tenesmus, and parturition, the alternate contractions and relaxations of the muscles exist, though the stimulus is perpetual. In our voluntary exertions it is experienced, as no one can hang long by the hands, how- ever vehemently he wills so to do; and in the associate motions, the constant change of our attitudes evinces the necessity of re- laxation to those muscles which have been long in action. This relaxation of a muscle, after its contraction, even though the stimulus continues to be applied, appears to arise from the expenditure or diminution of the spirit of animation previously resident in the muscle, according to the second law of animal causation in Sect. IV. In those constitutions which are termed weak, the spirit of animation becomes sooner exhausted, and tremulous motions are produced, as in the hands of infirm peo- ple, when they lift up a cup to their mouths. This quicker exhaustion of the spirit of animation is probably owing to a less quantity of it residing in the acting fibres, which therefore more frequently require a supply from the nerves which be- long to them. 4. If the sensorial power continues to act, whether it acts in the mode of irritation, sensation, volition, or association, a new contraction of the animal fibre succeeds after a certain interval; which interval is of shorter continuance in weak people than in strong ones. This is exemplified in the shaking of the hands of weak people, when they attempt to write. In a manuscript epistle of one of my correspondents, which is written in a small hand, I observed from four to six zigzags in the perpendicular stroke of every letter, which shews that both the contractions of the fingers, and intervals between them, must have been performed in very short periods of time. The times of contraction of the muscles of enfeebled people being less, and the intervals between those contractions being less also, accounts for the quick pulse in fevers with debility, and in dying animals. The shortness of the intervals, between one contraction and another in weak constitutions, is probably owing to the general deficiency of the quantity of the spirit of animation, and therefore there is a less quantity of it to be received at each interval of the activity of the fibres. Hence, in repeated motions, as of the fingers in performing on the harpsichord, it would at first sight appear, that swiftness and 47 SECT. XII. 1. OF STIMULUS AND EXERTION. and strength are incompatible; nevertheless, the single contrac- tion of a muscle is performed with greater velocity, as well as with greater force, by vigorous constitutions, as in throwing a javelin. There is, however, another circumstance, which may often contribute to cause the quickness of the pulse in nervous fe- vers, as in animals bleeding to death in the slaughter-house, which is the deficient quantity of blood; whence the heart is but half distended, and in consequence sooner contracts. See Sect. XXXII. 2. 1. For we must not confound frequency of repetition with quickness of motion, or the number of pulsations with the velocity, with which the fibres, which constitute the coats of the arteries, contract themselves. For where the frequency of the pulsations is but seventy-five in a minute, as in health; the contracting fibres, which constitute the side of the arteries, may move through a greater space in a given time, than where the frequency of pulsation is one hundred and fifty in a minute, as in some fevers with great debility. For if in those fevers the arteries do not expand themselves in their diastole to more than half the usual diameter of their diastole in health, the fibres which constitute their coats will move through a less space in a minute than in health, though they make two pulsations for one. Suppose the diameter of the artery during its systole to be one line, and that the diameter of the same, artery during its diastole, in health, is four lines, and in a fever, with great debi- lity, is only two lines—It follows, that the arterial fibres con- tract, in health, from a circle of twelve lines in circumference to a circle of three lines in circumference; that is, they move through a space of nine lines in length; while the arterial fibres in the fever, with debility, would twice contract from a circle of six lines, to a circle of three lines; that is, while they move through a space equal to six lines. Hence, though, the fre- quency of pulsation in fever be greater, as two to one, yet the velocity of contraction in health is greater, as nine to six, or as three to two. On the contrary, in inflammatory diseases with strength, as in the pleurisy, the velocity of the contracting sides of the arte- ries, is much greater than in health; for if we suppose the number of pulsations in a pleurisy to be half as much more than in health; that is, one hundred and twenty to eighty, (which is about what generally happens in inflammatory dis- eases) and if the diameter of the artery in diastole be one third greater than in health, which I believe is near the truth, the result 48 OF STIMULUS AND EXERTION. SECT. XII. 1. result will be, that the velocity of the contractile sides of the ar- teries will be in a pleurisy, as two and an half to one, compar- ed to the velocity of their contraction in a state of health; for if the circumference of the systole of the artery be three lines, and the diastole in health be twelve lines in circumfe- rence, and in a pleurisy eighteen lines; and secondly, if the ar- tery pulsates thrice in the diseased state for twice in the healthy one, it follows, that the velocity of contraction in the diseased state to that in the healthy state, will be forty-five to eighteen, or as two and a half to one. From hence it would appear, that if we had a criterion to determine the velocity of the arterial contractions, it would at the same time give us their strength, and thus be of more ser- vice in distinguishing diseases, than the knowledge of their fre- quency. As such a criterion cannot be had, the frequency of pulsation, the age of the patient being allowed for, will in some measure assist us to distinguish arterial strength from arterial debility; since, in inflammatory diseases, with strength, the fre- quency seldom exceeds one hundred and eighteen, or one hun- dred and twenty pulsations in a minute, unless under peculiar circumstances, as the great additional stimuli of wine or of external heat. 5. After a muscle or organ of sense has been excited into contraction, and the sensorial power ceases to act, the last situ- ation or configuration of it continues, unless it be disturbed by the action of some antagonist fibres, or other extraneous power. Thus, in weak or languid people, wherever they throw their limbs on their bed or sofa, there they lie, till ano- ther exertion changes their attitude; hence one kind of ocular spectra seems to be produced after looking at bright objects: thus, when a fire-stick is whirled round in the night, there ap- pears in the eye a complete circle of fire, the action or configu- ration of one part of, the retina not ceasing before the return of the whirling fire. Thus, if any one looks at the setting sun for a short time, and then covers his closed eyes with his hand, he will, for many seconds of time, perceive the image of the sun on his retina. A similar image of all other bodies would remain some time in the eye, but is effaced by the eternal change of the motions of the extremity of this nerve in our attention to other objects. See Sect. XVII. 1. 3. on sleep. Hence the dark spots, and other ocular spectra, are more frequently attended to, and re- main longer in the eyes of weak people, as after violent exer- cise, intoxication, or want of sleep. 6. A contraction of the fibres somewhat greater than usual, introduces 49 SECT. XII. 1. OF STIMULUS AND EXERTION. introduces pleasurable sensation into the system, according to the fourth law of animal causation. Hence the pleasure in the beginning of drunkenness is owing to the increased action of the system from the stimulus of vinous spirit, or of opium. If the contractions be still greater in energy or duration, pain- ful sensations are introduced, as in consequence of great heat, or caustic applications, or fatigue. If any part of the system, which is used to perpetual ac- tivity, as the stomach, or heart, or the fine vessels of the skin, acts for a time with less energy, another kind of painful sen- sation ensues, which is called hunger, or faintness, or cold. This occurs in a less degree in the locomotive muscles, and is called wearisomeness. In the two former kinds of sensation there is an expenditure of sensorial power; in these latter there is an accumulation of it. 7. We have used the words exertion of sensorial power as a general term to express either irritation, sensation, volition, or association; that is, to express the activity or motion of the spirit of animation, at the time it produces the contractions of the fibrous parts of the system. It may be supposed that there may exist a greater or less mobility of the fibrous parts of our system, or a propensity to be stimulated into contraction by the greater or less quantity or energy of the spirit of animation; and that hence, if the exertion of the sensorial power be in its natural state, and the mobility of the fibres be increased, the same quantity of fibrous contractions will be caused, as if the mobility of the fibres continues in its natural state, and the sensorial exertion be increased. Thus it may be conceived, that in diseases accompanied with strength, as in inflammatory fevers, with arterial strength, that the cause of greater fibrous contraction may exist in the in- creased mobility of the fibres, whose contractions are thence both more forcible and more frequent. And that in diseases attended with debility, as in nervous fevers, where the fibrous contractions are weaker and more frequent, it may be con- ceived that the cause consists in a decrease of mobility of the fibres; and that those weak constitutions, which are attended with cold extremities and large pupils of the eyes, may possess less mobility of the contractile fibres, as well as less quantity of exertion of the spirit of animation. In answer to this mode of reasoning, it may be sufficient to observe, that the contractile fibres consist of inert matter; and when the sensorial power is withdrawn, as in death, they possess no power of motion at all, but remain in their last state, whe- ther of contraction or relaxation, and must thence derive the whole 50 OF STIMULUS AND EXERTION. SECT. XII. 1. whole of this property from the spirit of animation. At the same time it is not improbable, that the moving fibres of strong people may possess a capability of receiving or containing a greater quantity of the spirit of animation than those of weak people. In every contraction of a fibre there is an expenditure of the sensorial power, or spirit of animation; and where the ex- ertion of this sensorial power has been for some time increase- ed, and the muscles or organs of sense have in consequence acted with greater energy, its propensity to activity is propor- tionally lessened; which is to be ascribed to the exhaustion or diminution of its quantity. On the contrary, where there has been less fibrous contraction than usual for a certain time, the sensorial power, or spirit of animation, becomes accumu- lated in the inactive part of the system. Hence vigour suc- ceeds rest; and hence the propensity to action, of all our or- gans of sense and muscles, is in a state of perpetual fluctuation The irritability, for instance, of the retina; that is, its quan- tity of sensorial power, varies every moment, according to the brightness or obscurity of the object last beheld, compared with the present one. The same occurs to our sense of heat, and to every part of our system, which is capable of being excited into action. When this variation of the exertion of the sensorial power becomes much and permanently above or beneath the natural quantity, it becomes a disease. If the irritative motions be too great or too little, it shews that the stimulus of external things affects this sensorial power too violently or too inertly. If the sensitive motions be too great or too little, the cause arises from the deficient or exuberent quantity of sensation produced in consequence of the motions of the muscular fibres or organs of sense. If the voluntary actions are diseased, the cause is to be looked for in the quantity of volition produced, in consequence of the desire or aversion occasioned by the painful or pleasur- able sensations above mentioned. And the diseases of associ- ations probably depend on the greater or less quantity of the other three sensorial powers by which they were formed. From whence it appears, that the propensity to action, whe- ther it be called irritability, sensibility, voluntarily, or associ- ability, is only another mode of expression for the quantity of sensorial power, rending in the organ, to be excited. And that, on the contrary, the words irritability and insensibility, toge- ther with inaptitude to voluntary and associate motions, are synonimous with deficiency of the quantity of sensorial power, or of the spirit of animation, residing in the organs to be ex- cited. II. Of 51 SECT. XII.2. OF STIMULUS AND EXERTION. II. Of sensorial Exertion. 1 . There are three circumstances to be attended to in the pro- duction of animal motions 1st. The stimulus. 2d. The sensorial power. 3d. The contractile fibre.— 1st. A stimu- lus, external to the organ, originally induces into action the sensorial faculty termed irritation; this produces the contrac- tion of the fibres, which, if it be perceived at all, introduces pleasure or pain; which, in their active state, are termed sen- sation, which is another sensorial faculty, and occasionally produces contraction of the fibres: this pleasure or pain is therefore to be considered as another stimulus, which may either act alone or in conjunction with the former faculty of the sensorium, termed irritation. This new stimulus of plea- sure or pain either induces into action the sensorial faculty, termed sensation, which then produces the contraction of the fibres; or it introduces desire or aversion, which excite into action another sensorial faculty, termed volition, and may therefore he considered as another stimulus, which either alone, or in conjunction with one or both of the two former facul- ties of the sensorium, produces the contraction of animal fibres. There is another sensorial power, that of association, which perpetually, in conjuction with one or more of the above, and frequently singly, produces the contraction of animal fibres, and which is itself excited into action by the previous motions of contracting fibres. Now, as the sensorial power, termed irritation, residing in any particular fibres, is excited into exertion by the stimulus of external bodies acting on those fibres; the sensorial power, termed sensation, residing in any particular fibres, is excited into exertion by the stimulus of pleasure or pain acting on those fibres; the sensorial power, termed volition, residing in any particular fibres, is excited into exertion by the stimulus of desire or aversion; and the sensorial power, termed associ- ation, residing in any particular fibres, is excited into action by the stimulus of other fibrous motions, which had frequent- ly preceded them. The word stimulus may therefore be used, without impropriety of language, for any of these four causes, which excite the four sensorial power into exertion. For though the immediate cause of volition has generally been termed a motive, and that of irritation only, has generally ob- tained the name of stimulus; yet, as the immediate cause which excites the sensorial powers of sensation, or of associa- tion, into exertion, have obtained no general name, we shall use the word stimulus for them all. I Hence 52 OF STIMULUS AND EXERTION. Sect. XII. 2. Hence the quantity of motion produced m any particular part of the animal system, will be as the quantity of stimulus and the quantity of sensorial power, or spirit of animation, re- siding in the contracting fibres. Where both these quantities are great, strength is produced, when that word is applied to the motions of animal bodies. Where either of them is defi- cient, weakness is produced, as applied to the motions of ani- mal bodies. Now, as the sensorial power, or spirit of animation, is per- petually exhausted by the expenditure of it in fibrous contrac- tions, and is perpetually renewed by the secretion or produc- tion of it in the brain and spinal marrow, the quantity of ani- mal strength must be in a perpetual state of fluctuation on this account; and if to this be added the unceasing variation of all the four kinds of stimulus above described, which produce the exertion of the sensorial powers, the ceaseless vicissitude of animal strength becomes easily comprehended. If the quantity of sensorial power remains the same, and the quantity of stimulus he lessened, a weakness of the fibrous con- tractions ensues, which may be denominated debility from defect of stimulus. If the quantity of stimulus remains the same, and the quantity of sensorial power be lessened, another kind of .weakness ensues, which may be termed debility from defect of sensorial power the former of these is called by Dr. Brown, in his Elements of Medicine, direct debility, and the latter indirect debility. The coincidence of some parts of this work, with correspondent deductions in the Brunonian Ele- menta Medicina, a work (with some exceptions) of great ge- nius, must be considered as confirmations of the truth or the theory, as they were probably arrived at by different trains of reasoning. Thus, in those who have been exposed to cold and hunger, there is a deficiency of stimulus. While in nervous fever there is a deficiency of sensorial power: and in habitual drunk- ards, in a morning before their usual potation, there is a defi- ciency both of stimulus and of sensorial power; while, on the other hand, in the banning of intoxication, there is an excess of stimulus; in the hot ach, after the hands have been immers- ed in snow, there is a redundancy of sensorial power; and in inflammatory diseases with arterial strength, there is an excess of both. Hence, if the sensorial power be lessened, while the quantity of stimulus remains the same quantity as in nervous fever, the frequen- cy of repetition of the arterial contractions may continue; but their force, in respect to removing obstacles, as in promoting the 53 SECT. XII. 2. OF STIMULUS AND EXERTION. the circulation of the blood, or the velocity of each contraction, will be diminished; that is, the animal strength will be lessened. And, secondly, if the quantity of sensorial power be lessened, and the stimulus be increased to a certain degree, as in giving opium in nervous fevers, the arterial contractions may be performed more frequently than natural, yet with less strength. And thirdly, if the sensorial power continues the same in respect to quantity, and the stimulus be somewhat diminished, as in going into a darkish room, or into a coldish bath, sup- pose of about eighty degrees of heat, as Buxton-bath, a tem- porary weakness of the affected fibres is induced, till an accu- mulation of sensorial power gradually succeeds, and counter- balances the deficiency of stimulus; and then the bath ceases to feel cold, and the room ceases to appear dark; because the fibres of the subcutaneous vessels, or of the organs of sense, act with their usual energy. A set of muscular fibres may thus be stimulated into violent exertion; that is, they may act frequently, and with their whole sensorial power, but may nevertheless not act strongly; because the quantity of their sensorial power was originally small, or was previously exhausted. Hence a stimulus may be great, and the irritation in consequence act with its full force, as in the hot paroxysms of nervous fever; but if the sensorial power, termed irritation, be small in quantity, the force of the fibrous contractions, and the times of their continuance in their contracted state, will be proportionally small. In the same manner, in the hot paroxysm of putrid fevers, which are shewn in Sect. XXXIII. to be inflammatory fe- vers, with arterial debility, the sensorial power, termed sensa- tion, is exerted with great activity; yet the fibrous contrac- tions, which produce the circulation of the blood, are perform ed without strength, because the quantity of sensorial power, then residing in that part of the system, is small. Thus, in irritative fever, with arterial strength, that is, with excess of spirit of animation, the quantity of exertion during the hot part of the paroxysm, is to be estimated from the quan- tity of stimulus, and the quantity of sensorial power; while in sensitive (or inflammatory) fever, with arterial strength, that is, with excess of spirit of animation, the violent and for- cible actions or the vascular system, during the hot part of the paroxysm, are induced by the exertions of two sensorial powers, which are excited by two kinds of stimulus. These are the sensorial power of irritation, excited, by the stimulus of bodies external to the moving fibres, and the sensorial power of 54 OF STIMULUS AND EXERTION. SECT. XII. 2. of sensation, excited by the pain in consequence of the increased contractions of those moving fibres. And in insane people, in some cases, the force of their mus- cular actions will be in proportion to the quantity of sensorial power which they possess, and the quantity of the stimulus of desire or aversion which excites their volition into action. At the same time, in other cases, the stimulus of pain or plea- sure, and the stimulus of external bodies, may excite into ac- tion the sensorial powers of sensation and irritation, and thus add greater force to their muscular actions. 2. The application of the stimulus, whether that stimulus be some quality of external bodies, or pleasure or pain, or de- sire or aversion, or a link of association, excites the corres- pendent sensorial power into action, and this causes the con- traction of the fibre. On the contraction of the fibre, a part of the spirit of animation becomes expended, and the fibre ceases to contract, though the stimulus continues to be applied, till, in a certain time, the fibre having received a supply of senso- rial power, is ready to contract again, if the stimulus continues to be applied. If the stimulus, on the contrary, be with drawn, the same quantity of quiescent sensorial power becomes resident in the fibre as before its contraction; as appears from the readiness for action of the large locomotive muscles of the body, in a short time after common exertion. But in those muscular fibres which are subject to constant stimulus, as the arteries, glands, and capillary vessels, another phenomenon occurs, if their accustomed stimulus be with- drawn; which is, that the sensorial power becomes accumu- lated in the contractile fibres, owing to the want of its be with perpetually expended, or carried away, by their usual unre- mitted contractions. And, on this account, those muscular fibres become afterwards excitable into their natural actions by a much weaker stimulus; or into unnatural violence of ac- tion, by their accustomed stimulus, as is seen in the hot fits of intermittent fevers, which are in consequence of the previous cold ones. Thus the minute vessels of the skin are constantly stimulated by the fluid matter of heat; if the quantity of this stimulus of heat be a while diminished, as in covering the hands with snow, the vessels cease to act, as appears from the paleness of the skin; if this cold application of snow be conti- nued but a short time, the sensorial power, which had habitu- ally been supplied to the fibres, becomes now accumulated in them owing to the want of its being expended by their accus- tomed contractions. And thence a less stimulus of heat will now excite them into violent contractions. It 55 SECT. XII. 2. OF STIMULUS AND EXERTION. If the quiescence of fibres, which had previously been sub- ject to perpetual stimulus, continues a longer time, or their ac- customed stimulus be more completely withdrawn, the accu- mulation of sensorial power becomes still greater, as in those exposed to cold and hanger; pain is produced, and the organ gradually dies from the chemical changes which take place in it; or it is, at a great distance of time, restored to action by sti- mulus applied with great caution, in small quantity, as hap- pens to some larger animals, and to many infects, which, dur- ing the winter months, lie benumbed with cold, and are said to deep, and to persons apparently drowned, or apparently frozen to death. Snails have been said to revive by throwing them into water, after having been many years shut up in the cabi- nets of the curious; and eggs and deeds in general, are restored to life after many months of torpor by the stimulus of warm water and moisture. The inflammation of schirrous tumours, which have long existed in a state of inaction, is a process of this kind, as well as the sensibility acquired by inflamed tendons and bones, which had, at their formation, a similar sensibility, which had so long lain dormant in their uninflamed state. 3. If, after long quiescence from defect of stimulus, the fi- bres, which had previously been habituated to perpetual sti- muls, are again exposed to but their usual quantity of it, as in those who have suffered the extremes of cold or hunger, a violent exertion of the affected organ commences, owing, as above explained, to the great-accumulation of sensorial power. This violent exertion not only diminishes the accumulated spi- rit of animation, but, at the same time, induces pleasure or pain into the system, which, whether it be succeeded by in- flammation or not, becomes an additional stimulus, and acting along with the former one, produces still greater exertions, and thus reduces the sensorial power, in the contracting fibres, be neath its natural quantity. When the spirit of animation is thus exhausted by useless exertions, the organ becomes torpid, or unexcitable into action, and a second fit of quiescence succeeds that of abundant acti- vity. During this second fit of quiescence, the sensorial power becomes again accumulated, and another fit of exer- tion follows in train. These vicissitudes of exertion and in- ertion of the arterial system, constitute the paroxysms of re- mittent fevers; or intermittent ones, when there is an interval of the natural action of the arteries between the exacerbations. In these paroxysms of fevers, which consist of the libration of the arterial system, between the extremes of exertion and quiescence, 56 OF STIMULUS AND EXERTION. SECT. XII. 3. quiescence, either the fits become less and less violent, from the contractile fibres becoming less and less excitable to the sti- mulus by habit, that is, by becoming accustomed to it, as ex- plained below, XII. 3. 1. or the whole sensorial power be comes exhausted, and the arteries cease to beat, and the patient dies in the cold part of the paroxysm. Or, secondly, so much pain is introduced into the system by the violent contractions of the fibres, that inflammation arises, which prevents future cold fits, by expending a part of the sensorial power in the ex- tension of old vessels or the production of new ones, and thus preventing the too great accumulation or exertion of it in other parts of the system; or which, by the great increase of stimu- lus, excites into great action the whole glandular system, as well as the arterial, and thence a greater quantity of sensorial power is produced in the brain, and thus its exhaustion in any peculiar part of the system, ceases to be affected. 4. Or, thirdly, in consequence of the painful or pleasurable sensation above mentioned, desire and aversion are introduced; and inordinate volition succeeds; which, by its own exertions, expends so much of the spirit of animation, that the two other sensorial faculties, or irritation and sensation, act so much fee- bler, that the paroxysms of fever, or that libration between the extremes of exertion and inactivity of the arterial system, gra- dually subsides. On this account a temporary insanity is a favourable sign in fevers, as I have had some opportunities of observing. III. Of repeated Stimulus. 1. When a stimulus is repeated more frequently than the expenditure of sensorial power can be renewed in the acting organ, the effect of the stimulus becomes gradually diminish- ed. Thus, if two grains of opium be swallowed by a person unused to so strong a stimulus, all the vascular systems in the body act with greater energy; all the secretions and the absorp- tion from those secreted fluids are increased in quantity; and pleasure or pain are introduced into the system, which adds an additional stimulus to that already too great. After some hours the sensorial power becomes diminished in quantity ex- pended by the great activity of the system; and thence, when the stimulus of the opium is withdrawn, the fibres will not obey their usual degree of natural stimulus, and a consequent torpor, or quiescence succeeds, as is experienced by drunkards, who, on the day after a great excess of spirituous potation, feel indigestion, head-ach, and general debility. In this fit of torpor or quiescence of a part or of the whole of. 57 SECT. XII. 3. OF STIMULUS AND EXERTION. of the system, an accumulation of the sensorial power in the affected fibres is formed, and occasions a second paroxysm of exertion, by the application only of the natural stimulus; and thus a libration of the sensorial exertion between one excess and the other, continues for two or three days, where the sti- mulus was violent in degree; and for weeks in some fevers, from the stimulus of contagious matter. But if a second dose of opium be exhibited before the fibres have regained their natural quantity of sensorial power, its ef- fect will be much less than the former, because the spirit of animation, or sensorial power, is in part exhausted by the pre- vious excess of exertion. Hence all medicines, repeated too frequently, gradually lose their effect, as opium and wine. Many things of disagreeable taste at first, cease to be disagree- ble by frequent repetition, as tobacco; grief and pain gradually diminish, and at length cease altogether; and hence life itself becomes tolerable. Besides the temporary diminution of the spirit of animation or sensorial power, which is naturally stationary or resident in every living fibre, by a single exhibition of a powerful stimulus, the contractile fibres themselves, by the perpetual application of a new quantity of stimulus, before they have regained their natural quantity of sensorial power, appear to suffer in their capability of receiving so much as the natural quantity of sen- sorial power; and hence a permanent deficiency of spirit of ani- mation takes place, however long the stimulus may have been withdrawn. On this cause depends the permanent debility of those who have been addicted to intoxication, the general weak- ness of old age, and the natural debility or irritability of those who have pale skins and large pupils of their eyes. There is a curious phenomenon belongs to this place, which has always appeared difficult of solution; and that is, that opium or aloes may be exhibited in small doses at first, and gradually increased to very large ones, without producing stupor or diarr- hœa. In this case, though the opium and aloes are given in such small doses as not to produce intoxication or catharsis, yet they are exhibited in quantities sufficient, in some degree, to exhaust the sensorial power, and hence a stronger and a stronger dose is required; otherwise the medicine would soon cease to act at all. On the contrary, if the opium or aloes be exhibited in a large dose at first, so as to produce intoxication or diarrhœa, after a few repetitions the quantity of either of them may be diminished, and they will still produce this effect. For the more powerful stimulus dissevers the progressive catenations of animal 58 OF STIMULUS AND EXERTION. SECT. XII. 3. animal motions, described in Sect. XVII. and introduces a new link between them; whence every repetition strengthens this new association or catenation, and the stimulus may be gradually decreased, or be nearly withdrawn, and yet the effect shall continue, because the sensorial power of association or catenation, being united with the stimulus, increases in energy with every repetition of the catenated circle; and it is by these means that all the irritative associations of motions are origi- nally produced. 2. When a stimulus is repeated at such distant intervals of time, that the natural quantity of sensorial power becomes completely restored in the acting fibres, it will act with the same energy as when first applied. Hence those who have lately accustomed themselves to large doses of opium, by begin- ning with small ones, and gradually increasing them, and re- peating them frequently, as mentioned in the preceding para- graph, if they intermit the use of it for a few days only, must Begin again with as small doses as they took at first; otherwise they will experience the inconveniences of intoxication. On this circumstance depend the constant unfailing effects of the various kinds of stimulus, which excite into action all the vascular systems in the body; the arterial, venous, absorb- ent, and glandular vessels, are brought into perpetual, unwea- ried action by the fluids, which are adapted to stimulate them; but these have the sensorial power of association added to that of irritation, and even, in some degree, that of sensation, and even of volition, as will be spoken of in their places; and life itself is thus carried on by the production of sensorial power being equal to its waste or expenditure in the perpetual move- ment of the vascular organization. 3. When a stimulus is repeated at uniform intervals of time, with such distances between them that the expenditure of sen- sorial power in the acting fibres becomes completely renewed, the effect is produced with greater facility or energy. For the sensorial power of association is combined with the senso- rial power of irritation; or, in common language, the acquired habit assists the power of the stimulus. This circumstance not only obtains in the annual and diur- nal catenations of animal motions, explained in Sect. XXXVI. but in every less circle of actions or ideas, as in the burthen of a song, or the iterations of a dance, and constitutes the plea- sure we receive from repetition and imitation, as treated of in Sect. XXII. 2. 4. When a stimulus has been many times repeated at uni- form intervals, so as to produce the complete action of the or- gan, 59 SECT. XII. 3. OF STIMULUS AND EXERTION. gan, it may then be gradually diminished, or totally with- drawn, and the action of the organ will continue; for the sensorial power of association becomes United with that of ir- ritation, and by frequent repetition becomes at length of suffi- cient energy to carry on the new link in the circle of actions, without the irritation which at first introduced it. Hence, when the bark is given at stated intervals for the cure of intermittent fevers, if sixty grains of it be given every three hours for the twenty-four hours preceding the expected parox- ysm, so as to stimulate the defective part of the system into action, and by that means to prevent the torpor or quiescence of the fibres, which constitutes the cold fit; much less than half the quantity, given before the time at which another pa- roxysm of quiescence would have taken place, will be suffi- cient to prevent it; because now the sensorial power, termed association, acts in a twofold manner. First, in respect to the period of the catenation in which the cold fit was produced, which is now dissevered by the stronger stimulus of the first doses of the bark; and, secondly, because each dose of bark being repeated at periodical times, has its effect increased by the sensorial faculty of association being combined with that of irritation. Now, when sixty grains of Peruvian bark are taken twice a day, suppose at ten o'clock and at six, for a fortnight, the ir- ritation excited by this additional stimulus becomes a part of the diurnal circle of actions, and will at length carry on the increased action of the system without the assistance of the sti- mulus of the bark. On this theory the bitter medicines, cha- lybeates, and opiates in appropriated doses, exhibited for a fortnight, give permanent strength to pale, feeble children, and other weak constitutions. 5. When a defect of stimulus, as of heat, recurs at certain diurnal intervals, which induces some torpor, or quiescence of a part of the system, the diurnal catenation of actions becomes disordered, and a new association with this link of torpid ac- tion is formed, on the next period the quantity of quiescence will be increased, suppose the same defect of stimulus to recur; because now the new association conspires with the defective irritation in introducing the torpid action of this part of the diurnal catenation. In this manner many fever-fits commence, where the patient is for some days indisposed at certain hours, before the cold paroxysm of fever is completely formed; See Sect. XVII. 3. 3. on catenation of animal motions. 6. If a stimulus, which at first excited the affected organ into so great exertion as to produce sensation, be continued K for 60 OF STIMULUS AND EXERTION. SECT. XII. 4. for a certain time, it will cease to produce sensation both then and when repeated, though the irritative motions in conse- quence of it may continue or be re-excited. Many catenations of irritative motions were at first suc- ceeded by sensation, as the apparent motions of objects when we walk past them, and probably the vital motions themselves in the early state of our existence. But as those sensations were followed by no movements of the system in consequence of them, they gradually ceased to be produced, not being join- ed to any succeeding link of catenation. Hence contagious matter, which has for some weeks stimulated the system into, great and permanent sensation, ceases afterwards to produce general sensation, or inflammation, though it may still induce topical irritations. See Sect. XXXIII. 2. 8. XIX. 10. Our absorbent system then seems to receive those contagious. matters, which it has before experienced, in the same manner as it imbibes common moisture, or other fluids; that is, with out being thrown into so violent action as to produce sensa- tion; the consequence of which is an increase of daily energy or activity, till inflammation and its consequences succeed. 7. If a stimulus excites an organ into such violent contrac- tions as to produce sensation, the motions of which organ had not usually produced sensation, this new sensorial power, added, to the irritation occasioned by the stimulus, increases the acti- vity of the organ. And if this activity be catenated with the diurnal circle of actions, an increasing inflammation is produc- ed, as in the evening paroxysms of small-pox, and other fevers with inflammation: and hence schirrous tumours, tendons, and membranes, and probably the arteries themselves, become in- flamed, when they are strongly stimulated. IV. Of Stimulus greater than natural. A quantity of stimulus greater than natural, producing an increased exertion of sensorial power, whether that exertion be in the mode of irritation, sensation, volition, or association, diminishes the general quantity of it. This fact is observable in the progress of intoxication, as the increased quantity or energy of the irritative motions, owing to the stimulus of vi- nous spirit, introduces much pleasurable sensation into the sys- tem, and much exertion of muscular or sensual motions in con- sequence of this increased sensation; the voluntary motions, and even the associate ones, become much impaired or dimi- nished, and delirium and staggering succeed. See Sect. XXI. on drunkenness. A hence the great prostration of the strength oi the locomotive muscles in some fevers, is owing to the 61 SECT. XII. 4. OF STIMULUS AND EXERTION. the exhaustion of sensorial power, by the increased action of the arterial system. In like manner a stimulus greater than natural, applied to a part of the system, increases the exertion of sensorial power in that part, and diminishes it in some other part. As in the commencement of scarlet fever, it is usual to see great redness and heat on the faces and breasts of children, while, at the same time, their feet are colder than natural: partial heats are observ- able in other fevers with debility, and are generally attended with torpor, or quiescence of some other part of the system. But these partial exertions of sensorial power are sometimes attended with increased partial exertions in other parts of the system, which sympathize with them, as the flushing of the face after a full meal. But these, therefore, are to be ascribed to sympathetic associations, explained in Sect. XXXV. and not to general exhaustion or accumulation of sensorial power. 2. A quantity of stimulus greater than natural, producing an increased exertion of sensorial power in any particular or- gan, diminishes the quantity of it in that organ. This appears from the contractions of animal fibres being not so easily excit- ed by a less stimulus, after the organ has been subjected to a greater. Thus, after looking at any luminous object of a small size, as at the letting sun for a short time, so as not much to fatigue the eye, this part of the retina becomes less sensible to smaller quantities of light: hence, when the eyes are turned on other less luminous parts of the sky, a dark spot is seen re- sembling the shape of the sun, or other luminous object which we last beheld. See Sect. XL. No. 2. Thus we are some time before we can distinguish objects in an obscure room after coming from bright day-light, though the iris presently contracts itself. We are not able to hear weak founds after loud ones. And the stomachs of those who have been much habituated to the stronger stimulus of ferment- ed or spirituous liquors, are not excited into due action by weaker ones. 3. A quantity of stimulus something greater than the last mentioned, or longer continued, induces the organ into spas- modic action, which ceases and recurs alternately. Thus, on looking for a time on the setting sun, so as not greatly to fatigue the sight, a yellow spectrum is seen when the eyes are closed and covered, which continues for a time, and then disappears and recurs repeatedly before it entirely vanishes. See Sect. XL. No. 5. Thus the action of vomiting ceases and is re- newed by intervals, although the emetic drug is thrown up with the first effect. A tenesmus continues by intervals some time 62 OF STIMULUS AND EXERTION. SECT. XII. 4. time after the exclusion of acrid excrement; and the pulsations of the heart of a viper are said to continue some time after it is cleared from its blood. In these cases, the violent contractions of the fibres produce pain, according to law 4; and this pain constitutes an additional kind or quantity of excitement, which again induces the fi- bres into contraction; and which painful excitement is again renewed, and again induces contractions of the fibres with gra- dually diminishing effect. 4. A quantity of stimulus greater than that last mentioned, or longer continued, induces the antagonist muscles into spas- modic action. This is beautifully illustrated by the ocular spectra, described in Sect. XL. No. 6, to which the reader is referred. From these experiments there is reason to conclude, that the fatigued part of the retina throws itself into a contrary mode of action, like of citation or pandiculation, as soon as the stimulus, which has fatigued it, is withdrawn; but that it still remains liable to be excited into action by any other colour except the colour with which it has been fatigued. Thus the yawning and stretching the limbs after a continued action or attitude, seems occasioned by the antagonist muscles being sti- mulated by their extension during the contractions of those in action, or in the situation in which that action last left them. 5. A quantity of stimulus greater than the last, or longer continued, induces variety of convulsions or fixed spasms, ei- ther of the affected organ, or of the moving fibres in other parts of the body. In parts respect to the spectra in the eye, this is well illustrated in No. 7 and 8 of Sect. XL. Epileptic convul- sions, as the emprosthotonos and opisthotonos, with the cramp of the calf of the leg, locked jaw, and other cataleptic fits, ap- pear to orignate from pain, as some of these patients scream aloud before the convulsion takes place; which seems at first to be an effort to relieve painful sensation, and afterwards an effort to prevent it. In these cases the violent contractions of the fibres produce so much pain, as to constitute a perpetual excitement; and that in so great degree, as to allow but small intervals of relaxation of the contracting fibres, as in convulsions; or no intervals at all, as in fixed spasms. 6. A quantity of stimulus greater than the last, or longer continued produces a paralysis of the organ. In many cases this paralysis is only a temporary effect, as on looking long on a small æra of bright red silk, placed on a sheet of white pa- per on the floor in a strong light, the red silk gradually becomes paler, and at length disappears; which evinces that a that a of part of the 63 SECT.XII. 5. OF STIMULUS AND EXERTION. the retina, by being violently excited, becomes for a time un- affected by the stimulus of that colour. Thus, cathartic me- dicines, opiates, poisons, contagious matter, cease to influence our system, after it has been habituated to the use of them, ex- cept by the exhibition of increased quantities of them; our fi- bres not only become unaffected by stimuli, by which they have previously been violently irritated, as by the matter of the small- pox or measles; but they also become unaffected by sensation, where the violent exertions, which disabled them, were in consequence of too great quantity of sensation. And, lastly, the fibres, which become disobedient to volition, are probably disabled by their too violent exertions, in consequence of too great a quantity of volition. After every exertion of our fibres, a temporary paralysis succeeds, whence intervals of all muscular contractions, as mentioned in No. 3 and 4 of this Section: the immediate cause of these more permanent kinds of paralysis is probably owing, in the same manner, to the too great exhaustion of the spirit of animation in the affected part; so that a stronger stimulus is required, or one of a different kind from that which occasion- ed those two violent contractions, to again excite the affected organ into activity; and if a stronger stimulus could be appli- ed, it must again induce paralysis. For these powerful stimuli excite pain at the same time that they produce irritation; and this pain not only excites fibrous motions by its stimulus, but it also produces volition; and thus all these stimuli acting at the same time, and sometimes with the addition of their associations, produce so great exertion as to expend the whole of the sensorial power in the affected fibres V. Of Stimulus less than natural. 1. A quantity of stimulus less than natural, producing a decreased exertion of sensorial power, occasions an accumula- tion of it. This circumstance is observable in the hæmipla- gia, in which the patients are perpetually moving the muscles which are unaffected. On this account we awake with greater vigour after sleep, because, during so many hours, the great usual expenditure of sensorial power in the performance of vo- luntary actions, and in the exertions of our organs of sense in consequence or the irritations occasioned by external objects had been suspended, and a consequent accumulation had taken place. In like manner the exertion of the sensorial power less than natural m one part of the system, is liable to produce an increase of 64 OF STIMULUS AND EXERTION. SECT. XII. 5. of the exertion of it in some other part. Thus, by the action of vomiting, in which the natural exertion of the motions of the stomach are destroyed or diminished, an increased absorp- tion of the pulmonary and cellular lymphatics is produced, as is known by the increased absorption of the fluid deposited in them in dropsical cases. But these partial quiescences of sen- sorial power, are also sometimes attended with other partial quiescences, which sympathize with them, as cold and pale ex- tremities from hunger. These, therefore, are to be ascribed to the associations of sympathy, explained in Sect. XXXV. and not to the general accumulation of sensorial power. 2. A quantity of stimulus less than natural, applied to fibres previously accustomed to perpetual stimulus, is succeeded by accumulation of sensorial power in the affected organ. The truth of this proportion is evinced, because a stimulus less than natural, if it be somewhat greater than that above men- tioned, will excite the organ so circumstanced into violent ac- tivity. Thus, on a frosty day with wind, the face of a person exposed to the wind is at, first pale and shrunk; but on turning the face from the wind, it becomes soon of a glow with warmth and flushing. The glow of the skin in emerging from the cold-bath, is owing to the same cause. It does not appear that an accumulation of sensorial power above the natural quantity, is acquired by those muscles which are not subject to perpetual stimulus, as the locomotive mus- cles: these, after the greatest fatigue, only acquire by rest their usual aptitude to motion; whereas the vascular system, as the heart and arteries, after a short quiescence, are thrown into violent action by their natural quantity of stimulus. Nevertheless, by this accumulation of sensorial power during the application of decreased stimulus, and by the exhaustion of it during the action of increased stimulus, it is wisely pro- vided, that the actions of the vascular muscles and organs of sense are not much deranged by small variations of stimulus as the quantity of sensorial power becomes, in some measure, inversely as the quantity of stimulus. 3. A quantity of stimulus less than that mentioned above and continued for some time, induces pain in the affected or- gan; as the pain of cold in the hands, when they are immersed in snow, is owing to a deficiency of the stimulation of heat. Hunger is a pain from the deficiency of the stimulation of food. Pain in the back at the commencement of ague-fits, and the head-achs which attend feeble people, are pains from defect of stimulus, and are hence relieved by opium, essential oils, and spirit of wine. As 65 SECT. XII. 5. OF STIMULUS AND EXERTION. As the pains which originate from defect of stimulus only occur in those parts of the system which have been previously subjected to perpetual stimulus; and as an accumulation of sensorial power is produced in the quiescent organ along with the pain, as in cold or hunger, there is reason to believe, that the pain is owing to the accumulation of sensorial power. For, in the locomotive muscles, in the retina of the eye, and other organs of senses, no pain occurs from the absence of sti- mulus, nor any great accumulation of, sensorial power beyond their natural quantity, since these organs have not been used to a perpetual supply of it. There is, indeed, a greater accumu- lation occurs in the organ of vision after its quiescence, because it is subject to more constant stimulus. 4. A certain quantity of stimulus less than natural, induces the moving organ into feebler and more frequent contractions, as mentioned in No. I. 4. of this Section. For each contrac- tion moving through a less space, or with less force, that is, with less expenditure of the spirit of animation, is sooner relax- ed, and the spirit of animation, derived at each interval into the acting fibres, being less, these intervals likewise become shorter. Hence the tremours of the hands of people accustomed to vinous spirit, till they take their usual stimulus; hence the quick pulse in fevers attended with debility, which is greater than in fevers attended with strength; in the latter, the pulse seldom beats above 120 times in a minute, in the former it fre- quently exceeds 140. It must be observed, that in this and the two following arti- cles, the decreased action of the system is probably more fre- quently occasioned by deficiency in the quantity of sensorial power, than in the quantity of stimulus. Thus those feeble constitutions which have large pupils of their eyes, and all who labour under nervous fevers, seem to owe their want of natural quantity of activity in the system, to the deficiency of sensorial power; since, as far as can be seen, they frequently possess the natural quantity of stimulus. 5. A certain quantity of stimulus, less than that above men- tioned, inverts the order of successive fibrous contractions; as in vomiting, the vermicular motions of the stomach and duo- denum are inverted, and their contents ejected; which is pro- bably owing to the exhaustion of the spirit of animation in the acting muscles, by a previous excessive stimulus, as by the root of ipecacuanha, and the consequent defect of sensorial power. The same retrogade motions affect the whole intestinal canal in ileus; and the œsophagus, in globus hystericus. See this farther explained in Sect. XXIX. No. 11 on Retrogade Mo- tions. I must 66 OF STIMULUS AND EXERTION. SECT. XII. 6. I must observe, also, that something similar happens in the production of our ideas, or sensual motions, when they are too weakly excited: when any one is thinking intensely about one thing, and carelessly conversing about another, he is liable to use the word of a contrary meaning to that which he designed, as cold weather for hot weather, summer for winter. 6. A certain quantity of stimulus less than that above men- tioned, is succeeded by paralysis, first of the voluntary and sen- sitive motions, and afterwards of those of irritation and of association, which constitute death. VI. Cure of increased exertion. 1. The cure which nature has provided for the increased exertion of any part of the system, consists in the consequent expenditure of the sensorial power. But as a greater torpor follows this exhaustion of sensorial power, as explained in the next paragraph, and a greater exertion succeeds this torpor, the constitution frequently finks under these increasing libra- tions, between exertion and quiescence, till at length complete quiescence. that is, death, closes the scene. For, during the great exertion of the system in the hot fit of fever, an increase of stimulus is produced from the greater mo- mentum of the blood, the greater distention of the heart and arteries, and the increased production of heat, by the violent actions of the system, occasioned by this augmentation of sti- mulus; the sensorial power becomes diminished in a few hours much beneath its natural quantity, the vessels at length cease to obey even these great degrees of stimulus, as shewn in Sect. XL. 9. 1. and a torpor of the whole or of a part of the system ensues. Now, as this second cold fit commences with a greater de- ficiency of sensorial power, it is also attended with a greater deficiency of stimulus than in the preceding cold fit; that is, with less momentum of blood, less distention of the heart. On this account the second cold fit becomes more violent and of longer duration than the first; and as a greater accumulation of sensorial power must be produced before the system of ves- sels will again obey the diminished stimulus, it follows, that the second hot fit of fever will be more violent than the former one: and that unless some other causes counteract either the violent exertions in the hot fit, or the great torpor in the cold fit, life will at length be extinguished, by the expenditure of the whole of the sensorial power. And from hence it appears, true means of curing fevers must be such as decrease the action of the system in the hot fit, and increase it in the cold 67 SECT. XII. 7. OF STIMULUS AND EXERTION. cold fit; that is, such as prevent the too great diminution of sensorial power in the hot fit, find the too great accumulation of it in the cold one. 2. Where the exertion of the sensorial powers is much in- creased, as in the hot fits of fever or inflammation, the follow- ing are the usual means of relieving it. Decrease the irrita- tions by blood-letting, and other evacuations; by cold water taken into the stomach, or injected as enema, or used external- ly; by cold air breathed into the lungs, and diffused over the skin; with food of less stimulus than the patient has been ac- customed to. 3. As a cold fit, or paroxysm of inactivity of some parts of the system, generally precedes the hot fit, or paroxysm of exertion, by which the sensorial power becomes accumulated; this cold paroxysm should be prevented by stimulant medicines and diet, as wine, opium, bark, warmth, cheerfulness, anger, surprise. 4. Excite into greater action some other part of the sys- tem, by which means the spirit of animation may be in part expended, and thence the inordinate actions of the diseased part may be lessened. Hence, when a part of the skin acts violently, as of the face in the eruption of the small-pox, if the feet be cold they should be covered. Hence the use of a blister applied near a topical inflammation. Hence opium and warm bath relieve pains both from excess and defect of stimulus. 5. First increase the general stimulation above its natural quantity, which may in some degree exhaust the spirit of ani- mation; and then decrease the stimulation beneath its natural quantity. Hence, after sudorific medicines and warm air, the application of refrigerants may have greater effect, if they could be administered without danger of producing too great torpor of some part of the system; as frequently happens to people in health from coming out of a warm room into the cold air, by which a topical inflammation, in consequence of torpor of the mucous membrane of the nostril, is produced, and is termed a cold in the head. VII. Cure of decreased Exertion. 1. Where the exertion of the sensorial powers is much decreased, as in the cold fits of fever, a gradual accumulation of the spirit of animation takes place; as occurs in all cases where inactivity or torpor of a part of the system exists; this accumulation of sensorial power increases, till stimuli less than natural are efficient to throw it into action, then the L cold 68 OF STIMULUS AND EXERTION. Sect. XII. 7. cold fit ceases; and, from the action of the natural stimuli, a hot one succeeds with increased activity of the whole system. So, in fainting fits, or syncope, there is a temporary deficien- cy of sensorial exertions, and a consequent quiescence of a great part of the system. This quiescence continues, till the sensorial power becomes again accumulated in the torpid or- gans; and then the usual diurnal stimuli excite the revivescent parts again into action; but as this kind of quiescence conti- nues but a short time compared to the cold paroxysm of an ague, and less affects the circulatory system, a less superabun- dency of exertion succeeds in the organs previously torpid, and a less excess of arterial activity. See Sect. XXXIV. 1. 6. 2. In the diseases occasioned by a defect of sensorial exer- tion, as in cold fits of ague, hysteric complaint, and nervous fever, the following means are those commonly used. 1. In- crease the stimulation above its natural quantity for some weeks, till a new habit of more energetic contraction of the fibres is established. This is to be done by wine, opium, bark, steel, given at exact periods, and in appropriate quantities; for if these medicines be given in such quantity as to induce the least degree of intoxication, a debility succeeds from the useless ex- haustion of spirit of animation, in consequence of too great exertion of the muscles, or organs of sense. To these irrita- tive stimuli should be added the sensitive ones of cheerful ideas, hope, affection. 3. Change the kind of stimulus. The habits acquired by the constitution depend on such nice circumstances, that when one kind of stimulus ceases to excite the sensorial power into the quantity of exertion necessary to health, it is often suffici- ent to change the stimulus for another apparently similar in quantity and quality. Thus, when wine ceases to stimulate the constitution, opium, in appropriate doses, supplies the de- fect; and the contrary. This is also observed in the effects of cathartic medicines; when one loses its power, another, ap- parently less efficacious, will succeed. Hence a change of diet, drink, and stimulating medicines, is often advantageous in diseases of debility. 4. Stimulate the organs, whose motions are associated with the torpid parts of the system. The actions of the minute ves- sels of the various parts of the external skin, are not only asso- ciated with each other, but are strongly associated with those; of some of the internal membranes, and particularly of the stomach. Hence, when the exertion of the stomach is less than natural, and indigestion and heart-burn succeed, nothing so certainly removes these symptoms, as the stimulus of a blis- ter 69 SECT. XII.7. OF STIMULUS AND EXERTION. ter on the back. The coldness of the extremities, as of the nose, ears, or fingers, are hence the best indication for the suc- cessful application of blisters. 5. Decrease the stimulus for a time. By lessening the quan- tity of heat for a minute or two, by going into the cold bath, a great accumulation of sensorial power is produced; for, not only the minute vessels of me whole external skin, for a time become inactive, as appears by their paleness, but the minute vessels of the lungs lose much of their activity also, by concert with those of the skin, as appears from the difficulty of breath- ing at first going into cold water. On emerging from the bath, the sensorial power is thrown into great exertion by the stimu- lus of the common degree of me warmth of the atmosphere, and a great production of animal heat is the consequence. The longer a person continues in the cold bath, the greater must he the present inertion of a great part of the system, and in consequence, a greater accumulation of sensorial power. Whence M. Pomè recommends some melancholy patients to be kept from two to six hours in spring-water, and in baths still colder. 6. Decrease the stimulus for a time below the natural, and then increase it above natural. The effect of this process, improperly used, is seen in giving much food, or applying much warmth, to those who have been previously exposed to great hunger, or to great cold. The accumulated sensorial power is thrown into so violent exertion, that inflammations and mortifications supervene, and death closes the catastrophe. In many diseases this method is the most successful; hence the bark in agues produces more certain effect after the previous exhibition of emetics. In diseases attended with violent pain, opium has double the effect, if venesection and a cathartic have been previously used. On this seems to have been founded the successful practice of Sydenham, who used venesection and, a cathartic in cholorisis, before the exhibition of the bark, steel, and opiates. 7. Prevent any unnecessary expenditure of sensorial power. Hence, in fevers with debility, a decumbent posture is prefer- red, with silence, little light, and such a quantity of heat as may prevent any chill sensation, or any coldness of the extremities. The pulse of patients in fevers with debility, increases in fre- quency above ten pulsations in a minute on their rising out of bed. For the expenditure of sensorial power to preserve an erect posture of the body, adds to the general deficiency of it, and thus affects the circulation. 8. The longer in time, and the greater in degree, the quie- scence 70 OF STIMULUS AND EXERTION. SECT. XII. 7. scence or inertion of an organ has been, so that it still retains life or excitability, the less stimulus should at first be applied to it. The quantity of stimulation is a matter of great nicety to determine, where the torpor or quiescence of the fibres has been experienced in a great degree, or for a considerable time, as in cold fits of the ague, in continued fevers with great debi- lity, or in people famished at sea, or perishing with cold. In the two last cases, very minute quantities of food should be first supplied, and very few additional degrees of heat. In the two former cases, but little stimulus of wine or medicine, above what they had been lately accustomed to, should be exhibited, and this at frequent and dated intervals, so that the effect of one quantity may be observed before the exhibition of another. If these circumstances are not attended to, as the sensorial power becomes accumulated in the quiescent fibres, an inor- dinate exertion takes place, by the increase of stimulus acting on the accumulated quantity of sensorial power, and either the paralysis, or death of the contractile fibres ensues, from the to- tal expenditure of the sensorial power in the affected organ, owing to this increase of exertion, like the debility after intox- ication. Or, secondly, the violent exertions above mentioned, produce painful sensation, which becomes a new stimulus, and by thus producing inflammation, and increasing the activity of the fibres already too great, sooner exhausts the whole of the sensorial power in the acting organ, and mortification; that is, the death of the part, supervenes. Hence there have been many instances of people, whose limbs have been long benumbed by exposure to cold, who have lost them by mortification, on their being too hastily brought to the fire; and of others, who were nearly famished at sea, who have died soon after having taken not more than an usual meal of food. I have heard of two well attested instances of pa- tients, in the cold fit of ague, who have died from the exhibit- tion of gin and vinegar, by the inflammation which ensued. And in many fevers attended with debility, the unlimited use of wine, and the wanton application of blisters, I believe, have de- stroyed numbers, by the debility consequent to too great stimu- lation; that is, by the exhaustion of the sensorial power by its inordinate exertion. Wherever the least degree of intoxication , exists, a propor- tional debility is the consequence; but there is a golden rule by which the necessary and useful quantity of stimulus, in fevers with debility may be ascertained. When wine or beer are exhibited, either alone, or diluted with water, if the pulse be comes flower, the stimulus is of a proper quantity, and should be 71 SECT. XIII. 1. OF VEGETABLE ANIMATION. be repeated every two or three hours, or when the pulse again becomes quicker. In the chronical debility, brought on by drinking spirituous or fermented liquors, there is another golden rule, by which I have successfully directed the quantity of spirit which they may safely lessen, for there is no other means by which they can re- cover their health. It should be premised, that, where the power of digestion in these patients is totally destroyed, there is not much reason to expect: a return to healthful vigour. I have directed several of these patients to omit one fourth part of the quantity of vinous spirits they have been lately ac- customed to; and if in a fortnight their appetite increases, they are advised to omit another fourth part; but if they perceive that their digestion becomes impaired for the want or this quan- tity of spirituous potation, they are advised to continue as they are, and rather bear the ills they have, than risk the encounter of greater. At the same time, fresh-meat, with or without spice, is recommended, with Peruvian bark, and steel, in small quan- tities, between their meals, and half a grain of opium, or a grain, with five or eight grains of rhubarb at night. SECT. XIII. OF VEGETABLE ANIMATION. I. 1. Vegetables are irritable, mimosa, dionæa muscipula. Vegetable secretions. 2. Vegetable buds are inferior ani- mals, are liable to greater or less irritability. II. Sta- mens and pistils of plants shew marks of sensibility. III. Vegetables possess some degree of volition. IV. Motions of plants are associated like those of animals. V. 1. Ve- getable structure like that of animals, their anthers and stigmas are living creatures. Male-flowers of Vallisne- ria. 2. Whether vegetables possess ideas? They have organs of sense, as of touch and smell, and ideas of exter- nal things. I. 1. THE fibres of the vegetable world, as well as those of the animal, are excitable into a variety of motion by the ir- ritations of external objects. This appears particularly in the mimosa or sensitive plant, whose leaves contract on the slightest injury: the dionæa muscipula, which was lately brought over from the marshes of America, presents us with another curi- ous instance of vegetable irritability; its leaves are armed with spines 72 OF VEGETABLE ANIMATION. SECT. XIII. 1. spines on their upper edge, and are spread on the ground around their stem; when an infect creeps on any of them in its pas- sage to the flower or seed, the leaf shuts up like a steel rat-trap, and destroys its enemy. See Botanic Garden, Part II. note on Silene. The various secretions of vegetables, as of odour, fruit, gum, resin, wax. honey, seem brought about in the same man- ner as in the glands of animals: the tasteless moisture of the earth is converted by the hop-plant, into a bitter juice; as by the caterpillar in the nut-shell, the sweet kernel is converted into a bitter powder. While the powder of absorption in the roots and barks of vegetables, is excited into action by the flu- ids applied to their mouths, like the lacteals and lympatics of animals. 2. The individuals of the vegetable world may be considered as inferior or less per sea animals; a tree is a congeries of many living buds, and in this respect resembles the branches of coral line, which are a congeries of a multitude of animals. Each of these buds of a tree has its proper leaves or petals for lungs, produces its viviparous or its oviparous offspring in buds or feeds; has its own roots, which, extending down the stem of the tree, are interwoven with the roots of the other buds, and form the bark, which is the only living part of the stem, is annually renewed, and is superinduced upon the former bark, which then dies, and, with its stagnated juices gradually har- dening into wood, forms the concentric circles which we see in blocks of timber. The following circumstances evince the individuality of the buds of trees. First, there are many trees whose whole internal wood is perished, and yet the branches are vegete and healthy. Secondly, the fibres of the barks of trees are chiefly longitude- nal, resembling roots, as is beautifully seen in those prepared barks that were lately brought from Otaheita. Thirdly, in ho- rizontal wounds of the bark of trees, the fibres of the upper lip are always elongated downwards like roots, but those of the lower lip do not approach to meet them. Fourthly, if you wrap wet moss round any joint of a vine, or cover it with moist earth, roots will shoot out from it. Fifthly, by the inoculation or engrafting of trees, many fruits are produced from one stem. Sixthly, a new tree is produced from a branch plucked from an old one, and set in the ground. Whence it appeals, that the buds of deciduous trees are so many annual plants; that the bark is a contexture of the roots of each individual bud; and that the internal wood is of no other use but to support them in the air; and that thus they resemble the animal world in their individuality. The 73 SECT. XIII. 4. OF VEGETABLE ANIMATION. The irritability of plants like that of animals, appeals li- able to be increased or decreased by habit; for those trees or shrubs, which are brought from a colder climate to a warmer, put on their leaves and blossoms a fortnight sooner than the indigenous ones. Professor Kalm, in his travels in New-York, observes, that the apple-trees brought from England, blossom a fortnight sooner than native ones. In our country, the shrubs that are brought a degree or two from the north, are observed to flou- rish better than those which come from the south. The Sibe- rian barley and cabbage are said to grow larger in this climate, than the similar more southern vegetables. And our hoards of roots, as of potatoes and onions, germinate with less heat in spring, after they have been accustomed to the winter's cold, than in autumn, after the summer's heat. II. The stamens and pistils of flowers mew evident marks of sensibility, not only from many of the stamens and some pistils approaching to each other at the season of impregnation, but from many of them closing their petals and calyxes during the cold parts of the day. For this cannot be ascribed to irri- tation, because cold means a defect of the stimulus of heat; but, as the want of accustomed stimuli produces pain, as in coldness, hunger, and thirst of animals, these motions of vege- tables, in closing up their flowers, must be ascribed to the disa- greeable sensation, and not to the irritation of cold. Others close up their leaves during darkness, which, like the former, cannot be owing to irritation, as the irritating material is withdrawn. The approach of the anthers in many flowers to the stig- mas, and of the pistils of some flowers to the anthers, must be ascribed to the passion of love, and hence belongs to sensation not to irritation. III. That the vegetable world possesses some degree of vo- luntary powers, appears from their necessity to sleep, which we have shewn, in Sect. XVIII. to consist in the temporary aboli- tion of voluntary power. This voluntary power seems to be exerted in the circular movement of the tendrils of vines and other climbing vegetables; or in the efforts to turn the upper surface of their leaves, or their flowers to the light. IV. The association of fibrous motions are observable in the vegetable world as well as in the animal. The divisions of the leaves of the sensitive plant have been accustomed to con- tract at the same time from the absence of light hence, if by any other circumstance, as a slight stroke or injury, one div- sion is irritated into contraction, the neighbouring ones con- tract 74 OF VEGETABLE ANIMATION. SECT. XIII. 5. tract also, from their motions being associated with those of the irritated part. So the various stamina of the class of syn- genesia have been accustomed to contract together in the even- ing, and thence, if you stimulate one of them with a pin, ac- cording to the experiment of M. Colvolo, they all contract from their acquired associations. To evince that the collapsing of the sensitive plant is not owing to any mechanical vibrations propagated along the whole branch, when a single leaf is struck with the finger, a leaf of it was slit with sharp scissors, and some seconds of time passed before the plant seemed sensible of the injury; and then the whole branch collapsed as far as the principal stem. This ex- periment was repeated several , times with the least possible im- pulse to the plant. V. 1. For the numerous circumstances in which vegeta- ble buds are analogous to animals, the reader is referred to the additional notes at the end of the Botanic Garden, Part I. It is there shewn, that the roots of vegetables referable the lac- teal system of animals; the sap-vessels in the early spring, be- fore their leaves expand, are analogous to the placental vessels of the fœtus; that the leaves of land-plants resemble lungs, and those of aquatic plants the gills of fish; that there are other systems of vessels resembling the vena portarum of quadrupeds, or the aorta of fish; that the digestive power of vegetables is similar to that of animals converting, the fluids which they absorb into sugar; that their feeds referable the eggs of animals, and their buds and bulbs their viviparous off- spring. And, lastly, that the anthers and stigmas are real animals, attached, indeed, to their parent tree, like polypi or coral insects, but capable of spantaneous motion; that they are affected with the passion of love, and furnished with powers of re-producing their species, and are fed with honey like the moths and butterflies, which plunder their nectaries. See Botanic Garden, Part I. add. note XXXIX. The male flowers of vallisneria approach still nearer to apparent animality, as they detach themselves from the parent plant, and float on the surface of the water to the female ones. Botanic Garden, Part II. art. Vallisneria. Other flowers, of the classes of monecia and diecia, and polygamia, discharge the fecundating ferina, which, floating in the air, is carried to the stigma of the female flowers, and that at considerable distances. Can this be affected by any specific attraction? or, like the diffusion of the odorous particles of flowers, is it left to the currents of winds and the accidental miscarriages of it coun- tracted by the quantity of its production? 2. This 75 SECT. XIII. 5. OF VEGETABLE ANIMATION. 75 2. This leads us to a curious enquiry, whether vegetables have ideas of external things? As all our ideas are originally received by our senses, the question may be changed to, whe- ther vegetables possess any organs of sense? Certain it is, that they possess a sense of heat and cold, another of moisture and dryness, and another of light and darkness; for they close their petals occasionally from the presence of cold, moisture, or darkness. And it has been already shewn, that these actions cannot be performed simply from irritation, because cold and darkness are negative quantities, and on that account sensation or volition are implied, and, in consequence, a sensorium or union of their nerves. So when we go into the light, we contract the iris; not from any stimulus of the light on the fine muscles of the iris, but from its motions being associated with the sensation of too much light on the retina, which could not take place without a sensorium or centre of union of the nerves of the iris with those of vision. See Botanic Garden, Part I. Canto 3. 1. 440, note. Besides these organs of sense, which distinguish cold, mois- ture, and darkness, the leaves of mimosa, and of dionæa, and of drosera, and the stamens of many flowers, as of the berber- ry, and the numerous class of syngenesia, are sensible to me- chanic impact; that is, they possess a sense of touch, as well as a common sensorium; by the medium of which their muscles are excited into action. Lastly, in many flowers the anthers, when mature, approach the stigma; in others the female or- gan approaches to the male. In a plant of collinsonia, a branch of which is now before me, the two yellow stamens are about three eighths of an inch high, and diverge from each other, at an angle of about fifteen degrees; the purple style is half an inch high, and in some flowers is now applied to the stamen on the right hand, and in others to that of the left; and will, I suppose, change place to-morrow in those where the an- thers have not yet effused their power. I ask, by what means are the anthers in many flowers, and stigmas in other flowers, directed to find their paramours? How do either of them know that the other exists in their vi- cinity? Is this curious kind of storge produced by mechanic attraction, or by the sensation of love? The latter opinion is supported by the strongest analogy, because a re-production of the species is the consequence; and then another organ of sense must be wanted to direct these vegetable amourettes to find each other, one probably analogous to our sense of smell, which in the animal world directs the new-born infant to its source of nourishment, and they may thus possess a faculty of perceiving as well as of producing odours. M Thus 76 PRODUCTION OF IDEAS. SECT. XIV. 1. Thus, besides a kind of taste at the extremities of their roots, similar to that of the extremities of our lacteal vessels, for the purpose of selecting their proper food; and besides different kinds of irritability residing in the various glands, which separate honey, wax, resin, and other juices from their blood; vegetable life seems to possess an organ of sense to dis- tinguish the variations of heat, another to distinguish the va- rying degrees of moisture, another of light, another of touch, and probably another analogous to our sense of smell. To these must be added the indubitable evidence of their passion of love; and I think we may truly conclude, that they are furnish- ed with a common sensorium belonging to each bud, and that they must occasionally repeat those perceptions either in their dreams or waking hours, and consequently possess ideas of so many of the properties of the external world and of their own existence. SECT. XIV. OF THE PRODUCTION OF IDEAS. I. Of material and immaterial beings. Doctrine of St. Paul. II. I. Of the sense of touch. Of solidity. 2. Of figure. Motion. Time. Place. Space. Number. 3. Of the penetrability of matter. 4. Spirit of ani- mation possesses solidity, figure, visibility, &c. Of spi- rits and angels. 5. The existence of external things. III. Of vision. IV. Of hearing. V. Of smell and taste. VI. Of the organ of sense by which we perceive heat and cold, not by the sense of touch. VII. Of the sense of extension; the whole of the locomotive muscles may be considered as one organ of sense. VIII. Of the senses of hunger, thirst, want of fresh air, suckling chil- dren, and lust. IX. Of many other organs of sense be longing to the glands. Of painful sensations from the excess of light, pressure, heat, itching, caustics, and electricity. I. PHILOSOPHERS have been much perplexed to understand, in what manner we become acquainted with the exter- nal world; insomuch that Dr. Berkly even doubted its exist- ence, from having observed, (as he thought) that none of our ideas resemble their correspondent objects. Mr. Hume asserts that our belief depends on the greater distinctness or energy of our ideas from perception; and Mr. Reid has lately contended, that 77 SECT. XIV. 2. PRODUCTION OF IDEAS. that our belief of external objects is an innate principle, neces- sarily joined with our perceptions. So true is the observation of the famous Malbranch, " that our senses are not given us to discover the essences of things, but to acquaint us with the means of preserving our existence," (L. I. ch. v.) a melancholy reflection to philosophers! Some philosophers have divided all created beings into ma- terial and immaterial: the former including all that part of be- ing, which obeys the mechanic laws of action and re-action, but which can begin no motion of itself; the other is the cause of all motion, and is either termed the power, of gravity, or of specific attraction, or the spirit of animation. This immate- rial agent is supposed to exist in or with. matter, but to be quite distinct from it, and to be equally capable of existence, after the matter, which now possesses it, is decomposed. Nor is this theory ill supported by analogy, since heat, electricity, and magnetism can be given to or taken from a piece or iron; and must therefore exist, whether separated from the metal, or combined with it. From a parity of rea- soning, the spirit of animation would appear to be capable of existing as well separately from the body as with it. I beg to be understood, that I do not wish to dispute about words, and am ready to allow, that the powers of gravity, specific attraction, electricity, .magnetism, and even the spirit of animation, may consist of matter of a finer kind; and to believe, with St. Paul and Malbranch, that the ultimate cause only of all motion is immaterial, that is, God. St. Paul says, in him we live, and move, and have our being;" and, in the 15th chapter of the Corinthians, distinguishes between the psyche or living spirit, and the pneuma or reviving spirit. By the words spirit of animation or sensorial power, I mean only that animal life which mankind possesses in common with brutes, and in some degree even with vegetables, and leave the consideration of the immortal part of us, which is the object of religion, to those who treat of revelation. II. 1. Of the Sense of Touch. The first ideas we become acquainted with, are those of the sense of touch; for the fœtus must experience some varieties of agitation, and exert some muscular action, in the womb; and may, with great probability, be supposed thus to gain some ideas of its own figure, of that of the uterus, and of the tenacity of the fluid that surrounds it, (as appears from the facts mention- ed in the succeeding Section upon Instinct.) Many of the organs of sense are confined to a small part of the 78 PRODUCTION OF IDEAS. Sect. XIV. 2. the body, as the nostrils, ear or eye, whilst the sense of touch is diffused over the whole skin, but exists, with a more exqui- site degree of delicacy, at the extremities of the fingers and thumbs, and in the lips. The sense of touch is thus very com- modiously disposed, for the purpose of encompassing smaller bo- dies, and for adapting itself to the inequalities of larger ones. The figure of small bodies seems to be learnt by children by their lips as much as by their fingers; on which account they put every new object to their mouths, when they are satiated with food, as well as when they are hungry. And puppies seem to learn their ideas of figure principally by the lips in their mode of play. We acquire our tangible ideas of objects either by the sim- ple pressure of this organ of touch against a solid body, or by moving our organ of touch along the surface of it: in the for- mer case, we learn the length and breadth of the object by the quantity of our organ of touch that is impressed by it: in the latter case, we learn the length and breadth of objects by the continuance of their pressure on our moving organ of touch. It is hence that we are very slow in acquiring our tangible ideas, and very slow in recollecting them; for if I now think of the tangible idea of a cube, that is, if I think of its figure, I must conceive myself as passing my fingers over it, and seem in some measure to feel the idea, as I formerly did the impres- sion at the ends of them, and am thus very slow in distinctly recollecting it. When a body compresses any part of our sense of touch, what happens? First, this part of our sensorium undergoes a mechanical compression, which is termed a stimulus; second- ly, an idea, or contraction of a part of the organ of sense, is excited; thirdly, a motion of the central parts, or of the whole sensorium, which is termed sensation, is produced; and these three constitute the perception of solidity. 2. Figure, Motion, Time, Place, Space, Number. No one will deny, that the medulla of the brain and nerves has a certain figure; which, as it is diffused through nearly the whole of the body, must have nearly the figure of that body. Now it follows, that the spirit of animation, or living principle, as it occupies this medulla, and no other part, (which is evinced by a great variety of cruel experiments on living animals) it follows, that this spirit of animation has also the same figure as the medulla above described. I appeal to common sense! the spirit of animation acts; where does it act? It acts wherever there is the medulla above mentioned; and 79 SECT. XIV. 2. PRODUCTION OF IDEAS. and that whether the limb is yet joined to a living animal, or whether it be recently detached from it; as the heart of a viper or frog will renew its contractions, when pricked with a pin, for many minutes of time after its exsection from the body.— Does it act any where else? No; then it certainly exists in this part of space, and no where else; that is, it hath figure; name- ly, the figure of the nervous system, which is nearly the figure of the body. When the idea of solidity is excited, as above explained, a part of the extensive organ of touch is compressed by some external body; and this part of the sensorium so com- pressed, exactly resembles in figure, the figure of the body that compressed it. Hence, when we acquire the idea of solidity, we acquire, at the same, the idea of figure; and this idea of figure, or motion of a part of the organ of touch, exactly re- sembles, in its figure, the figure of the body that occasions it; and thus exactly acquaints us with this property of the exter- nal world. Now, as the whole universe, with all its parts, possesses a certain form or figure, if any part of it moves, that form or figure of the whole is varied: hence, as MOTION is no other than a perpetual variation of figure, our idea of motion is also a real resemblance of the motion that produced it. It may be said, in objection to this definition of motion, that an ivory globe may revolve on its axis, and that here will be a motion without change of figure. But the figure of the parti- cle x on one side of this globe, is not the same figure as die figure of y on the other side, anymore than the particles them- selves are the same, though they are similar figures; and hence they cannot change place with each other, without disturbing or changing the figure of the whole. Our idea of TIME is from the same source, but is more ab- stracted, as it includes only the comparative velocities of these variations of figure: hence, if it be asked, how long was this book in printing? it may be answered, whilst the sun was pas- sing through Aries. Our idea of PLACE includes only the figure of a group of bodies, not the figure of the bodies themselves. If it be ask- ed, where is Nottinghamshire? the answer is, it is surrounded by Derbyshire, Lincolnshire, and Leicestershire: hence place is our idea of the figure of one body surrounded by the figures of other bodies. The idea of SPACE is a more abstracted idea of place ex- cluding the group of bodies. The idea of NUMBER includes only the particular arrange- ments, or distributions of a group of bodies, and is therefore only 80 PRODUCTION OF IDEAS. SECT. XIV. 2. only a more abstracted idea of the parts of the figure of the group of bodies: thus, when I say England is divided into forty counties, I only speak of certain divisions of its figure. Hence arises the certainty of the mathematical sciences, as they explain these properties of bodies, which are exactly re- sembled by our ideas of them, whilst we are obliged to col- lect almost all our other knowledge from experiment; that is, by observing die effects exerted by one body upon another. 3. Of the Penetrability of Matter. The impossibility of two bodies existing together, in the fame space, cannot he deduced from our idea of solidity, or of figure. As soon as we perceive the motions of objects that surround us, and learn that we possess a power to move our own bodies, we experience, that those objects, which excite in us the idea of solidity and of figure, oppose this voluntary movement of our own organs; as whilst I endeavour to compress between my hands an ivory ball into a spheroid. And we are hence taught by experience, that our own body, and those which we touch, cannot exist in the same part of space. But this by no means demonstrates, that no two bodies can exist together in the same part of space. Galilæo, in the pre- face to his works, seems to be of opinion, that matter is not impenetrable. Mr. Michel, and Mr. Boscowich, in his Theo- ria. Philos. Natur. have espoused this hypothesis: which has been lately published by Dr. Priestley, to whom the world is much indebted for so many important discoveries in science. (Hist. of Light and Colours, p. 391.) The uninterrupted passage of light through transparent bodies, of the electric æther through metallic and aqueous bodies, and of the magnetic effluvia through all bodies, would seem to give some probabi- lity to this opinion. Hence it appears, that beings may exist without possessing the property of solidity, as well as they can exist without possessing the properties which excite our smell or taste, and can thence occupy space without detruding other bodies from it; but we cannot become acquainted with such beings by our sense of touch, any more than we can with odours or flavours without our senses of smell and taste. But that any being can exist without existing in space, is to my ideas utterly incomprehensible. My appeal is to common sense. To be implies a when and a where; the one is com- paring it with the motions of other beings, and the other with their situations. If there was but one object, as the whole creation may be considered 81 SECT. XIV.2. PRODUCTION OF IDEAS. considered as one object, then I cannot ask where it exists? for there are no other objects to compare its situation with. Hence, if any one denies that a being exists in space, he de- nies that there are any other beings but that one; for to an- swer the question, " Where does it exist?" is only to men- tion the situation of the objects that surround it. In the same manner, if it be asked, " When does a being exist?" the answer only specifies the successive motions ei- ther of itself, or of other bodies: hence, to say a body exists not in time, is to say, that there is, or was, no motion in the world. 4. Of the Spirit of Animation. But though there may exist beings in the universe, that have not the property of solidity; that is, which can possess any part of space, at the same time that it is occupied by other bo- dies; yet there may be other beings that can assume this pro- perty of solidity, or disrobe themselves of it occasionally, as we are taught of spirits, and of angels ; and it would seem, that THE SPIRIT OF ANIMATION must be endued with this property, otherwise how could it occasionally give motion to the limbs of animals?—or be itself stimulated into motion by the obtrusions of surrounding bodies, as of light, or odour? If the spirit of animation was always necessarily penetrable, it could not influence or be influenced by the solidity of mat- ter; they would exist together, but could not detrude each other from the part of space where they exist; that is, they could not communicate motion to each other. No two things can influ- ence or affect each other, which have not some property com- mon to both of them; for, to influence or affect another body, is to give or communicate some property to it, that it had not before; but how can one body give that to another which it does not possess itself?—The words imply, that they must agree in having the power or faculty of possessing some com- mon property. Thus, if one body removes another from the part of space that it possesses, it must have the power of occu- pying that space itself: and if one body communicates heat or motion to another, it follows, that they have alike the property of possessing heat or motion. Hence, the spirit of animation, at the time it communicates or receives motion from solid bodies, must itself possess some pro- perty of solidity. And in consequence, at the time it receives other kinds of motion from light, it must possess that property which light possesses, to communicate that kind of motion; and for which no language has a name, unless it may be termed Visi- bility. 82 PRODUCTION OF IDEAS. SECT. XIV. 2. bility. And, at the rime it is stimulated into other kinds of ani- mal motion, by the particles of sapid and odorous bodies affect- ing the senses of taste and smell, it must resemble these particles of flavour, and of odour, in possessing some similar or corres- pondent property; and for which language has no name, un- less we may use the words Saporosity and Odorosity for those common properties which are possessed by our organs of taste and smell, and by the particles of sapid and odorous bodies ; as the words Tangibility and Audibility may possess the common property possessed by our organs of touch, and of hearing, and by the solid bodies, or their vibrations, which affect those organs. 5. Finally, though the figures of bodies are in truth resem- bled by the figure of the part of the organ of touch, which is stimulated into motion; and that Organ resembles the solid bo- dy which stimulates it, in its property of solidity; and though the sense of hearing resembles the vibrations of external bo- dies, in its capability of being stimulated into motion by those vibrations; and though our other organs of sense resemble the bodies that stimulate them, in their capability of being stimu- lated by them; and we hence become acquainted with these properties of the external world; yet, as we can repeat all these motions of our organs of sense by the efforts of volition, or in consequence of the sensation of pleasure or pain, or by their association with other fibrous motions, as happens in our reve- ries or in sleep, there would still appear to be some difficulty in demonstrating the existence of any thing external to us. In our dreams we cannot determine this circumstance, be- cause our power of volition is suspended, and the stimuli of external objects are excluded; but in our waking hours we can compare our ideas belonging to one sense, with those be- longing to another, and can thus distinguish the ideas occa- sioned by irritation, from those excited by sensation, volition, or association. Thus, if the idea of the sweetness of sugar should be excited in our dreams, the whiteness and hardness of it occur at the same time by association; and we believe a material lump of sugar present before us. But if, in our waking hours, the idea of the sweetness of sugar occurs to us, the stimuli of surrounding objects, as the edge of the table on which we press, or green colour of the grass on which we tread, prevent the other ideas of the hardness and white- ness of the sugar from being exerted by association. Or if they should occur, we voluntarily compare them with the ir- ritative ideas of the table or grass above mentioned, and detect their fallacy. We can thus distinguish the ideas caused by the 83 SECT. XIV. 3. PRODUCTION OF IDEAS. the stimuli of external objects, from those which are introduce- ed by association, sensation, or volition; and during our wak- ing hours, can thus acquire a knowledge of the external world. Which, nevertheless, We cannot do in our dreams, because we have neither perceptions of external bodies, nor the power of volition, to enable us to compare them with the ideas of imagination. III. Of Vision. Our eyes observe a difference of colour, or of shade, in the prominences and depression of objects, and that those shades uniformly vary, when the sense of touch observes any varia- tion. Hence, when the retina becomes stimulated by colours or shades of light in a certain form, as in a circular spot, we know by experience, that this is a sign, that a tangible body is before us; and that its figure is resembled by the miniature fi- gure of the part of the organ of vision that is thus stimulated. Here, whilst the stimulated part of the retina resembles ex- actly the visible figure of the whole in miniature, the various kinds of stimuli form different colours, mark the visible figures of the minuter parts; and, by habit, we instantly recall the tan- gible figures. Thus, when a tree is the object of sight, a part of the reti- na, resembling a flat branching figure, is stimulated by vari- ous shades of colours; but it is by suggestion, that the gibbo- sity of the tree, and the moss that fringes its trunk, appear be- fore us. These are ideas of suggestion, which we feel or at- tend to, associated with the motions of the retina, or irritative ideas, which we do not attend to. So that, though our visible ideas resemble in miniature the outline of the figure of coloured bodies, in other respects they serve only as a language, which, by acquired associations, in- troduce the tangible ideas of bodies. Hence it is, that this sense is so readily deceived by the art of the painter, to our amusement and instruction. The readers will find much very curious knowledge on this subject, in Bishop Berkley's Essay on Vision, a work of great ingenuity. The immediate object, however, of the sense of vision, is light; this fluid, though its velocity is so great, appears to have no preceptible mechanical impulse, as was mentioned in the third Section, but seems to stimulate the retina into animal motion by its transmission through this part of the sensorium: for though the eyes of cats or other animals appear luminous in obscure places, yet it is probable, that none of the light, which falls on the retina, is reflected from it, but adheres to or enters into combination with the choroide coat behind it. N The 84 PRODUCTION OF IDEAS. SECT. XIV. 4. The combination of the particles of light with opake bo- dies, and therefore with the choroide coat of the eye, is evince- ed from the heat, which is given out, as in other chemical combinations. For the sun beams communicate no heat in their passage through transparent bodies, with which they do not combine, as the air continues Cool even in the focus of the largest burning-glasses, which in a moment vitrifies a par- ticle of opaque matter. IV. Of the Organ of Hearing. It is generally believed, that the tympanum of the ear vi- brates mechanically, when exposed to audible founds, like the strings of one musical instrument, when the same notes are struck upon another. Nor is this opinion improbable, a the muscles and cartileges of the lyranx are employed in produc- ing variety of tones by mechanical vibration: so the muscles and bones of the ear seem adapted to increase or diminish the tension of the tympanum, for the purposes of similar mecha- nical vibrations. But it appears from dissection, that tire tympanum is not the immediate organ of hearing, but that, like the humours and cornea of the eye, it is only of use to prepare the object for the immediate organ. For the portio mollis of the auditory nerve is not spread upon the tympanum, but upon the vistibu- lum, and cochlea, and semicircular canal of the ear; while, between the tympanum and the expansion of the auditory nerve, the cavity is said, by Dr. Cotunnus and Dr. Meckel, to be filled with water; as they had frequently observed by freezing the heads of dead animals before they dissected them; and wa- ter being a more dense fluid than air, is much better adapted to the propagation of vibrations. We may add, that even the external opening of the ear is not absolutely necessary for the perception of sound: for some people who, from these defects, would have been completely deaf, have distinguished acute of grave sounds by the tremours of a stick held between their teeth, propagated along the bones of the head. (Haller. Phys. T. V. p. 295.) Hence it appears, that the immediate organ of hearing is not affected by the particles or the air themselves, but is stimulated into animal motion by the vibrations of them. And it is pro- bable, from the loose bones which are found in the heads of some fishes, that the vibrations of water are sensible to the in- habitants of that element by a similar organ. The motions of the atmosphere, which we become acquaint- ed with by the sense of touch, are combined with its solidity, weight, 85 SECT. XIV. 5. PRODUCTION OF IDEAS. weight, or vis inertiæ; whereas those that are perceived by this organ depend alone on its elasticity. But though the vi- bration of the air is the immediate object of the sense of hear- ing, yet the ideas we receive by this sense, like those received from light, are only as a language, which, by acquired associ- ations, acquaints us with those motions of tangible bodies which depend on their elasticity, and which we had before learned by our sense of touch. V. Of Smell and of Taste. The objects of smell are dissolved in the fluid atmospheres and those of taste in the saliva, or other aqueous fluid, for the better defusing them on their respective organs, which seem to be stimulated into animal motion, perhaps by the chemical af- finities of these particles, which constitute the sapidity and odorosity of bodies with the nerves of sense, which perceive them. Mr. Volta has lately observed a curious circumstance rela- tive to our sense of taste. If a bit of clean lead and a bit of clean silver be separately applied to the tongue and palate, no taste is perceived; but by applying them in contact, in respect to the parts out of the mouth, and nearly so in respect to the parts which are immediately applied to the tongue and palate, a saline or acidulous taste is perceived, as of a fluid like a stream of electricity passing from one of them to the other. This new application of the sense of taste deserves further investiga- tion, as it may acquaint us with new properties of matter. From the experiments above mentioned of Galvani, Volta, Fowler, and others, it appears, that a plate of zinc and a plate of silver have a greater effect than lead and silver. If one edge of a plate of silver, about the size of half a crown piece, be placed upon the tongue, and one edge of a plate of zinc, about the same size, beneath the tongue, and if their opposite edges are then brought into contact before the point of the tongue, a taste is perceived at the moment of their coming into contact: secondly, if one of the above plates be put between the upper lip and the gum of the fore-teeth, and the other be placed under the tongue, and their exterior edges be then brought into con- tact in a darkish room, a flash of light is perceived in the eyes. These effects, I imagine, only shew the sensibility of our nerves of sense, to very small quantities of the electric fluid, as it passes through them; for I suppose these sensations are oc- casioned by slight electric shocks, produced in the following manner. By the experiments published by Mr. Bennet, with his ingenious doubler of electricity, which is the greatest dis- covery 86 PRODUCTION OF IDEAS. SECT. XIV. 6. covery made in that science since the coated jar, and the educ- tion of lightning from the skies, it appears that zinc was always found minus, and silver was always found plus, when both of them were in their separate state. Hence, when they are placed in the manner above described, as soon as their exterior edges come nearly into contact, so near as to have an extreme- ly thin plate of air between them, that plate of air becomes charged in the same manner as a plate of coated glass; and is, at the same instant, discharged through the nerves of taste or of sight, and gives the sensations, as above described, of light or of saporocity; and only shews the great sensibility of these organs of sense to the stimulus of the electric fluid in suddenly passing through them. VI. Of the Sense of Heat. There are many experiments in chemical writers, that evince the existence of heat as a fluid element, which covers and per- vades all bodies, and is attracted by the solutions of some of them, and is detruded from the combination of others. Thus, from the combinations of metals with acids, and from those combinations of animal fluids, which are termed secretions, this fluid matter of heat is given out amongst the neighbour- ing bodies; and in the solutions of salts in water, or of water in air, it is absorbed by the bodies that surround them; whilst, in its facility in passing through metallic bodies, and its difficulty in pervading resins and glass, it resembles the properties of the electric aura; and is like that excited by friction, and seems like that to gravitate amongst other bodies in its uncombined state, and to find its equilibrium. There is no circumstance of more consequence in the ani- mal economy, than a due proportion of this fluid of heat; for the digestion of our nutriment in the stomach and bowels, and die proper qualities of all our secreted fluids, as they are pro- duced or prepared, partly by animal, and partly by chemical processes, depend much on the quantity of heat; the excess of which, or its deficiency, alike gives us pain, and induces us to avoid the circumstances that occasion them. And in this the perception of heat essentially differs from the perceptions of the sense of touch, as we receive pain from too great pressure of solid bodies, but none from the absence of it. It is hence pro- bable, that nature has provided us with a set of nerves for the perception of this fluid, which anatomists have not yet attend- ed to. There may be some difficulty in the proof of this assertion: if we look at a hot fire, we experience no pain of the optic nerve, 87 SECT. XIV. 7. PRODUCTION OF IDEAS. nerve, though the heat along with the light must be concen- trated upon it. Nor does warm water or warm oil poured into the ear give pain to the organ of hearing; and hence, as these organs of sense do not perceive small excesses or deficien- cies of heat, and as heat has no greater analogy to the solidity or to the figures of bodies, than it has to their colours or vi- brations, there seems no sufficient reason for our ascribing the perception of heat and cold to the sense of touch, to which it has been generally attributed, either because its is diffused be neath the whole skin like the sense of touch, or owing to the inaccuaracy of our observations, or the defect of our lan- guages. There is another circumstance which would induce us to believe that the perceptions of heat and cold do not belong to the organ of touch; since the teeth, which are the least adapted for the perceptions of solidity or figure, are the most sensible to heat or cold; whence we are forewarned from swallowing those materials, whose degree of coldness or of heat would in- jure our stomachs. The following is an extract from a letter of Dr. R. W. Darwin, of Shrewsbury, when he was a student at Edinburgh. I made an experiment yesterday in our hospital, which much favours your opinion, that the sensation of heat and of touch depend on different sets of nerves. A man who had lately re- covered from a fever, and was still weak, was seized with vi- olent cramps in his legs and feet, which were removed by opi- ates, except that one of his feet remained insensible. Mr. Ew- art pricked him with a pin in five or six places, and the pa- tient declared he did not feel it in the least, nor was he sensi- ble of a very smart pinch. I then held a red hot poker at some distance, and brought it gradually nearer, till it came, within three inches, when he asserted that he felt it quite dis- tinctly. I suppose some violent irritation on the nerves of touch had caused the cramps, and had left them paralytic; while the nerves of heat, having suffered no increase of sti- mulus, retained their irritability. VII. Of the Sense of Extension. The organ of touch is properly the sense of pressure, but the muscular fibres themselves constitute the organ of sense, that feels extension. The sense of pressure is always attend- ed with the ideas of the figure and solidity of the object, nei- ther of which accompany our perception of extension. The whole set of muscles, whether they are hollow ones, as the heart, arteries, and intestines, or longitudinal ones attached to bones, 88 PRODUCTION OF IDEAS. SECT. XIV. 7. bones, contract themselves, whenever they are stimulated by forcible elongation; and it is observable, that the white mus- cles, which constitute the arterial system, seem to be excited into contraction from no other kinds of stimulus, according to the experiments of Haller. And hence the violent pain in some inflammations, as in the paronychia, obtains immediate relief by cutting the membrane, that was stretched by the tu- mour of the subjacent parts. Hence the whole muscular system may be considered as one organ of sense, and the various attitudes of the body, as ideas belonging to this organ; of many of which we are hourly con- scious, while many others, like the irritative ideas of the other senses, are performed without our attention. When the muscles of the heart cease to act, the refluent blood again distends or elongates them; and thus irritated, they contract as before. The same happens to tire arterial system, and I suppose to the capillaries, intestines, and various glands of the body. When the quantity of urine, or of excrement, distends the, bladder, or rectum, those parts contract, and exclude their contents, and many other muscles, by association, act along with them; but if these evacuations are not soon complied with, pain is produced by a little further extension of the muscular fibres: a similar pain is caused in the muscles, when a limb is much extended for the reduction of dislocated bones; and in the punishment of the rack, and in the painful cramps of the calf of the leg, or of other muscles; for a greater degree of con- traction of a muscle, than the movement of the two bones to which its ends are affixed will admit of, must give similar pain to that which is produced by extending it beyond its due length. And the pain from punctures or mentions arises from the dis- tention of the fibres, as the knife passes through them; for it nearly ceases as soon as the division is completed. All these motions of the muscles, that are thus naturally ex- cited by the stimulus of distending bodies, are also liable to be called into strong action, by their catenation with the irrita- tions or sensations produced by the momentum of the progres- sive particles of blood in the arteries, as in inflammatory fe- vers; or by acrid substances on other sensible organs, as in the strangury, or tenesmus, or cholera. We shall conclude this account of the sense of extension by observing, that the want of its object is attended with a, disa- greeable sensation, as well as the excess of it. In those hollow muscles which have been accustomed to it, this disagreeable sensation is called faintness, emptiness, and sinking; and, when it 89 SECT. XIV. 8. PRODUCTION OF IDEAS. it arises to a certain degree, is attended with syncope, or a total quiescence of all motions but the internal irritative ones, as happens from hidden loss of blood, or in the operation of tap- ping in the dropsy. VIII. Of the Appetites of Hunger, Thirst, Heat, Extension, the want of fresh Air, animal Love, and the suckling of Children. Hunger is most probably perceived by those numerous rami- fications of nerves that are seen about the upper opening of the stomach; and thirst, by the nerves about the fauces, and the top of the gula. The ideas of these senses are few in the generality of mankind, but are more numerous in those who, by disease or indulgence, desire particular kinds of foods or liquids. A sense of heat has already been spoken of, which may with propriety be called an appetite, as we painfully define it, when it is deficient in quantity. A sense of extension may be ranked amongst these appetites, since the deficiency of its object gives disagreeable sensation: when this happens in the arterial system, it is called faintness, and seems to bear some analogy to hunger and to cold; which, like it, are attended with emptiness of a part of the vascular system. The sense of want of fresh air has not been attended to, but is as distinct as the others, and the first perhaps that we ex- perience after our nativity: from the want of the object of this sense many diseases are produced, as the jail-fever, plague, and other epidemic maladies. Animal love is another appe- tite, which occurs later in life; and the females of lactiferous animals have another natural inlet of pleasure or pain from the suckling their offspring. The want of which, either owing to the death of their progeny, or to the fashion of their country, has been fatal to many of the sex. The males have also pec- toral glands, which are frequently turgid with a thin milk at their nativity, and are furnished with nipples, which erect on titillation like those of the female; but which seem now to be of no further use, owing perhaps to some change which these ani- mals have undergone in the gradual progression of the forma- tion of the earth, and of all that it inhabit. These seven last mentioned senses may properly be termed appetites, as they differ from those of touch, sight, hearing, taste, and smell, in this respect; that they are affected with pain, as well by the defect of their objects, as by the excess of them, which is not so in the latter. Thus cold and hunger give us pain, as well as an excess of heat or satiety : but it is not so with darkness and silence. IX. Before we conclude this Section on the organs of sense, we 90 CLASSES OF IDEAS. SECT. XV. 1. we must observe, that, as far as we know, there are many more senses than have been here mentioned, as every gland seems to he influenced to separate from the blood, or to absorb from the cavities of the body, or from the atmosphere, its appropriated fluid, by the stimulus of that fluid on the living gland; and not by mechanical capillary absorption, nor by chemical affinity. Hence it appears, that each of these glands must have a pecu- liar organ to perceive these irritations; but, as these irritations are not succeeded by sensation, they have not acquired the names of senses. However, when these glands are excited into motions strong- er than usual, either by the acrimony of their fluids, or by their own irritability being much increased, then the sensation of pain is produced in them as in all the other senses of the body ; and these pains are all of different kinds ; and hence the glands at this time really become each a different organ of sense, though these different kinds of pain have received no names. Thus, a great excess of light does not give the idea of light, but of pain; as in forcibly opening the eye when it is much inflamed. The great excess of pressure or distention, as when the point of a pin is pressed upon our skin, produces pain, ( and when this pain of the sense of touch is slighter, it is term- ed itching or tickling) without any idea of solidity or of figure: an excess of heat produces smarting, of cold another kind of pain: it is probable by this sense of heat the pain produced by caustic bodies is perceived, and of electricity, as all these are flu- ids, that permeate, distend, or decompose the parts that feel them. SECT. XV. OF THE CLASSES OF IDEAS. I. 1. Ideas received in tribes. 2. We combine them fur- ther, or abstract from these tribes. 3. Complex ideas. 4. Compounded ideas. 5. Simple ideas, modes, substances, relations; general ideas. 6. Ideas of reflexion. 7. Memory and imagination imperfectly defined. Ideal pre- sence. Memorandum-rings. II. 1. Irritative ideas; perception. 2. Sensitive ideas; imagination. 3. Volun- tary ideas; recollection. 4. Associated ideas; suggestion. III. 1. Definitions of perception; memory. 2. Reason- ing, judgment, doubting, distinguishing, comparing. 3. Invention. 4. Consciousness. 5. Identity. 6. Lapse of time. 7. Free-will. I. AS the constituent elements of the material world are only perceptible to our organs of sense in a state of combina- tion; 91 SECT. XV. 1. CLASSES OF IDEAS. tion; it follows, that the ideas or sensual motions excited by them, are never received singly, but ever with a greater or less degree of combination. So the colours of bodies, or their hard- nesses, occur with their fingers: every smell and taste has its degree of pungency, as well as its peculiar flavour: and each note in music is combined with the tone of some instrument. It appears from hence, that we can be sensible of a number of ideas at the same time, such as the whiteness, hardness, and coldness of a snow-ball, and can experience, at the same time, many irritative ideas of surrounding bodies, which we do not attend to, as mentioned in Sect. VII. 3. 2. But those ideas which belong to the same sense, seem to be more easily com- bined into synchronous tribes, than those which were not re- ceived by the same sense, as we can more easily think of the whiteness and figure of a lump of sugar at the same time, than the whiteness and sweetness of it. 2. As these ideas, or sensual motions, are thus excited with greater or less degrees of combination, so we have a power, when we repeat them either by our volition or sensation, to in- crease or diminish this degree of combination; that is, to form compounded ideas from those which were more simple, and abstract ones from those which were more complex, when they were first excited; that is, we can repeat a part, or the whole of those sensual motions which did constitute our ideas of perception; and the repetition of which now constitutes our ideas of recollection, or of imagination. 3. Those ideas which we repeat without change of the quantity of that combination, with which we first received them, are called complex ideas, as when you recollect West- minster Abbey, or the planet Saturn; but it must be observed, that these complex ideas, thus re-excited by volition, sensation, or association, are seldom perfect copies of their correspond- ent perceptions, except in our dreams, where other external ob- jects do not detract our attention. 4. Those ideas which are more complex than the natural objects that first excited them, have been called compounded ideas, as when we think of a sphinx or griffin. 5. And those that are less complex than the correspondent natural objects, have been termed abstracted ideas: thus sweet- ness, and whiteness, and solidity, are received at the same time from a lump of sugar; yet I can recollect any of these qualities without thinking of the others, that were excited along with them. When ideas are so far abstracted as in the above example, they have been termed simple by the writers of metaphysics, O and 92 CLASSES OF IDEAS. SECT. XV. 1. and seem indeed to be more complete repetitions of the ideas or sensual motions, originally excited by external objects. Other classes of these ideas, where the abstraction has not been so great, have been termed, by Mr. Locke, modes, sub- stances, and relations; but they seem only to differ in their de- gree of abstraction from the complex ideas that were at first excited; for as these complex or natural ideas are themselves im- perfect copies of their correspondent perceptions; so these ab- stract or general ideas are only still more imperfect copies of the same perceptions. Thus, when I have seen an object but once, as a rhinoceros, my abstract idea of this animal is the same as ray complex one. I may think more or less distinctly of a rhinoceros, but it is the very rhinoceros that I saw, or some part or property of him which recurs to my mind. But when any class of complex objects becomes the subject of conversation, of which I have seen many individuals, as a castle or an army, some property or circumstance belonging to it is peculiarly alluded to; and then I feel in my own mind that my abstract idea of this complex object is only an idea of that part, property, or attitude of it, that employs the present conversation, and varies with every sentence that is spoken con- cerning it. So, if any one should say, " one may fit upon a horse safer than on a camel," my abstract idea of the two ani- mals includes only an outline of the level back of the one, and the gibbosity on the back of die other. What noise is that in the street? Some horses trotting over the pavement. Here my idea of the horses includes principally the shape and mo- tion of their, legs. So also the abstract ideas of goodness and courage are still more imperfect representations of the objects they were received from; for here we abstract the material parts, and recollect only the qualities. Thus, we abstract so much from some of our complex ideas that at length it becomes difficult to determine of what percep- tion they partake; and in many instances our idea seems to be no other than of the found or letters of the word, that stands for the collective tribe, of which we are said to have an ab- stracted idea, as noun, verb, chimera, apparition. 6. Ideas have been divided into those of perception, and those of reflection; but as whatever is perceived must be external to the organ that perceives it, all our ideas must originally be ideas of perception. 7. Others have divided our ideas into those of memory, and those of imagination; they have said that a recollection of ideas, in the order they were received, constitutes memory, and with out that order, imagination; but all the ideas of imagination, except 93 SECT. XV. 2. CLASSES OF IDEAS. except the few that are termed simple ideas, are parts of trains or tribes in the order they were received: as, if I think of a sphinx, or a griffin, the fair face, bosom, wings, claws, tail, are all complex ideas in the order they were received; and it behoves the writers, who adhere to this definition, to determine how small the trains must be, that shall be called imagination, and how great those which shall be called memory. Others have thought that the ideas of memory have a greater vivacity than those of imagination; but the ideas of a person in sleep, or in a waking reverie, where the trains connected with sensation are uninterrupted, are more vivid and distinct than those of memory, so that they cannot be distinguished by this criterion. The very ingenious author of the Elements of Criticism has described what he conceives to be a species of memory, and calls it ideal presence ; but the instances he produces are the reveries of sensation, and are, therefore, in truth, connec- tions of the imagination, though they are recalled in the order they were received. The ideas connected by association are, in common dis- course, attributed to memory, as we talk of memorandum- rings, and tie a knot on our handkerchiefs to bring something into our minds at a distance of time. And a school-boy, who can repeat a thousand unmeaning lines in Lilly's Grammar, is said to have a good memory. But these have been already shewn to belong to the class of association, and are termed ideas of suggestion. II. Lastly, the method already explained, of classing ideas into those excited by irritation, sensation, volition, or associa- tion, we hope will be found more convenient, both for explain- ing the operations of the mind, and for comparing them with those of the body; and for the illustration and the cure of the diseases of both/and which we shall here recapitulate. 1. Irritative ideas are those which are preceded by irrita- tion, which is excited by objects external to the organs of sense; as the idea of that tree, which either I attend to, or which I shun in walking near it without attention. In the former case, it is termed perception, in the latter, it is termed limply an ir- ritative idea. 2. Sensitive ideas are those which are preceded by the sen- sation of pleasure or pain, as the ideas which constitute our dreams or reveries: this is called imagination. 3. Voluntary ideas are those which are preceded by volun- tary exertion, as when I repeat the alphabet backwards: this is called recollection. A. Associate 94 CLASSES OF IDEAS. SECT. XV. 3. 4. Associate ideas are those which are preceded by other ideas, or muscular motions, as when we think over or repeat the alphabet by rote in its usual order, or sing a tune we are accustomed to: this is called suggestion. III. 1. Perceptions signify those ideas which are preceded by irritation, and succeeded by the sensation of pleasure or pain; for whatever excites our attention interests us; that is, it is accompanied with pleasure or pain, however slight may be the degree or quantity of either of them. The word memory includes two classes of ideas, either those which are preceded by voluntary exertion, or those which are suggested by their associations with other ideas. 2. Reasoning is that operation of the sensorium by which we excite two or more tribes of ideas, and then re-excite the ideas in which they differ, or correspond. If we determine this difference, it is called judgment; if we in vain endeavour to determine it, it is called doubting. If we re-excite the ideas in which they differ, it is called; distinguishing. If we re-excite those in which they correspond, it is called comparing. 3. Invention is an operation of the sensorium, by which we voluntarily continue to excite one train of ideas; suppose the design of railing water by a machine; and at the same time attend to all other ideas which are connected with this by eve- ry kind of catenation, and combine or separate them volunta- rily for the purpose of obtaining some end. For we can create nothing new, we can only combine or se- parate the ideas which we' have already received by our per- ceptions: thus, if I, wish to represent a monster, I call to my mind the ideas of every thing disagreeable and horrible, and combine the nastiness and gluttony of a hog, the stupidity and obstinacy of an ass, with the fur and awkwardness of a bear, and call the new combination Caliban. Yet such a monster may exist in nature, as all his attributes are parts of nature. So, when I wish to represent every thing that is excellent and ami- able; when I combine benevolence with cheerfulness, wisdom, knowledge, taste, wit, beauty of person, and elegance of man- ners, and associate them in one lady, as a pattern to the world, it is called invention; yet such a person may exist,—such a person does exist!—It is, who is as much a mon- ster as Caliban. 4. In respect to consciousness, we are only conscious of our existence when we think about it; as we only perceive the lapse of time when we attend to it; when we are bulled about other objects, neither the lapse of the time, nor the con- sciousness 95 SECT. XV. 3. CLASSES OF IDEAS. sciousness of our own existence, can occupy our attention. Hence, when we think of our own existence, we only excite abstracted or reflex ideas (as they are termed) of our principal pleasures or pains, of our desires or aversions, or of the figure, solidity, colour, or other properties of our bodies, and call that act of the sensorium a consciousness of our existence. Some philosopher, I believe it is Des Cartes, has said, " I think, therefore I exist." But this is not right reasoning, because thinking is a mode of existence; and it is thence only saying, I exist, therefore I exist." For there are three modes of existence, or in the language of grammarians, three kinds of verbs. First, simply, I am, or exist. Secondly, I am acting, or exist in a state of activity, as I move. Thirdly, I am suf- fering, or exist in a state of being acted upon, as I am moved. The when, and the where, as applicable to this existence, de- pends on the successive motions of our own or of other bodies, and on their respective situations, as spoken of, Sect XIV. 2. 5. 5. Our identity is known by our acquired habits, or catenat- ed trains of ideas and muscular motions; and, perhaps, when we compare, infancy with old age, in those alone can our iden- tity be supposed to exist. For what else is there of similitude between the first speck of living entity and the mature man? Every deduction of reasoning, every sentiment or passion, with every fibre of the corporeal part of our system, has been sub- ject almost to annual mutation; while some catenations alone of our ideas and muscular actions, have continued in part un- changed. By the facility with which we can, in our waking hours, voluntarily produce certain successive trains of ideas, we know by experience, that we have before re-produced them; that is, we are conscious of a time of our existence, previous to the present time; that is, of our identity now and heretofore. It is these habits of action, these catenations of ideas and muscular motion, which begin with life, and only terminate with it; and which we can in some measure deliver to our posterity, as ex- plained in Sect. XXXIX. 6. When the progressive motions of external bodies make a part of our present catenation of ideas, we attend to the lapse of time, which appears the longer the more frequently we thus attend to it; as when we expect something at a certain hour, which much interests us, whether it be an agreeable or disagreeable event, or when we count the passing seconds on a stop- watch. When an idea of our own person, or a reflex idea of our pleasures and pains, desires and aversions, makes a part of this catenation, 96 OF INSTINCT. SECT. XVI. catenation, it is termed consciousness; and if this idea of con- ciousness make a part of a catenation, which we excite by recollection, and know by the facility with which we excite it, that we have before experienced it, it is called identity, as ex- plained above. 7. In respect to free-will, it is certain, that we cannot will to think of a new train of ideas, without previously thinking of the first link of it; as I cannot will to think of a black swan without previously thinking of a black swan. But, if I now think of a tail, I can voluntarily recollect all animals which have tails; my will is so far free, that I can pursue the ideas linked to this life a of tail, as far as my knowledge of the subject extends; but to will without motive is to will without desire or aversion, which is as absurd as to feel without plea- sure or pain; they are both solescisms in the terms. So far are we governed by the catenations of motions, which affect both the body and the mind of man, and which begin with our ir- ritability, and end with it. SECT. XVI. OF INSTINCT. Haud equidem credo, quia sit divinitus illis Ingenium, aut rerum sato prudentia major. Virg.Georg. L. I. 415. I. Instinctive action defined. Of connate passions. II. Of the sensations and motions of the fœtus in the womb. III. Some animals are more perfectly formed than others before nativity. Of learning to walk. IV. Of the swal- lowing, breathing, sucking, pecking, and lapping of young animals. V. Of the sense of smell, and its uses to ani- mals. Why cats do not eat their kittens. VI. Of the accuracy of sight in mankind, and their sense of beauty. Of the sense of touch in elephants, monkies, beavers, men. VII. Of natural language. VIII. The origin of natural language: 1. The language of fear; 2. of grief; 3. of tender pleasure; 4. of serene pleasure; 5. of anger; 6. of attention. IX. Artificial language of turkies, hens, ducklings, wagtails, cuckoos, rabbits, dogs and nightin- gales. X. Of music; of tooth-edge; of a good ear; of architecture. XI. Of acquired knowledge; of foxes, rooks, fieldfares, lapwings, dogs, cats, horses, crows and pelicans. XII. Of birds of passage, dormice, snakes, bats, swallows, quails, ring doves stare, chassinch, hoopoe, chat- terer, 97 SECT. XVI. 1. OF INSTINCT. 97 terer, hau finch, crossbill, rails, and cranes. XIII. Of birds' nests; of the cuckoo; of swallows nests; of the tay- lor bird. XIV. Of the old soldier; of haddocks, cods, and dog-fish; of the remora; of crabs, herrings, and sal- mon. XV. Of spiders, caterpillars, ants, and the ich- neumon. XVI. 1. Of locusts, gnats; 2. bees; 3. dor- mice, flics, worms, ants, and wasps. XVII. Of the fa- culty that distinguishes man from the brutes. I. ALL those internal motions of animal bodies which contribute to digest their aliment, produce their secretions, re- pair their injuries, or increase their growth, are performed without our attention or consciousness. They exist as well in our sleep as in our waking hours, as well in the fœtus dur- ing the time of gestation, as in the infant after nativity, and proceed with equal regularity in the vegetable as in the ani- mal system. These motions have been shewn, in a former part of this work, to depend on the irritations of peculiar fluids, and as they have never been classed amongst the instinctive actions of animals, are precluded from our present disquisition. But all those actions of men or animals that are attended with consciousness, and seem neither to have been directed by their appetites, taught by their experience, nor deduced from observation or tradition, have been referred to the power of in- stinct. And this power has been explained to be a divine something, a kind of inspiration, whilst the poor animal that possesses it, has been thought little better than a machine. The irksomeness that attends a continued attitude of the body, or the pains that we receive from heat, cold, hunger, or other injurious circumstances, excite us to general locomotion: and our senses are so formed and constituted by the hand of na- ture, that certain objects present us with pleasure, others with pain; and we are induced to approach and embrace these, to avoid and abhor those, as such sensations direct us. Thus, the palates of some animals are gratefully affected by the mastication of fruits, others of grains, and others of flesh; and they are thence instigated to attain, and to consume those materials, and are furnished with powers of muscular motion, and of digestion proper for such purposes. These sensations and desires constitute a part of our system, as our muscles and bones constitute another part: and hence they may alike be termed natural or connate; but neither of them can properly be termed instinctive: as the word instinct, in its usual acceptation, refers only to the actions of animals, as above explained: the origin of these actions is the subject of our present enquiry. The 98 OF INSTINCT. SECT. XVI. 2. The reader is intreated carefully to attend to this definition of instinctive actions, lest, by using the word instinct without adjoining any accurate idea to it, he may not only include the natural desires of love and hunger, and the natural sensations of pain or pleasure, but the figure and contexture of the body, and the faculty of reason itself under this general term. II. We experience some sensations, and perform some ac- tions before our nativity; the sensations of cold and warmth, agitation and rest, fulness and inanition, are instances of the former; and the repeated struggles of the limbs of the fœtus, which begin about the middle of gestation, and those motions by which it frequently wraps the umbilical chord around its neck or body, and even sometimes ties it on a knot, are instances of the latter. Smellie's Midwifery, vol. I. p. 192. By a due attention to these circumstances, many of the ac- tions of young animals, which at first fight seemed only refer- able to an inexplicable instinct, will appear to have been ac- quired like all other animal actions, that are attended with con- sciousness, by the repeated efforts of our muscles under the conduct of our sensations or desires. The chick in the shell begins to move its feet and legs on the sixth day of incubation (Mattreican, p. 131); or on the seventh day (Langley); afterwards they are seen to move themselves gently in the liquid that surrounds them, and to open and shut their mouths, (Hervei de Generat. p. 62, and 197. Form de Poulet. ii. p. 129). Puppies, before the membranes are broken that involve them, are seen to move themselves, to put out their tongues, and to open and shut their mouths, (Hervey, Gipson, Riolan, Haller). And calve, lick themselves, and swallow many of their hairs before their nativity: which, however, puppies do not, (Swammerden, p. 319. Flemyng Phil. Trans. Ann. 1755. 42). And towards me end of ges- tation, the fœtus of all animals are proved to drink part of the liquid in which they swim, (Haller. Physiol. T. 8. 204). The white of egg is found in the mouth and gizzard of the chick, and is nearly or quite consumed before it is hatched, (Harvei de Generat. 58). And the liquor ammi is found in the mouth and stomach of the human fœtus, and of calves; and how else should that excrement be produced in the intes- tines of all animals, which is voided in great quantity soon af- ter their birth? (Gipson. Med. Essays, Edinb. V. 1. 13. Halle- ri Physiolog. T. 3. p. 318. and T. 8). In the stomach of a calf, the quantity of this liquid amounted to about three pints, and the hairs amongst it were of the same colour with those on its skin, (Blasii Anat. Animal, p. m. 122). These facts are attested 99 SECT. XVI. 3, 4. OF INSTINCT. attested by many other writers of credit besides those above mentioned. III. It has been deemed a surprising instance of instinct, that calves and chickens should be able to walk by a few ef- forts, almost immediately after their nativity; whilst the human infant, in those countries where he is not incumbered with clothes, as in India, is five or six months, and in our climate al- most a twelvemonth, before he can safely stand upon his feet. The struggles of all animals in the womb must resemble their mode of swimming, as by this kind of motion they can best change their attitude in water. But the swimming of the calf and chicken resembles their manner of walking, which they have thus, in part, acquired before their nativity, and hence accomplish it afterwards with very few efforts; whilst the swimming of the human creature resembles that of the frog, and totally differs from his mode of walking. There is another circumstance to be attended to in this affair, that not only the growth of those peculiar parts of animals which are first wanted to secure their subsistence, are, in general, furthest advanced before their nativity; but some animals come into the world more completely formed throughout their whole system than others, and are thence much forwarder in all their habits of motion. Thus the colt and the lamb are much more perfect animals than the blind puppy and the naked rabbit; and the chick of the pheasant and the partridge has more perfect plumage and more perfect eyes, as well as greater aptitude to locomotion, than the callow nestlings of the dove and of the wren. The parents of the former only find it necessary to shew them their food, and to teach them to take it up; whilst those of the latter are obliged, for many days, to obtrude it into their gaping mouths. IV. From the facts mentioned in No 2. of this section, it is evinced, that the fœtus learns to swallow before its nativity; for it is seen to open its mouth, and its stomach is found filled with the liquid that surrounds it. It opens its mouth, either instigated by hunger, or by the irksomeness of a continued attitude of the muscles of its face; the liquor amnii, in which it swims, is agreeable to its palate, as it consists of a nourishing material. (Haller Phys. T. 8. p. 204). It is tempted to experience its taste further in the mouth, and by a few efforts learns to swallow, in the same manner as we learn all other animal actions, which are attended with consciousness, by the repeated efforts of our muscles under the conduct of our sensations or volitions. The inspiration of air into the lungs is so totally different from that of swallowing a fluid in which we are immersed, P that 100 OF INSTINCT SECT. XVI.4 that it cannot be acquired before our nativity. But at this time, when the circulation of the blood is no longer continued through the placenta, that suffocating sensation which we feel about the præcordia when we are in want of fresh air, disagree ably affects the infant: and all the muscels of the body are ex- cited into action to relieve this oppression: those of the breast, ribs, and diaphragm are found to answer this purpose; and thus respiration is discovered, and is continued throughout our lives, as often as the oppression begins to recur. Many infants, both of the human creature and of quadrupeds, struggle for a mi- nute after they are born before they begin to breathe, (Haller Phys.T. 8. p.400). ib.pt.2.p. 1). Mr. Buffon thinks the action of the dry air upon the nerves of smell of new-born animals, by producing an endeavour to sneeze, may contribute to in- duce this first inspiration; and that the rarefaction of the air, by the warmth of the lungs, contributes to induce expiration, (Hist. Nat. Tom. 4. p. 174.) Which latter it may effect by producing a disagreeable sensation by its delay, and a consequent effort to relieve it. Many children sneeze before they respire, but not all, as far as I have observed, or can learn from others. At length, by the direction of its sense of smell, or by the officious care of its mother, the young animal approaches fluid odoriferous rill of its future nourishment, already experienced so swallow. But in the act of swallowing, it is necessary nearly to dose the mouth, whether the creature be immersed in the fluid it is about to drink or not: hence, when the child first attempts to suck, it does not slightly compress the nipple between its lips, and suck as an adult person would do, by absorbing the milk; but it takes the whole nipple into its mouth for this purpose, compresses it between its gums, and thus repeatedly chewing (as it were) the nipple, presses out the milk; exactly in the same manner as it is drawn from the teats of cows by the hands of the milkmaid. The celebrated Hervey observes, that the fœtus in. the womb must have sucked in a part of its nourishment, be cause it knows how to suck the minute it is born, as any one may experience by putting a finger between its lips, and because in a few days it forgets this art of sucking, and cannot without some difficulty again acquire it, (Exercit. de Gener. Anim. 48.) The same observation is made by Hippocrates. A little further experience teaches the young animal to suck by absorption, as well as by compression; that is, to open the chest as in the beginning of respiration, and thus to rarefy the air in the mouth, that the pressure of the denser external at- mosphere may contribute to force out the milk. The chick yet in the shell has learnt to to drink by swallow- ing 101 SECT. XVI. 5. OF INSTINCT. in a part of the white of the egg for its food; but not having experienced how to take up and swallow solid feeds, or grains, is either taught by the felicitous industry of its mother; or by many repeated attempts is enabled at length to distinguish and to swallow this kind of nutriment. And puppies, though they know how to suck like other ani- mals, from their previous experience in swallowing, and in re- spiration, yet are they long in acquiring the art of lapping with their tongues, which, from the flaccidity of their cheeks and length of their mouths, is afterwards a more convenient way for them to take in water. V. The senses of smell and taste in many other animals greatly excell those of mankind; for in civilized society, as our victuals are generally prepared by others, and are adulterated with salt, spice, oil, and empyreuma, we do not hesitate about eating whatever is set before us, and neglect to cultivate these senses; whereas other animals try every morsel by the smell be- fore they take it into their mouths, and by the taste before they swallow it: and are set not only each to his proper nourish- ment by this organ of sense, but it also, at a maturer ape, di- rects them in the gratification of their appetite of love. Which may be further understood by considering the sympathies of these parts described in Class IV. 2. 1.7. While the human animal is directed to the object of his love by his sense of beau- ty, as mentioned in No. VI. of this Section. Thus, Virgil, Georg. III. 250. Nonne vides, tit tota tremor pertentet equorum Corpora, si tantum notas odor attulit auras? Nonne canis nidum veneris nasutus odore Quaerit, et errand trahitur sublambere lingua? Respuit at gustum cupidus, labiisque retractis Escvat os, trepidansque novis pertutitur æstris, Inserit et vivum felici votnere semen.— Quam tenui filo cæcos adnectit amores Docta Venus, vitæque monet renovare savillam! ANON. The following curious experiment is related by Galen.— " On dissecting a goat great with young, I found a brisk em- bryon, and having detached it from the matrix, and snatching it away before it saw its dam, I brought it into a certain room, where there were many vessels, some filled with wine, others with oil, some with honey, others with milk, or some other liquor; and in others were grains and fruits: we first observed the young animal get upon its feet and walk; then it shook it- self, and afterwards scratched its side with one of its feet: then we 102 OF INSTINCT. SECT. XVI. 6. we saw it smelling to every one of these things that were set in the room; and when it had smelt to them all, it drank up the milk." L. 6. de locis. cap. 6. Parturient quadrupeds, as cats, and bitches, and sows, are led by their sense of smell to eat the pleacenta as other common food; why then do they not devour their whole progeny, as is represented in an ancient emblem of TIME? This is said some- times to happen in the unnatural state in which we confine sows; and indeed nature would seem to have endangered her offspring in this nice circumstance! But at this time the stimu- lus of the milk in the tumid teats of the mother excites her to look out for, and to desire some unknown circumstance to re- lieve her. At the same time the smell of the milk attracts the exertions of the young animals towards its source, and thus the delighted mother discovers a new appetite, as mentioned in Sect. XIV. 3. and her little progeny are led to receive and to com- municate pleasure by this most beautiful contrivance. VI. But though the human species in some of their sensa- tions are much inferior to other animals, yet the accuracy of the sense of touch, which they possess in so eminent a degree, gives them a great superiority of understanding; as is well ob- served by the ingenious Mr. Buffon. The extremities of other animals terminate in horns, and hoofs, and claws, very unfit for the sensation of touch; whilst the human hand is finely adapted to encompass its object with this organ of sense. The elephant is indeed endued with a fine sense of feeling at the extremity of his proboscis, and hence has acquired much more accurate ideas of touch and of fight than most other crea- tures. The two following instances of the sagacity of these animals may entertain the reader, as they were told me by some gentlemen of distinct observation, and undoubted veracity, who had been much conversant with our eastern settlements. First, the elephants that are used to carry the baggage of our armies, are put each under the care of one of the natives of Indostan, and whilst himself and his wife go into the woods, to collect leaves and branches of trees for his food, they fix him to the ground by a length of chain, and frequently leave a child yet unable to walk, under its protection; and the intelligent animal not only defends it, but as it creeps about, when it arrives near the extremity of his chain, he wraps his trunk gently round its body, and brings it again into the centre of his circle. Secondly, the traitor elephants are taught to walk on a narrow path be tween two pit-falls, which are covered with turf, and then to go into the woods, and to seduce the wild elephants to come that way, who fall into these wells, whilst he passes safe between them; 103 SECT. XVI. 6. OF INSTINCT. them: and it is universally observed, that those wild elephants that escape the snare, pursue the traitor with the utmost vehe- mence, and if they can overtake him, which sometimes hap- pens, they always beat him to death. The monkey has a hand well enough adapted for the sense of touch, which contributes to his great facility of imitation; but in taking objects with his hands, as a stick or an apple, he puts his thumb on the same side of them with his fingers, instead of counteracting the pressure of his fingers with it: from this neglect he is much flower in acquiring the figures of objects, as he is less able to determine the distances or diameters of their parts, or to distinguish their vis inertiæ from their hardness. Helvetius adds, that the shortness of his life, his being fugitive before mankind, and his not inhabiting all climates, combine to prevent his improvement. (De l'Esprit. T. 1 . p.) There is, however, at this time, an old monkey shewn in Exeter Change, London, who having lost his teeth, when nuts are given him, takes a stone into his hand, and cracks them with it one by one: thus using tools to effect his purpose like man- kind. The beaver is another animal that makes much use of his hands, and if we may credit the reports of travellers, is pos- sessed of amazing ingenuity. This, however, M. Buffon af- firms, is only where they exist in large numbers, and in coun- tries thinly peopled with men; while in France, in their solitary state, they shew no uncommon ingenuity. Indeed, all the quadrupeds that have collar-bones, (clavi- culæ) use their fore-limbs in some measure as we use our hands, as the cat, squirrel, tyger, bear and lion; and as they exercise the sense of touch more universally than other animals, so are they more sagacious in watching and surprising their prey. All those birds that use their claws for hands, as the hawk, parrot, and cuckoo, appear to be more docile and intelligent; though the gregarious tribes of birds have more acquired knowledge. Now, as the images that are painted on the retina of the eye are no other than signs, which recall to our imaginations the objects we had before examined by the organ of touch, as is fully demonstrated by Dr. Berkley, in his treatise on vision; it follows, that the human creature has greatly more accurate and distinct sense of vision than that of any other animal. Whence, as he advances to maturity, he gradually acquires a sense of female beauty, which, at this time, directs him to the object of his new passion. Sentimental love, as distinguished from the animal passion of that name, with which it is frequently accompanied, con- sists 104 OF INSTINCT. SECT. XVI. 6. sists in the desire Of sensation of beholding, embracing, and saluting a beautiful object. The characteristic of beauty therefore is, that it is the object of love; and though many other objects are in common lan- guage called beautiful, yet they are only called so metaphor- rically, and ought to be termed agreeable. A Grecian temple may give us the pleasurable idea of sublimity, a Gothic temple may give us the pleasurable idea of variety, and a modern house the pleasurable idea of utility; music and poetry may inspire our love by association of ideas; but none of these, ex- cept metaphorically, can be termed beautiful, as we have no wish to embrace or salute them. Our perception of beauty consists in our recognition, by the sense of vision, of those objects, first, which have before in- spired our love by the pleasure which they have afforded to many of our senses; as to our sense of warmth, of touch, of smell, of taste, hunger and thirst; and, secondly, which beat any analogy of form to such objects. When the babe, soon after it is born into this cold world, is applied to its mother's bosom, its sense of perceiving warmth is first agreeably affected; next its sense of smell is delighted with the odour of her milk; then its taste is gratified by the flavour of it; afterwards the appetites of hunger and of thirst afford pleasure by the possession of their objects, and by the subsequent digestion of the aliment; and, lastly, the sense of touch is delighted by the softness and smoothness of the milky fountain, the source of such variety of happiness. All these various kinds of pleasure at length become associ- ated with the form of the mother's bread; which the infant embraces with its hands, presses with its lips, and watches with its eyes; and thus acquires more accurate ideas of the form of its mother's bosom, than of the odour and flavour, or warmth, which it perceives by its other senses. And hence, at our maturer years, when any object of vision is presented to us, which, by its waving or spiral lines, bears any similitude to the form of the female bosom, whether it be found in a land- scape with soft gradations of rising and descending surface, or in the forms of some antique vases, or in other works of the pencil or the chissel, we feel a general glow of delight, which seems to influence all our senses; and, if the object be not too large, we experience an attraction to embrace it with our arms, and to salute it with our lips as we did in our early in- fancy the bosom of our mother. And thus we find, according to the ingenious idea of Hogarth, that the waving lines of beau- ty were originally taken from the temple of Venus. This 105 SECT. XVI. 7. OF INSTINCT. This animal attraction is love; which is a sensation, when the object is present; and a desire, when it is absent. Which constitutes the purest source of human felicity. The cordial drop in the otherwise vapid cup of life, and which overpays mankind for the care and labour, which are attached to the pre-eminence of his situation above other animals. It should have been observed, that colour, as well as form, sometimes enters into our idea of a beautiful object, as a good complexion for instance; because a fine or fair colour is in ge- neral a sign of health, and conveys to us an idea of the warmth of the object; and a pale countenance, on the contra- ry, gives an idea of its being cold to the touch. It was before remarked, that young animals use their lips to distinguish the forms of things, as well as their fingers; and hence we learn the origin of our inclination to salute beautiful objects with our lips. VII. There are two ways by which we become acquainted with the passions of others: first, by having observed the effects of them, as of fear or anger, on our own bodies, we know, at sight, others are under the influence of these affections. So, when two cocks are preparing to fight, each feels the feathers rise round his own neck, and knows, from the same sign, the disposition of his adversary: and children, long before they can speak, or understand the language of their parents, may be frightened by an angry countenance, or soothed by smiles and blandishments. Secondly, when we put ourselves in the attitude that any passion naturally occasions, we soon, in some degree, acquire that passion; hence, when those that scold indulge themselves in loud oaths, and violent actions of the arms, they increase their anger by the mode of expressing themselves: and, on the contrary, the counterfeited smile of pleasure in disagreeable company, soon brings along with it a proportion of the reality, as is well illustrated by Mr. Burke. (Essay on the sublime and beautiful.) This latter method of entering into the passions of others is rendered of very extensive use by the pleasure we take in imi- tation, which is every day presented before our eyes, in the actions of children, and indeed in all the customs and fashions of the world. From this our aptitude to imitation arises, what is generally understood by the word sympathy, so well explain- ed by Dr. Smith of Glasgow. Thus the appearance of a cheerful countenance gives us pleasure, and of a melancholy one makes us sorrowful. Yawning and sometimes vomiting are thus propagated by sympathy; and some people of delicate fibres, 106 OF INSTINCT. SECT. XVI. 8. fibres, at the presence of a spectacle of misery, have felt pain in the same parts of their own bodies that were diseased or mangled in the other. Amongst the writers of antiquity, Aristotle thought this aptitude to imitation an essential property of the human species, and calls man an imitative animal. To ξωον μιμωμενον. These, then, are the natural signs by which we understand each other, and on this slender basis is built all human lan- guage. For without some natural signs, no artificial ones could have been invented or understood, as is very ingeniously observed by Dr. Reid. (Inquiry into the Human Mind.) VIII. The origin of this universal language is a subject of the highest curiosity, the knowledge of which has always been thought utterly inaccessible. A part of which we shall, how ever, here attempt. Light, sound, and odours, are unknown to the fœtus in the womb, which, except the few sensations and motions already mentioned, sleeps away its time insensible of the busy world. But the moment he arrives into day, he begins to experience many vivid pains and pleasures; these are, at the same time, at- tended with certain muscular motions, and from this their ear- ly and individual association, they acquire habits of occur- ring together, that are afterwards indissoluble. I. Of Fear. As soon as the young animal is born, the first important sensations that occur to him, are occasioned by the oppres- sion about his præcordia for want of respiration, and by his sudden transition from ninety-eight degrees of heat into so cold a climate.—He trembles, that is, he exerts alternately all the muscles of his body, to enfranchise himself from the oppres- sion about his bosom, and begins to breathe with frequent and short respirations; at the same time the cold contracts his red skin, gradually turning it pale; the contents of the bladder and of the bowels are evacuated; and from the experience of these first disagreeable sensations, the passion of fear is excited, which is no other than the expectation of disagreeable sensa- tions. This early association of motions and sensations persists throughout life; the passion of fear produces a cold and pale skin, with tremblings, quick respiration, and an evacuation of the bladder and bowels, and thus constitutes the natural or universal language of this passion. On observing a Canary bird this morning, January 28, 1772, at the house of Mr. Harvey, near Tutbury, in Der- By shire, I was told it always fainted away, when its cage was cleaned, 107 SECT. XVI. 8. OF INSTINCT. 107 cleaned, and defined to see the experiment. The cage being taken from the ceiling, and its bottom drawn out, the bird be- gan to tremble, and turned quite white about the root of his bill: he then opened his mouth as if for breath, and respired quick, flood straighter up on his perch, hung his wings, spread his tail, closed his eyes, and appeared quite stiff and ca- taleptic, for near half an hour, and at length, with much trem- bling and deep respiration, came gradually to himself. 2. Of Grief. That the internal membrane of the nostrils may be kept al- ways moist, for the better perception of odours, there are two canals that conduct the tears, after they have done their office in moistening and cleaning the ball of the eye, into a sack, which is called the lacrymal sack, and from which there is a duct that opens into the nostrils: the aperture of this duct is formed of exquisite sensibility; and when it is stimulated by odorous parti- cles, or by the dryness or coldness of the air, the sack contracts itself, and pours more of its contained moisture on the organ of smell. By this contrivance the organ is rendered more fit for perceiving such odours, and is preserved from being injured by those that are more strong or corrosive. Many other receptacles of peculiar fluids disgorge their contents, when the ends of their ducts are stimulated; as the gall bladder, when the con- tents of the duodenum stimulate the extremity of the common bile duct; and the salivary glands, when the termination of their ducts in the mouth are excited by the stimulus of the food we masticate. Atque vesiculæ seminales suum exprimunt flui- dum glande penis fricatâ. The coldness and dryness of the atmosphere, compared with the warmth and moisture which the new-born infant had just before experienced, disagreeably affects the aperture of this lacrymal sack: the tears that are contained in this sack, are poured into the nostrils, and a further supply is secreted by the lacrymal glands, and diffused upon the eye-balls; as is very visible in the eyes and nostrils of children soon after their na- tivity. The same happens to us at our maturer age; for in severe frosty weather, snivelling and tears are produced by the coldness and dryness of the air. But the lacrymal glands, which separate the tears from the blood, are situated on the upper external part of the globes of each eye; and, when a greater quantity of tears are wanted, we contract the forehead, and bring down the eye-brows, and use many other distortions of the face, to compress these glands. Now, as the suffocating sensation that produces respiration, Q is 108 OF INSTINCT. SECT. XVI. 8. is removed almost as soon as perceived, and does not recur again; this disagreeable irritation of the lacrymal ducts, as it must frequently, recur, till the tender organ becomes used to a variety of odours, is one of the first pains that is repeatedly attended to: and hence, thoughout our infancy, and in many people throughout their lives, all disagreeable sensations are attended with snivelling at the nose, a profusion of tears, and some peculiar distortions of countenance; according to the laws of early association before mentioned, which constitutes the natural or universal language of grief. You may assure yourself of the truth of this observation, if you will attend to what passes, when you read a distressful tale alone: before the tears overflow your eyes, you will invari- ably feel a titillation at that extremity of the lacrymal duct which terminates in the nostril; then the compression of the eyes succeeds, and the profusion of tears. Linnæus asserts, that the female bear sheds tears in grief; the same has been said of the hind, and some other animals. 3. Of Tender Pleasure. The first most lively impression of pleasure that the infant enjoys after its nativity, is excited by the odour of its mother's milk. The organ of smell is irritated by this perfume, and the lacrymal sack empties itself into the nostrils, as before explain- ed, and an increase of tears is poured into the eyes. Anyone may observe this, when very young infants are about to suck; for, at those early periods of life, the sensation affects the organ of smell much more powerfully than after the repeated ha- bits of smelling have inured it to odours of common strength; and in our adult years, the stronger smells, though they are at the same time agreeable to us, as of volatile spirits, continue to produce an increased secretion of tears. This pleasing sensation of smell is followed by the early af- fection of the infant to the mother that suckles it; and hence the tender feelings of gratitude and love, as well as of hopeless grief, are ever after joined with the titillation of the extremity of the lacrymal ducts, and a profusion of tears. Nor is it singular, that the lacrymal sack should be influ- enced by pleating ideas, as the sight of agreeable food produces the same effect on the salivary glands. Ac dum vidimus in fomniis lascivæ puellæ simulacrum tenditur penis. Lambs shake or wriggle their tails, at the time when they first suck, to get free of the hard excrement which had been long lodged in their bowels. Hence this becomes afterwards a mark of pleasure in them, and in dogs, and other tailed ani- mals. 109 SECT. XVI. 8. OF INSTINCT. mals. But cats gently extend and contract their paws when they are pleased, and purr, by drawing in their breath, both which resemble their manner of fucking, and thus become their language of pleasure; for these animals having collar-bones, use their paws like hands when they suck, which dogs and sheep do not. 4. Of Serene Pleasure. In the action of sucking, the lips of the infant are closed around the nipple of its mother, till he has filled his stomach, and the pleasure occasioned by the stimulus of this grateful food succeeds. Then the sphincter of the mouth, fatigued by the continued action of sucking, is relaxed; and the antagonist muscles of the face gently acting, produce the smile of plea- sure; as cannot but be seen by all who are conversant with children. Hence this smile, during our dives, is associated with gentle pleasure; it is visible in kittens and puppies, when they are played with and tickled; but more particularly marks the hu- man features. For in children this expression of pleasure is much encouraged, by their imitation of their parents, or friends, who generally address them with a smiling countenance: and hence some notions are more remarkable for the gaiety, and others for the gravity of their looks. 5. Of Anger. The actions that constitute the mode of fighting, are the immediate language of anger in all animals; and a preparation for these actions is the natural language of threatening. Hence the human creature clenches his fist, and sternly surveys his adversary, as if meditating where to make the attack; the ram, and the bull, draws himself some steps backwards, and levels his horns; and the horse, as he fights by striking with his hinder feet, turns his heels to his foe, and bends back his ears, to listen out the place of his adversary, that the threatened blow may not be inffectual. 6. Of Attention. The eye takes in at once but half our horizon, and that on- ly in the day; and our smell informs us of no very distant ob- jects: hence we confide principally in the organ of hearing to apprize us of danger: when we hear any the smallest sound, that we cannot immediately account for, our fears are alarmed, we suspend our steps, hold every muscle still, open our mouths a little, erect our ears, and listen to gain further information: and this by habit becomes the general language of attention to objects of sight, as well as of hearing; and even to the succes- sive trains of our ideas. The 110 OF INSTINCT. SECT. XVI. 9. The natural language of violent pain, which is expressed by writhing the body, grinning, and screaming; and that of tumultuous pleasure, expressed in loud laughter, belong to Sec- tion XXXIV. on Diseases from Volition. IX. It must have already appeared to the reader, that all other animals, as well as man, are possessed of this natural language of the passions, expressed in signs or tones; and we shall endeavour to evince, that those animals which have pre- served themselves from being enslaved by mankind, and are as- sociated in flocks, are also possessed of some artificial language, and of some traditional knowledge. The mother-turkey, when the eyes a kite hovering high in air, has either seen her own parents thrown into fear at his presence, or has, by observation, been acquainted with his dangerous designs upon her young. She becomes agitated with fear, and uses the natural language of that passion; her young ones catch the fear by imitation, and in an instant conceal themselves in the grass. At the same time that she shews her fears by her gesture and, deportment, she uses a certain exclamation, Koe-ut, Koe-ut ; and the young ones afterwards know, when they hear this note, though they do not see their dam, that the presence of their adversary is denounced, and hide themselves as before. The wild tribes of birds have frequent opportunities of know- ing their enemies, by observing the destruction they make among their progeny, of which every year but a small part escapes to maturity: but to our domestic birds these opportunities so rarely occur, that their knowledge of their distant enemies must frequently be delivered by tradition, in the manner above explained, through many generations. This note of danger, as well as the other notes of the mother- turkey, when she calls her flock to their food, or to sleep un- der her wings, appears to be an artificial language, both as ex- pressed by the mother, and as understood by the progeny. For a hen teaches this language with equal ease to the ducklings she has hatched from suppositious eggs, and educates as her own offsprng: and the wagtails, or hedge-sparrows, learn it from the young cuckoo, their foster nursling, and supply him with food long after he can fly about, whenever they hear his cuckoo- ing; which Linnæus tells us is his call of hunger. (Syst. Nat.) And all our domestic animals are readily taught to come to us for food, when we use one tone of voice, and to fly from our anger, when we use another. Rabbits, as they cannot easily articulate sounds, and are form ed into societies, that live under ground, have a very different method 111 SECT. XVI. 19. OF INSTINCT. method of giving alarm. When danger is threatened, they thump on the ground with one of their hinder feet, and produce a sound that can be heard a great way by animals near the surface of the earth, which would seem to be an artificial sign both from its Angularity and its aptness to the situation of the animal. The rabbits on the island of Sor, near Senegal, have white flesh, and are well tasted, but do not burrow in the earth, so that we may suspect their digging themselves houses in this cold climate is an acquired art, as well as their note of alarm. (Adanson's Voyage to Senegal.) The barking of dogs is another curious note of alarm, and would seem to be an acquired language, rather than a natural sign: for, " in the island of Juan Fernandes, the dogs did not attempt to bark, till some European dogs were put among them, and then they gradually begun to imitate them, but in a strange manner at first, as if they were learning a thing that was not natural to them." (Voyage to South-America by Don G. Juan, and Don Ant. de Ulloa. B. 2. c. 4.) Linnæus also observes, that the dogs of South-America do not bark at strangers. (Syst. Nat.) And the European dogs, that have been carried to Guinea, are said in three or four ge- nerations to cease to bark, and only howl, like the dogs that are natives of that coast. (World Displayed, vol. xvii. p. 26.) A circumstance not dissimilar to this, and equally curious, is mentioned by Kircherus de Musurgia, in his chapter de Lusciniis. " That the young nightingales, that are hatched under other birds, never sing till they are instructed by the company of other nightingales." And Johnston affirms, that the nightingales that visit Scotland, have not the fame harmony as those of Italy, (Pennant's Zoology, 8vo. p. 255;) which would lead us to suspect, that the singing of birds, like hu- man music, is an artificial language rather than a natural ex- pression of passion. X. Our music, like our language, is perhaps entirely con- stituted of artificial tones, which, by habit, suggest certain agree- able passions. For the same combination of notes and tones do not excite devotion, love, or poetic melancholy in a native of Indostan and of Europe. And " the Highlander has the same warlike, ideas annexed to the sound of a bagpipe (an in- strument which an Englishman derides), as the Englishman has to that of a trumpet or fife." (Dr. Brown's Union of Po- etry and Music, p. 58.) So " the music of the Turks is very different from the Italian; and the people of Fez and Moroc- co have again a different kind, which to us appears very rough and 112 OF INSTINCT. SECT. XVI. 10 and horrid, but is highly pleasing to them." (L' Arte Armo- niaca a Giorgio Antoniotto.) Hence we see why the Italian opera does not delight an untutored Englishman; and why those who are unaccustomed to music are more pleased with a tune the second or third time they hear it, than the first: for then the same melodious train of sounds excites the melancholy they had learned from the song; or the same vivid combination of them recalls all the mirthful ideas of the dance and company. Even the sounds that were once disagreeable to us may, by habit, be associated with other ideas, so as to become agreeable. Father Lafitau, in his account of the Iroquois, says, " the music and dance of those Americans have something in them extremely barbarous, which at first disgusts. We grow reconciled to them by degrees, and in the end partake of them with pleasure: the savages themselves are fond of them to distraction." (Mœurs des Savages, torn, ii.) There are, indeed, a few sounds that we very generally asso- ciate with agreeable ideas, as the whistling of birds, or purring of animals, that are delighted; and same others, that we as gene- rally associate with disagreeable ideas, as the cries of animals in pain, the hiss of some of them in anger, and the mid-night howl of beasts of prey. Yet we receive no terrible or sublime ideas from the lowing of a cow, or the braying of an ass; which evinces, that these emotions are owing to previous associations. So, if the rumbling of a carriage in the street be for a moment mistaken for thunder, we receive a sublime sensation, which ceases as soon as we know it is the noise of a coach and six. There are other disagreeable sounds, that are said to set the teeth on edge; which, as they have always been thought a ne- cessary effect of certain discordant notes, become a proper sub- ject of our enquiry. Every one in his childhood has repeatedly hit a part of the glass or earthen vessel, in which his food has been given him, and has thence had a very disagreeable sensa- tion in the teeth; which sensation was designed by nature to prevent us from exerting them on objects harder than them- selves. The jarring sound produced between the cup and the teeth is always attendant on this disagreeable sensation: and ever after, when such a sound is accidentally produced by the conflict of two hard bodies, we feel, by association of ideas, the concomitant disagreeable sensation in our teeth. Others have in their infancy frequently held the corner of a silk handkerchief in their mouth, or the end of the velvet of their cape coat, whilst their companions in play have plucked it from them, and have given another disagreeable sensation to their teeth, which has afterwards recurred on touching those materials. 113 SECT. XVI.11. OF INSTINCT. materials. And the sight of a knife drawn along a china plate. though no sound is excited by it, and even the imagination of such a knife and plate so scraped together, I know, by repeated experience, will produce the same disagreeable sensation of the teeth. These circumstances indisputably prove, that this sensation of the tooth-edge is owing to associated ideas; as it is equally excitable by light, touch, hearing, or imagination. In respect to the artificial proportions of sound excited by musical instruments, those who have early in life associated them with agreeable ideas, and have nicely attended to distin- guish them from each other, are said to have a good ear, in that country where such proportions are in fashion; and not from any superior perfection in the organ of hearing, or any instinctive sympathy between certain sounds and passions. I have observed a child to be exquisitely delighted with mu- sic, and who could with great facility learn to sing any tune that he heard distinctly, and yet whole organ of hearing was so imperfect, that it was necessary to speak louder to him in com- mon conversation than to others. Our music, like our architecture, seems to have no founda- tion in nature; they are both arts purely of human creation, as they imitate nothing. And the professors of them have only classed those circumstances that are most agreeable to the accidental taste of their age, or country; and have called it Proportion. But this proportion must always fluctuate, as it rests on the caprices that are introduced into our minds by our various modes of education. And these fluctuations of taste must become more frequent in the present age, where mankind have infranchised themselves from the blind obedience to the rules of antiquity in perhaps every science, but that of archi- tecture. See Sect. XII. No. 7. 3. XI. There are many articles of knowledge, which the ani- mals in cultivated countries seem to learn very early in their lives, either from each other, or from experience, or observa- tion: one of the most general of these is to avoid mankind. There is so great a resemblance in the natural language of the passions of all animals, that we generally know when they are in a pacific, or in a malevolent humour; they have the same knowledge of us; and hence we can scold them from us by some tones and gestures, and could possibly attract them to us by others, if they were not already apprized of our general malevolence towards them. Mr. Gmelin, professor at Peter- burg, assures us, that in his journey into Siberia, undertaken by order of the Empress of Russia, he saw foxes that expres- sed 114 OF INSTINCT. SECT. XVI. 11. sed no fear of himself or companions, but permitted him to come quite near them, having never seen the human creature before. And Mr. Bougainville relates, that at his arrival at the Malouine, or Falkland's islands, which were not inhabited by men, all the animals came about himself and his people; the fowls settling upon their heads and shoulders, and the quadru- peds running about their feet. From the difficulty of acquiring the confidence of old animals, and the ease of taming young ones, it appears that the fear they all conceive at the sight of mankind, is an acquired article of knowledge. This knowledge is more nicely understood by rooks, who are formed into societies, and build, as it were, cities over our heads; they evidently distinguish, that the danger is greater when a man is armed with a gun. Every one has seen this, who, in the spring of the year, has walked under a rookery with a gun in his hand: the inhabitants of the trees rise on their wings, and scream to the unfledged young, to shrink in to their rests from the sight of the enemy. The vulgar, ob- serving this circumstance so uniformly to occur, assert that rooks can smell gun-powder. The fieldfairs (turdus pilarus) which breed in Norway, and come hither in the cold season for our winter berries, as they are associated in flocks, and are in a foreign country, have evident marks of keeping a kind of watch, to remark and announce the appearance of danger. On approaching a tree, that is covered with them, they continue fearless, till one at the extremity of the bush, rising on his wings, gives a loud and peculiar note of alarm, when they all immediately fly, except one other, who continues till you approach still nearer, to cer- tify, as it were, the reality of the danger, and then he also flies off repeating the note of alarm. And in the woods about Senegal there is a bird called uett- uett by the negroes, and squallers by the French, which, as soon as they see a man, set up a loud scream, and keep flying round him, as if their intent was to warn other birds, which, upon hearing the cry, immediately take wing. These birds are the bane of sportsmen, and frequently put me into a pas- sion, and obliged me to shoot them. (Adanson's Voyage to Se- negal, 78). For the same intent the lesser birds of our climate seem to fly after a hawk, cuckoo, or owl, and scream to pre- vent their companions from being surprised by the general ene- mies of themselves, or of their eggs and progeny. But the lap-wing, (charadrius pluviaiis Lin.) when her un- fledged offspring run about the marshes, where they were hatched, not only gives the note of alarm at the approach of men 115 SECT. XVI. 11. OF INSTINCT. men or dogs, that her young may conceal themselves; but fly- ing and screaming near the adversary, the appears more solici- tous and impatient as he recedes from her family, and thus en- deavours to mislead him, and frequently succeeds in her design. These last instances are so appetite to the situation, ra- ther than to the natures of the creatures that use them, and are so similar to the actions of men in the same circumstances, that we cannot but believe, that they proceed from a similar principle. On the northern coast of Ireland a friend of mine saw above a hundred crows at once preying upon muscles; each crow took a muscle up into the air twenty or forty yards high, and let it fall on the stones, and thus, by breaking the shell, got pos- session of the animal.—A certain philosopher (I think it was Anaxagoras) walking along the sea-shore to gather shells, one of these unlucky birds mistaking his bald head for a stone, drop- ped a shell-fish upon it, and killed at once a philosopher and an oyster. Our domestic "animals, that have some liberty, are also pos- sessed of some peculiar traditional knowledge; dogs and cats have been forced into each other's society, though naturally animals of a very different kind, and have hence learned from each other to eat the knot-grass, when they are sick, to pro- mote vomiting. I have seen a cat mistake the blade of barley for this grass, which evinces it is an acquired knowledge. They have also learnt of each other, to cover their excrement and urine; about a spoonful of water was spilt upon my hearth from the tea-kettle, and I observed a kitten cover it with ashes. Hence this must also be an acquired art, as the creature mis- took the application of it. To preserve their fur clean, and especially their whiskers, cats wash their faces, and generally quite behind their ears, every time they eat. As they cannot lick those places with their tongues, they first wet the inside of the leg with saliva, and then repeatedly wash their faces with it, which must ori- ginally be an effect of reasoning, because a means is used to produce an effect; and seems afterwards to be taught or ac- quired by imitation, like the greatest part of hi man arts. These animals seem to possess something like an additional sense by means of their whiskers; which have perhaps some analogy to the antennae of moths and butterflies. The whis- kers of cats consist not only of the long hairs on their upper- lips, but they have also four or five long hairs standing up from each eyebrow, and also two or three on each cheek; all which, when the animal erects them, make with their points R so 116 OF INSTINCT. SECT. XVI. 11 so many parts of the periphery of a circle, of an extent at least equal to the circumference of any part of their own bodies. With this instrument I conceive, by a little experience, they can at once determine whether any aperture amongst hedges or shrubs in which animals of this genus live in their wild state, is large enough to admit their bodies; which, to them, is a mat- ter of the greatest consequence, whether pursuing or pursued. They have likewise a power of erecting and bringing forward the whiskers on their lips; which, probably, is for the purpose of feeling whether a dark hole be further permeable. The antenna, or horns, of butterflies and moths, who have awkward wings, the minute feathers of which are very liable to injury, serve, I suppose. a similar purpose of measuring, as they fly or creep amongst the leaves of plants and trees, whe- ther their wings can pass without touching them. Mr. Leonard, a very intelligent friend of mine, saw a cat catch a trout by darting upon it in a deep clear water, at the mill of Weaford. near Litchfield. The cat belonged to Mr. Stanley, who had often seen her catch fish in the same manner in summer, when the mill-pool was drawn so low that the fish could be seen. I have heard of other cats taking fish in shallow water, as they stood on the bank. This seems a natural art of taking their prey in cats, which their acquired delicacy, by do- mestication, has in general prevented them from using, though their desire of eating fish continues in its original strength, Mr. White, in his ingenious history of Selbourn, was witness to a cat's suckling a young hare, which followed her about the garden, and came jumping to her call of affection. At Elford, near Litchfield, the Rev. Mr. Sawley had taken the young ones out of a hare, which was shot; they were alive and die cat, who had just lost her own kittens, carried them away, as it was supposed, to eat them, but it presently ap- peared, that it was affection, not hunger, which incited her, as she suckled them, and brought them up as their mother. Other instances of the mistaken application of what has been termed instict may be observed in flies in the night, who, mistak- ing a candle for day-light, approach, and perish in the flame.-- So the putrid smell or the stapelia, or carrion-flower, allures the large flesh-fly to deposit its young worms on its beautiful petals, which perish there for want of nourishment. This, therefore, cannot be a necessary instinct, because the creature mistakes the application of it. Though in this country horses shew little vestiges of policy, yet in the desarts of Tartary and Siberia, when hunted by the Tartars, they are seen to form a kind of community, set watches 117 SECT. XVI. 11. OF INSTINCT. watches to prevent their being surprised, and have commanders, who direct, and hasten their slight. (Origin of Language, vol. 1. p. 212.) In this country, where four or five horses travel in a line, the first always points his ears forward, and the last points his backward, while the intermediate ones seem quite careless in this respect; which seems a part of policy to prevent sur- prise; as all animals depend most on the ear to apprize them of the approach of danger, the eye taking in only half the ho- rizon at once, and horses possess a great nicety of this sense, as appears from their mode of fighting, mentioned No. 8. 5. of this Section, as well as by common observation. There are some parts of a horse, which he cannot conve- niently rub, when they itch, as about the shoulder, which he can neither bite with his teeth, nor scratch with his hind foot; when this part itches, he goes to another horse, and gently bites him in the part which he wishes to be bitten, which is im- mediately done by his intelligent friend. I once observed a young foal thus bite its large mother, who did not chuse to drop the grass she had in her mouth, and rubbed her nose against: the foal's neck instead of biting it; which evinces that she knew the design of her progeny, and was not governed by a necessary instinct, to bite where she was bitten. Many of our shrubs, which would otherwise afford an agreeable food to horses, are armed with thorns or prickles, which secure them from those animals; as the holly, hawthorn, gooseberry, gorse. In the extensive moorlands of Staffordshire, the horses have learnt to damp upon a gorse-bush, with one of their fore-feet, for a minute together, and when the points are broken, they eat it without injury; which is an art other horses in the fertile parts of the country do not possess, and prick their mouths till they bleed, if they are induced by hun- ger or caprice to attempt eating gorse. Swine have a sense of touch as well as of smell at the end of their nose, which they use as a hand, both to root up the soil, and to turn over and examine objects of food, somewhat like the proboscis of an elephant. As they require shelter from the cold in this climate, they have learnt to collect straw in their mouths to make their nest, when the wind blows cold; and to call their companions by repeated cries to assist in the work, and add to their warmth by their numerous bed-fellows. Hence these animals, which are esteemed so unclean, have also learned never to befoul their dens, where they have liberty, with their own excrement; an art which cows and horses, which have open hovels to run into, have never acquired. I have observed great sagacity in swine; but the short lives we allow them, and their 118 OF INSTINCT. SECT. XVI. 12. their general confinement, prevents their improvement, which might probably be otherwise greater than that of dogs. Instances of the sagacity and knowledge of animals are very numerous to every observer; and their docility in learning va- rious arts from mankind, evinces that they may learn similar arts from their own species, and thus be possessed of much ac- quired and traditional knowledge. A dog, whose natural prey is sheep, is taught by mankind, not only to leave them unmolested, but to guard them; and to hunt, to set, or to destroy other kind of animals, as birds, or vermin; and, in some countries, to catch fish; in others, to find truffles, and to practise a great variety of tricks: is it more surprising that the crows should teach each other, that the hawk can catch ids birds, by the superior swiftness of his wing, and if two of them follow him, till he succeeds in his design, that they can by force share a part of the capture? This I have for- merly observed with attention and astonishment. There is one kind of; pelican mentioned by Mr. Osbeck, one of Linnaeus's travelling pupils, (the pelicanus acquilus) whose food is fish; and which it takes from other birds, because it is not formed to catch them itself; hence it is called by the Eng- lish, a man-of-war bird. (Voyage to China, p. 88.) There are many other interesting anecdotes of the pelican and cor- morant, collected from authors of the best authority, in a well-managed Natural History for Children, published by Mr. Galton. Johnson. London. And the following narration, from the very accurate Mons. Adanson, in his voyage to Senegal, may gain credit with the render, as his employment in this country was solely to make observations in natural history. On the river Niger, in his road to the island Grid, he law a great number of pelicans, or wide throats. " They moved with great state, like swans upon the water, and are the largest bird next to the ostrich; the bill of the one I killed, was upwards of a foot and half long, and the bag fastened underneath it held two-and-twenty pints of water. They swim in flocks, and form a large circle, which they contract afterwards, driving the fish before them with their legs: when they see the fish in sufficient number confined in this space, they plunge their bill wide open into the water, and shut it again with great quickness. They thus get fish into their throat-bag, which they eat afterwards on shore at their leisure." Page 247. XII. The knowledge and language of those birds, that fre- quently change their climate with the seasons, are still more ex- tensive; as they perform these migrations in large societies, and 119 SECT. XVI.12. OF INSTINCT. and are less subject to the power of man, than the resident tribes of birds. They are said to follow a leader during the day, who is occasionally changed, and to keep a continual cry during the night to keep themselves together. It is probable that these emigrations were at first undertaken as accident directed, by the more adventurous of their species, and learned from one another like the discoveries of mankind in navigation. The following circumstances strongly support this opinion. 1. Nature has provided these animals, in the climates where they are produced, with another resource, when, the season becomes too cold for their constitutions, or the food they were supported with ceases to be supplied: I mean that of sleeping. Dormice, shakes, and bats have not the means of changing their country; the two former from the want of wings, and the lat- ter from his being not able to bear the light of the day. Hence, these animals are obliged to make use of this resource, and deep during the winter. And those swallows that have been hatched too late in the year to acquire their full strength of pi- nion, or that have been maimed by accident or disease, have been frequently found in the hollows of rocks on the sea coasts, and even under water in this torpid state, from which they have been revived by the warmth of a fire. This torpid state of swallows is testified by innumerable evidences, both of ancient and modern names. Aristotle, speaking of the swallows, says, " They pass into warmer climates in winter, if such places are at no great distance; if they are, they bury themselves in the climates where they dwell." (8 Hist. c. 16. See also Der- ham's Phys. Theol. 11. p. 177.) Hence their emigrations cannot depend on a necessary in- stinct, as the emigrations themselves are not necessary! 2. When the weather becomes cold, the swallows in the neighbourhood assemble in large flocks; that is, the unexperi- enced attend those that have before experienced the journey they are about to undertake: they are then seen some time to hover on the coast, till there is calm weather, or a wind that suits the direction of their flight. Other birds of passage have been drowned by thousands in the sea, or have settled on ships, quite exhausted with fatigue. And others, either by mistaking their course, or by distress of weather, have arrived in countries where they were never seen before, and thus are evidently subject to the same hazards that the human species undergo, in the exe- cution of their artificial purposes. 3. The same birds are emigrant from some countries, and not so from others; the swallows were seen at Goree, in Ja- nuary, by an ingenious philosopher of my acquaintance, and he was 120 OF INSTINCT. SECT. XVI. 12 was told that they continued there all the year; as the warmth of the climate was at all seasons sufficient for their own consti- tutions, and for the production of the flies that supply them with nourishment. Herodotus says, that in Lybia, about the springs of the Nile, the swallows continue all the year. (L. 2.) Quails (tetrao corturnix, Lin.) are birds of passage, from the coast of Barbary to Italy, and have frequently settled in large shoals, on ships, fatigued with their flight. (Ray, Wisdom of God, p. 129. Dm ham Physic. Theol. vol. ii. p. 178.) Dr. Russel, in his History of Aleppo, observes, that the swallows visit that country about the end of February, and having hatched their young, disappear about the end of July; and, re- turning again about the beginning of October, continue about a fortnight, and then again disappear.(P. 70.) When my late friend Dr. Chambers, of Derby, was on the island of Caprea, in the bay of Naples, he was informed that great flights of quails annually settle on that island, about the beginning of May, in then passage from Africa to Europe. And that they always come when the south-east wind blows, are fatigued when they rest on this island, and are taken in such amazing quantities, and sold to the continent, that the inhabit- ants pay the bishop his stipend out of the profits arising from the sale of them. The flights of these birds across the Mediterranean are re- corded near three thousand years ago. " There went forth a wind from the Lord, and brought quails from the sea, and let them fall upon the camp, a day's journey round about it, and they were two cubits above the earth." (Numb. ii. 31 .) In our country, Mr. Pennant informs us, that some quails migrate, and others only remove from the internal parts of the island to the coasts, (Zoology, other, 210.) Some of the ring- doves and stares breed here, others migrate. (Ibid. 510, 511.) And the slender billed small birds do not all quit these kingdoms in the winter, though the difficulty of procuring the worms and insects that they feed on, supplies the same reason for migra- tion to them all. (Ibid. 511.) Linnæus has observed, that in Sweden the female chaffinches quit that country in September, migrating into Holland, and leave their mates behind till their return in the spring. Hence he has called them Fringilla cælebs. (Amæn. Acad. ii. 42. iv. 595.) Now, in our climate, both sexes of them are perennial birds. And Mr. Pennant observes, that the hoopoe, chatterer, hawfinch, and crossbill, migrate into England so rarely, and at such uncertain times, as not to deserve to be ranked among our birds of passage. (Ibid. 511.) The 121 SECT. XVI. 13. OF INSTINCT. The water fowl, as geese and ducks, are better adapted for long migrations, than the other tribes of birds, as, when the weather is calm, they cannot only rest themselves, or sleep up on the ocean, but possibly procure some kind of food from it. Hence, in Siberia, as soon as the lakes are frozen, the water fowl, which are very numerous, all disappear, and are supposed to fly to warmer climates, except the rail, which, from its in ability for long flights, probably deeps, like our bat, in their winter. The following account, from the Journey of Profes- sor Gmelin, may entertain the reader. "In the neighbour- hood of Krasnotark, amongst many other emigrant water fowls, we observed a great number of rails, which, when pursued, ne- ver took flight, but endeavoured to escape by running. We enquired how these birds, that could not fly, could retire into other countries in the winter, and were told, both by the Tartars and Affanians, that they well, knew those birds could not alone pass into other countries; but when the crains (les grues) re- tire in autumn, each one takes a rail (un rale) upon his back, and carries him to a warmer climate.” Recapitulation. 1. All birds of passage can exist in the climates where they are produced. 2. They are subject, in their migrations, to the same accidents and difficulties that mankind are subject to in navigation. 3. The same species of birds migrate from some countries, and are resident in others. From all these circumstances it appears, that the migrations of birds are not produced by a necessary instinct, but are acci- dental improvements, like the arts among mankind, taught by their cotemporaries, or delivered, by tradition, from one gene- ration of them to another. XIII. In that season of the year which supplies the nourish- ment proper for the expected brood, the birds enter into a contract of marriage, and, with joint labour, construct a bed for the reception of their offspring. Their choice of the proper season, their contracts of marriage, and the regularity with which they construct their nests, have in all ages excited the admiration of naturalists; and have always been attributed to the power of instinct, which, like the ocult qualities of the ancient philoso- phers, prevented all further enquiry. We shall consider them in their order. Their Choice of the Season. Our domestic birds that are plentifully supplied throughout the year with their adapted food, and are covered with houses from 122 OF INSTINCT. SCET. XVI. 13 from the inclemency of the weather, lay their eggs at any sea- son; which evinces that the spring of the year is not pointed out to them by a necessary instinct. Whilst the wild tribes of birds choose this time of the year from their acquired knowledge, that the mild temparature of the air is more convenient for hatching their eggs, and is soon likely to supply that kind of nourishment that is wanted for their young. If the genial warmth of the spring produced the passion of love, as it expands the foliage of trees, all other animals should feel its influence as well as birds; but, the viviparous creatures, as they suckle their young, that is, as they previously digest the natural food, that it may better suit the tender stomachs of their offspring, experience the influence of this passion at all seasons of the year, as cats and bitches. The graminivorous animals, indeed, generally produce their young about the time when grass is supplied in the greatest plenty; but this is without any degree of exactness, as appears from our cows, sheep, and hares, and may be a part of the traditional knowledge which they learn from the example of their parents. Their Contracts of Marriage. Their mutual passion, and their acquired knowledge, that their joint labour is necessary to procure sustenance for their numerous family, induce the wild birds to enter into a con- tract of marriage, which does not, however, take place among the ducks, geese, and fowls, that are provided with their daily food from our barns. An ingenious philosopher has lately denied that animals can enter into contracts, and thinks this an essential difference be- tween them and the human creature: but does not daily ob- servation convince us, that they form contracts of friendship with each other, and with mankind? When puppies and kit- tens play together, is there not a tacit contract, that they will not hurt each other. And does not your favourite dog expect you should give him his daily food, for his services and atten- tion to you, and thus barters his love for your protection in the same manner that all contracts are made amongst men that do not understand each other's arbitrary language? The Construction of their Nests. 1. They seem to be instructed how to build their nests from their observation of that in which they were educated, and from their knowledge of those things that are most agreeable to their touch in respect to warmth, cleanliness and stability. They choose 123 SECT. XVI. 13. OF INSTINCT. Choose their situations from their ideas of safety from their ene- mies, and of shelter from the weather. Nor is the colour of their nests a circumstance unthought of; the finches, that build in green hedges, cover their habitations with green moss; the swal- low or martin, that builds against rocks and houses, covers her's with clay; whilst the lark chooses vegetable straw nearly of the colour of the ground she inhabits: by this contrivance, they are all less liable to be discovered by their adversaries. 2. Nor are the nests of the same species of birds constructed always of the same materials, nor in the fame form; which is another circumstance that ascertains that they are led by ob- servation. In the trees before Mr. Levet's house, in Litchfield, there are annually nests built by sparrows, a bird which usually builds under the tiles of houses, or the thatch of barns. Not finding such convenient situations for their nests, they build a covered nest bigger than a man's head, with an opening like a mouth at the side, resembling that of a magpye, except that it is built with straw and hay, and lined with feathers, and so nicely managed as to be a defence against both wind and fain. So the jackdaw (corvus monedula) generally builds in church steeples, or under the roofs of high houses; but at Selbourn, in Southamptonshire, where towers and steeples are not sufficiently numerous, these same birds build in forsaken rabit burrows.— See a curious account of these subterranean nests in White's History of Selbourn, p. 59. Can the skilful change of architect- ture in these birds and the sparrows above mentioned be govern- ed by instinct? Then they must have two instincts, one for common, and the other for extraordinary occasions. I have seen green worsted in a nest, which no where exists in nature ; and the down of thirties in those nests that were by some accident constructed later in the hammer, which material could not be procured for the earlier nests: in many different climates they cannot procure the same materials that they use in ours. And it is well known, that the Canary birds, that are propagated in this country, and the finches, that are kept tame, will build their nests of any flexile ma- terials that are given them. Plutarch, in his Book on Rivers, speaking of the Nile, says, " that the swallows collect a ma- terial, when the waters recede, with which they form nests, that are impervious to water." And in India there is a swallow that collects a glutinous substance for this purpose, whose nest is esculent, and esteemed a principal rarity amongst epicures. (Lin. Syst. Nat.) Both these must be constructed of very differ- ent materials from those used by the swallows of our country. S In 124 OF INSTINCT. SECT. XVI. 13. In India the birds exert more artifice in building their nests, on account of the monkeys and snakes: some form their pen- sile nests in the shape of a purse, deep, and open at the top; others with a hole in the side; and others, still more cautious, with an entrance at the very bottom, forming their lodge near the summit. But the taylor-bird will not ever trust its nest to the extremity of a tender twig, but makes one more advance to safety, by fixing it to the leaf itself. It picks up a dead leaf, and sews it to the side of a living one; its slender bill being its needle, and its thread some fine fibres; the lining consists of fea- thers, gossamer, and down; its eggs are white, the colour of the bird light yellow its length three inches, its weight three six- tenths of an ounce; so that the materials of the nest and the weight of the bird are not likely to draw down an habitation so slightly suspended. A nest of this bird is preserved in the Bri- tish museum. (Pennant's Indian Zoology). This calls to one's mind the Mosaic account of the origin of mankind; the first dawing of art there ascribed to them, is that of sewing leaves to- gether. For many other curious kinds of nests, see Natural History for Children, by Mr. Galton. Johnson. London. Part. I. p. 47. Gen. Oriolus. 3. Those birds that are brought up by our care, and have had little communication with others of their own species, are very defective in this acquired knowledge; they are not only very awkward in the construction of their nests, but generally scatter their eggs in various parts of the room of cage, where they are confined, and seldom produce young ones, till, by fail- ing in their first attempt, they have learnt something from their own observation. 4. During the time of incubation birds are said in general to turn their eggs every day; some cover them, when they leave the nest, as ducks and geese; in some the male is said to bring food to the female, that she may have less occasion of ab- sence; in others he is said to take her place, when she goes in quest of food; and all of them are said to leave their eggs a shorter time in cold weather than in warm. In Senegal the ostrich fits on her eggs only during the night, leaving them in the day to the heat of the sun; but at the Cape of Good Hope, where the heat is less, she fits on them day and night. If it should be asked, what induces a bird to fit weeks on its first eggs unconscious that a brood of young ones will be the product? The answer must be, that it is the same passion that induces the human mother to hold her offspring whole nights and days in her fond arms, and press it to her bosom, uncon- scious of its future growth to sense and manhood, till observa- tion or tradition have informed her. 5. And 125 SECT. XVI. 14. OF INSTINCT. 5. And as many ladies are too refined to nurse their own children, and deliver them to the care and provision of others; so is there one instance of this vice in the feathered world.— The cuckoo, in some parts of England, as I am well informed by a very distinct and ingenious gentleman, hatches and edu- cates her own young; whilst in other parts she builds no nest, but uses that of some lesser bird, generally either of the wag- tail, or hedge sparrow, and depositing one egg in it, takes no fur- ther care of her progeny. As the Rev. Mr. Stafford was walking in Glosop Dale, in the Peak of Derbyshire, he saw a cuckoo rife from its nest. The nest was on the stump of a tree, that had been some time felled, among some chips that were in part turned grey, so as much to resemble the colour of the bird: in this nest were two young cuckoos: tying a string about the leg of one of them, he pegged the other end of it to the ground, and very frequently for many days beheld the old cuckoo feed these her young, as he stood very near them. Nor is this a new observation, though it is entirely overlooked by the modern naturalists; for Aristotle, speaking of the cuckoo, asserts that she sometimes builds her nest among broken rocks, and on high mountains; (L. 6. H. c. 1.) but adds, in another place, that she generally possesses the nest of another bird. (L. 6. H. c. 7.) And Niphus says, that cuckoos rarely build for themselves, most frequently laying their eggs in the nests of other birds. (Gesner, L. 3. de Cuculo.) The philosopher who is acquainted with these facts concerning the cuckoo, would seem to have very little reason himself, if he could imagine this neglect of her young to be a necessary instinct. XIV. The deep recedes of the ocean are in accessible to mankind, which prevents us from having much knowledge of the arts and government of its inhabitants. 1. One of the baits used by the fisherman is an animal, called an Old Soldier: his size and form are somewhat like the craw- fish, with this difference, that his tail is covered with a tough membrane instead of a shell; and to obviate this defect, he seeks out the uninhabited shell of some dead fish, that is large enough to receive his tail, and carries it about with him as part of his clothing or armour. 2. On the coasts about Scarborough, where the haddocks, cods, and dog-fish are in great abundance, the fishermen uni- versally believe that the dog-fish make a line, or semicircle, to encompass a shoal of haddocks and cods, confining than within certain limits near the shore, and eating them as occasion re- quires. For the haddocks and cods are always found near the shore without any dog-fish among them, and the dog-fish fur- ther 126 OF INSTINCT. SECT. XVI. 14. ther off, without any haddocks or cod; and yet the former are known to prey upon the latter, and in some years devour such immense quantities as to render this fishery more expensive than profitable. 3. The remora, when he wishes to remove his situation, as he Is a very slow swimmer, is content to take an outside place on whatever conveyance is going his way; nor can the cunning animal be tempted to quit his hold of a ship when she is sailing, not even for the lucre of a piece of pork, left it should endanger the loss of his passage: at other times he is easily caught with the hook. 4. The crab-fish, like many other testaceous animals, an- nually changes its shell; it is then in a soft state, covered only with a mucous membrane, and conceals itself in holes in the sand or under weeds: at this place a hard-shelled crab always stands centinel. to prevent the sea insects from injuring the other in its desenceless state; and the fishermen, from his appearance, know where to find the soft ones, which they use for baits in catching other fish. And though the hard-shelled crab, when he is on this duty, advances boldly to meet the foe, and will with difficulty quit the field; yet at other times he shews great timidity, and has a won- derful speed in attempting his escape; and, if often interrupted, will pretend death like the spider, and watch an opportunity to fink himself into the sand, keeping only his eyes above.— My ingenious friend Mr. Burdett, who favoured me with these accounts at the time lie was surveying the coasts, thinks the com- merce between the sexes takes place at this time, arid inspires the courage of the creature. 5. The shoals of herrings, cods, haddocks, and other fish, which approach our shores at certain seasons, and quit them at other seasons without leaving one behind; and the salmon, that periodically frequent our rivers, evince, that there are va- grant tribes of fish, that perform as regular migrations as the birds of passage already mentioned. 6. There is a cataract on the river Liffey, in Ireland, about nineteen feet high; here, in the salmon season, many of the in- habitants am use themselves in observing these fish leap up the torrent. They dart themselves quite out of the water as they ascend, and frequently fall back many times before they sur- mount it; and baskets made of twigs are placed near the edge of the dream to catch them in their fall. I have observed, as I have sat by a spout of water, which de- scends from a stone trough about two feet into a stream below, at particular seasons of the year, a great number of little fish called 127 SECT. XVI. 15. OF INSTINCT. called minums, or pinks, throw themselves about twenty times their own length out of the water, expecting to get into the trough above. This evinces that the storgee, or attention of the dam to provide for the offspring, is strongly exerted amongst the nations of fish, where it would teem to be the most neglected; as these salmon cannot be supposed to attempt so difficult and dangerous a task without being conscious of the purpose or end of their endea- vours. It is further remarkable, that most of the old salmon return to the sea before it is proper for the young shoals to attend them; yet. that a few old ones continue in the rivers so late, that they become perfectly emaciated by the inconvenience of their situation, and this apparently to guide or protect the un- experienced brood. Of the smaller water animals we have still less knowledge, who nevertheless probably possess many superior arts; some of these are mentioned in Botanic Garden, P. I. Add. Note XXVII. and XXVIII. The nympha of the water-moths of our rivers, which cover themselves with cases of straw, gravel, and shell, contrive to make their habitations nearly in equilibrium with the water: when too heavy, they add a bit of wood or straw; when too light, a bit of gravel. Edinb. Trans. All these circumstances bear a near resemblance to the de- liberate actions of human reason. XV. We have a very imperfect acquaintance with the various tribes of insects: their occupation, manner of life, and even the number of their senses, differ from our own, and from each other; but there is reason to imagine, that those which possess the sense of touch in the most exquisite degree, and whose occupations require the most constant exertion of their powers, are endued with a greater proportion of knowledge and ingenuity. The spiders of this country manufacture nets of various forms, adapted to various situations, to arrest the flies that are their food; and some of them have a house or lodging-place in the middle of the net, well contrived for warmth, security, or concealment. There is a large spider in South-America, who constructs nets of so strong a texture as to entangle small birds, particularly the humming bird. And in Jamaica there is ano- ther spider, who digs a hole in the earth, obliquely, downwards, about three inches in length, and one inch in diameter: this ca- vity she lines with a tough thick web, which, when taken out, resembles a leathern purse: but what is most curious, this house has a door with hinges, like the operculum of some sea-shells; and herself and family, who tenant this nest, open and shut the door, 128 OF INSTINCT. SECT. XVI. 15. door, whenever they pass or repass. This history was told me, and the nest, with its operculum, shewn me by the late Dr. Butt of Bath, who was some years physician in Jamaica. The production of these nets is indeed a part of the nature or conformation of the animal, and their natural use is to supply the place of wings, when she wishes to remove to another situation. But when she employs them to entangle her prey. there are marks of evident design; for she adapts the form of each net to its situation, and strengthens those lines that require it, by joining others to the middle of them, and attaching those others to distant objects, with the same individual art that is used by mankind in supporting the mads and extending the sails of ships. This work is executed with more mathematical ex- actness and ingenuity by the field spiders, than by those in our houses, as their constructions are more subjected to the injuries of dews and tempests. Besides the ingenuity shewn by these little creatures in taking their prey, the circumstance of their counterfeiting death, when they are put into terror, is truly wonderful; and as soon as the object of terror is removed, they recover and run away. Some beetles are also said to possess this piece of hypocrisy. The curious webs, or chords, constructed by some young caterpillars to defend themselves from cold, or from insects of prey; and by silk-worms and some other caterpillars, when they transmigrate into aureliæ or larvæ, have deservedly excit- ed the admiration of the inquisitive. But our ignorance of their manner of life, and even of the number of their senses, to tally precludes us from understanding the means by which they acquire this knowledge. The care of the salmon in chusing a proper situation for her spawn, the structure of the nests of birds, their patient incuba- tion, and the art of the cuckoo in depositing her egg in her neighbour's nursery, are instances of great sagacity in those creatures; and yet they are much inferior to the arts exerted by many of the insect tribes on similar occasions. The hairy ex- crescences on briars, the oak apples, the blasted leaves of trees, and the lumps on the backs of cows, are situations that are ra- ther produced than chosen by the mother insect for the conve- nience of her offspring. The cells of bees, wasps, spiders, and of the various coraline insects, equally astonish us, whether we attend to the materials or to the architecture. But the conduct of the ant, and of some species of the ich- neumon-fly in the incubation of their eggs, is equal to any ex- ertion of human science. The ants, many times in a day, move their eggs nearer the surface of their habitation, or deeper be- low 129 SECT. XVI. 16. OF INSTINCT. low it, as the heat of the weather varies; and in colder days lie upon them in heaps for the purpose of incubation: if their man- sion is too dry, they carry them to places where there is mois- ture, and you may distinctly see the little worms move and suck up the water. When too much moisture approaches their nest, they convey their eggs deeper in the earth, or to some other place of safety. (Swammerd. Epil. ad Hist. Insects, p. 153. Phil. Trans. No. 23. Lowthrop. V. 2. p. 7.) There is one species of ichneumon-fly that digs a hole in the earth, and carrying into it two or three living caterpillars, de- posits her eggs, and nicely closing up the nest leaves them there; partly, doubtless to assist the incubation, and partly to supply food to her future young. (Derham. B. 4. c. 13. Aristotle Hist. Animal, L. 5. c. 20.) A friend of mine put about fifty large caterpillars, collected from cabbages, on some bran, and a few leaves, into a box, and covered it with gauze to prevent their escape. After a few days we saw, from more than three-fourths of them, about eight or ten little caterpillars of the ichneumon-fly come out of their backs, and spin each a small cocoon of silk, and in a few days the large caterpillars died. This small fly, it seems, lays it egg in the back of the cabbage caterpillar, which, when hatched, preys upon the material, which is produced there for the purpose of making silk for the future nest of the cabbage caterpillar; of which being deprived, the creature wanders about till it dies, and thus our gardens are preserved by the ingenuity of this cruel fly. This curious property of producing a silk thread, which is common to some sea animals, see Botanic Garden, Part I. Note XXVII. and is designed for the purpose of their transformation, as in the silk-worm, is used for conveying themselves from higher bran- ches to lower ones of trees, by some caterpillars, and to make themselves temporary nests or tents; and by the spider for en- tangling his prey. Nor is it strange that so much knowledge should be acquired by such small animals; since there is reason to imagine, that these insects have the sense of touch, either in their proboscis, or their antennæ, to a great degree of perfec- tion; and thence may possess, as far as their sphere extends, as accurate knowledge, and as subtle invention, as the discoverers of human arts. XVI. 1. If we were better acquainted with the histories of those insects that are formed into societies, as the bees, wasps, and ants, I make no doubt but we should find, that their arts and im- provements are not so similar and uniform as they now appear to us, but that they arose in the same manner from experience and tradition, as die arts of our own species; though their rea- soning 130 OF INSTINCT. SECT. XVI. 16. soning is from fewer ideas, is busied about fewer objects, and is exerted with less energy. There are some kinds of insects that migrate like the birds be- fore mentioned. The locust of warmer climates has sometimes come over to England; it is shaped like a grasshopper, with ve- ry large wings, and a body above an inch in length. It is men- tioned as coming into Egypt with an east wind: " The Lord brought an east wind upon the land all that day and night, and in the morning the east wind brought the locusts, and covered the face of the earth, so that the land was dark." Exod. x. 13. The migrations of these insects are mentioned in another part of the scripture: " The locusts have no kings, yet go they forth all of them in bands." Prov. xxx. 27. The accurate Mr. Adanson, near the river Gambia, in Africa, was witness to the migration of these insects “About eight in the morning, in the month of February, there suddenly arose over our heads a thick cloud, which darkened the air and de- prived us of the rays of the sun. We found it was a cloud of locusts, raised about twenty or thirty fathoms from the ground, and covering an extent of several leagues: at length a shower of these insects descended, and after devouring every green herb, while they rested, again resumed their flight. This cloud was brought by a strong east wind, and was ail the morning in pas- sing over the adjacent country." (Voyage to Senegal, 158.) In this country the gnats are sometimes seen to migrate in clouds, like the musketoes of warmer climates; and our warms of bees frequently travel many miles, and are said in North- America always to fly towards the south. The prophet Isaiah has a beautiful allusion to these migrations: " The Lord shall call the fly from the rivers of Egypt, and shall hiss for the bee that is in the land of Assyria," Isa. vii. 18. which has been late- ly explained by Mr. Bruce, in his travels to discover the source of the Nile. 2. I am well informed that the bees that were carried into Barbadoes, and other western islands, ceased to lay up any ho- ney after the first year, as they found it not useful to them; and are now become very troublesome to the inhabitants of those is- lands, by infecting their sugar houses; but those in Jamaica con- tinue to make honey, as the cold north winds, or rainy sea- sons of that island, confine them at home for several weeks to- gether. And the bees of Senegal, which differ from those of Europe only in size, make their honey not only superior to ours in delicacy of flavour, but it has this singularity, that it never concretes, but remains liquid as syrup. (Adanson). From some observations of Mr. Wildman, and of other people of veracity, it 131 SECT. XVI. 16. OF INSTINCT. it appears, that during the severe part of the winter season, for weeks together, the bees are quite benumbed and torpid from the cold, and do not consume any of their provision. This state of sleep, like that of swallows and bats, seems to be the natural re- source of those creatures in cold climates, and the making of honey to be an artificial improvement. As the death of our hives of bees appears to be owing to their being kept so warm as to require food when their stock is exhausted, a very observing gentleman, at my request, put two hives for many weeks into a dry cellar, and observed, during all that time, they did not consume any of their provision, for their weight did not decrease, as it had done when they were kept in the open air. The same observation is made in the Annual Register for 1768, p. 113. And the Rev. Mr. White, in his method of preserving bees, adds, that those on the north side of his house consumed less honey in die winter than those on the south side. There is another observation on bees well ascertained, that they, at various times, when the season begins, to be cold, by a general motion of their legs, as they hang in clusters, pro- duce a degree of warmth, which is easily perceptible by the hand. Hence, by this ingenious exertion, they, for a long time, prevent the torpid state they would naturally fall into. According to the late observations of Mr. Hunter, it appears that the bees-wax is not made from the dust of the anthers of flowers, which they bring home on their thighs, but that this makes what is termed bee-bread, and is used for the purpose of feeding the bee-maggots; in the same manner butterflies live on honey, but the previous caterpillar lives on vegetable leaves, while the maggots of large flies require flesh for their food, and those of the ichneumon-fly require insects for their food. What induces the bee, who lives on honey, to lay up vegetable proven- der for its young? What induces the butterfly to lay its eggs on leaves, when itself feeds on honey? What induces the other flies to seek a food for their progeny different from what they consume themselves? If these are not deductions from their own previous experience or observation, all the actions of mankind must be resolved into instinct. 3. " The dormouse consumes but little of its food during the rigour of the season, for they roll themselves up, or sleep or lie torpid the greatest part of the time; but on warm sunny days experience a short revival, and take a little food, and then relapse into their former state." (Pennant's Zoology, p. 67.) Other animals that sleep in winter, without laying up any provender, are observed to go into their winter beds fat and strong, but T return 132 OF INSTINCT. SECT. XVI. 16 return to day-light, in the spring season, very lean and feeble. The common flies sleep during the winter without any provision for their nourishment, and are daily revived by the warmth of the sun or of our fires. These, whenever they see light, endea- vour to approach it, having observed, that by its greater vicinity they get free from the degree of torpor that the cold produces; and are hence induced perpetually to bum themselves in our candles; deceived, like mankind, by the misapplication of their knowledge. Whilst many of the subterraneous insects, as the common worms, seem to retreat so deep into the earth, as not to be enlivened or awakened by the difference of our winter days; and stop up their holes with leaves or draws, to pre- vent the frosts from injuring them, or the centipes from devour- ing them. The habits of peace, or the stratagems of war, of these subterranean nations, are covered from our view; but a friend of mine prevailed on a distressed worm to enter the hole of another worm on a bowling-green, and he presently return- ed much wounded about his head. And I once saw a worm rise hastily out of the earth into the sunshine, and observed a centipes hanging at his tail; the centipes nimbly quitting the tail, and seizing the worm about its middle, cut it in half with its forcepts, and preyed upon one part, while the other escaped. Which evinces they have design in stopping the mouths of their habitations. 4. The Wasp of this country fixes his habitation under ground, that he may not be affected with the various changes of our cli- mate; but in Jamaica he hangs it on the bough of a tree, where the seasons are less severe. He weaves a very curious paper of vegetable fibres to cover his nest, which is constructed on the same principle with that of the bee, but with a different mate- rial; but as his prey consists of flesh, fruits, and insects, which are perishable commodities, he can lay up no provender for the winter. M. de Loubiere, in his relation of Siam, says, " That in a part of that kingdom, which lies open to great inundations, all the ants make their settlements upon trees; no ants' nests are to be seen any where else;" whereas, in our country, the ground is their only situation. From the scriptural account of these in- sects, one might be led to suspect, that in some climates they lay up a provision for the winter. Origen affirms the same; (Cont. Cels. L. 4.) but it is generally believed that in this country they do not. (Prov. vi. 6. xxx. 25.) The white ants of the coast of Africa make themselves pyramids, eight or ten feet high, on a base of about the same width, with a smooth surface of rich clay, excessively hard and well built, which appear at a distance like an 133 SECT. XVI. 17. OF INSTINCT. an assemblage of the huts of the negroes. (Adanson.) The his- tory of these has been lately well described in the Philosoph. Transactions, under the name of termes, or termites. These differ very much from the nests of our large ant; but the real history of this creature, as well as of the wasp, is yet very im- perfectly known. Wasps are said to catch large spiders, and to cut off their legs, and carry their mutilated bodies to their young. (Dict. Raison. Tom. 1. p. 152.) One circumstance I shall relate which fell under my own eye, and shewed the power of reason in a wasp, as it is exer- cised among men. A wasp, on a gravel walk, had caught a fly nearly as large as himself; kneeling on the ground, I ob- served him separate the tail and the head from the body part, to which the wings were attached. He then took the body part in his paws, and rose about two feet from the ground with it; but a gentle breeze wasting the wings of the fly, turned him round in the air, and he settled again with his prey upon the gravel. I then distinctly observed him cut off with his mouth, first one of the wings, and then the other, after which he flew away with it unmolested by the wind. Go, thou sluggard, learn arts and industry from the bee, and from the ant! Go, proud reasoner, and call the worm thy sister! XVII. Conclusion. It was before observed how much the superior accuracy of our sense of touch contributes to increase our knowledge; but it is the greater energy and activity of the power of volition (as explained in the former Sections of this work) that marks mankind, and has given him the empire of the world. There is a criterion by which we may distinguish our vo- luntary acts or thoughts from those that are excited by our sen- sations. " The former are always employed about the means to acquire pleasureable objects, or to avoid painful ones: while the latter are employed about the possession of those that are already in our power." If we turn our eyes upon the fabric of our fellow animals, we find they are supported with bones, covered with skins, moved by muscles; that they possess the same senses, acknow- ledge the same appetites, and are nourished by the same ali- ment with ourselves; and we should hence conclude, from the strongest analogy, that their internal faculties were also in some measure similar to our own. Mr. Lock indeed published an opinion, that other animals possessed 134 CATENATION OF MOTIONS. SECT. XVII. 1. possessed no abstract or general ideas, and thought this circum- stance was the barrier between the brute and the human world. But these abstracted ideas have been since demonstrated by bishop Berkley, and allowed by Mr. Hume, to have no existence in nature, not even in the mind of their inventor, and we are hence necessitated to look for some other mark of distinction. The ideas and actions of brutes, like those of children, are almost perpetually produced by their present pleasures, or their present pains; and, except in the few instances that have been mentioned in this Section, thay seldom busy themselves about the means of procuring future bliss, or of avoiding future misery. Whilst the acquiring of languages, the making of tools, and the labouring for money, which are all only the means of pro- curing pleasure; and the praying to the Deity, as another means to procure happiness, are characteristic of human nature. SECT. XVII. THE CATENATION OF MOTIONS. I. I. Catenations of animal motion. 2. Are produced by irritations, by sensations, by volitions. 3. They continue some time after they have been excited. Cause of cate- nation. 4. We can then exert our attention on other ob- jects. 5. Many catenations of motions go on together. 6. Some links of the catenations of motions may be left out without disuniting the chain. 7. Interrupted circles of motion continue confusedly till they come to the part of the circle where they were disturbed. 8. Weaker catena- tions are dissevered by stronger. 9. Then new catena- tions take place. 10. Much effort prevents their re-unit- ing. Impediment of speech. 11. Trains more easily dis- severed than circles. 12. Sleep detroys volition and ex- ternal stimulus. II. Instances of various catenations in a young lady playing on the harpsichord. III. 1. What catenations are the strongest. 2. Irritations joined with associations form strongest connections. Vital motions. 3. New links with increased force; cold fits of fever pro- duced. 4. New links with decreased force. Cold bath. 5. Irritation joined with sensation. Inflammatory fever. Why children cannot tickle themselves. 6. Volition join- ed with sensation. Irritative ideas of sound become sen- sible. 7. lacas of imagination dissevered by irritations, by volition, production of surprise. I. 1. TO investigate with precision the catenations of ani- mal motions, it would be well to attend to the manner of their production; 135 SECT. XVII. 1. CATENATION OF MOTIONS. production; but we cannot begin this disquisition early enough for this purpose, as the catenations of motion seem to begin with life, and are only extingushable with it. We have spo- ken of the power of irritation, of sensation, of volition, and of association, as preceding the fibrous motions; we now step forwards, and consider, that conversely they are, in their turn, preceded by those motions; and that all the successive trains or circles of our actions are composed of this two-fold concate- nation. Those we shall call trains of action, which continue to proceed without any stated repetitions; and those circles of action, when the parts of them return at certain periods, though the trains of which they consist are not exactly similar. The reading an epic poem is a train of actions; the reading a song, with a chorus at equal distances in the measure, constitutes so many circles of action. 2. Some catenations of animal motion are produced by rei- terated successive irritations, as when we learn to repeat the alphabet in is order, by frequently reading the letters of it. Thus, the vermicular motions of the bowels were originally produced by the successive irritations of the passing aliment; and the succession of actions of the auricles and ventricles of the heart, was originally formed by successive stimulus of the blood; these afterwards become part of the diurnal circles of animal actions, as appears by the periodical returns of hun- ger, and the quickened pulse of weak people in the evening. Other catenations of animal motion are gradually acquired by successive agreeable sensations, as in learning a favourite song or dance; others by disagreeable sensations, as in coughing or nictiration; these become associated by frequent repetition, and afterwards compose parts of greater circles of action, like those above-mentioned. Other catenations of motions are gradually acquired by fre- quent voluntary repetitions; as when we deliberately learn to march, read, fence, or any mechanic art, the motions of many of our muscles become gradually linked together in trains, tribes, or circles of action. Thus, when any one at first begins to use the tools in turning wood or metals in a lathe, he wills the motions of his hand or fingers, till at length these actions be- come so connected with the effect, that he seems only to will the point of the chissel. These are caused by volition, connected by association, like those above described, and afterwards become parts of our diurnal trains or circles of action. 3. All these catenations of animal motions are liable to pro- ceed some time after they are excited, unless they are disturbed or impeded by other irritations, sensations, or volitions; and in many 136 CATENATION OF MOTIONS. SECT. XVII. 1. many instances in spite of our endeavours to stop them; and this property of animal motions is probably the cause of their catenation. Thus, when a child revolves some minutes on one foot, the spectra of the ambient objects appear to circulate round him some time after he falls upon the ground. Thus the palpitation of the heart continues some time after the object of fear, which occasioned it, is removed. The blush of shame, which is an excess of sensation, and the glow of anger, which is an excess of volition, continue some time, though the af- fected person finds that those emotions were caused by mis- taken facts, and endeavours to extinguish their appearance. See Sect. XII. 1. 5. 4. When a circle of motions becomes connected by fre- quent repetitions as above, we can exert our attention strongly on other objects, and the concatenated circle of motions will nevertheless proceed in due order; as whilst you are thinking on this subject, you use variety of muscles in walking about your parlour, or in fitting at your writing-table. 5. Innumerable catenations of motions may proceed at the same time, without incommoding each other. Of these are the motions of the heart and arteries; those of digestion and glandular secretion; of the ideas, or sensual motions; those of progression, and of speaking; the great annual circle of actions, so apparent in birds in their times of breeding and moulting; the monthly circles of many female animals; and the diurnal circles of sleeping and waking, of fulness and inanition. 6. Some links of successive trains, or of synchronous tribes of action, may be left out without disjoining the whole. Such are our usual trains of recollection: after having travelled through an entertaining country, and viewed many delightful lawns, rolling rivers, and echoing rocks; in the recollection of our journey, we leave out the many districts that we crossed which were marked with no peculiar pleasure. Such also are our complex ideas; they are catenated tribes of ideas, which do not perfectly resemble their correspondent perceptions, because some of the parts are omitted. 7. If an interrupted circle of actions is not entirely dissever- ed, it will continue to proceed confusedly, till it comes to the part of the circle where it was interrupted. The vital motions in a fever from drunkenness, and in other periodical diseases, are instances of this circumstance. The accidental inebriate does not discover himself perfectly till about the same hour on the succeeding day. The accustomed drunk- ard is disordered, if he has not his usual potation of fermented liquor. So, if a considerable part of a connected tribe of action be 137 SECT. XVII. 1. CATENATION OF MOTIONS. be disturbed, that whole tribe goes on with confusion, till the part of the tribe affected regains its accustomed catenations. So vertigo produces vomiting, and a great secretion of bile, as in sea-sickness, all these being parts of the tribe of irritative catenations. 8. Weaker catenated trains may be dissevered by the sudden exertion of the stronger. When a child first attempts to walk across a room, call to him and he instantly falls upon the ground. So, while I am thinking over the virtues of my friends, if the tea- kettle spurt out some hot water on my docking, the sudden pain breaks the weaker chain of ideas and introduces a new group of figures of its own. This circumstance is extended to some unnatural trains of action, which have not been confirm- ed by long habit; as the hiccough, or an ague-fit, which are frequently curable by surprise. A young lady, about eleven years old, had, for five days, a contraction of one muscle in her fore-arm, and another in her arm, which occurred four or five times every minute; the muscles were seen to leap, but without bending the arm. To counteract this new morbid ha- bit an issue was placed over the convulsed muscle of her arm, and an adhesive plaster, wrapped tight like a bandage over the whole fore-arm, by which the new motions were immediately destroyed, but the means were continued some weeks to pre- vent a return. 9. If any circle of actions is dissevered, either by omission of some of the links, as in sleep, or by insertion of other links, as in surprise, new catenations take place in a greater or less de- gree. The last link of the broken chain of actions becomes connected with the new motion which has broken it, or with that which was nearest the link omitted; and these new cate- nations proceed instead of the old ones. Hence the periodic re- turns of ague-fits, and the chimeras of our dreams. 10. If a train of actions is dissevered, much effort of volition or sensation will prevent its being restored. Thus, in the com- mon impediment of speech, when the association of the motions of the muscles of enunciation with the idea of the word to be spoken is disordered, the great voluntary efforts, which distort the countenance, prevent the rejoining of the broken associa- tions. See No. II. 10. of this Section. It is thus likewise observable in some inflammations of the bowels, the too strong ef- forts made by the muscles to carry forwards the offending ma- terial fixes it more firmly in its place, and prevents the cure.— So, in endeavouring to recall to our memory some particular word of a sentence, if we exert ourselves too strongly about it, we are less likely to regain it. 11. Catenated 138 CATENATION OF MOTIONS. SECT. XVII. 2. 11. Catenated trains or tribes of action are easier dissevered than catenated circles of action. Hence in epileptic fits the syn- chronous connected tribes of action, which keep the body erect, are dissevered, but the circle of vital motions continues undisturbed. 12. Sleep destroys the power of volition, and precludes the stimuli of external objects, and thence dissevers the trains, of which these are a part; which confirms the other catenations, as those of the vital motions, secretions, and absorptions; and produces the new trains of ideas, which constitute our dreams. II. 1. All the preceding circumstances of the catenations of animal motions, will be more clearly understood by the fol- lowing example of a person learning music; and when we re- collect the variety of mechanic arts, which are performed by associated trains of muscular actions, catenated with the effects they produce, as in knitting, netting, weaving; and the greater variety of associated trains of ideas caused, or catenated by vo- litions, or sensations, as in our hourly modes of reasoning, or imagining, or recollecting, we shall gain some idea of the innu- merable catenated trains and circles of action, which form the tenor of our lives, and which began, and will only cease en- tirely with them. 2. When a young lady begins to learn music, she voluntarily applies herself to the characters of her music-book, and by ma- ny repetitions endeavours to catenate them with the proportions of sound, of which they are symbols. The ideas excited by the musical characters are slowly connected with the keys of the harpsichord, and much effort is necessary to produce every note with the proper singer, and in its due place and time; till at length a train of voluntary exertions becomes catenated with certain irritations. As the various notes, by frequent repetitions, become connected in the order in which they are produced, a new catenation of sensitive exertions becomes mixed with the voluntary ones above described; and not only the musical sym- bols of crotchets and quavers, but the auditory notes and tones, at the same time, become so many successive or synchronous links in this circle of catenated actions. At length the motions of her fingers become catenated with the musical characters; and these no sooner strike the eye than the finger presses down the key without any voluntary atten- tion between them: the activity of the hand being connected with the irritation of the figure, or place of the musical symbol on the retina; till at length, by frequent repetitions of the same tune, the movements of her fingers in playing, and the muscles of the larynx in singing, become associated with each other, and form 139 SECT. XVII. 2. CATENATION OF MOTIONS. form part of those intricate trains and circles of catenated mo- tions, according with the second article of the preceding propo- sitions in No. 1. of this Section. 3. Besides the facility, which, by habit, attends the execution of this musical perfomance, a curious circumstance occurs, which is, that when our young musician has began a tune, she finds herself inclined to continue it, and that even when she is care- lessly singing alone, without attending to her own song, accord- ing with the third preceding article. 4. At the same time that our young performer continues to play with great exactness this accustomed tune, she can bend her mind, and that intensely, on some other object, according with the fourth article of the preceding propositions. The manuscript copy of this work was lent to many of my friends, at different times, for the purpose of gaining their opinions and criticisms on many parts of it, and I found the following anecdote written with a pencil opposite to this page, but am not certain by whom : " I remember seeing the pretty young actress, who succeeded Mrs. Arne in the performance of the celebrated Padlock, rehearse the musical parts at her harpsichord, under the eye of her master, with great taste and accuracy, though I observed her countenance full of emotion, which I could not account for; at last she suddenly burst into tears; for she had all this time been eyeing a beloved Canary bird suffering great agonies, which at that instant fell dead from its perch. 5. At the same time many other catenated circles of action are going on in the person of our fair musician, as well as the motions of her fingers, such as the vital motions, respiration, the movements of her eyes and eyelids, and of the intricate muscles of vocality, according with the fifth preceding article. 6. If by any strong impression on the mind of our fair mu- sician, she should be interrupted for a very inconsiderable time, she can still continue her performance, according to the sixth article. 7. If, however, this interruption be greater, though the chain of actions be not dissevered, it proceeds confusedly, and our young performer continues indeed to play, but in a hurry, with out accuracy and elegance, till she begins the tune again, ac- cording to the seventh of the preceding articles. 8. But if this interruption be still greater, the circle of ac- tions becomes entirely dissevered, and she finds herself imme- diately under the necessity to begin over again to recover the lost catenation, according to the eighth preceding article. 9. Or, in trying to recover it, she will sing some dissonant U notes, 140 CATENATION OF MOTIONS. SECT. XVII. 2. notes, or strike some improper keys, according to the ninth preceding article. 10. A very remarkable thing attends this breach of catena- tion: if the performer has forgotten some word of her song, the more energy of mind she uses about it, the more distant is she from regaining it; and artfully employs her mind, in part, on some other object, or endeavours to dull its perceptions, con- tinuing to repeat, as it were inconsciously, the former part of the song, that she remembers, in hopes to regain the lost con- nection. For if the activity of the mind itself be more energetic, or takes its attention more, than the connecting word, which is wanted, it will not perceive the slighter link of this lost word; as who listens to a feeble sound, must be very silent and motion- less; so that in this case the very vigour of the mind itself seems to prevent it from regaining the lost catenation, as well as the too great exertion in endeavouring to regain it, according to the tenth preceding article. We frequently experience, when we are doubtful about the spelling of a word, that the greater voluntary exertion we use, that is, the more intensely we think about it, the further are we from regaining the lost association between the letters of it, but which readily recurs when we have become careless about it. In the same manner, after having for an hour laboured to recol- lect the name of some absent person, it shall seem, particularly after sleep, to come into the mind as it were spontaneously; that is, the word we are in search of, was joined to the preceding one by association; this association being dissevered, we endeavour to recover it by volition; this very action of the mind strikes our attention more than the faint link of association, and we find it impossible, by this means, to retrieve the lost word. After, sleep, when volition is entirely suspended, the mind becomes capable of perceiving the fainter link of association, and the word is regained. On this circumstance depends the impediment of speech be- fore mentioned; the first syllable of a word is causable by voli- tion, but the remainder of it is, in common conversation, intro- duced by its associations with this first syllable, acquired by long habit. Hence, when the mind of the stammerer is vehemently employed on some idea or ambition of shining, or fear of not succeeding, the associations of the motions of the muscles of ar- ticulation with each other become dissevered by this greater ex- ertion, and he endeavours, in vain, by voluntary efforts, to rejoin the broken association. For this purpose he continues to repeat the first syllable, which is causable by volition, and strives in vain, by 141 SECT. XVII.3. CATENATION OF MOTIONS. by various distortions of countenance, to produce the next links which are subject to association. See Class IV. 3.1.1. 11 . After our accomplished musician has acquired great va- riety of tunes and songs, so that some of them begin to cease to be easily recollected, she finds progressive trains of musical notes more frequently forgotten than those which are composed of reiterated circles, according with the eleventh preceding article. 12. To finish our example with the preceding articles, we must at length suppose, that our fair performer falls asleep over her harpsichord; and thus, by the suspension of volition, and the exclusion of external stimuli, she dissevers the trains and circles of her musical exertions. III. 1. Many of these circumstances of catenations of mo- tions receive an easy explanation from the four following con- sequences to the seventh law of animal causation in Sect. IV. These are, first, that those successions or combinations of ani- mal motions, whether they were united by causation, associa- tion, or catenation, which have been most frequently repeated, acquire the strongest connection. Secondly, that of these, those which have been less frequently mixed with other trains or tribes of motion, have the strongest connection. Thirdly, that of these, those which were first formed, have the strongest con- nection. Fourthly, that if an animal motion be excited by more than one causation, association, or catenation, at the same time, it will be -performed with greater energy. 2. Hence also we understand why the catenations of irri- tative motions are more strongly connected than those of the other classes, where the quantity of unmixed repetition has been equal; because they were first formed. Such are those of the secerning and absorbent systems of vessels, where the action of the gland produces a fluid, which stimulates the mouths of its correspondent absorbents. The associated mo- tions seem to be the next most strongly united, from their fre- quent repetition; and where both these circumstances unite, as in the vital motions, their catenations are indissoluble, but by the destruction of the animal. 3. Where a new link has been introduced into a circle of actions by some accidental defect of stimulus; if that defect of stimulus be repeated at the same part of the circle a second or a third time, the defective motions thus produced, both by the re- peated defect of stimulus and by their catenation with the parts of the circle of actions, will be performed with less and less ener- gy. Thus if any person is exposed to cold at a certain hour to- day, so long as to render some part of the system for a time tor- pid, and is again exposed to it at the same hour to-morrow, and the 142 CATENATION OF MOTIONS. SECT. XVII. 3 the next day, he will be more and more affected by it, till at length a cold fit of fever is completely formed, as happens at the beginning of many of those fevers which are called nervous or low fevers; where the patient has slight periodical shiver- ings and paleness for many days before the febrile paroxysm is completely formed. 4. On the contrary, if the exposure to cold be for so short a time as not to induce any considerable degree of torpor or quiescence, and is repeated daily as above-mentioned, it loses its effect more and more at every repetition, till the constitution can bear it without inconvenience, or indeed without being conscious of it; as in walking into cold air in frosty weather. The same rule is applicable to increased stimulus, as of heat or of vinous spirit, within certain limits, as is applied in the two last paragraphs to Deficient Stimulus, as is further ex- plained in Sect. XXXVI. on the Periods of Diseases. 5. Where irritation coincides with sensation to produce the same catenations of motion, as in inflammatory fevers, they are excited with still greater energy than by the irrita- tion alone. So, when children expect to be tickled in play, by a feather lightly passed over the lips, or by gently vellicat- ing the soles of their feet, laughter is most vehemently excit- ed; though they can stimulate these parts with their own sin- gers unmoved. Here the pleasureable idea of playfulness coin- cides with the vellication; and there is no voluntary exertion used to diminish the sensation, as there would be if a child should endeavour to tickle himself. See Sect. XXXIV. I. 4. 6. And, lastly, the motions excited by the junction of vo- luntary exertion with irritation, are performed with more ener- gy than those by irritation singly; as when we listen to small noises, as to the ticking of a watch in the night, we perceive the most weak sounds, that are at other times unheeded. So, when we attend to the irritative ideas of sound in our ears, which are generally not attended to, we can hear them; and can see the spectra of objects, which remain in the eye, when ever we please to exert our voluntary power in aid of those weak actions of the retina, or of the auditory nerve. 7. The temporary carnations of ideas, which are caused by the sensations of pleasure or pain, are easily dissevered either by irritations, as when a sudden noise disturbs a day-dream; or by the power of volition, as when we awake from sleep. Hence, in our waking hours, whenever an idea occurs, which is in congruous to our former experience, we instantly dissever the train of imagination by the power of volition, and compare the incongruous idea with our previous knowledge of nature, and 143 SECT. XVIII. OF SLEEP. and reject it. This operation of the mind has not yet acquir- ed a specific name, though it is exerted every minute of our waking hours; unless it may be termed INTUITIVE ANA- LOGY. It is an act of reasoning, of which we are unconsci- ous, except from its effects in preserving the congruity of our ideas, and bears the same relation to the sensorial power of vo- lition, that irritative ideas, of which we are inconscious, except by their effects, do to the sensorial power of irritation; as the former is produced by volition without our attention to it, and the latter by irritation without our attention to them. If, on the other hand; a train of imagination or of voluntary ideas are excited with great energy, and passing on with great vivacity, and become dissevered by some violent stimulus, as the discharge of a pistol near one's ear, another circumstance takes place; which is termed SURPRISE; which, by exciting violent irritation, and violent sensation, employs, for a time, the whole sensorial energy, and thus dissevers the passing trains of ideas, before the power of volition has time to compare them with the usual phænomena of nature. In this case fear is generally the companion of surprise, and adds to our embarrassment, as every one experiences, in some degree, when he hears a noise in the dark, which he cannot instantly account for. This catenation of fear, with surprise, is owing to our perpetual experience of injuries from external bodies in motion, unless we are upon our guard against them. See Sect. XVIII. 17. and XIX. 2. Many other examples of the catenations of animal motions are explained in Sect. XXXVI. on the Periods of Diseases. SECT. XVIII. OF SLEEP. I. Volition is suspended in sleep. 2. Sensation continues. Dreams prevent delirium and inflammation. 3. Night- mare. 4. Ceaseless flow of ideas in dreams. 5. We seem to receive them by the senses. Optic nerve perfectly sen- sible in sleep. Eyes less dazzled after dreaming of visible objects. 6. Reverie, belief. 7. How we distinguish ideas from perceptions. 8. Variety of scenery in dreams, excel- lence of the sense of vision. 9. Novelty of combination in dreams. 10. Distinctness of imagery in dreams. 11. Rapidity of transaction in dreams. 12. Of measuring lime. Of dramatic time and place. Why a dull play in- duces sleep, and an interesting one reverie. 13. Conscious- ness of our existence and identity in dreams. 14. How we 144 OF SLEEP. SECT. XVIII. 1. we awake sometimes suddenly, sometimes frequently. 15. Irritative motions continue in sleep; internal irritations are succeeded by sensation. Sensibility increases during sleep, and irritability. Morning dreams. Why epilepsies occur in sleep. Ecstacy of children. Case of convulsions in sleep. Cramp, why painful. Asthma. Morning sweats. Increase of heat. Increase of urine in sleep. Why more liable to take cold in sleep. Catarrh from thin night-caps. Why we feel chilly at the approach of sleep, and at wak- ing in the open air. 16. Why the gout commences in sleep. Secretions are more copious in sleep; young animals and plants grow more in sleep. 17. Inconsistency of dreams. Absence of surprise in dreams. 18. Why we forget some dreams and not others. 19. Sleep-talkers awake with surprise. 20. Remote causes of sleep. Atmosphere with less oxygene. Compression of the brain in spina bifida. By whirling on an horizontal wheel. By cold. 21. Defi- nition of sleep. 1. THERE are four situations of our system, which, in their moderate degrees, are not usually termed diseases, and yet abound with many very curious and instructive phænomena; these are sleep, reverie, vertigo, drunkenness. These we shall previously confider, before we step forwards to develope the causes and cures of diseases with the modes of the operation of medicines. As all those trains and tribes of animal motion, which are subjected to volition, were the last that were caused, their connection is weaker than that of the other classes; and there is a peculiar circumstance attending this causation, which is, that it is entirely suspended during sleep; whilst the other clas- ses of motion, which are more immediately necessary to life, as those caused by internal stimuli, for instance, the pulsa- tions of the heart and arteries, or those catenated with plea- sureable sensation, as the powers of digestion, continue to strengthen their habits without interruption. Thus, though man, in his sleeping date, is a much less perfect animal than in his waking hours; and though he consumes more than one third of his life in this his irrational situation; yet is the wisdom of the Author of nature manifest, even in this seeming imper- fection of his work! The truth of this assertion, with respect to the large muscles of the body, which are concerned in locomotion, is evi- dent; as no one in perfect sanity walks about in his sleep, or performs any domestic offices; and in respect to the mind, we never 145 SECT. XVIII. 2, 3. OF SLEEP. never exercise our reason or recollection in dreams; we may sometimes seem distracted between contending passions, but we never compare their objects, or deliberate about the ac- quisition of those objects, if our sleep is perfect. And though many synchronous tribes, or successive trains of ideas, may re- present the houses or walks which have real existence, yet are they here introduced by their connection with our sensations, and are in truth ideas of imagination, not of recollection. 2. For our sensations of pleasure and pain are experienced with great vivacity in our dreams; and hence, all that motley group of ideas, which are caused by them, called the ideas of imagination, with their various associated trains, are in a very vivid manner acted over in the sensorium; and these some times call into action the larger muscles, which have been much associated with them; as appears from the muttering sentences which some people utter in their dreams, and from the obscure barking of sleeping dogs, and the motions of their feet and nostrils. This perpetual flow of the trains of ideas which constitute our dreams, and which are caused by painful or pleasureable sensations, might, at first view, be conceived to be an useless ex- penditure of sensorial power. But it has been shewn, that those motions which are perpetually excited, as those of the arterial system by the stimulus of the blood, are attended by a great ac- cumulation of sensorial power, after they have been for a time suspended; as the hot-fit of fever is the consequence of, the cold one. Now, as these trains of ideas, caused by sensation are perpetually excited during our waking hours, if they were to be suspended in sleep like die voluntary motions, which are exerted only by intervals during our waking hours) an accumulation of sensorial power would follow; and on our awaking, a delirium would supervene; since these ideas, caused by sensation, would be produced with such energy, that we should mistake the trains of imagination for ideas excited by irritation; as perpetually happens to people debilitated by fevers on their first awaking; for in these fevers with debility, the general quantity of irritation being diminished, that of sensation is increased. In like manner, if the actions of the stomach, interlines, and various glands, which are, perhaps, in part at least, caused by or catenated with agreeable sensation, and which perpetually exist during our waking hours, were, like the voluntary motions, suspended in our sleep, the great accumulation of sensorial power which would necessarily follow, would be liable to excite inflamma- tion in them. 3. When, by our continued posture in sleep, some uneasy sensations 146 OF SLEEP. SECT. XVIII. 4, 5. sensations are produced, we either gradually awake by the ex- ertion of volition, or the muscles, connected by habit with such sensations, alter the position of the body: but where the sleep is uncommonly profound, and those uneasy sensations great, the disease called the incubus, or nightmare, is produced. Here the desire of moving the body is painfully exerted, but the power of moving it, or volition, is incapable of action, till we awake. Many lets disagreeable druggies in our dreams, as when we wish in vain to fly from terrifying objects, constitute a slighter degree of this disease. In awakening from the nightmare, I have more than once observed, that there was no disorder in my pulse; nor do I believe the respiration is laborious, as some have affirmed. It occurs to people whose sleep is too pro- found, and some disagreeable sensation exists, which, at other times would have awakened them, and have thence prevented the disease of nightmare; as after great fatigue or hunger, with too large a supper and wine, which occasion our sleep to be uncommonly profound. See No. 14, of this Section. 4. As the larger muscles of the body are much more fre- quently excited by volition than by sensation, they are but seldom brought into action in our sleep: but the ideas of the mind are, by habit, much more frequently connected with sen- sation than with volition; and hence the ceaseless flow of our ideas in dreams. Every one's experience will teach him this truth, for we all daily exert much voluntary muscular motion; but few of mankind can bear the fatigue of much voluntary thinking. 5. A very curious circumstance attending these our sleeping imaginations is, that we seem to receive them by the senses. The muscles, which are subservient to the external organs of sense, are connected with volition, and cease to act in sleep; hence the eyelids are closed, and the tympanum of the ear re- laxed; and it is probable a similarity of voluntary exertion may be necessary for the perceptions of the other nerves of sense; for it is observed, that the papillæ of the tongue can be seen to become erected when we attempt to taste any thing extremely grateful. (Hewson Exper. Enquir. V. 2. 186. Albini Annor. Acad. L. i. c. 15.) Add to this, that the immediate organs of sense have no objects to excite them in the darkness and silence of the night; but their nerves of sense nevertheless continue to possess their perfect activity, subservient to all their numerous sensitive connections. This vivacity of our nerves of sense during the time of sleep is evinced by a circumstance, which almost every one must, at some time or other, have experienced; that is, if we sleep in the day-light, and endeavour to see some object 147 SECT. XVIII.5. OF SLEEP. object in our dream, the light is exceedingly painful to our eyes; and, after repeated struggles, we lament in our sleep, that we cannot see it. In this case I apprehend the eyelid is in some degree opened by the vehemence of our sensations; and the iris being dilated, the optic nerve shews as great, or greater sensibility than in our waking hours. See No. 15. of this Section. When we are forcibly waked at midnight from profound sleep, our eyes are much dazzled with the light of the candle for a minute or two, after there has been sufficient time allowed for the contraction of the iris; which is owing to the accumulation of sensorial power in the organ of vision during its date of less activity. But when we have dreamt much of visible objects, this accumulation of sensorial power in the organ of vision is lessened or prevented, and we awake in the morning without being dazzled with the light, after the iris has had time to con- tract itself. This is a matter of great curiosity, and may be thus tried by any one in the day-light. Close your eyes, and cover them with your hat; think for a minute on a tune which you are accustomed to, and endeavour to sing it with as little activity of mind as possible. Suddenly uncover and open your eyes, and in one second of time the iris will contract itself, but you will perceive the day more luminous for several seconds, owing to the accumulation of sensorial power in the optic nerve. Then again close and cover your eyes, and think intensely on a cube of ivory two inches diameter, attending first to the north and south sides of it, and then to the other four sides of it; then get a clear image in your mind's eye of all the sides of the same cube, coloured red, and then of it coloured green, and then of it coloured blue; lastly, open your eyes as in the former ex- periment, and after the first second of time allowed for the con- traction of the iris, you will not perceive any increase of the light of the day, or dazzling; because now there is no accumu- lation of sensorial power in the optic nerve, that having been expended by its action in thinking over visible objects. This experiment is not easy to be made at first, but by a few patient trials the fact appears very certain, and shews clearly, that our ideas of imagination are repetitions of the motions of the nerve, which were originally occasioned by the stimulus of external bodies; because they equally expend the sensorial power in the organ of sense. See Sect. III. 4. which is analogous to our being as much fatigued by thinking as by labour. 6. Nor is it in our dreams alone, but even in our waking reveries, and in great efforts of invention; so great is the vi- vacity of our ideas, that we do not, for a time, distinguish X them 148 OF SLEEP. SECT. XVIII. 7, 8. them from the real presence of substantial objects; though the external organs of sense are open, and surrounded with their usual stimuli. Thus, whilst I am thinking over the beautiful valley, through which I yesterday travelled, I do not perceive the furniture of my room: and there are some, whose waking imaginations are so apt to run into perfect reverse, that in their common attention to a favourite idea, they do not hear the Voice of the companion, who accosts them, unless it is re- peated with unusual energy. This perpetual mistake in dreams and reveries, where our ideas of imagination are attended with a belief of the presence of external objects, evinces, beyond a doubt, that all our ideas are repetitions of the motions of the nerves of sense, by which they were acquired; and that this belief is not, as some late philosophers contend, an instinct necessarily connected only with our perceptions. 7. A curious question demands our attention in this place; as we do not distinguish in our dreams and reveries between our perceptions of external objects, and our ideas of them in. their absence, how do we distinguish them at any time? In a dream, if the sweetness of sugar occurs to my imagination, the whiteness and hardness of it, which were ideas usually connected with the sweetness, immediately follow in the train; and I be- lieve a material lump of sugar present before my senses: but in my waking hours, if the sweetness occurs to my imagination, the stimulus of the table to my hand, or of the window to my eye, prevents the other ideas of the hardness and whiteness of the sugar from succeeding; and hence I perceive the fallacy, and disbelieve the existence of objects correspondent to those ideas whose tribes or trains are broken by the stimulus of other ob- jects. And further, in our waking hours we frequently exert our volition in comparing present appearances with such as we have usually observed; and thus correct the errors of one sense by our general knowledge of nature by intuitive analogy. See Sect. XVII. 3. 7. Whereas in dreams the power of volition is suspended, we can recollect and compare our present ideas with none of our acquired knowledge, and are hence incapable of observing any absurdities in them By this criterion we distinguish our waking from our sleep- ing hours; we can voluntarily recollect our sleeping ideas, when we are awake, and compare them with our waking ones; but we cannot in our sleep voluntarily recollect our waking ideas at all. 8. The vast variety of scenery, novelty of combination, and distinctness of imagery, are other curious circumstances of 149 SECT. XVIII. 9, 10, 11. OF SLEEP. of our sleeping imaginations. The variety of scenery seems to arise from the superior activity and excellence of our sense of vision; which, in an instant, unfolds to the mind extensive fields of pleasureable ideas, while the other senses collect their object slowly, and with little combination; add to this, that the ideas, which this organ presents us with, are more fre- quently connected with our sensation than those of any other. 9. The great novelty of combination is owing to another circumstance; the trains of ideas, which are carried on in our waking thoughts, are, in our dreams, dissevered in a thousand places, by the suspension of volition, and the absence of irri- tative ideas, and are hence perpetually falling into new cate- nations, as explained in Sect. XVI. 1. 9. For the power of volition is perpetually exerted during our waking hours, in comparing our passing trains of ideas with our acquired know- ledge of nature, and thus forms many intermediate links in their catenation. And the irritative ideas excited by the stimulus of the objects, with which we are surrounded, are every moment intruded upon us, and form other links of our unceasing ca- tenations of ideas. 10. The absence of the stimuli of external bodies, and of volition, in our dreams, renders the organs of sense liable to be more strongly affected by the powers of sensation, and of as- sociation. For our desires or aversions, or the obtrusions of surrounding bodies, dissever the sensitive and associate tribes of ideas in our waking hours, by introducing those ,of irritation and volition amongst them. Hence proceeds the superior dis- tinctness of pleasureable or painful imagery in our sleep: for we recal the figure and the features of a long loft friend, whom we loved, in our dreams, with much more accuracy and vi- vacity than in our waking thoughts. This circumstance con- tributes to prove, that our ideas of imagination are reiterations of those motions of our organs of sense, which were excited by external objects; because, while we are exposed to the sti- muli of present objects, our ideas of absent objects cannot be so distinctly formed. 11. The rapidity of the succession of transactions in our dreams is almost inconceivable; insomuch, that when we are accidentally awakened by the jarring of a door which is open- ed into our bed-chamber, we sometimes dream a whole history of thieves or fire in the very instant of awaking. During the suspension of volition we cannot compare our other ideas with those of the parts of time in which they exist; that is, we cannot compare the imaginary scene, which is be- fore us, with those changes of it which precede or follow it; because 150 OF SLEEP. SECT. XVIII. 12. because this act of comparing requires recollection or voluntary exertion: whereas, in our waking hours, we are perpetually making this comparison, and by that means our waking ideas are kept confident with each other by intuitive analogy; but this comparison retards the succession of them, by occasioning their repetition. Add to this, that the transactions of our dreams consist chiefly of visible ideas, and that a whole history of thieves and fire may be beheld in an instant of time, like the figures in a picture. 12. From this incapacity of attending to the parts of time in our dreams, arises our ignorance of the length of the night; which, but from our constant experience to the contrary, we should conclude was but a few minutes when our sleep is per- fect. The same happens in our reveries: thus, when we are possessed with vehement joy, grief, or anger, time appears short, for we exert no volition to compare the present scenery with the past or future; but when we are compelled to perform those exercises of mind or body, which are unmixed with passion, as in travelling over a dreary country, time appears long; for our desire to finish our journey occasions us more frequently to compare our present situation with the parts of time or place which are before and behind us. So, when we are enveloped in deep contemplation of any kind, or in reverie, as in reading a very interesting play or ro- mance, we measure time very inaccurately; and hence, if a play greatly affects our passions, the absurdity of passing over many days or years, and of perpetual changes of place, are not perceived by the audience, as is experienced by every one who reads or sees some plays of the immortal Shakespeare; but it is necessary for interior authors to observe those rules of the πιθανον and πςεπον inculcated by Aristotle, because their works do not interest the passions diffidently to produce complete reverie. Those works, however, whether a romance, or a sermon, which do not interest us so much as to induce reverie, may, nevertheless, incline us to sleep. For those pleasureable ideas, which are presented to us, and are too gentle to excite laugh- ter, (which is attended with interrupted voluntary exertions, as explained Sect. XXXIV. 1.4.) and which are not accom- panied with any other emotion, which usually excites some vo- voluntary exertion, as anger, or fear, are liable to produce sleep; which consists in a suspension of all voluntary power. But if the ideas thus presented to us, and interest our atten- tion, are accompanied with so much pleasureable or painful sensation as to excite our voluntary exertion at the same time, reverie is the consequence. Hence, an interesting play pro- duces 151 SECT. XVIII. 13, 14. OF SLEEP. duces reverie, a tedious one produces sleep: in the latter we become exhausted by attention, and are not excited to any voluntary exertion, and therefore sleep; in the former we are excited by some emotion, which prevents, by its pain, the sus- pension of volition, and in as much as it interests us, induces reverie, as explained in the next Section. But when our sleep is imperfect, as when we have deter- mined to rise in half an hour, time appears longer to us than in most other situations. Here our solicitude not to oversleep the determined time, induces us, in this imperfect sleep, to compare the quick changes of imagined scenery with the parts of time or place they would have taken up, had they real existence; and that more frequently than in our waking hours; and hence the time appears longer to us: and I make no doubt but the per- mitted time appears long to a man going to the gallows, as the fear of its quick lapse will make him think frequently about it. 13. As we gain our knowledge of time by comparing the present scenery with the past and future, and of place by com- paring the situations of objects with each other; so we gain our idea of consciousness by comparing ourselves with the scenery around us; and of identity by comparing our present conscious- ness with our past consciousness: as we never think of time or place, but when we make the comparisons above mentioned; so we never think of consciousness, but when we compare our own existence with that of other objects; nor of identity, but when we compare our present and our past consciousness. Hence the consciousness of our own existence, and of our identity, is owing to a voluntary exertion of our minds: and on that account, in our complete dreams we neither measure time, are surprised at the sudden changes of place, nor attend to our own existence or identity, because our power of volition is suspended. But all these circumstances are more or less observable in our incom- plete ones; for then we attend a little to the lapse of time and the changes of place, and to our own existence, and even to our identity of person; for a lady seldom dreams that she is a soldier; nor a man, that he is brought to bed. 14. As long as our sensations only excite their sensual mo- tions, or ideas, our sleep continues sound; but as soon as they exite desires or aversions, our sleep becomes imperfect; and when that desire or aversion is so strong as to produce volun- tary motions, we begin to awake; the larger muscles of the body are brought into action, to remove that irritation or sen- sation, which a continued posture has caused; we stretch our limbs, and yawn, and our sleep is thus broken by the accumu- lation of voluntary power Sometimes 152 OF SLEEP. SECT. XVIII. 15. Sometimes it happens, that the act of waking is suddenly produced, and this soon after the commencement of deep; which is occasioned by some sensation so disagreeable, as in- stantaneously to excite the power of volition; and a temporary action of all the voluntary motions suddenly succeeds, and we start awake. This is sometimes accompanied with loud noise in the cars, and with some degree of fear; and when it is in great excess, so as to produce continued convulsive motions of those muscles, which are generally subservient to volition, it becomes epilepsy; the fits of which, in some patients, generally commence during sleep. This differs from the nightmare, de- scribed in No. 3. of this Section, because in that the disagree able sensation is not so great as to excite the power of volition into action; for as soon as that happens, the disease ceases. Another circumstance, which sometimes awakes people soon after the commencement of their deep, is where the voluntary power is already so great in quantity, as almost to prevent them from falling asleep, and then a little accumulation of it soon again awakens them; this happens in cases of insanity, or where the mind has been lately much agitated by fear or anger. There is another circumstance in which deep is likewise of short duration, which arises from great debility, as after great over-fatigue, and in some fevers, where the strength of the pa- tient is greatly diminished; as in these cases the pulse inter- mits or flutters, and the respiration is previously affected, it seems to originate from the want of some voluntary efforts to facilitate respiration, as when we are awake; and is further treated of in vol. ii. Class i. 2. 1, 2. on the Diseases of the Voluntary Power. Art. Somnus interruptus. 15. We come now to those motions which depend on irrita- tion. The motions of the arterial and glandular systerns continue in our deep, proceeding flower indeed, but stronger and more uniformly, than in our waking hours, when they are income- moded by external stimuli, or by the movements of volition: the motions of the muscles subservient to respiration continue to be stimulated into action; and the other internal senses of hunger, thirst, and lust, are not only occasionally excited in our sleep, but their irritative motions are succeeded by their usual sensations, and make a part of the farrago of our dreams. These sensations of the want of air, of hunger, thirst, and lust, in our dreams, contribute to prove, that the nerves of the external senses are asfo alive and excitable in our sleep; but as the stimuli of exter- nal objects are either excluded from them by the darkness and silence of the night, or their access to them is prevented by the suspension of volition, these nerves of sense fall more readily into their 153 SECT. XVIII. 15. OF SLEEP. their connections with sensation and with association; because much sensorial power, which, during the day, was expended in moving the external organs of sense in consequence of irritation from external stimuli, or in consequence of volition, becomes now in some degree accumulated, and renders the internal or immediate organs of sense more easily excitable by the other sensorial powers. Thus, in respect to the eye, the irritation from external stimuli, and the power of volition during our wak- ing hours, elevate the eyelids, adapt the aperture of the iris to the quantity of light, the focus of the crystalline humour, and the angle of the optic axises to the distance of the object; all, which perpetual activity during the day expends much sensorial power, which is saved during our sleep. Hence it appears, that not only those parts of the system which are always excited by internal stimuli, as the stomach, intestinal canal, bile-ducts, and the various glands , but the or- gans of sense also, may be more violently excited into action by the irritation from internal stimuli, or by sensation, during our sleep, than in our waking hours; because, during the suspension of volition, there is a greater quantity of the spirit of ani- mation to be expended by the other sensorial powers. On this account our irritability to internal stimuli, and our sensibility to pain or pleasure, is not only greater in sleep, but increases as our sleep is prolonged. Whence digestion and secretion are performed better in sleep than in our waking hours; and out dreams in the morning have greater variety and vivacity, as our sensibility increases, than at night when we first lie down. And hence, epileptic fits, which are always occasioned by some dis- agreeable sensation, so frequently attack those who are subject to them, in their sleep; because, at this time, the system is more, excitable by painful sensation, in consequence of internal sti- muli; and the power of volition is then suddenly exerted to re- lieve this pain, as explained Sea. XXXIV. 1.4. There is a disease which frequently affects children in the cradle, which is termed ecstacy, and seems to consist in certain exertions to relieve painful sensation, in which the voluntary power is not so far excited as totally to awaken them, and yet is sufficient to remove the disagreeable sensation which excites it; in this case changing the posture of the child frequently re- lieves it. I have at this time under my care an elegant young man, about twenty-two years of age, who seldom sleeps more than an hour without experiencing a convulsion fit, which ceases in about half a minute without any subsequent stupor. Large doses of opium only prevented the paroxysms, so long as they prevented 154 OF SLEEP. SECT. XVIII. 15. prevented him from sleeping by the intoxication which they in- duced. Other medicines had no effect on him. He was gently awaked every half hour for one night, but without good effect, as he soon slept again, and the fit returned at about the same pe- riods of time; for the accumulated sensorial power, which oc- casioned the increased sensibility to pain, was not thus exhausted. This case evinces, that the sensibility of the system to internal excitation increases as our sleep is prolonged, till the pain thus occasioned produces voluntary exertion; which, when it is in its usual degree, only awakens us; but when it is more violent, it occasions convulsions. The cramp in the calf of the leg is another kind of convulsion which generally commences in sleep, occasioned by the conti- nual increase of irritability from internal stimuli, or of sensibili- ty, during that date of our existence. The cramp is a violent exertion to relieve pain, generally either of the skin from cold, or of the bowels, as in some diarrhœas, or from the muscles having been previously overstretched, as in walking up or down deep hills. But in these convulsions of the muscles which form the calf of the leg, the contraction is so violent as to occasion another pain in consequence of their own too violent contrac- tion, as soon as the original pain which caused the contraction is removed. And hence the cramp, or spasm, of these muscles is continued without intermission by this new pain, unlike the alternate convulsions and remissions in epileptic fits. The reason that the contraction of these muscles of the calf of the leg is more violent during their convulsion than that of others, de- pends on the weakness of their antagonist muscles; for after these have been contracted in their usual action, as at every step in walking, they are again extended, not, as most other muscles are, by their antagonists, but by the weight of the whole body on the balls of the toes; and that weight applied to great mechanical advantage on the heel, that is, on the other end of the bone of the foot, which thus acts as a lever. Another disease, the periods of which generally commence during our sleep, is the asthma. Whatever may be the re- mote cause of paroxysms of asthma, the immediate cause of the convulsive respiration, whether in the common asthma, or in what is termed the convulsive asthma, which are perhaps only different degrees of the same disease, must be owing to violent voluntary exertions to relieve pain, as in other con- vulsions; and the increase of irritability to internal stimuli, or of sensibility during sleep, must occasion them to commence at this time. Debilitated people, who have been unfortunately accustomed to 155 SECT. XVIII. 16. OF SLEEP. to great ingurgitation of spirituous potation, frequently part with a great quantity of water during the night, but with not more than usual in the day-time. This is owing to a be- ginning torpor of the absorbent system, and precedes anasarca, which commences in the day, but is cured in the night by the increase of the irritability of the absorbent system during sleep, which thus imbibes, from the cellular membrane, the fluids which had been accumulated there during the day; though it is pos- sible the horizontal position of the body may contribute some- thing to this purpose, and also the greater irritability of some branches of the absorbent vessels, which open their mouths in the cells of the cellular membrane, than that of other branches. As soon as a person begins to sleep, the irritability and sen- sibility of the system begin to increase, owing to the suspension of volition and the exclusion of external stimuli. Hence me actions of the vessels, in obedience to internal stimulation, be come stronger and more energetic, though less frequent in re- spect to number. And as many of the secretions are increased, so the heat of the system is gradually increased; and the extremi- ties of feeble people, which had been cold during the day, be- come warm. Towards morning many people become so warm, as to find it necessary to throw off some of their bed- clothes, as soon as they awake; and in others sweats are so liable to occur towards morning during their sleep. Thus, those who are not accustomed to sleep in the open air, are very liable to take cold, if they happen to fall asleep on a garden bench, or in a carriage with the win ow open: for, as the system is warmer during sleep, as above explained, if a current of cold air affects any part of the body, a torpor of that part is more effectually produced, as when a cold blast of air through a key-hole or casement falls upon a person in a Warm room. In those cases the affected part possesses less irri- tability in respect to heat, from its having previously been ex- posed to a greater stimulus of heat, as in the warm room, or during sleep; and hence, when the stimulus of heat is, diminish- ed, a torpor is liable to ensue; that is, we take cold. Hence, people who sleep in the open air generally feel chilly both at the approach of sleep and on their awaking; and hence many people are perpetually subject to catarrhs it they sleep in a less warm head-dress than that which they wear in the day. 16. Not only the sensorial powers of irritation and of sen- sation, but that of association also appear to act with greater vigour during the suspension of volition in sleep. It will be shewn in another place, that the gout generally first attacks the liver, and that afterwards an inflammation of the ball of the Y great 156 OF SLEEP. SECT. XVIII. 16. great toe commences by association, and that of the liver ceases. Now, as this change or metastasis of the activity of the system generally commences in sleep, it follows, that these associations of motion exist with greater energy at that time; that is, that the sensorial faculty of association, like those of irritation and of sensation, becomes in some measure accumulated during the suspension of volition. Other associate tribes and trains of motions, as well as the irritative and sensitive ones, appear to be increased in their ac- tivity during the suspension of volition in sleep: as those which contribute to circulate the blood, and to perform the various secretions, as well as the associate tribes and trains of ideas, which contribute to furnish the perpetual dreams of our dream- ing imaginations. In sleep, the secretions have generally been supposed to be diminished, as the expectorated mucus in coughs, the fluids discharged in diarrhœas, and in salivation, except indeed the secretion of sweat, which is often visibly increased. This er- ror seems to have arisen from attention to the excretions, rather than to the secretions. For the secretions, except that of sweat, are generally received into reservoirs, as the urine into the blad- der, and the mucus of the intestines and lungs into their re- spective cavities; but these reservoirs do not exclude these fluids immediately by their stimulus, but require, at the same time some voluntary efforts, and therefore permit them to remain during sleep. And as they thus continue longer in those re- ceptacles in our sleeping hours, a greater part is absorbed from them, and the remainder becomes thicker, and sometimes in less quantity, though at the time it was secreted, the fluid was in greater quantity than in our waking hours. Thus, the urine is higher coloured after long sleep; which shews that a greater quantity has been secreted, and that more of the aque- ous and saline part has been re-absorbed, and the earthy part left in the bladder: hence, thick urine in fevers shews only a greater action of the vessels which secrete it in the kidneys, and of those which absorb it from the bladder. The same happens to the mucus expectorated in coughs, which is thus thickened by absorption of its aqueous and saline parts; and the same of the feces of the intestines. From hence it appears, and from what has been said in No. 15, of this Sec- tion, concerning the increase of irritability and of sensibility during sleep, that the secretions are, in general, rather increas- ed than diminished during these hours of our existence; and it is probable that nutrition is almost entirely performed in sleep; and that young animals grow more at this time than in their waking 157 SECT. XVIII. 17, 18. OF SLEEP. waking hours, as young plants have long since been observed to grow more in the night, which is their time of sleep. 17. Two other remarkable circumstances of our dreaming ideas are their inconsistency, and the total absence of surprise. Thus we seem to be present at more extraordinary metamor- phoses of animals or trees, than are to be met with in the fa- bles of antiquity; and appear to be transported from place to place, which sects divide, as quickly as the changes of scenery are performed in a play-house; and yet are not sensible of their inconsistency, nor in the lead degree affected with surprise. We must consider this circumstance more minutely. In our waking trains of ideas, those that are inconsistent with the usual order of nature so rarely have occurred to us, that their con- nection is the slightest of all others: hence, when a consistent train of ideas is exhausted, we attend to the external stimuli that usually surround us, rather than to any inconsistent idea which might otherwise present itself: and if an inconsistent idea should intrude itself, we immediately compare it with the pre- ceding one, and voluntarily reject the train it would introduce. This appears further in the Section on Reverie, in which state of the mind external stimuli are not attended to, and yet the dreams of ideas are kept consistent by the efforts of volition. But as our faculty of volition is suspended, and all external. stimuli are excluded in sleep, this slighter connection of ideas takes place, and the train is said to be inconsistent; that is, dissimilar to the usual order of nature. But, when any consistent train of sensitive or voluntary ideas is flowing along, if any external stimulus affects us so violent- ly as to intrude irritative ideas forcibly into the mind, it dis- unites the former train of ideas, and we are affected with sur- prise. These stimuli of unusual energy or novelty, not only disunite our common trains of ideas, but the trains of muscu- lar motions also, which have not been long established by ha- bit, and disturb those that have. Some people become motion- less by great surprise: the fits of hiccough and of ague have been often removed by it; and it even affects the movements of the heart and arteries: but in our sleep, all external stimuli are excluded, and in consequence no surprise can exist. See Sect. XVII. 3. 7. 18. We frequently awake with pleasure from a dream, which has delighted us, without being able to recollect the transactions of it; unless perhaps at a distance of time, some analogous idea may introduce afresh this forgotten train; and, in our waking reveries, we sometimes in a moment lose the train of thought, but continue to feel the glow of pleasure, or the 158 OF SLEEP. SECT. XVIII. 19, 20. the depression of spirits, it occasioned: whilst, at other times, we can retrace with ease these histories of our reveries and dreams. The ab we explanation of surprise throws light upon this subject. When we are suddenly awaked by any violent sti- mulus, the surprise totally disunites the trains of our sleeping ideas from those of our waking ones; but if we gradually awake, this does not happen; and we readily unravel the pre- ceding trains of imagination. 19. There are various degrees of surprise; the more intent we are upon the train of ideas which we are employed about, the more violent must be the stimulus that interrupts them, and the greater is the degree of surprise. I have observed dogs, who have slept by the fire, and by their obscure barking and struggling have appeared very intent on their prey, that shew- ed great surprise for a few seconds after their awaking, by looking eagerly around them, which they did not do at other times of waking. And an intelligent friend of mine has remarked, that his lady, who frequently speaks much and articulately in her sleep, could never recollect her dreams in the morning, when this happened to her: but that when she did not speak in her sleep, she could always recollect them. Hence, when our sensations act so strongly in sleep as to influence the larger muscles, as in those who talk or struggle, in their dreams, or in those who are affected with complete reverie, (as described in the next Section) great surprise is produced when they awake; and these, as well as those who are completely drunk or delirious, totally forget afterwards their imaginations at those times. 20. As the immediate cause of sleep consists in the suspen- sion of volition, it follows, that whatever diminishes the gene- ral quantity of sensorial power, or derives it from the faculty of volition, will constitute a remote cause of sleep; such as fatigue from muscular or mental exertion, which diminishes the general quantity of sensorial power; or an increase of the sen- sitive motions, as by attending to soft music, which diverts the sensorial power from the faculty of volition; or lastly, by in crease of the irritative motions, as by wine, or food, or warmth; which not only, by their expenditure of sensorial power, diminish the quantity of volition; but also, by their producing pleasureable sensations (which occasion other muscular or sensual motions in consequence) doubly decrease the voluntary power, and thus more forcibly produce sleep. See Sect. XXXlV. 1. 4. Another method of inducing sleep is delivered in a very in- genious work lately published by Dr. Beddoes; who, after la- menting that opium frequently occasions restlessness, thinks, " that 159 SECT. XVIII. 20. OF SLEEP. " that in most cases it would be better to induce sleep by the abstraction of stimuli, than by exhausting the excitability " and adds, " upon this principle, we could not have a better soporific than an atmosphere, with a diminished proportion of oxygene air, and that common air might be admitted after the patient was asleep." (Observ. on Calculus, &c. by Dr. Bed- does. Murray.) If it should be found to be true, that the ex- citability of the system depends on the quantity of oxygene absorbed by the lungs in respiration, according to the theory of Dr. Beddoes, and of M. Girtanner, this idea of sleeping in an atmosphere, with less oxygene in its composition, might be of great service in epileptic cases, and in cramp, and even in fits of the asthma, where their periods commence from the increase of irritability during sleep. Sleep is likewise said to be induced by mechanic pressure on the brain, in the cases of spina bifida. Where there has been a defect of one of the vertebra of the back, a tumour is pro- truded in consequence; and, whenever this tumour has been compressed by the hand, sleep is said to be induced, because the whole of the brain, both within the head and spine, becomes compressed by the retrocession of the fluid within the tumour. But by what means a compression of the brain induces sleep has not been explained, but probably by diminishing the secre- tion of sensorial power, and then the voluntary motions be come suspended previously to the irritative ones, as occurs in most dying persons. Another way of procuring sleep mechanically was related to me by Mr. Brindley, the famous canal engineer, who was brought up to the business of a mill-wright; he told me, that he had more than once seen the experiment of a man extending himself a- cross the large done of a corn-mill, and that by gradually let- ting the done whirl, the man fell asleep before the done had gained its full velocity, and he supposed would have died with out pain by the continuance or increase of the motion. In this case the centrifugal motion of the head and feet mud accumu- late the blood in both these extremities of the body, and thus compress the brain. Lastly, we should mention the application of cold; which, when in a less degree, produces watchfulness, by the pain it occa- sions, and the tremulous convulsions of the subcutaneous mus- cles; but when it is applied in great degree, is said to produce sleep. To explain this effect it has been said, that as the ves- sels of the skin and extremities become first torpid by the want pf the stimulus of heat, and as thence less blood is circulated through them, as appears from their paleness, a greater quantity of 160 OF REVERIE. SECT. XIX. 1. of blood poured upon the brain produces sleep by its compres- sion of that organ. But I should rather imagine, that the sen- sorial power becomes exhausted by the convulsive actions in consequence of the pain of cold, and of the voluntary exercise previously used to prevent it; and that the sleep is only the be ginning to die, as the suspension of voluntary power in linger- ing deaths precedes for many hours the extinction of the irrita- tive motions. 21. The following are the characteristic circumstances at- tending perfect sleep. I. The power of volition is totally suspended. 2. The trains of ideas caused by sensation proceed with grea- ter facility and vivacity; but become inconsistent with the usual order of nature. The muscular motions caused by sensation continue; as those concerned in our evacuations during infan- cy, and afterwards in digestion, and in priapismus. 3. The irritative muscular motions continue, as those con- cerned in the circulation, in secretion, in respiration. But the irritative sensual motions or ideas are not excited; as the imme- diate organs of sense are not stimulated into action by external objects, which are excluded by the external organs of sense; which are not in sleep adapted to their reception by the power of volition, as in our waking hours. 4. The associate motions continue; but their first link is not excited into action by volition, or by external stimuli. In all respects, except those above mentioned, the three last senso- rial powers are somewhat increased in energy during the sus- pension of volition, owing to the consequent accumulation of the spirit of animation. SECT. XIX. OF REVERIE. 1. Various degrees of reverie. 2. Sleep-walkers. Case of a young lady. Great surprise at awaking. And total for- getfulness of what passed in reverie. 3. No suspension of volition in reverie. 4. Sensitive motions continue, and are consistent. 5. Irritative motions continue, but are not succeeded by sensation. 6. Volition necessary for the per- ception of feeble impressions. 7. Associated motions con- tinue. 8. Nerves offense are irritable in sleep, but not in reverie. 9. Somnambuli are not asleep. Contagion received but once. 10. Definition of reverie. 1. WHEN we are employed with great sensation of pleasure, or with great efforts of volition, in the pursuit of some interest- ing 161 SECT. XIX. 2. OF REVERIE. ing train of ideas, we cease to be conscious of our existence, are inattentive to time and place, and do not distinguish this train of sensitive and voluntary ideas from the irritative ones excited by the presence of external objects, though our organs of sense are surrounded with their accustomed stimuli, till at length this interesting train of ideas becomes exhausted, or the appulses of external objects are applied with unusual violence, and we re- turn with surprise, or with regret, into the common track of life. This is termed reverie or studium. In some constitutions these reveries continue a considerable time, and are not to be removed without greater difficulty, but are experienced in a less degree by us all; when we attend earnestly to the ideas excited by volition or sensation, with their associated connections, but are at the same time conscious at intervals of the stimuli of surrounding bodies. Thus, in being present at a play, or in reading a romance, some persons are so totally absorbed as to forget their usual time of sleep, and to- neglect their meals; while others are said to have been so in- volved in voluntary study, as not to have heard the discharge of artillery; and there is a dory of an Italian politician, who could think so intensely on other subjects, as to be insensible to the torture of the rack. From hence it appears, that these catenations of ideas and muscular motions, which form the trains of reverie, are com- posed both of voluntary and sensitive associations of them; and that these ideas differ from those of delirium or of sleep, as they are kept confident by the power of volition; and they differ also from the trains of ideas belonging to insanity, as they are as frequently excited by sensation as by volition. But lastly, that the whole sensorial power is so employed on these trains of complete reverie, that, like the violent efforts of volition, as in convulsions or insanity, or like the great activity of the ir- ritative motions in drunkenness, or of the sensitive motions in delirium, they preclude all sensation consequent to external stimulus. 2. Those persons who are said to walk in their sleep, are affected with reverie to so great a degree, that it becomes a formidable disease; the essence of which consists in the inapti- tude of the mind to attend to external stimuli. Many histories of this disease have been published by medical writers; of which there is a very curious one in the Lausanne Trans- actions. I shall here subjoin an account of such a case, with its cure, for the better illustration of this subject. A very ingenious and elegant young lady, with light eyes and hair, about the age of seventeen, in other respects well, was sud- denly 162 OF REVERIE. SECT. XIX. 2. denly seized, soon after her usual menstruation, with this very wonderful malady. The disease began with vehement convul- sions of almost every muscle of her body, with great but vain efforts to vomit, and the most violent hiccoughs, that can be conceived: these were succeeded in about an hour with a fixed spasm; in which one hand was applied to her head, and the other to support it: in about half an hour these ceased, and the reverie began suddenly, and was at first manifest by the look of her eyes and countenance, which seemed to express attention.— Then she converted aloud with imaginary persons, with her eyes open, and could not, for about an hour, be brought to attend to the stimulus of external objects by any kind of violence, which it was proper to use: these symptoms returned in this order eve- ry day for five or six weeks. These conversations were quite consistent, and we could un- derstand what she supposed her imaginary companions to an- swer, by the continuation of her part of the discourse. Some- times she was angry, at other times shewed much wit and viva- city, but was most frequently inclined to melancholy. In these reveries she sometimes sung over some music with accuracy, and repeated whole pages from the English poets. In repeating some lines from Mr. Pope's works, she had forgot one word, and be- gan again, endeavouring to recollect it; when she came to the forgotten word, it was shouted aloud in her ear, and this repeat- edly, to no purpose; but by many trials she at length regained it herself. These paroxysms were terminated with the appearance of inexpressible surprise, and great fear, from which she was some minutes in recovering herself, calling on her sister with great agitation, and very frequently underwent a repetition of con- vulsions, apparantly from the pain of fear. See Sect. XVII. 3. 7. After having thus returned, for about an hour every day, for two or three weeks, the reveries seemed to become less com- plete, and some of their circumstances varied; so that she could walk about the room in them without running against any of the furniture; though these motions were at first very unsteady and tottering. And afterwards she once drank a dish of tea, when the whole apparatus of the tea-table was set before her, and expressed some suspicion, that a medicine was put into it; and once seemed to smell to a tuberose, which was in flower in her chamber, and deliberated aloud about breaking it from the stem, saying, " it would make her sister so charmingly angry." At another time in her melancholy moments she heard the sound of a passing bell; " I wish I was dead," she cried, listening to the 163 SECT. XIX. 3, 4, 5, 6. OF REVERIE. the bell; and then taking off one of her shoes, as she sat upon the bed, " I love the colour black," says she, " a little wider and a little longer, even this might make me a coffin!"—Yet it is evident die was not sensible at this time, any more than former- ly, of seeing or hearing any person about her; indeed, when great light was thrown upon her, by opening the shutters of the window, her trains of ideas seemed less melancholy; and when I have forcibly held her hands, or covered her eyes, she appear- ed to grow impatient, and would say, she could not tell what to do, for she could neither see nor move. In all these circum- stances her pulse continued unaffected as in health. And when the paroxysm was over, she could never recollect a single idea of what had passed in it. This astonishing disease, after the use of many other medicines and applications in vain, was cured by very large doses of opi- um, given about an hour before the expected returns of the pa- roxysms; and after a few relapses, at the intervals of three or four months, entirely disappeared. But she continued at times, to have other symptoms of epilepsy. 3. We shall only here consider what happened during the time of her reveries, as that is our present subject; the fits of convul- sion belong to another part of this treatise. Sect. XXX IV. 44. There seems to have been no suspension of volition during the fits of reveries, because she endeavoured to regain the lost idea in repeating the lines of poetry, and deliberated about break- ing the tuberose, and suspected the tea to have been medicated. 4. The ideas and muscular movements depending on sensa- tion were exerted with their usual vivacity, and were kept from being inconsistent by the power of volition, as appeared from her whole conversation, and was explained in Sect. XVII. 3. 7. and XVIII. 16. 5. The ideas and motion dependant on irritation during the first weeks of her disease, whilst the reverie was complete, were never succeeded by the sensation of pleasure or pain; as she neither saw, heard, nor felt any of the surrounding objects.— Nor was it certain that any irritative motions succeeded the sti- mulus of external objects, till the reverie became less complete, and then she could walk about the room without running against the furniture of it. Afterwards, when the reverie be- came still less complete from the use of opium, some few irri- tations were at times succeeded by her attention to them. As when she smelt at a tuberose, and drank a dish of tea; but this only when she seemed voluntarily to attend to them. 6. In common life, when we listen to distant sounds, or wish to distinguish objects in the night, we are obliged strongly to ex- Z ert 164 OF REVERIE. SECT. XIX. 7, 8 ert our volition to dipose the organs of sense to perceive them, and to suppress the other trains of ideas, which might interrupt these feeble sensations. Hence, in the present history the strong- est stimuli were not perceived, except when the faculty of vo- lition was exerted on the organ of sense ; and then even com- mon stimuli were sometimes perceived: for her mind was so strenuously employed in pursuing its own trains of voluntary or sensitive ideas, that no common stimuli could so far excite her attention as to disunite them; that is, the quantity of volition or of sensation already existing, was greater than any which could be produced in consequence of common degrees of stimu- lation. But the few stimuli of the tuberose, and of the tea, which she did perceive, were such, as accidentally coincided with the trains of thought which were passing in her mind; and hence did not disunite those trains, and create surprise.— And their being perceived at all was owing to the power of vo- lition preceding or coinciding with that of irritation. This explication is countenanced by a fact mentioned con- cerning a somnambulist in the Lausanne Transactions, who sometimes opened his eyes for a short time, to examine where he was, or where his inkpot stood, and then shut them again, dipping his pen into the pot every now and then, and writing on, but never opening his eyes afterwards, although he wrote on from line to line regularly, and corrected some errors of the pen, or in spelling: so much easier was it to him to refer to his idea of the positions of things, than to his perceptions of them. 7. The associated motions persisted in their usual channel, as appeared by the combinations of her ideas, and the use of her muscles, and the equality of her pulse; for the natural motions of the arterial system, though originally excited like other mo- tions by stimulus, seem in part to continue by their association with each other. As the heart of a viper pulsates long after it is cut out of the body, and removed from the stimulus of the blood. 8. In the section on sleep it was observed that the nerves of sense are equally alive and susceptible to irritation in that state, as when we are awake; but that they are secluded from stimu- lating objects, or rendered unfit to receive them: but in com- plete reverie the reverie happens, the immediate organs of sense are exposed to their usual stimuli; but are either not excited into action at all, or not into so great action as to produce at- tention or sensation. The total forgetfulness of what passes in reveries; and the surprise on recovering from them, are explained in Section XVIII. 19. and in Section XVII. 3. 7. 9. It 165 SECT. XX. OF VERTIGO. 9. It appears from hence, that reverie is a disease of the epi- leptic or cataleptic kind, since the paroxysms of this young lady always began and frequently terminated with convulsions; and though in its greatest degree it has been called somnambulation, or sleep-walking, it is totally different from sleep; because the essential character of sleep consists in the total suspension of vo- lition, which in reverie is not affected; and the essential cha- racter of reverie consists not in the absence of those irritative motions of our senses, which are occasioned by the stimulus of external objects, but in their never being productive of sensation. So that during a fit of reverie that strange event happens to the whole system of nerves, which occurs only to some particular branches of them in those who are a second time exposed to the action of contagious matter. If the matter of the small-pox be inserted into the arm of one who has previously had that di- sease, it will stimulate the wound; but the general sensation or inflammation of the system does not follow, which constitutes the disease. See Sect. XII. 7. 6. XXXIII. 2. 8. 10. The following is the definition, or character, of complete reverie. 1. The irritative motions occasioned by internal sti- muli continue; those from the stimuli of external objects are ei- ther not produced at all, or are never succeeded by sensation or attention, unless they are at the same time excited by volition. 2. The sensitive motions continue, and are kept consistent by the power of volition. 3. The voluntary motions continue un- disturbed. 4. The associate motions continue undisturbed. Two other cases of reverie are related in Section XXXIV. 3. which further evince, that reverie is an effort of the mind, to relieve some painful sensation, and is hence allied to con- vulsion, and to insanity. SECT. XX. OF VERTIGO. 1. We determine our perpendicularity by the apparent mo- tions of objects. A person hood-winked cannot walk in a straight line. Dizziness on looking from a tower, in a room stained with uniform lozenges, on riding over snow. 2. Dizziness from moving objects. A whirling wheel. Fluctuations of a river. Experiment with a child. 3. Dizziness from our own motions and those of other ob- jects. Riding over a broad stream. Sea-sickness. 5. Of turning round on one foot. Dervises in Turkey. At- tention of the mind prevents slight sea-sickness. After a voyage 166 OF VERTIGO. SECT. XX. 1 voyage ideas of vibratory motions are still perceived on, shore. 6. Ideas continue some time after they are excited. Circumstances of turning on one foot, standing on a tower, and walking in the dark explained. 7. Irritative ideas of apparent motions. Irritative ideas of sounds. Batte- ment of the sound of bells and organ-pipes. Vertiginous noise in the head. Irritative motions of the stomach, in- testines, and glands. 8. Symptoms that accompany verti- go. Why vomiting comes on in strokes of the palsey. By the motion of a ship. By injuries on the head. Why mo- tion makes sick people vomit. 9. Why drunken people are vertiginous. Why a stone in the ureter, or bile-duct, pro- duces vomiting. 10. Why after a voyage ideas of vi- bratory motions are perceived on shore, 11. Kinds of ver- tigo and their cure. 12. Definition, of vertigo. 1. IN learning to walk, we judge of the distances of the objects which we approach, by the eve; and by observing their perpendicularity determine our own. This circumstance not having been attended to by the writers on vision, the dis- ease called vertigo, or dizziness, has been little understood. When any person loses the power of muscular action, whe- ther he is erect, or in a sitting posture, he sinks down upon the ground; as is seen in fainting fits, and other instances of great debility. Hence it follows, that some exertion of muscular power is necessary to preserve our perpendicular attitude. This is performed by proportionally exerting the antagonist mus- cles of the trunk --- limbs; and if at anytime in our locomotions, we find ourselves inclining to one side, we either restore our equilibrium by the efforts of the muscles on the other side, or by moving one of our feet, extend the base, which we rest upon, to the new centre of gravity. But the most easy and. habitual manner of determining our want of perpendicularity, is by attending to the apparent mo- tion of the objects within the sphere of 'distinct vision; for this apparent motion of objects, when we incline from our perpendicularity, or begin to fall, is as much greater than the real motion of the eye, as the diameter of the sphere of dis- tina vision is to our perpendicular height. Hence, no one who is hood-winked, can walk in a straight line for a hundred steps together; for he inclines so greatly, before he is warned of his want of perpendicularity by the sense of touch, not having the apparent motions of ambient ob- jects to measure this inclination by, that he is necessitated to move one of his feet outwards, to the right or to the left, to support. 167 SECT. XX. 2,3. OF VERTIGO. support the new centre of gravity, and thus errs from the line he endeavours to proceed in. For the same reason many people become dizzy, when they look from the summit of a tower, which is raised much above all other objects, as these objects are out of the sphere of dis- tinct vision, and they are obliged to balance their bodies by the less accurate feelings of their muscles. There is another curious phenomenon belonging to this place, if the circumjacent visible objects are so small, that we do not distinguish their minute parts; or so similar, that we do not know them from each other, we cannot determine our perpendicularity by them. Thus, in a room hung with a pa- per which is coloured over with similar small black lozenges or rhomboids, many people become dizzy; for when they be- gin to fall, the next, and the next lozenge succeeds upon the eye; which they mistake for the first, and are not aware that they have any apparent motion. But if you fix a sheet of pa- per, or draw any other figure, in the midst of these lozenges, the charm ceases, and no dizziness is perceptible. The same occurs when we ride over a plain covered with snow, with out trees or other eminent objects. 2. But after having compared visible objects at rest with the sense of touch, and learnt to distinguish their shapes and shades, and to measure our want of perpendicularity by their apparent motions, we come to consider them in real motion. Here a new difficulty occurs, and we require some experience to learn the peculiar mode of motion of any moving objects, before we can make use of them for the purpose of determining our per- pendicularity. Thus some people become dizzy at the sight of a whirling wheel, or by gazing on the fluctuations of a river, if no steady objects are at the same time within the sphere of their distinct vision; and when a child first can stand erect upon his legs, if you gain his attention to a white handkerchief steadily extended like a sail, and afterwards make it undulate, he instantly loses his prependicularity, and tumbles on the ground. 3. A second difficulty we have to encounter is to distinguish our own real movements from the apparent motions of ob- jects. Our daily practice of walking and riding on horseback, soon instructs us, with accuracy, to discern these modes of mo- tion, and to ascribe the apparent motions of the ambient ob- jects to ourselves; but those which we have not acquired by repeated habit, continue to confound us. So, as we ride on horseback, the trees and cottages which occur to us appear at rest; we can measure their distances with our eye, and re- gulate 168 OF VERTIGO. SECT. XX. 4, 5. gulate our attitude by them; yet if we carelessly attend to dis- tant hills or woods, through a thin hedge, which is near us, we observe the jumping and progressive motions of them; as this is increased by the paralax of these objects, which we have not habituated ourselves to attend to. When first an Euro- pean mounts an elephant sixteen feet high, and whose mode of motion he is not accustomed to, the objects seem to undulate as he passes, and he frequently becomes sick and vertiginous, as I am well informed. Any other unusual movement of our bodies has the same effect, as riding backwards in a coach, swinging on a rope, turning round swiftly on one leg, scating on the ice, and a thousand others. So, after a patient has been long confined to his bed, when he first attempts to walk, he finds himself vertiginous, and is obliged, by practice, to learn again the particular modes of the apparent motions of objects, as lie walks by them. 4. A third difficulty which occurs to us in learning to ba- lance ourselves by the eye, is, when both ourselves and the cir- cumjacent objects are in real motion. Here it is necessary, that we should be habituated to both these modes of motion in order to preserve our perpendicularity. Thus, on horseback, we accurately observe another person, whom we meet trotting towards us, without confounding his jumping and progressive motion with our own, because we have been accustomed to them both; that is, to undergo the one, and to see the other at the same time. But in riding over a broad and fluctuating dream, though we are well experienced in the motions of our horse, we are liable to become dizzy from our experience in that of the water. And when first we go on ship-board, where the movements of ourselves, and the movements of the large waves are both new to us, the vertigo is almost unavoidable with the terrible sickness which attends it. And this I have been assured has happened to several from being removed from a large ship into a small one; and again, from a small one into a man of war. 5. From the foregoing examples it is evident, that when we are surrounded with unusual motions, we lose our perpen- dicularity: but there are some peculiar circumstances attend- ing this effect of moving objects, which we come now to mention, and shall hope, from the recital of them, to gain some insight into the manner of their production. When a child moves round quick upon one foot, the cir- cumjacent objects become quite indistinct, as their distance increases their apparent motions; and this great velocity con- founds both their forms and their colours, as is seen in whirl- ing 169 SECT. XX. 6. OF VERTIGO. ing round a many coloured wheel; he then loses his usual method of balancing himself by vision, and begins to stagger, and attempts to recover himself by his muscular feelings. This staggering adds to the instability of the visible objects, by giving a vibratory motion besides their rotatory one. The child then drops upon the ground, and the neighbouring objects seem to continue for some seconds of time to circulate around him, and the earth under him appears to librate like a balance. In some seconds of time these sensations of a continuation of the motion of objects vanish; but if he continues turning round some what longer, before he falls, sickness and vomiting are very liable to succeed. But none of these circumstances affect those who have habituated themselves to this kind of motion, as the dervises in Turkey, amongst whom these swift gyrations are a ceremony of religion. In an open boat passing from Leith to Kinghorn, in Scot- land, a sudden change of the wind shook the undistended sail, and stopt our boat: from this unusual movement the passengers all vomited except myself. I observed that the undulation of the ship, and the instability of all visible objects, inclined me strongly to be sick; and this continued, or increased, when I closed my eyes, but as often as I bent my attention with energy on the management and mechanism of the ropes and sails, the sickness ceased, and recurred again as often as I relaxed this attention; and I am assured, by a gentleman of observation and veracity, that he has more than once observed, when the ves- sel has been in immediate danger, that the sea-sickness of the passengers has instantaneously ceased, and recurred again when the danger was over. Those who have been upon the water, in a boat or ship, so long that they have acquired the necessary habits of motion upon that unstable element, at their return on land frequently think, in their reveries, or between sleeping and waking, that they observe the room they sit in, or some of its furniture, to librate like the motion of the vessel. This I have experienced myself, and have been told, that after long voyages it is some time before these ideas entirely vanish. The same is observable in a less degree after having travelled some days in a stage- coach, and particularly when we lie down in bed, and compose ourselves to sleep: in this case it is observable that the rattling noise of the coach, as well as the undulatory motion, haunts us. The drunken vertigo, and the vulgar custom of rocking children, will be considered in the next Section. 6. The motions which are produced by the power of voli- tion, may be immediately stopped by the exertion of the same power 170 OF VERTIGO. SECT. XX. 6. power on the antagonist muscles, otherwise these, with all the other classes of motion, continue to go on some time after they are excited, as the palpitation of the heart continue; after the object of fear, which occasioned it, is removed. But this cir- cumstance is in no class of motions more remarkable than in those dependent on irritation: thus, if any one looks at the sun, and then covers his eyes with his hand, he will, for many seconds of time, perceive the image of the sun marked on his retina: a similar image of all other visible objects would re- main some time formed on the retina, but is extinguished by the perpetual change of the motions of this nerve in our atten- tion to other objects. To this must be added, that the longer time any movements have continued to be excited without fa- tigue to the organ, the longer will they continue spontaneously, after the excitement is withdrawn: as the taste of tobacco in the mouth after a person has been smoaking it. This taste remains so strong, that if a person continues to draw air through a tobacco pipe in the dark, after having been smoaking some time, he cannot distinguish whether his pipe be lighted or not. From these two considerations it appears, that the dizziness felt in the head, after seeing objects in unusual motion, is no other than a continuation of the motions of the optic nerve, excited by those objects, and which engage our attention. Thus, on turning round on one foot, the vertigo continues for some seconds of time after the person is fallen on the ground; and the longer he has continued to revolve, the longer will con- tinue these successive motions of the parts of the optic nerve. After revolving, with your eyes open, till you become verti- ginous, as soon as you cease to revolve, not only the circum- ambient objects appear to circulate round you in a direction contrary to that in which you have been turning, but you are liable to roll your eyes forwards and backwards, as is well ob- served, and ingeniously demonstrated by Dr. Wells in a late publication on vision. The same occurs, if you revolve with your eyes closed, and open them immediately at the time of your ceasing to turn; and even during the whole time of revolving, as may be felt by your hand pressed lightly on your closed eye- lists. To these movements of the eyes, of which he supposes the observer to be inconscious, Dr. Wells ascribes the apparent circumgyration of objects on ceasing to revolve. The cause of thus turning our eyes forwards, and then back again, after our body is at rest, depends, I imagine, on the same circumstance which induces us to follow the indis- tinct spectra which are formed on one side of the centre of the retina, when we observe them apparently on clouds, as described 171 SECT. XX. 6. OF VERTIGO. described in Sect. XL. 2. 2. and then dot being able to gain a more distinct vision of them, we turn our eyes back, and again and again pursue the flying shade. But this rolling of the eyes, after revolving till we become ver- tiginous, cannot cause the apparent circumgyration of objects, in a direction contrary to that in which we have been revolving, for the following reasons. 1. Because, in pursuing a spectrum in the sky, or on the ground, as above-mentioned, we perceive no retrograde motions of objects. 2. Because the apparent retrograde motions of objects, when we have revolved till we are vertiginous, continues much longer than the rolling of the eyes above described. 3. When we have revolved from right to left, the apparent motion of objects, when we stop, is from left to right; and when we have revolved from left to right, the apparent circulation of objects is from right to left; yet in both these cases the eyes of the revolver are seen equally to roll forwards and backwards. 4. Because this rolling of the eyes backwards and forwards takes place during our revolving, as may be perceived by the hand lightly pressed on the closed eyelids, and therefore exists before the effect ascribed to it. And, fifthly, I now come to relate an experiment in which the rolling of the eyes does not take place at all after revolving, and yet the vertigo is more distressing than in the situations above mentioned. If any one looks steadily at a spot in the ceiling over his head, or indeed at his own finger held up high over his head, and in that situation turns round till he becomes giddy, and then stops, and looks horizontally, he now finds that the apparent rotation of objects is from above downwards, or from below upwards; that is, that the apparent circulation of objects is now vertical instead of horizontal, making part of a circle round the axis of his eye; and this without any rolling of the eyeballs. The reason of there being no rolling of his eyeballs perceived after this experiment, is, because the images of objects are formed in rotation round the axis of the eye, and not from one side to the other of he axis of it; so that, as the eyeball has not power to turn in its socket round its own axis, it can not follow the apparent motions of these evanescent spectra, either before or after the body is at rest, from all which ar- guments it is manifest, that these apparent retrograde gyra- tions of objects are not caused by the rolling of the eyeballs: First, because no apparent retrogression of objects is observed in other rollings of the eyes. Secondly, because the apparent re- trogression of objects continues many seconds after the rolling of the eyeballs ceases. Thirdly, because the apparent retro- A a gression 172 OF VERTIGO. SECT. XX. 6. gression of objects is sometimes one way, and sometimes ano- ther, yet the rolling of the eyeballs is the same. Fourthly, be- cause the rolling of the eyeballs exists before the apparent re- trograde motions of objects is observed; that is, before the re- volving person stops. And, fifthly, because the apparent retro- grade gyration of objects is produced, when there is no rolling of the eyeballs at all. Doctor Wells imagines, that no spectra can be gained in the eye, if a person revolves with his eyelids closed; and thinks this a sufficient argument against the opinion, that the appa- rent progression of the spectra of light or colours in the eye, can cause the apparent retrogression of objects in the vertigo above described; but it is certain, when any person revolves in a light room with his eyes closed, that he nevertheless perceives differences of light both in quantity and colour through his eye- lids, as he turns round; and readily gains spectra of those dif- ferences. And these spectra are not very different, except in vivacity, from those which he acquires when he revolves with unclosed eyes; since, if he then revolves very rapidly, the co- lours and forms of surrounding objects are, as it were, mixed together in his eye, as when the prismatic colours are painted on a wheel, they appear white as they revolve. The truth of this is evinced by the staggering or vertigo of men perfectly blind, when they turn round; which is not attended with ap- parent circulation of objects, but is a vertiginous disorder of the sense of touch. Blind men balance themselves by their sense of touch; which, being less adapted for perceiving small deviations from their perpendicular, occasions them to carry themselves more erect in walking. This method of balancing themselves by the direction of their pressure against the floor, becomes disordered by the unusual mode of action in turning round, and they begin to lose their perpendicularity; that is, they become vertiginous, but without any apparent circular motions of visible objects. It will appear from the following experiments, that the ap- parent progression of the ocular spectra of light or colours, is the cause of the apparent retrogression of objects, after a per- son has revolved till he is vertiginous. First, when a person turns round in a light room with his eyes open, but closes them before he stops, he will seem to be carried forwards in the direction he was turning for a short time after he stops. But if he opens his eyes again, the ob- jects before him instantly appear to move in a retrograde di- rection, and he loses the sensation of being carried forwards. The same occurs if a person revolves in a light room with his eyes 173 SECT. XX. 6. OF VERTIGO. eyes closed; when he stops, he seems to be for a time carried forwards, if his eyes are still closed; but the instant he opens them, the surrounding objects appear to move in a retrograde gyration. From hence it may be concluded, that it is the sen- sation or imagination of our continuing to go forwards in the direction in which we were turning, that causes the apparent retrograde circulation of objects. Secondly, though there is an andable vertigo, as is known by the battement, or undulations of sound in the ears, which many vertiginous people experience; and though there is also a tangible vertigo, as when a blind person turns round, as men- tioned above; yet as this circumgyration of objects is an hallu- cination or deception of the sense of sight, we are to look for the cause of our appearing to move forward, when we stop with our eyes closed after gyration, to some affection of this sense. Now, thirdly, if the spectra formed in the eye during our rota- tion, continue to change, when we stand still, like the spectra described in Sect. III. 3. 6. such changes must suggest to us the idea or sensation of our still continuing to turn round; as is the case when we revolve in a light room, and close our eyes be- fore we stop. And, lastly, on opening our eyes in the situation above described, the objects we chance to view amid these chang- ing spectra in the eye, must seem to move in a contrary direc- tion; as the moon sometimes appears to move retrograde, when swift-gliding clouds are passing forwards so much nearer the eye of the beholder. To make observations on faint ocular spectra requires some degree of habit and composure of mind, and even patience; some of those described in Sect. XL. were found difficult to see, by many who tried them; now, it happens that the mind, dur- ing the confusion of vertigo, when all the other irritative tribes of motion, as well as those of vision, are in some degree dis- turbed, together with the fear of falling, is in a very unfit state for the contemplation of such weak sensations, as are occasioned by faint ocular spectra. Yet after frequently revolving, both with my eyes closed, and with them open, and attending to the spectra remaining in them, by shading the light from my eye- lids more or less with my hand, I at length ceased to have the idea of going forward, after I stopped with my eyes closed; and saw changing spectra in my eyes, which seemed to move, as it were, over the field of vision; till at length, by repeated trials on sunny days, I persuaded myself, on opening my eyes, after revolving some time, on a shelf of gilded books in my library, that I could perceive the spectra in my eyes move forwards over one or two of the books, like the vapours in the air of a sum- mer's 174 OF VERTIGO. SECT. XX. 6. mer's day; and could so far undeceive myself, as to perceive the books to stand still. After more trials I sometimes brought myself to believe that I saw changing spectra of lights and shades moving in my eyes, after turning round for some time, but did not imagine either the spectra or the objects to be in a state of gyration. I speak, however, with diffidence of these facts, as I could not always make the experiments succeed, when there was not a strong light in my room, or when my eyes were not in the most proper state for such observations. The ingenious and learned M. Savage has mentioned other theories to account for the apparent circumgyration of objects in vertiginous people. As the retrograde motions of the par- ticles of blood in the optic arteries, by spasm, or by fear, as is seen in the tails of tadpoles, and membranes between the fingers of frogs. Another cause he thinks may be from the librations to one side, and to the other, of the crystalline lens in the eye, by means of involuntary actions of the muscles, which consti- tute the ciliary process. Both these theories lie. under the same objection as that of Dr. Wells before-mentioned; namely, that the apparent motions of objects, after the observer has revolved for some time, should appear to vibrate this way and that; and not to circulate uniformly in a direction contrary to that in which the observer had revolved. M. Savage has, lastly, mentioned the theory of colours left in the eye, which he has termed impressions on the retina. He says, " Experience teaches us, that impressions made on the retina, by a visible object, remain some seconds after the object is re- move; as appears from the circle of fire which we see when a fire-stick is whirled round in the dark; therefore, when we are carried round our own axis in a circle, we undergo a tem- porary vertigo, when we stop; because the impressions of the circumjacent objects remain for a time afterwards on the reti- na." "Nosolog. Method. Clas. VIII. 1. 1. We have before observed, that the changes of these colours remaining in the eye, evinces them to be motions of the fine terminations of the reti- na, and not impressions on it; as impressions on a passive sub- stance must either remain, or cease intirely. Any one who stands alone on the top of a high tower, if he has not been accustomed to balance himself by objects placed at such distances and with such inclinations, begins to stagger, and endeavours to recover himself by his muscular feelings. During this time the apparent motion of objects at a distance below him is very great, and the impressions of these apparent motions continue a little time after he has experienced them; and he is persuaded to incline the contrary way to counteract their 175 SECT. XX. 7. OF VERTIGO. their effects; and either immediately falls, or, applying his hands to the building, uses his muscular feelings to preserve his perpen- dicular attitude, contrary to the erroneous persuasions of his eyes: whilst the person who walks in the dark staggers, but without dizziness; for he neither has the sensation of moving objects to take off his attention from his muscular feelings, nor has he the spectra of those motions continued on his retina to add to his coufusion. It happens indeed sometimes to one stand- ing on a tower, that the idea of his not having room to extend his base, by moving one of his feet outwards when he begins to in- cline, superadds fears to his other inconveniencies; which, like surprise, joy, or any great degree of sensation, enervates him in a moment, by employing the whole sensorial power, and by thus breaking all the associated trains and tribes of motion. 7. The irritative ideas of objects, whilst we are awake, are perpetually present to our sense of sight; as we view the furni- ture of our rooms, or the ground we tread upon, throughout the whole day without attending to it. And as our bodies are never at perfect rest during our waking hours, these irritative ideas of objects are attended perpetually with irritative ideas of their apparent motions. The ideas of apparent motions are always irritative ideas, because we never attend to them, whe- ther we attend to the objects themselves, or to their real mo- tions, or to neither. Hence the ideas of the apparent motions of objects are a complete circle of irritative ideas, which conti- nue thoughout the day. Also during our waking hours, there is a perpetual confused sound of various bodies, as of the wind in our rooms, the fire, distant conventions, mechanic business: this continued buzz, as we are seldom quite motionless, changes its loudness perpe- tually, like the sound of a bell, which rises and falls as long as it continues, and seems to pulsate on the ear. This any one may experience by turning himself round near a water-fall; or by striking a glass bell, and then moving the direction of its mouth towards the ears, or from them, as long as its vibrations continue. Hence this undulation of indistinct sound makes another concomitant circle of irritative ideas, which continues thoughout the day. We hear this undulating sound, when we are perfectly at red ourselves, from other sonorious bodies besides bells; as from two organ-pipes, which are nearly but not quite in uni- son, when they are sounded together. When a bell is struck, the circular form is changed into an eliptic one; the longed axis of which, as the vibrations continue, moves round the peri- pher of the bell; and when either axis of this elipse is point- ed 176 OF VERTIGO. SECT. XX. 8,9. ed towards our ears, the sound is louder; and less when the intermediate parts of the elipse are opposite to us. The vibra- tions of the two organ-pipes may be compared to Nonius's rule; the sound is louder when they coincide, and less at the intermediate times. But, as the sound of bells is the most fami- liar of those sounds, which have a considerable battement, the vertiginous patients, who attend to the irritative circles of sounds above described, generally compare it to the noise of bells. The peristaltic motions of our stomach and intestines, and the secretions of the various glands, are other circles of irrita- tive motions, some of them more or less complete, according to our abstinence or satiety. So, that the irritative ideas of the apparent motions of ob- jects, the irritative battements of sounds, and the movements of our bowels and glands compose a great circle of irritative tribes of motion: and when one considerable, part of this circle of motions becomes interrupted, the whole proceeds in confu- sion, as described in Section XVII. 1. 7, on Catenation of Motions. 8. Hence, a violent vertigo, from whatever cause it hap- pens, is generally attended with undulating noise in the head, perversions of the motions of the stomach and duodenum, un- usual execretion of bile and gastic juice, with much pale urine, sometimes with yellowness of the skin, and a disordered secre- tion of almost every gland of the body, till at length the arte- rial system is affected, and fever succeeds. Thus bilious vomitings accompany the vertigo occasioned by the motion of a ship; and when the brain is rendered ver- tiginous by a paralytic affection of any part of the body, a vo- miting generally ensues, and a great discharge of bile: and hence great injuries of the head from external violence are suc- ceeded, with bilious vomiting, and sometimes with abscesses of the liver. And hence, when a patient is inclined to vomit from other causes, as in some fevers, any motions of the attendants in his room, or of himself, when he is raised or turned in his bed, presently induces the vomiting, by superadding a degree of vertigo. 9. And conversely it is very usual with those whose stomachs are affected from internal causes, to be afflicted with ver- tigo, and noise in the head; such is the vertigo of drunken peo- ple, which continues, when their eyes are closed, and them selves in a recumbent posture, as well as when they are in an erect posture, and have their eyes open. And thus the irrita- tion of a stone in the bile-duct, or in the ureter, or an inflam- mation of any of the intestines, are accompanied with vomit- ings and vertigo. In 177 SECT. XX. 10. OF VERTIGO. In these cases, the irritative motions of the stomach, which are in general not attended to, become so changed by some unnatural stimulus, as to become uneasy, and excite our sen- sation or attention. And thus the other irritative trains of mo- tions, which are associated with it, become disordered by their sympathy. The same happens when a piece of gravel sticks in the ureter, or when some part of the intestinal canal be comes inflamed. In these cases, the irritative muscular mo- tions are first distributed by unusual stimulus, and a disordered action of the sensual motions, or dizziness ensues. While in sea-sickness the irritative sensual motions, as vertigo, precedes; and the disordered irritative muscular motions, as those of the stomach in vomiting, follow. 10. When these irritative motions are disturbed, if the de- gree be not very great, the exertion of voluntary attention to any other object, or any sudden sensation, will disjoin these new habits of motion. Thus some drunken people have become sober immediately when any accident has strongly excited their attention; and sea-sickness has vanished when the ship has been in danger. Hence, when our attention to other objects is most relaxed, as just before we fall asleep, or between our reveries when awake, these irritative ideas of motion and sound are most liable to be perceived; as those who have been at sea, or have travelled long in a coach, seem to perceive the vibrations of the ship, or the rattling of the wheels, at these intervals; which cease again, as soon as they exert their attention. That is, at those intervals they attend to the apparent motions, and to the battement of sounds of the bodies around them, and for a moment mistake them for those real motions of the ship, and noise of wheels, which they had lately been accustomed to; or at these intervals of reverie, or on the approach of sleep, these supposed motions or sounds may be produced intirely by imagination. We may conclude from this account of vertigo, that sea- sickness is not an effort of nature to relieve herself. but a ne- cessary consequence of the associations or catentations of ani- mal motions; and may thence infer, that the vomiting, which attends the gravel in the ureter, inflammations of the bowels, and the commencement of some fevers, has a similar origin, and is not always an effort of the vis medicatrix naturæ. But where the action of the organ is the immediate consequence of the stimulating cause, it is frequently exerted to dislodge that stimulus, as in vomiting up an emetic drug; at other times, the action of an organ is a general effort to relieve pain, as in con- vulsions of the locomotive muscles; other actions drink up and 178 OF VERTIGO. SECT. XX. 11. and carry on the fluids, as in absorption and secretion; all which may be termed efforts of nature to relieve, or to pre- serve herself. 11. The cure of vertigo will frequently depend on our pre- viously investigating the cause of it, which, from what has been delivered above, may originate from the disorder of any part of the great tribes of irritative motions, and of the associ- ate motions catenated with them. Many people, when they arrive at fifty or sixty years of age, are affected with slight vertigo, which is generally, but wrongly ascribed to indigestion, but in reality arises from a beginning defect of their sight; as about this time, they also find it ne- cessary to begin to use spectacles, when they read small prints, especially in winter, or by candle light, but are yet able to read without them during the summer days, when the light is stronger. These people do not see objects so distinctly as formerly, and by exerting their eyes more than usual, they perceive the apparent motions of objects, and confound them with the real motions of them; and therefore cannot accurately balance themselves so as easily to preserve their perpendicularity by them. That is, the apparent motions of objects, which are at rest, as we move by them, should only excite irritative ideas: but as these are now become less distinct, owing to the beginning imperfection of our sight, we are induced, voluntarily, to at- tend to them; and then these apparent motions become suc- ceeded by sensation; and thus the other parts of the trains of irritative ideas, or irritative muscular motions, become disor- dered, as explained above. In these cases of slight vertigo, I have always promised my patients, that they would get free from it in two or three months, as they should acquire the ha- bit of balancing their bodies by less distinct objects, and have seldom been mistaken in my prognostic. There is an auditory vertigo, which is called a noise in the head, explained in No. 7. of this section, which also is very liable to affect people in the advance of life, and is owing to their hearing less perfectly than before. This is sometimes called a ringing, and sometimes a singing, or buzzing, in the cars, and is occasioned by our first experiencing a disagreeable sensation from our not being able distinctly to hear the sounds we used for- merly to hear distinctly. And this disagreeable sensation excites desire and consequent volition; and when we voluntarily attend to small indistinct sounds, even the whispering of the air in a room, and the pulsations of the arteries of the ear, are succeed- ed by sensation; which minute sounds ought only to have pro- duced irritative sensual motions, or unperceived ideas. See Sect. XVII. 179 SECT. XXI. OF DRUNKENNESS. XVII. 3. 6. These patients after a while lose this auditory vertigo, by acquiring a new habit of not attending voluntarily to these indistinct sounds, but contenting themselves with the less accuracy of their sense of hearing. Another kind of vertigo begins with the disordered action of some irritative muscular motions, as those of the stomach from intoxication, or from emetics; or those of the ureter, from the stimulus of a stone lodged in it; and it is probable, that the disordered motions of some of the great collieries of glands, as of those which form the liver, or of the intestinal ca- nal, may occasion vertigo in consequence of their motions be- ing associated or catenated with the great circles of irritative motions ; and from hence it appears that the means of cure must be adapted to the cause. To prevent sea-sickness, it is probable, that the habit of swinging, for a week or two before going on shipboard, might be of service. For the vertigo from failure of sight, spectacles may be used. For the auditory vertigo, æther may be dropt into the ear to stimulate the part, or to dissolve ear-wax, if such be a part of the cause. For the vertigo arising from indiges- tion, the Peruvian bark, and a blister, are recommended. And for that owing to a stone in the ureter, venesection, cathartics, opiates, sal soda aerated. 12. Definition of vertigo. 1. Some of the irritative sensual, or muscular motions, which were usually not succeeded by sen- sation, are in this disease succeeded by sensation; and the trains or circles of motions, which were usually catenated with them, are interrupted, or inverted, or proceed in confusion. 2. The sensitive and voluntary motions continue undisturbed. 3. The associate trains or circles of motions continue; but their cate- nations with some of the irritative motions are disordered, or inverted, or dissevered. SECT. XXI. ON DRUNKENNESS. I. Sleep from satiety of hunger. From rocking children. From uniform sounds. 2. Intoxication from common food after fatigue and inanition. 3. From wine or opium. Chilness after meals. Vertigo. Why pleasure is produced by intoxication, and by swinging and rocking children. And why pain is relieved by it. 4. Why drunkards stag- ger and stammer, and are liable to weep. 5. And become delirious, sleepy, and stupid. 6. Or make pale urine and B b vomit. 180 OF DRUNKENNESS. SECT. XXI. 1,2. vomit. 7. Objects are seen double. 8. Attention of the mind diminishes drunkenness. 9. Disordered irritative motions of all the senses. 10. Diseases from drunkenness. II. Definition of drunkenness. 1. In the state of nature, when the sense of hunger is appeased by the stimulus of agreeable food, the business of the day is over, and the human savage is at peace with the world, he then exerts little attention to external objects, pleasing reveries of imagination succeed, and at length sleep is the result: till the nourishment which he has procured, is carried over every part of the system to repair the injuries of action, and he awakens with fresh vigour, and feels a renewal of his sense of hunger. The juices of some bitter vegetables, as of the poppy and the laurocerasus, and the ardent spirit produced in the fermentation of the sugar found in vegetable juices, are so agreeable to the nerves of the stomach, that, taken in a small quantity, they instantly pacify the sense of hunger; and the inattention to external sti- muli, with the reveries of imagination, and sleep, succeed, in the same manner as when the stomach is filled with other less in- toxicating food. This inattention to the irritative motions, occasioned by exter- nal stimuli, is, a very important circumstance in the approach of sleep, and is produced in young children by rocking their cra- dles; during which all visible objects become indistinct to them. An uniform soft repeated sound, as the murmurs of a gentle current, or of bees, are said to produce the same effect, by presenting indistinct ideas of inconsequential sounds, and by thus stealing our attention from other objects, whilst by their con- tinued reiterations they become familiar themselves, and we cease gradually to attend to any thing, and sleep ensues. 2. After great fatigue or inanition, when the stomach is sud- denly filled with flesh and vegetable food, the inattention to ex- ternal stimuli and the reveries of imagination become so conspi- cuous as to amount to a degree of intoxication. The same is at any time produced by superadding a little wine or opium to our common meals; or by taking these separately in consider- able quantity; and this more efficaciously after fatigue or ina- nition; because a less quantity of any stimulating material will excite an organ into energetic action, after it has lately been torpid from defect of stimulus; as objects appear more lumi- nous after we have been in the dark; and because the suspen- sion of volition, which is the immediate cause of sleep, is sooner induced, after a continued voluntary exertion has in part ex- hausted the sensorial power of volition; in the same manner as we 181 SECT. XXI. 3 OF DRUNKENNESS. we cannot contract a single muscle long together without inter- vals of inaction. 3. In the beginning of intoxication we are inclined to sleep, as mentioned above, but by the excitement of external circum- stances as of noise, light, business, or by the exertion of volition, we prevent the approaches of it, and continue to take into our stomach greater quantities of the inebriating materials. By these means the irritative movements of the stomach are excited into greater action than is natural; and, in consequence, all the irri- tative tribes and trains of motion which are catenated with them, become susceptible of stronger action from their accustomed sti- muli; because these motions are excited both by their usual ir- ritation, and by their association with the increased actions of the stomach and lacteals. Hence the skin glows, and the heat of the body is increased, by the more energetic action of the whole glandular system: and pleasure is introduced in conse- quence of these increased motions from internal stimulus. Ac- cording to Law 5. Sect. IV. on Animal Causation. From this great increase of irritative motions from internal stimulus, and the increased sensation introduced into the system in consequence; and secondly, from the increased sensitive mo- tions in consequence of this additional quantity of sensation, so much sensorial power is expended, that the voluntary power becomes feebly exerted, and the irritation from the stimulus of external objects is less forcible; the external parts of the eye are not, therefore, voluntarily adapted to the distances of objects; whence the apparent motions of those objects either are seen double, or become too indistinct for the purpose of balancing the body, and vertigo is induced. Hence we become acquainted with that very curious circum- stance, why the drunken vertigo is attended with an increase of pleasure; for the irritative ideas and motions occasioned by in- ternal stimulus, that were not attended to in our sober hours, are now just so much increased as to be succeeded by pleasure- able sensation, in the same manner as the more violent motions of our organs are succeeded by painful sensation. And hence a greater quantity of pleasure able sensation is introduced into the constitution; which is attended in some people with an increase of benevolence and good humour. If the apparent motions of objects are much increased, as when we revolve on one foot, or are swung on a rope, the ideas of these apparent motions are also attended to, and are succeeded with pleasure able sensation, till they become familiar to us by frequent use. Hence children are at first delighted with these kinds of exercise, and with riding, and sailing; and hence rock- ing 182 OF DRUNKENNESS. SECT. XXI. 4,5. ing young children inclines them to sleep. For though in the vertigo from intoxication the irritative ideas of the apparent mo- tions of objects are indistinct from their decrease of energy; yet, in the vertigo occasioned by rocking or swinging, the irritative ideas of the apparent motions of objects are increased in energy; and hence they induce pleasure into the system, but are equally indistinct, and in consequence equally unfit to balance ourselves by. This addition of pleasure precludes desire or aversion, and in consequence the voluntary power is feebly exerted; and on this account rocking young children inclines them to sleep. In what manner opium and wine act in relieving pain, is ano- ther article that well deserves our attention. There are many pains that originate from defect as well as from excess of stimu- lus; of these are those of the six appetites of hunger, thirst, lust, the want of heat, of distention, and of fresh air. Thus, if our cutaneous capillaries cease to act from the diminished stimulus of heat, when we are exposed to cold weather, or our stomach is uneasy for want of food; these are both pains from defect of stimulus, and in consequence opium, which stimulates all the moving system into increased action, must relieve them. But this is not the case in those pains which arise from excess of sti- mulus, as in violent inflammations; in these the exhibition of opium is frequently injurious, by increasing the action of the sys- tem, already too great, as in inflammation of the bowels mortifi- cation is often produced by the stimulus of opium. Where, however, no such bad consequences follow, the stimulus of opium, by increasing all the motions of the system, expends so much of the sensorial power, that the actions of the whole sys- tem soon become feebler, and in consequence those which pro- duced the pain and inflammation. 4. When intoxication proceeds a little further, the quantity of pleasureable sensation is so far increased, that all desire ceases, for there is no pain in the system to excite it. Hence, the voluntary exertions are diminished, staggering and stam- mering succeed; and the trains of ideas become more and more inconsistent, from this defect of voluntary exertion, as explained in the sections on sleep and reverie; whilst those passions which are unmixed with volition, are more vividly felt, and shewn with less reserve: hence pining love, or superstitious fear, and the maudling tear dropped on the remembrance of the most trifling distress. 5. At length all these circumstances are increased; the quan- tity of pleasure introduced into the system by the increased ir- ritative muscular motions of the whole sanguiferous, and glan- dular, and absorbent systems, becomes so great, that the or- gans 183 SECT. XXI. 6, 7, 8. OF DRUNKENNESS. gans of sense are more forcibly excited into action by this in- ternal pleasureable sensation, than by the irritation from the stimulus of external objects. Hence the drunkard ceases to attend to external stimuli; and as volition is now also suspended, the trains of his ideas become totally inconsistent, as in dreams or delirium; and at length a stupor succeeds from the great ex- haustion of sensorial power, which probably does not even admit of dreams, and in which, as in apoplexy, no motions continue but those from internal stimuli, from sensation, and from association. 6. In other people a paroxysm of drunkenness has another termination; the inebriate, as soon as he begins to be vertigi- nous, makes pale urine in great quantities, and very fre- quently, and at length becomes sick, vomits repeatedly, or purges, or has profuse sweats, and a temporary fever ensues, with a quick strong pulse. This in some hours is succeeded by sleep; but the unfortunate bacchanalian does not perfectly re- cover himself till about the same time of the succeeding day, when his course of inebriation began: as shewn in Sect. XVII. I. 7. on Catenation. The temporary fever, with strong pulse, is owing to the same cause as the glow on the skin mentioned in the third paragraph of this Section: the flow of urine and sickness arises from the whose system of irritative motions be- ing thrown into confusion by their associations with each other; as in sea-sickness, mentioned in Sect. XX. 4. on Vertigo; and which is more fully explained in Sect. XXIX. on Diabetes. 7. In this vertigo from internal causes we see objects double, as two candles instead of one, which is thus explained. Two lines drawn through the axes of our two eyes meet at the ob- ject we attend to: this angle of the optic axes increases or di- minishes with the less or greater distances of objects. All ob- jects before or behind the place where this angle is formed, appear double; as any one may observe by holding up a pen between his eyes and the candle; when he looks attentively at a spot on the pen, and carelessly at the candle, it will appear double; and the reverse when lie looks attentively at the can- dle, and carelessly at the pen; so that in this case the muscles of the eye, like those of the limbs, stagger and are disobedient to the expiring efforts of volition. Numerous objects are indeed sometimes seen by the inebriate, occasioned by the refractions made by the tears, which stand upon his eyelids. 8. This vertigo also continues, when the inebriate lies in his bed, in the dark, or with his eyes closed; and this more pow- erfully than when he is erect, and in the light. For the irri- tative ideas of the apparent motions of objects are now excited by 184 OF DRUNKENNESS. SECT. XXI. 9, 10. by irritation from internal stimulus, or by association with other irritative motions; and the inebriate, like one in a dream, believes the objects of these irritative motions to be present, and feels himself vertiginous. I have observed in this situation, so long as my eyes and mind were intent upon a book, the sick- ness and vertigo ceased, and were renewed again the moment I discontinued this attention; as was explained in the preced- ing account of sea-sickness. Some drunken people have been known to become sober instantly from some accident that has strongly excited their attention, as the pain of a broken bone, or the news of their house being on fire. 9. Sometimes the vertigo from internal causes, as from in- toxication, or at the beginning of some fevers, becomes so uni- versal, that the irritative motions which belong to other organs of sense, are succeeded by sensation or attention, as well as those of the eye. The vertiginous noise in the ears has been explained in Section XX. on Vertigo. The taste of the saliva, which in general is not attended to, becomes perceptible, and the patients complain of a bad taste in their mouth. The common smells of the surrounding air sometimes ex- cite the attention of these patients, and bad smells are com- plained of, which, to other people, are imperceptible. The irritative motions that belong to the sense of pressure, or of touch, are attended to, and the patient conceives the bed to librate, and is fearful of falling out of it. The irritative mo- tions belonging to the senses of distention, and of heat, like those above-mentioned, become attended to at this time: hence, we feel the pulsation of our arteries all over us, and complain of heat, or of cold, in parts of the body where there is no ac- cumulation or diminution of actual heat. All which are to be explained, as in the last paragraph, by the irritative ideas be- longing to the various senses being now excited by internal sti- muli, or by their associations with other irritative motions. And that the, inebriate, like one in a dream, believes the ex- ternal objects, which usually caused these irritative ideas, to be now present. 10. The diseases in consequence of frequent inebriety, or of daily taking much vinous spirit without inebriety, consist in the paralysis, which is liable to succeed violent stimulation. Organs, whose actions are associated with others, are fre- quently more affected than the organ which is stimulated into two violent action. See Sect. XXIV. 2. 8. Hence, in drunken people it generally happens, that the secretory vessels of the liver become first paralytic, and a torpor, with consequent gall- stones or schirrus of this viscus, is induced with concomitant jaundice; 185 SECT. XXI. 11. OF DRUNKENNESS. jaundice; otherwise it becomes inflamed in consequence of pre- vious torpor; and this inflammation is frequently transferred to a more sensible part, which is associated with it, and pro- duces the gout, or the rosy eruption of the face, or some other leprous eruption on the head, or arms, or legs. Sometimes the stomach is first affected, and paralysis of the lacteal system is induced; whence a total abhorrence from flesh-food, and general emaciation. In others, the lymphatic system is af- fected with paralysis, and dropsy is the consequence. In some inebriates, the torpor of the liver produces pain without ap- parent schirrus, or gall-stones, or inflammation, or consquent gout, and in these epilepsy or insanity are often the consequence. All which will be more fully treated of in the course of the work, I am well aware, that it is a common opinion, that the gout is as frequently owing to gluttony in eating, as to intemperance in drinking fermented or spirituous liquors. To this I answer, that I have seen no person afflicted with the gout, who has not drank freely of fermented liquor, as wine and water, or small beer; though, as the disposition to all the diseases which have orginated from intoxication, is in some degree hereditary, a less quantity of spirituous potation will induce the gout in those who inherit the disposition from their parents. To which I must add, that in young people the rheumatism is frequently mistaken for the gout. Spice is seldom taken in such quantity as to do any material injury to the system; flesh-meats, as well as vegetables, are the natural diet of mankind; with these a glutton may be crammed up to the throat, and fed fat like a stalled ox; but he will not be diseased, unless he adds spirituous or fermented liquor to his food. This is well known in the. distilleries, where the swine, which are fattened by the spirituous sediments of barrels, acquire diseased livers. But mark what happens to a man, who drinks a quart of wine or of ale, if he has not been habi- tuated to it. He loses the use both of his limbs and of his un- derstanding ! He becomes a temporary idiot, and has a tempo- rary stroke of the palsy! And though he slowly recovers after some hours, is it not reasonable to conclude, that a perpetual re- petition of so powerful a poison must at length permanently affect him?—If a person accidentally becomes intoxicated by eating a few mushrooms of a peculiar kind, a general alarm is excited, and he is said to be poisoned, and emetics are exhi- bited; but so familiarised are we to the intoxication from vinous spirit, that it occasions laughter rather than alarm. There is, however, considerable danger in too hastily dis- continuing the use of so strong a stimulus, lest the torpor of the system, 186 REPETITION AND SECT. XXII. 1. system, or paralysis, should sooner be induced by the omission than by the continance of this habit, when unfortunately ac- quired. A golden rule for determining the quantity which may with safety be discontinued, is delivered in Sect. XII. 7. 8. II. Definition of drunkenness. 1. Many of the irritative mo- tions are much increased in energy by internal stimulation. 2. A great additional quantity of pleasureable sensation is occasioned by this increased exertion of the irritative motions. And many sensitive motions are produced in consequence of this increased sensation. 3. The associated trains and tribes of motions, catenated with the increased irritative and sensitive motions, are disturbed, and proceed in confusion. 4. The faculty of volition is gradually impaired; whence proceed the instability of locomotion, inaccuracy of perception, and inconsistency of ideas; and is at length totally suspended, and a temporary apoplexy succeeds. SECT. XXII. OF PROPENSITY TO MOTION, REPETITION AND IMITATION. I. Accumulation of sensorial power in hemiplagia, in sleep, in cold fit of fever, in the locomotive muscles, in the organs of sense. Produces propensity to action. II. Repetition by three sensorial powers. In rhimes and alliterations, in music, dancing, architecture, landscape-painting, beauty III. I. Perception consists in imitation. Four kinds of imitation. 2. Voluntary. Dogs taught to dance. 3. Sen- sitive. Hence sympathy, and all our virtues. Conta- gious matter of venereal ulcers, of hydrophobia, of jail- fever, of small-pox, produced by imitation, and the sex of the embryon. 4. Irritative imitation. 5. Imitations re- solvable into associations. I. 1. IN the hemiplagia, when the limbs on one side have lost their power of voluntary motion, the patient is for many days perpetually employed in moving those of the other. 2. When the voluntary power is suspended during sleep, there commences a ceaseless flow of sensitive motions, or ideas of imagination, which compose our dreams. 3. When, in the cold fit of an intermittent fever, some parts of the system have for a time continued torpid, and have thus expended less than their usual expenditure of sensorial power, a hot fit succeeds, with violent action of those vessels which had previously been quiescent. 187 SECT. XXII. 2. IMITATION. quiescent. All these are explained from an accumulation of sensorial power during the inactivity of some part of the system. Besides the very great quantity of sensorial power perpetu- ally produced and expended in moving the arterial, venous, and glandular systems, with the various organs of digestion, as de- scribed in Section XXXII. 3. 2. there is also a constant ex- penditure of it by the action of our locomotive muscles and or- gans of sense. Thus, the thickness of the optic nerves, where they enter the eye, and the great expansion of the nerves of touch beneath the whole of the cuticle, evince the great con- sumption of sensorial power by these senses. And our perpe- tual muscular actions in the common offices of life, and in con- stantly preserving the perpendicularity of our bodies during the day, evince a considerable expenditure of the spirit of ani- mation by our locomotive muscles. It follows, that if the ex- ertion of these organs of sense and muscles be for a while inter- mitted, that some quantity of sensorial power must be accumu- lated, and a propensity to activity of some kind ensue from the increased excitability of the system. Whence proceeds the irk- someness of a continued attitude, and of an indolent life. However small this hourly accumulation of the spirit of ani- mation may be, it produces a propensity to some kind of action; but it nevertheless requires either desire or aversion, either plea- sure or pain, or some external stimulus, or a previous link of association, to excite the system into activity: thus it frequently happens, when the mind and body are so unemployed as not to possess any of the three first kinds of stimuli, that the last takes place, and consumes the small but perpetual accumulation of sensorial power. Whence some indolent people repeat the same verse for hours together, or hum the same tune. Thus the poet: Onward he trudged, not knowing what he sought, And whistled as he went, for want of thought. II. The repetitions of motions may be at first produced, ei- ther by volition, or by sensation or by irritation ; but they soon become easier to perform than any other kinds of action, be- cause they soon become associated together, according to law the seventh, Section IV. on Animal Causation. And, because their frequency of repetition, if as much sensorial power be produced during every reiteration as is expended, adds to the facility of their production. If a stimulus be repeated at uniform intervals of time, as described in Sect. XII. 3. 3. the action, whether of our mus- cles or organs of sense, is produced with still greater facility or energy; because the sensorial power of association, mentioned C c above, 188 REPETITION AND SECT. XXII. 2. above, is combined with the sensorial power of irritation; that is, in common language, the acquired habit assists the power of the stimulus. This not only obtains in the annual, lunar, and diurnal ca- tenations of animal motions, as explained in Sect. XXXVI. which are thus performed with great facility and energy; but in every less circle of actions or ideas, as in the burthen of a song, or the reiterations of a dance. To the facility and dis- tinctness with which we hear sounds at repeated intervals, we owe the pleasure which we receive from musical time, and from poetic time; as described in Botanic Garden, P. 2. Interlude 3. And to this the pleasure we receive from the rhimes and al- literations of modern versification; the source of which, with- out this key, would be difficult to discover. And to this like- wise should be ascribed the beauty of the duplicature in the per- fect: tense of the Greek verbs, and of some Latin ones, as tango tetegi, mordeo momordi There is no variety of notes referable to the gamut in the beating of the drum; yet if it be performed in musical time, it is agreeable to our ears; and therefore this pleasureable sensation must be owing to the repetition of the divisions of the sounds at certain intervals of time, or musical bars. Whether these times or bars are distinguished by a pause, or by in emphasis or accent, certain it is, that this distinction is perpetually repeated; other- wise the ear could not determine instantly, whether the succes- sions of sound were in common or in triple time. In common time there is a division between every two crotchets, or other notes of equivalent time, though the bar in written music is put after every fourth crotchet, or notes equivalent in time; in triple time the division or bar is after every three crotchets, or notes equivalent; so that in common time the repetition recurs more frequently than in triple time. The grave or heroic verses of the Greek and Latin poets are written in common time; the French heroic verses, and Mr. Anstie's humorous verses in his Bath Guide, are written in the same time as the Greek and La- tin verses, but are one bar shorter. The English grave or he- roic verses are measured by triple time, as Mr. Pope's transla- tion of Homer. But besides these little circles of musical time, there are the greater returning periods, and the still more distant chorusses, which, like the rhimes at the ends of verses, owe their beauty to repetition; that is, to the facility and distinctness with which we perceive sounds, which we expect to perceive, or have perceive- ed before; or, in the language of this work, to the greater ease and energy with which our organ is excited by the combined sensorial 189 SECT. XXII. 3. IMITATION. sensorial powers of association and irritation, than by the latter singly. A certain uniformity or repetition of parts enters the very composition of harmony. Thus two octaves nearest to each ether in the scale commence their vibrations together after every second vibration of the higher one. And where the first, third, and fifth compose a chord, the vibrations concur or coincide fre- quently, though less so than in the two octaves. It is proba- ble that these chords bear some analogy to a mixture of three alternate colours in the sun's spectrum, separated by a prism. The pleasure we receive from a melodious succession of notes referable to the gamut, is derived from another source, viz. to the pendiculation or counteraction of antagonist fibres. See Botanic Garden, P. 2. Interlude 3. If to these be added our early associations of agreeable ideas with certain proportions of sound, I suppose from these three sources springs all the delight of music, so celebrated by ancient authors, and so enthusiastical- ly cultivated at present. See Sect. XVI. No. 10. on Instinct. This kind of pleasure, arising from repetition; that is, from the facility and distinctness with which we perceive and under- stand repeated sensations, enters into all the agreeable arts, and when it is carried to excess, is termed formality. The art of dancing, like that of music, depends, for a great part of the plea- sure it affords, on repetition; architecture, especially the Gre- cian, consists of one part being a repetition of another; and hence the beauty of the pyramidal outline in landscape-painting, where one side of the picture may be said in some measure to balance the other. So universally does repetition contribute to our pleasure in the fine arts, that beauty itself has been defined, by some writers, to consist in a due combination of uniformity and variety. See Sect. XVI. 6. III. 1. Man is termed, by Aristotle, an imitative animal: this propensity to imitation not only appears in the actions of chil- dren, but in all the customs and fashions of the world: many thousands tread in the beaten paths of others, for one who tra- verses regions of his own discovery. The origin of this pro- pensity to imitation has not, that I recollect, been deduced from any known principle: when any action presents itself to the view of a child, as of whetting a knife, or threading a needle, the parts of this action, in respect of time, motion, figure, are imitated by a part of the retina of his eye: to perform this ac- tion, therefore, with his hands, is easier to him than to invent any new action, because it consists in repeating with another set of fibres, viz. with the moving muscles, what he had just performed by some parts of the retina; just as in dancing we transfer 190 REPETITION AND SECT. XXII. 3. transfer the times of motion from the actions of the auditory nerves to the muscles of the limbs. Imitation, therefore, consists of repetition, which we have shewn above to be the easiest kind of animal action, and which we perpetually fall into when we possess an accumulation of sensorial power, which is not other- wise called into exertion. It has been shewn, that our ideas are configurations of the organs of sense, produced originally in consequence of the sti- mulus of external bodies. And that these ideas, or configura- tions of the organs of sense, resemble, in some property, a cor- respondent property of external matter; as the parts of the senses of sight and of touch, which are excited into action, resemble, in figure, the figure of the stimulating body; and pro- bably also the colour and the quantity of density which they perceive: as explained in Sect. XIV. 2. 2. Hence it appears that our perceptions themselves are copies; that is, imitations of some properties of external matter; and the propensity to imi- tation is thus interwoven with our existence, as it is produced by the stimuli of external bodies, and is afterwards repeated by our volitions and sensations, and thus constitutes all the opera- tions of our minds. 2. Imitations resolve themselves into four kinds; voluntary, sensitive, irritative, and associate. The voluntary imitations are, when we imitate deliberately the actions of others, either by mimicry, as in acting a play, or in delineating a flower; or in the common actions of our lives, as in our dress, cookery language, manners, and even in our habits of thinking. Not only the greatest part of mankind learn all the common arts of life by imitating others, but brute animals seem capable of acquiring knowledge with greater facility by imitating each other, than by any methods by which we can teach them; as dogs and cats, when they are sick, learn of each other to eat grass; and I suppose, that by making an artificial dog perform certain tricks, as in dancing on his hinder legs, a living dog might be easily induced to imitate them; and that the readiest way of instructing dumb animals is by practising them with others of the same species, which have already learned the arts we wish to teach them. The important use of imitation in acquiring natural language is mentioned in Section XVI. 7 and 8. on Instinct. 3. The sensitive imitations are the immediate consequences of pleasure or pain, and these are often produced even contrary so the efforts of the will. Thus many young men, on seeing cruel surgical operations, become sick, and some even feel pain In the parts of their own bodies which they see tortured or wounded 191 SECT. XXII. 3 IMITATION. wounded in others; that is, they in some measure imitate, by the exertions of their own fibres, the violent actions which they wit- nessed in those of others. In this case a double imitation takes place; first, the observer imitates, with the extremities of the optic nerve, the mangled limbs which are present before his eyes; then, by a second imitation, he excites so violent action of the fibres of his own limbs, as to produce pain in those parts of his own body which he saw wounded in another. In these pains, pro- duced by imitation, the effect has some similarity to the cause which distinguishes them from those produced by association; as the pains of the teeth, called tooth-edge, which are produced by association with disagreeable sounds, as explained in Sect. XVI. 10. The effect of this powerful agent, imitation, in the moral world, is mentioned in Sect. XVI. 7. as it is the foundation of all our intellectual sympathies, with the pains and pleasures of others, and is, in consequence, the source of all our virtues. For in what consists our sympathy with the miseries, or with the joys, of our fellow creatures, but in an involuntary excitation of ideas, in some measure similar or imitative of those which we believe to exist in the minds of the persons whom we com- miserate or congratulate? There are certain concurrent or successive actions of some, of the glands, or other parts of the body, which are possessed of sensation, which become intelligible from this propensity to imitation. Of these are the production of matter by the mem- branes of the sauces, or by the skin, in consequence of the ve- nereal disease previously affecting the parts of generation. Since, as no fever is excited, and as neither the blood of such patients, nor even the matter from ulcers of the throat, or from cutaneous ulcers, will, by inoculation, produce the venereal dis- ease in others, as observed by Mr. Hunter, there is reason to con- clude, that no contagious matter is conveyed thither by the blood vessels; but that a milder matter is formed by the actions of the fine vessels in those membranes imitating each other. See Section XXXIII. 2. 9. In this disease the actions of these ves- sels producing ulcers on the throat and skin, are imperfect imi- tations of those producing chanker, or gonorrhœa; since the matter produced by them is not infectious, while the imitative actions in the hydrophobia appear to be perfect resemblances, as they produce a material equally infectious with the original one which induced them. The contagion from the bite of a mad dog differs from other contagious materials, from its being communicable from other animals to mankind, and from many animals to each other; the phenomena attending the hydro- phobia 192 REPETITION, &c. SECT. XXII. 3. phobia are, in some degree, explicable on the foregoing theory. The infectious matter does not appear to enter the circulation, as it cannot be traced along the course of the lymphatics from the wound, nor is there any swelling of the lymphatic glands, nor does any fever attend, as occurs in the small-pox, and in ma- ny other contagious diseases; yet, by some unknown process, the disease is communicated from the wound to the throat, and that many months after the injury, so as to produce pain and hy- drophobia, with a secretion of infectious saliva of the same kind as that of the mad dog which inflicted the wound. This subject is very intricate. It would appear, that by cer- tain morbid actions of the salivary glands of the mad clog, a peculiar kind of saliva is produced; which being instilled into a wound of another animal, stimulates the cutaneous or mu- cous glands into morbid actions, but which are ineffectual in respect to the production of a similar contagious materal; but the salivary glands, by irritative sympathy, are thrown into similar action, and produce an infectious saliva similar to that instilled into the wound. Though in many contagious fevers a material similar to that which produced the disease is thus generated by imitation, yet there are other infectious materials which do not thus pro- pagate themselves, but which seem to act like slow poisons. Of this kind was the contagious matter which produced the jail- fever at the assizes at Oxford about a century ago; which, though fatal to so many, was not communicated to their nurses or attendants. In these cases the imitations of the fine vessels, as above described, appear to be imperfect, and do not there- fore produce a matter similar to that which stimulates them; in this circumstance resembling the venereal matter in ulcers of the throat or skin, according to the curious discovery of Mr. Hunter above related, who found, by repeated inoculations, that it would not infect. Hunter on Venereal Disease, Part vi. chap. 1. Another example of morbid imitation is in the production of a great quantity of contagious matter; as in the inoculated small-pox, from a small quantity of it inserted into the arm, and probably diffused in the blood. These particles of conta- gious matter stimulate the extremities of the fine arteries of the skin, and cause them to imitate some properties of those par- ticles of contagious matter, so as to produce a thousand-fold of a similar material. See Sect. XXXIII. 2. 6. Other instan- ces are mentioned in the Section on Generation, which shew the probability that the extremities of the seminal glands may imitate certain ideas of the mind, or actions of the organs of sense, 193 SECT. XXIII. 1. CIRCULATORY SYSTEM. sense, and thus occasion the male or female sex of the embryon. See Sect. XXXIX. 6. 4. We come now to those imitations which are not attended with sensation. Of these are all the irritative ideas already ex- plained, as when the retina of the eye imitates, by its action or configuration, the tree or the bench which I shun in walking past without attending to them. Other examples of these irri- tative imitations are daily observable in common life: thus, one yawning person shall set a whole company a yawning; and some nave acquired winking of the eyes, or impediments of speech, by imitating their companions without being conscious of it. 5. Besides the three species of imitations above described, there may be some associate motions, which may imitate each other in the kind as well as in the quantity of their action; but it, is difficult to distinguish them from the associations of motions treated of in Section XXXV. Where the actions of other persons are imitated, there can be no doubt, or where we imi- tate a preconceived idea, by exertion of our locomotive muscles, as in painting a dragon; all these imitations may aptly be re- ferred to the sources above described, of the propensity to activity and the facility of repetition: at the same time I do not affirm, that all those other Apparent sensitive and irritative imitations may not be resolvable into associations of a peculiar kind, in which certain distant parts of similar irritability or sensibility, and which have habitually acted together, may affect each other exactly with the same kinds of motion; as many parts are known to sympathise in the quantity of their motions: and that, therefore, they may be ultimately resolvable into associa- tions of action, as described in Sect. XXXV. SECT. XXIII. OF THE CIRCULATORY SYSTEM. I. The heart and arteries have no antagonist muscles. Veins absorb the blood, propel it forwards, and distend the heart: contraction of the heart distends the arteries. Vena por- tarum. II. Glands which take their fluids from the blood. With long necks, with short necks. III. Absorbent system. IV. Heat given out from glandular secretions. Blood changes colour in the lungs and in the glands and capilla- ries. V. Blood is absorbed by veins, as chyle by lacteal vessels, otherwise they could not join their streams. VI. Two kinds of stimulus, agreeable and disagreeable. Glan- dular appetency. Glands originally possessed sensation. I. WE now step forwards to illustrate some of the pheno- mena of diseases, and to trace out their most efficacious me- thods 194 CIRCULATORY SYSTEM. SECT. XXIII. 2. thods of cure; and shall commence this subject with a short description of the circulatory system. As the nerves, whose extremities form our various organs of sense and muscles, are all joined, or communicate, by means of the brain, for the convenience perhaps of the distribution of a subtile ethereal fluid for the purpose of motion; so all those. vessels of the body which carry the grosser fluids for the pur- poses of nutrition, communicate with each other by the heart. The heart and arteries are hollow muscles, and are there fore endued with power of contraction in consequence of sti- mulus, like all other muscular fibres; but as they have no an- tagonist muscles, the cavities of the vessels which they form would remain for ever closed, after they have contracted them- selves, unless some extraneous power be applied to again distend them. This extraneous power, in respect to the heart, is the current of blood which is perpetually absorbed by the veins from the various glands and capillaries, and pushed into the heart by a power probably very similar to that which raises the sap in vegetables in the spring, which, according to Dr. Hale's ex- periment on the stump of a vine, exerted a force equal to a column of water above twenty feet high. This force of the current of blood in the veins is partly produced by their ab- sorbent power, exerted at the beginning of every fine ramifi- cation; which may be conceived to be a mouth absorbing blood, as the mouths of the lacteals and lymphatics absorb chyle and lymph: and partly by their intermitted compression by the pulsations of their generally concomitant arteries; by which the blood is perpetually propelled towards the heart, as the valves in many veins, and the absorbent mouths in them all, will not differ it to return. The blood, thus forcibly injected into the chambers of the heart, distends this combination of hollow muscles; till by the stimulus of distention they contract themselves; and, pushing forwards the blood into the arteries, exert sufficient force to overcome, in less than a second of time, the vis inertiæ, and perhaps some elasticity, of the very extensive ramifications of the two great systems of the aortal and pulmonary arteries. The power necessary to do this in so short a time must be con- siderable, and has been variously estimated by different physio- logists. The muscular coats of the arterial system are then brought into action by the stimulus of distention, and propel the blood to the mouths, or through the convulsions which precede the secretory apertures of the various glands and capillaries. In the vessels of the liver there is no intervention of the heart; 195 SECT.XXIII.2,3. CIRCULATORY SYSTEM. 195 heart; but the vena portarum, which does the office of an ar- tery, is distended by tire blood poured into it from the misen- teric veins, and is by this distention stimulated to contract it- self, and propel the blood to the mouths of the numerous glands which compose that viscus. II. The glandular system of vessels may be divided into those which take some fluid from the circulation, and those which give something to it. Those which take their fluid from the circulation are the various glands by which the tears, bile, urine, perspiration, and many other secretions, are produced; these glands probably consist of a mouth to idea, a belly to digest, and an excretory aperture to emit their appropriated fluids; the blood is conveyed by the power of the heartland arteries to the mouths of these glands, it is there taken up by the living power of the gland, and carried forward to its belly and excre- tory aperture, where a part is separated, and the remainder ab- sorbed by the veins for further purposes. Some of these glands are furnished with long convoluted necks or tubes, as the seminal ones, which are curiously seen when injected with quicksilver. Others seem to consist of shorter tubes, as that great congeries of glands which consti- tute the liver, and those of the kidneys. Some have their ex- cretory apertures opening into reservoirs, as the urinary and gall-bladders; and others on the external body, as those which secrete the tears and perspirable matter. Another great system of glands, which have very short necks, are the capillary vessels; by which the insensible per- spiration is secreted on the skin; and the mucus of various consistences, which lubricates the interstices of the cellular membrane, of the muscular fibres, and of all the larger cavi- ties of the body. From the want of a long convolution of vessels, some have doubted, whether these capillaries should be considered as glands, and have been led to conclude, that the perspirable matter rather exuded than was secreted. But the fluid of perspiration is not simple water, though that part of it which exhales into the air may be such; for there is another part of it which, in a date of health, is absorbed again; but which, when the absorbents are diseased, remains on the sur- face of the skin, in the form of scurf, or indurated mucus. Another thing which shews their similitude to other glands, is their sensibility to certain affections of the mind; as is seen in the deeper colour of the skin, in the blush of shame, or the greater paleness of it from fear. III. Another series of glandular vessels is called the absorb- ent system; these open their mouths into all the cavities, and D d upon 196 CIRCULATORY SYSTEM. SECT. XXIII. 4. upon all those surfaces of the body where the excretory aper- tures of the other glands pour out their fluids. The mouths of the absorbent system drink up a part or the whole of these fluids, and carry them forwards by their living power to their respective glands, which are called conglobate glands. There these fluids undergo some change before they pass on into the circulation; but if they are very acrid, the conglobate gland swells, and sometimes suppurates, as in inoculation of the small-pox, in the plague, and in venereal absorptions; at other times the fluid may perhaps continue there, till it under- goes some chemical change, that renders it less noxious; or, what is more likely, till it is regurgitated by the retrograde motion of the gland in spontaneous sweats or diarrhœas, as disagreeing food is vomited from the stomach. IV. As all the fluids that pass through these glands and capillary vessels undergo a chemical change, acquiring new combinations, the matter of heat is at the same time given out, this is apparent, since whatever increases insensible perspiration, increases the heat of the skin; and when the action of these vessels is much increased but for a moment, as in blushing, a vivid heat on the skin is the immediate consequence. So when great bilious secretions, or those of any other gland, are pro- duced, heat is generated in the part in proportion to the quantity of the secretion. The heat produced on the skin by blushing may be thought by some too sudden to be pronounced a chemical effect, as the fermentations or new Combinations taking place in a fluid is in general a slower process. Yet are there many chemical mixtures in which heat is given out as instantaneously; as in solutions of metals in acids, or in mixtures of essential oils and acids, as of oil of cloves and acid of nitre. So the bruised parts of an unripe apple become almost instantaneously sweet; and if the chemico-animal process of digestion be stopped but for a mo- ment, as by fear, or even by voluntary eructation, a great quan- tity of air is generated, by the fermentation which instantly succeeds the flop of digestion. By the experiments of Dr. Hales it appears, that an apple during fermentation gave up above six hundred times its bulk of air; and the materials in the stomach are such, and in such a situation, as immediately to run into fer- mentation, when digestion is impeded. As the blood passes through the small vessels of the lungs, Which connect the pulmonary artery and vein, it undergoes a change of colour, from a dark to a light red; which may be termed a chemical change, as it is known to be effected by an admixture of oxygene, or vital air; which, according to a dis- covery 197 SECT. XXIII. 5, 6. CIRCULATORY SYSTEM. covery of Dr. Priestley, passes through the moist membranes, which constitute the sides of these vessels. As the blood passes through the capillary vessels and glands, which connect the aorta and its various branches with their correspondent veins in the extremities of the body, it again loses the bright red co- lour, and undergoes some new combinations in the glands or capillaries, in which the matter of hot is given out from the secreted fluids. This process, therefore, as well as the process of respiration, has some analogy to combustion, as the vital air or oxygene seems to become united to some inflammable base, and the matter of heat escapes from the new acid, which is thus produced. V. After the blood has passed these glands and capillaries, and parted with whatever they chose to take from it, the re- mainder is received by the veins, which are a set of blood- ab- sorbing vessels, in general corresponding with the ramifications of the arterial system. At the extremity of the fine convolu- tions of the glands the arterial force ceases: this, in respect to the capillary vessels, which unite the extremities of the arteries with the commencement of the veins, is evident to the eye, on viewing the tail of a tadpole, by means of a solar or even by a common microscope; for globules of blood are seen to endea- vour to pass, and to return again and again, before they become absorbed by the mouths of the veins; which returning of these globules evinces, that the arterial force behind them has ceased. The veins are furnished with valves like the lymphatic absorb- ents; and the great trunks of the veins, and of the lacteals and lymphatic, join together before the ingress of their fluids into the left chamber of the heart; both which evince, that the blood in the veins, and the lymph and chyle in the lacteals and lym- phatics, are carried on by a similar force otherwise the stream, which was propelled with a less power, could not enter the ves- sels which contained the stream propelled with a greater power. From whence it appears, that the veins are a system of vessels absorbing blood, as the lacteals and lymphatics are a system of vessels absorbing chyle and lymph, See Sea. XXVII. 1 . VI. The movements of their adapted fluids in, the various vessels of the body are carried forwards, by the actions of those vessels, in consequence of two kinds of stimulus; one of which may be compared to a pleasureable sensation, or desire, inducing the vessel to seize, and, as it were, to swallow the particles thus selected from the blood; as is done by the mouths of the various glands, veins, and other absorbents, which may be called glan- dular appetency. The other kind of stimulus may be compared to disagreeable sensation, or aversion, as when the heart has re- ceived 198 OF THE SALIVA SECT. XXIV. 1. ceived the blood, and is stimulated by it to push it forwards into the arteries: the same again stimulates the arteries to contract, and carry forwards the blood to their extremities, the glands and capillaries. Thus the mesenteric veins absorb the blood from the intestines by glandular appetency, and carry it forward to the vena portarum; which, acting as an artery, contracts itself by disagreeable stimulus, and pushes it to its ramified extremi- ties, the various glands which constitute the liver. It seems probable, that at the beginning of the formation of these vessels in the embryon, an agreeable sensation was in reality felt by the glands during secretion, as is now felt in the act of swallowing palatable food: and that a disagreeable sen- sation was originally felt by the heart from the distention occa- sioned by the blood, or by its chemical stimulus; but that by habit these are all become irritative motions; that is, such mo- tions as do not affect the whole system, except when the vessels me diseased by inflammation. SECT. XXIV. OF THE SECRETIONS OF SALIVA, AND OF TEARS, AND OF THE LACRYMAL SACK. I. Secretion of saliva increased by mercury in the blood. 1. By the food in the mouth. Dryness of the mouth not from a deficiency of saliva. 2. By sensitive ideas. 3. By voli- tion. 4. By distasteful substances. It is secreted in a di- lute and saline state. It then becomes more viscid. 5. By ideas of distasteful substances. 6. By nausea. 7. By aver- sion. 8. By catenation with stimulating substances in the car. II. 1. Secretion of tears less in sleep. From stimula- tion of their excretory duct. 2. Lacrymal sack is a gland. 3. Its uses. 4. Tears are secreted, when the nasal duct is stimulated. 5. Or when it is excited by sensation. 6. Or by volition. 7. The lacrymal sack can regurgitate its con- tents into the eye. 8. More tears are secreted by association with the irritation of the nasal duct of the lacrymal sack, than the puncta lacrymalia can imbibe. Of the gout in the liver and stomach. T. THE salival glands drink up a certain fluid from the cir- cumfluent blood, and pour it into the mouth. They are some- times stimulated into action by the blood that surrounds their origin, or by some part of that heterogeneous fluid: for when mercurial salts, or oxydes, are mixed with the blood, they sti- mulate 199 SECT. XXIV. 1. AND TEARS. mulate these glands into unnatural exertions; and then an un- sual quantity of saliva is separated. As the saliva secreted by these glands is most wanted during the mastication of our food, it happens, when the terminations of their dusts in the mouth are stimulated into action, the sali- val glands themselves are brought into increased action at the same time by association, and separate a greater quantity of their juices from the blood; in the same manner as tears are produc- ed in greater abundance during the stimulus of the vapour of onions, or of any other acrid material in the eye. The saliva is thus naturally poured into the mouth only dur- ing the stimulus of our food in mastication; for when there is too great an exhalation of the mucilaginous secretion from the membranes which line the mouth, or too great an absorp- tion of it, the mouth becomes dry, though there is no deficiency in the quantity of saliva; as in those who deep with their mouths open, and in some fevers. 2. Though during the mastication of our natural food the sa- lival glands are excited into action by the stimulus on their ex- cretory ducts, and a due quantity of saliva is separated from the blood, and poured into the mouth; yet as this mastication of our food in always attended with a degree of pleasure, and that pleasureable sensation is also connected with our ideas of certain kinds of aliment, it follows, that when those ideas are reproduc- ed, the pleasureable sensation arises along with them, and the salival glands are excited into action, and fill the mouth with saliva from this sensitive association, as is frequently seen in dogs, who slaver at the fight of food. 3. We have also a voluntary power over the action of these salival glands, for we can at any time produce a flow of saliva into our mouth, and spit out, or swallow it at will. 4. if any very acrid material be held in the mouth, as the root of pyrethrum, or the leaves of tobacco, the salival glands are stimulated into stronger action than is natural, and thence secrete a much larger quantity of saliva; which is at the same time more viscid than its natural state; because the lymphatics, that open their mouths into the ducts of the salival glands, and on the membranes which line the mouth, are likewise stimu- lated into stronger action, and absorb the more liquid parts of the saliva with greater avidity: and the remainder is left both in greater quantity and more viscid. The increased absorption in the mouth by some stimulating substances, which are called astringents, as crab juice, is evi- dent from the instant dryness produced in the mouth by a small quantity of them. As 200 OF THE SALIVA SECT. XXIV. 2. As the extremities of the glands are of exquisite tenuity, as appears by their difficulty of injection, it was necessary for them to secrete their fluids in a very dilute state; and, probably for the purpose of stimulating them into action, a quantity of neu- tral salt is likewise secreted or formed by the gland. This aque- ous and saline part of all secreted fluids is again reabsorbed in to the habit. More than half of some secreted fluids is thus im- bibed from the reservoirs, into which they are poured; as in the urinary bladder much more than half of what is secreted by the kidneys becomes reabsorbed by the lymphatics, which are thickly dispersed around the neck of the bladder. This seems to be the purpose of the urinary bladders of fish, as otherwise such a receptacle for the urine could have been of no use to an animal immersed in water. 5. The idea of substances disagreeably acrid will also produce a quantity of saliva in the mouth; as when we smell very pu- trid vapours, we are induced to spit out our saliva, as if some- thing disagreeable was actually upon our palates. 6. When disagreeable food in the stomach produces nausea, a flow of saliva is excited in the mouth by association ; as ef- forts to vomit are frequently produced by disagreeable drugs in the mouth by the same kind of association. 7. A preternatural flow of saliva is likewise sometimes occa- sioned by a disease of the voluntary power; for if we think about our saliva, and determine not to swallow it, or not to spit it out, an exertion is produced by the will, and more saliva is secreted against our wish; that is, by our aversion, which bears the same analogy to desire as pain does to pleasure; as they are only modifications of the same disposition of the sensorium. See Class IV. 3. 2. 1. 8. The quantity of saliva may also be increased beyond what is natural, by the catenation of the motions of these glands with other motions, or sensations, as by an extraneous body in the ear, of which I have known an instance; or by the applica- tion of stizolobium, siliqua hirsuta, cowhage, to the seat of the parotis, as some writers have affirmed. II. 1. The lacrymal gland drinks up a certain fluid from, the circumfluent blood, and pours it on the ball of the eve, on the upper part of the external corner of the eyelids. Though it may perhaps be stimulated into the performance of its natu- ral action by the blood, which surrounds its origin, or by some part of that heterogeneous fluid; yet as the tears secreted by this gland are more wanted at some times than at others, its secretion is variable, like that of the saliva above mentioned, and is chiefly produced when its excretory duct is stimulated; for in 201 SECT. XXIV. 2. AND TEARS. in our common sleep there seems to be little or no secretion of tears; though they are occasionally produced by our sensations. in dreams. Thus, when any extraneous material on the eye-ball, or the dryness of the external covering of it, or the coldness of the air, or the acrimony of some vapours, as of onions, stimulates the excretory duct of the lacrymal gland, it discharges its con- tents upon the ball; a quicker secretion takes place in the gland, and abundant tears succeed, to moisten, clean, and lubricate the eye. These, by frequent nictitation, are diffused over the whole ball; and as the external angle of the eye in winking is closed sooner than the internal angle, the tears are gradually driven forwards, and downwards from the lacrymal gland to the puncta lacrymalia. 2. The lacrymal sack, with its puncta lacrymalia, and its nasal duct, is a complete gland; and is singular in this respect, that it neither derives Its fluid from, nor disgorges it into the circulation. The simplicity of the structure of this gland, and both the extremities of it being on the surface of the body, makes it well worthy our minuter observation; as the actions of more intricate and concealed glands may be better under- stood from their analogy to this. 3. This simple gland consists of two absorbing mouths, a belly, and an excretory duct. As the tears are brought to the internal angle of the eye, these two mouths drink them up, be- ing stimulated into action by this fluid, which they absord. The belly of the gland, or lacrymal sack, is thus filled, in which the saline part of the tears is absorbed; and when the other end of the gland, or nasal duct, is stimulated by the dry- ness, or pained by the coldness of the air, or affected by any acrimonious dust or vapour in the nostrils, it is excited into action, together with the sack, and the tears are disgorged upon the membrane which lines the nostrils, where they serve a second purpose to moisten, clean, and lubricate the organ of smell. 4. When the nasal duct of this gland is stimulated by any very acrid material, as the powder of tobacco, or volatile spirits, it not only disgorges the contents of its belly or receptacle (the lacrymal sack,) and absorbs hastily all the fluid that is ready for it in the cornea of the eye; but, by the association of its motions with those of the lacrymal gland, it excites that also into in- creased action, and a large flow of tears is poured into the eye. 5. This nasal duct is likewise existed into strong action by sensitive ideas, as in grief or joy; and then also by its associa- tions with the lacrymal gland, it produces a great flow of tears, without any external stimulus; as is more fully explained in Sect. XVI. 8. on Instinct. 6. There 202 OF THE SALIVA SECT. XXIV.2. 6. There are some, famous in the arts of exciting compas- sion, who are said to have acquired a voluntary power of pro- ducing a slow of tears in the eye; which, from what has been said in the section on Instinct above mentioned, I should sus- pect, is performed by acquiring a voluntary power over the action of this nasal duct. 7. There is another circumstance well worthy our attention, that when by any accident this nasal duct is obstructed, the la- crymal sack, which is the belly or receptacle of this gland, by slight pressure of the finger is enabled to disgorge its contents again into the eye: perhaps the bile in the same manner, when the biliary ducts are obstructed, is returned into the blood by the vessels which secrete it. 8. A very important though minute occurrence must here be observed, that though the lacrymal gland is only excited into action, when we weep at a distressful tale, by its association with this nasal duct as is more fully explained in Sect XVI. 8. yet the quantity of tears secreted at once is more than the puncta lacrymalia can readily absorb; which shews that the motions occasioned by associations are frequently more ener- getic than the original motions by which they were occa- sioned: which we shall have occasion to mention hereafter, to illustrate why pains frequently exist in a part distant from the cause of them, as in the other end of the urethra, when a stone slimulates the neck of the bladder; and why inflammations fre- quently arise in parts distant from their cause, as the gutta rosea of drinking people, from an inflamed liver. The inflammation of a part is generally preceded by a torpor or quiescence of it; if this exists in any large congeries of glands, as in the liver, or any membranous part, as the stomach, pain is produced, and chilliness in consequence of the torpor of the vessels. In this situation sometimes an inflammation of the part succeeds the torpor; at other times a distant, more sensible part becomes inflamed; whose actions have previously been associ- ated with it, and the torpor of the first part ceases. This I ap- prehend happens, when the gout of the foot succeeds a pain of the biliary duct, or of the stomach. Lastly, it sometimes hap- pens, that the pain of torpor exists without any consequent in- flammation of the affected part, or of any distant part associated with it, as in the membranes about the temple and eye-brows in hemicrania, and in these pains which, occasion convulsions: if this happens to gouty people, when it affects the liver, I sup- pose epileptic fits are produced; and, when it affects the sto- mach, death is the consequence. In these cases the pulse is weak, and the extremities cold, and such medicines as stimulate the 203 SECT. XXV. 1. OF THE STOMACH, &c. the quiescent parts into action, or which induce inflammation in them, or in any distant part which is associated with them, cures the present pain of torpor, and saves the patient. I have twice seen a gouty inflammation of the liver attended with jaundice; the patients, after a few days, were both of them affected with cold fits, like ague-fits, and their feet became af- fected with gout, and the inflammation of their livers ceased. It is probable, that the uneasy sensations about the stomach, and indigestion, which precede gouty paroxysms, are generally ow- ing to torpor, or slight inflammation of the liver and biliary ducts; but where great pain, with continued sickness, with feeble pulse, and sensation of cold, affect the stomach in patients debilitated by the gout, that it is a torpor of the stomach itself, and destroys the patient from the great connection of that viscus with the vi- tal organs. See Sect. XXV. 17. SECT. XXV. OF THE STOMACH AND INTESTINES. 1. Of swallowing our food. Ruminating animals. 2. Action of the stomach. 3. Action of the intestines. Ir- ritative motions connected with these. 4. Effects of re- pletion. 5. Stronger action of the stomach and intestines from more stimulating food. 6. Their action inverted by still greater stimuli. Or by disgustful ideas. Or by vo- lition. 7. Other glands strengthen or invert their mo- tions by sympathy. 8. Vomiting performed by intervals. 9. Inversion of the cutaneous absorbents. 10. Increased secretion of bile and pancreatic juice. 11. Inversion of the lacteals. 12. And of the bile-ducts. 13. Case of a cho- lera. 14. Further account of the inversion of lacteals. 15. Iliac passion. Valve of the colon. 16. Cure of the iliac passion. 17. Pain of gall-stone distinguished from pain of the stomach. Gout of the stomach from torpor; from inflammation. Intermitting pulse owing to indigestion. To over dose of foxglove. Weak pulse from emetics. Death from a blow on the stomach. From gout of the stomach. 1. THE throat, stomach and intestines, may be considered as one great gland; which, like the lacrymal sack above- mentioned, neither begins nor ends in the circulation. Though the act of masticating our aliment belongs to the sensitive class of motions, for the pleasure of its taste induces the muscles of the jaw into action; yet the deglutition of it, when masticated, is generally, if not always, an irritative motion, occasioned by E e the 204 OF THE STOMACH SECT. XXV. 2, 3, 4. the application of the food already masticated to the origin of the pharix; in the same manner as we often swallow our spit- tle without attending to it. The ruminating class of animals have the power to invert the motion of their gullet, and of their first stomach, from the stimulus of this aliment, when it is a little further prepared; as is their daily practice in chewing the cud; and appears to the eye of any one who attends to them, whilst they are em- ployed in this second mastication of their food. 2. When our natural aliment arrives into the stomach, this organ is stimulated into its proper vermicular action; which, beginning at the upper orifice of it, and terminating at the lower one, gradually mixes together and pushes forwards the digesting materials into the intestine beneath it. At the same time the glands, that supply the gastric juices, which are necessary to promote the chemical part of the pro- cess of digestion, are stimulated to discharge their contained fluids, and to separate a further supply from the blood-vessels; and the lacteals or lymphatics, which open their mouths into the stomach, are stimulated into action, and take up some part of the digesting materials. 3. The remainder of these digesting materials is carried for- wards into the upper intestines, and stimulates them into their peristaltic motion, similar to that of the stomach; which con- tinues gradually to mix the changing materials, and pass them along through the valve of the colon to the excretory end of this great gland, the sphincter ani. The digesting materials produce a flow of bile, and of pan- creatic juice, as they pass along the duodenum, by stimulating the excretory ducts of the liver and pancreas, which terminate in that intestine; and other branches of the absorbent or lym- phatic system, called lacteals, are excited to drink up, as it passes, those parts of the digesting materials, that are proper for their purpose, by its stimulus on their mouths. 4. When the stomach and intestines are thus filled with their proper food, not only the motions of the gastric glands, the pancreas, liver, and lacteal vessels, are excited into action; but at the same time the whole tribe of irritative motions are exerted with greater energy; a greater degree of warmth, co- lour, plumpness, and moisture, is given to the skin from the increased action of those glands called capillary vessels; plea- sureable sensation is excited, the voluntary motions are less easily exerted, and at length suspended; and sleep succeeds, un- less it be prevented by the stimulus of surrounding objects, or by voluntary exertion, or by an acquired habit, which was original- ly 205 SECT. XXV.5,6. AND INTESTINES. ly produced by one or other of these circumstances, as is ex- plained in Sect. XXI. on Drunkenness. At this time also, as the blood-vessels become replete with chyle, more urine is separated into the bladder, and less of it is reabsorbed; more mucus poured into the cellular membranes, and less of it reabsorbed; the pulse becomes fuller and softer, and in general quicker. The reason why less urine and cel- lular mucus is absorbed after a full meal, with sufficient drink, is owing to the blood-vessels being fuller; hence one means to promote absorption is to decrease the resistance, by emptying the vessels by venesection. From this decreased absorption the urine becomes pale as well as copious, and the skin ap- pears plump as well as florid. By daily repetition of these movements, they all become connected together, and make a diurnal circle of irritative ac- tion; and if one of this chain be disturbed, the whole is liable to be put into disorder. See Sect. XX. on Vertigo. 5. When the stomach and intestines receive a quantity of food, whose stimulus is greater than usual, all their motions, and those of the glands and lymphatics, are stimulated into stronger action than usual, and perform their offices with greater vigour, and in less time: such are the effects of certain quan- tities of spice or of vinous spirit. 6. But if the quantity or duration of these stimuli are still fur- ther increased, the stomach and throat are stimulated into a mo- tion, whose direction is contrary to the natural one above de- scribed; and they regurgitate the materials, which they contain, instead of carrying them forwards. This retrograde motion of the stomach may be compared to the stretchings of wearied limbs the contrary way, and is well elucidated by the follow- ing experiment. Look earnestly for a minute or two on an area, an inch square, of pink silk, placed in a strong light; the eye becomes fatigued, the colour becomes faint, and at length vanishes; for the fatigued eye can no longer be stimulated into direct motions; then, on closing the eye, a green spectrum will appear in it, which is a colour directly contrary to pink, and which will appear and disappear repeatedly, like the efforts in vomiting. See Section XXIX. 11. Hence all those drugs, which, by their bitter or astringent stimulus, increase the action of the stomach, as camomile and white vitriol, if their quantity is increased above a certain dose, become emetics. These inverted motions of the stomach and throat are gene- rally produced from the stimulus of unnatural food, and are attended with the sensation of nausea or sickness: but as this sensation 206 OF THE STOMACH SECT. XXV.7,8,9,10. sensation is again connected with an idea of the distasteful food which induced it. so an idea of nauseous food will also sometimes excite the action of nausea; and that give rise by as- sociation, to the inversion of the motions of the stomach and throat, as some, who have had horse-flesh or dogs-flesh given them for beef or mutton, are said to have vomited many hours afterwards, when they have been told of the imposition. I have been told of a person, who had gained a voluntary command over these inverted motions of the stomach and throat, and supported himself by exhibiting this curiosity to the pub- lic. At these exhibitions he swallowed a pint of red rough gooseberries, and a pint of white smooth ones; brought them up in small parcels in his mouth, and restored them separately to the spectators, who called for red or white as they pleased, till the whole were redelivered. 7. At the same time that these motions of the stomach and throat are stimulated into inversion, some of the other irritative motions, that had acquired more immediate connections with the stomach, as those of the gastric glands, are excited into stron- ger action by this association; and some other of these motions, which are more easily excited, as those of the gastric lympha- tics, are inverted by their association with the retrograde motions of the stomach, and rigurgitate their contents, and thus a greater quantity of mucus, and of lymph, or chyle, is poured into the stomach, and thrown up along with its contents. 8. These inversions of fine motions of the stomach in vomit- ing are performed by intervals, for the same reason that many other motions are reciprocally exerted and relaxed; for during the time of exertion, the stimulus, or sensation which caused this exertion, is not perceived; but begins to be perceived again as soon as the exertion ceases, and is some time in again produc- ing its effect, as explained in Sect. XXXIV. on Volition; where it is shewn, that the contractions of the fibres, and the sensation of pain which occasioned that exertion, cannot exist at the same time. The exertion ceases from another cause also, which is the exhaustion of the sensorial power of the part, and these two causes frequently operate together. 9. At the times of these inverted efforts of the stomach, not only the lymphatics, which open their mouths into the stomach, but those of the skin also, are for a time inverted; for sweats are sometimes pushed out, during the efforts of vomiting, with out an increase of heat. 10. Bur if, by a greater stimulus, the motions of the stomach are inverted still more violently, or more permanently, the duo- denum has its peristaltic motions inverted at the same time by their 207 SECT. XXV. 11,12,13. AND INTESTINES. their association with those of the stomach; and the bile and pancreatic juice which it contains, are, by the inverted motions, brought up into the stomach, and discharged along with its con- tents; while a greater quantity of bile and pancreatic juice is poured into this intestine; as the glands that secrete them are, by their association with the motions of the intestine, excited into stronger action than usual. 11 . The other intestines are, by association, excited into more powerful action, while the lymphatics, that open their mouths into them, suffer an inversion of their motions corresponding with the lymphatics of the stomach and duodenum, which, with a part of the abundant secretion of bile, is carried downwards, and contributes both to stimulate the bowels and to increase the quantity of the evacuations. This inversion of the motion of the lymphatics appears from the quantity of chyle, which comes away by stools; which is otherwise absorbed as soon as produced, and by the immense quantity of thin fluid which is evacuated along, with it. 12. But if the stimulus, which inverts the stomach, be still more powerful, or more permanent, it sometimes happens that the motions of the biliary glands, and of their excretory ducts, are, at the same time, inverted, and regurgitate their contained bile into the blood-vessels, as appears by the yellow colour of the skin, and of the urine; and it is probable the pancreatic se- cretion may suffer an inversion at the same time, though we have yet no mark by which this can be ascertained. 13. Mr. ------- eat two putrid pigeons out of a cold pigeon pye, and drank about a pint of beer and ale along with them, and immediately rode about five miles. He was then seized with vomiting, which was after a few periods succeeded by purg- ing; these continued alternately for two hours; and the purg- ing continued, by intervals, for six or eight hours longer. Dur- ing this time he could not force himself to drink more than one pint in the whole. This great inability to drink was owing to the nausea, or inverted motions of the stomach, which the voluntary exertion of swallowing could seldom and with diffi- culty overcome; yet he discharged in the whole at least six quarts. Whence came this quantity of liquid? First, the contents of the stomach were emitted, then of the duodenum, gall-blad- der, and pancreas, by vomiting. After this the contents of the lower bowels, then the chyle that was in the lacteal vessels and in the receptacle of chyle, was regurgitated into the intes- tines by a retrograde motion of these vessels. And afterwards the mucus deposited in the cellular membrane, and on the sur- face of all the other membranes, seems to have been absorbed; and 208 OF THE STOMACH SECT. XXV. 14, 15. and, with the fluid absorbed from the air, to have been carried up their respective lymphatic branches, by the increased energy of their natural motions, and down the visceral lymphatics, or lacteals, by the inversion of their motions. 14. It may be difficult to invent experiments to demonstrate the truth of this inversion of some branches of the absorbent system, and increased absorption of others; but the analogy of these vessels to the intestinal canal, and the symptoms of many diseases, render this opinion more probable than many other re- ceived opinions of the animal economy. In the above instance, after the yellow excrement was void- ed, the fluid ceased to have any smell, and appeared like curd- led milk, and then a thinner fluid, and some mucus, were eva- cuated. Did not these seem to partake of the chyle, of the mucus fluid from all the cells of the body; and lastly, of the atmos- phere moisture? All these facts may be easily observed by any one who takes a brisk purge. 15. Where the stimulus on the stomach, or on some other part of the intestinal canal, is still more permanent, not only the lacteal vessels, but the whole canal itself, becomes inverted from its associations: this is the iliac passion, in which all the fluids mentioned above are thrown up by the mouth. At this time the valve in the colon, from the inverted motions of that bowel, and the inverted action of this living valve, does not prevent the regurgitation of its contents. The structure of this valve may be represented by a flexile leathern pipe standing up from the bottom of a vessel of wa- ter: its sides collapse by the pressure of the ambient fluid, as a small part of that fluid passes through it; but if it has a liv- ing power, and by its inverted action keeps itself open, it be- comes like a rigid pipe, and will admit the whole liquid to pass. See Sect. XXIX. 2. 5. In this case the patient is averse to drink, from the constant inversion of the motions of the stomach; and yet many quarts are daily ejected from the stomach, which at length smell of excrement, and at last seem to be only a thin mucilaginous or aqueous liquor. From whence is it possible, that this great quantity of fluid, for many successive days, can be supplied, after the cells of the body have given up their fluids, but from the atmosphere? When the cutaneous branch of absorbents acts with unna- rural strength, it is probable the intestinal branch has its motions inverted, and thus a fluid is supplied without entering the arte- rial system. Could oiling or painting the skin give a check to this disease? So, 269 SECT. XXV. 16. AND INTESTINES. So, when the stomach has its motions inverted, the lympha- tics of the stomach, which are most strictly associated with it, invert their motions at the fame time. But the more distant branches of lymphatics, which are less strictly associated with it, act with increased energy; as the cutaneous lymphatics in the cholera, or iliac passion, above described. And other irritative motions become decreased, as the pulsations of the arteries, from the extra-derivation or exhaustion of the sensorial power. Sometimes, when stronger vomiting takes place, the more distant branches of the lymphatic system invert their motions with those of the stomach, and loose stools are produced, and cold sweats. So, when the lacteals have their motions inverted, as during the operation of strong purges, the urinary and cutaneous ab- sorbents have their motions increased, to supply the want of fluid in the blood, as in great third; but after a meal, with sufficient potation, the urine is pale; that is, the urinary absorb- ents act weakly, no supply of water being wanted for the blood. And when the intestinal absorbents act too violently, as when too great quantities of fluid have been drank, the urinary absorbents invert their motions to carry off the super- fluity, which is a new circumstance of association, and a temporary diabetes supervenes. 16. I have had the opportunity of seeing four patients in the iliac passion, where the ejected material smelled and look- ed like excrement. Two of these were so exhausted at the time I saw them, that more blood could not be taken from. them; and as their pain had ceased, and they continued to vo- mit up every thing which they drank, I suspected that a mor- tification of the bowel had already taken place; and as they were, both women advanced in life, and a mortification is pro- duced with less preceding pain in old and weak people, these both died. The other two, who were both young men, had still pain and strength sufficient for further venesection, and they neither of them had any appearance of hernia; both re- covered by repeated bleeding, and a scruple of calomel given to one, and half a dram to the other, in very small pills: the usual means of clysters, and purges, joined with opiates, had been in vain attempted. I have thought an ounce or two of crude mercury in less violent diseases of this kind has been of use, by contributing to restore its natural motion to some part of the intestinal canal, either by its weight or stimulus; and that hence the whole tube recovered its usual associations of progressive peristaltic motion. I have in three cases seen crude mercury given in small doses, as one or two ounces, twice a day, have great effect in stopping pertinaceous vomiting. 17. Beside 210 OF THE STOMACH, &c. SECT. XXV. 17. 17. Besides the affections above described, the stomach is liable, like many other membranes of the body, to torpor, with- out consequent inflammation; as happens to the membranes about the head in some cases of hemicrania, or in general headach. This torpor of the stomach is attended with indi- gestion, and consequent flatulency, and with pain, which is usually called the cramp of the stomach, and is relievable by aromatics, essential oils, alcohol, or opium. The intrusion of a gall-stone into the common bile-duct, from the gall-bladder, is sometimes mistaken for a pain of the stomach, as neither of them are attended with fever; but in the passage of a gall-done, the pain is confined to a less space, which is exactly where the bile-duct enters the duodenum, as explained in Section XXX. 3. Whereas, in this gastrodynia the pain is diffused over the whole stomach; and, like other diseases from torpor, the pulse is weaker, and the extremities colder, and the general debility greater than in the passage of a gall-stone; for in the former the debility is the conse- quence of the pain, in the latter it is the cause of it. Though the first fits of the gout, I believe, commence with a torpor of the liver; and the ball of the toe becomes inflame- ed, instead of the membranes of the liver, in consequence of this torpor, as a coryza or catarrh frequently succeeds a long ex- posure of the feet to cold, as in snow, or on a moist brick- floor; yet in old of exhausted constitutions, which have been long habituated to its attacks, it sometimes commences with a torpor of the stomach, and is transferable to every membrane of the body. When the gout begins with torpor of the sto- mach, a painful sensation of cold occurs, which the patient compares to ice, with weak pulse, cold extremities, and sick- ness; this, in its slighter degree, is relievable by spice, wine, or opium; in its greater degree it is succeeded by sudden death, which is owing to the sympathy of the stomach with the heart, as explained below. If the stomach becomes inflamed in consequence of this gou- ty torpor of it, or in consequence of its sympathy with some other part, the danger is less. A sickness and vomiting conti- nues many days, or even weeks, the stomach rejecting every thing stimulant, even opium or alcohol, together with much viscid mucus, till the inflammation at length ceases, as hap- pens when other membranes, as those of the joints, are the seat of gouty inflammation, as observed in Sect. XXIV. 2. 8. The sympathy, or association of motions, between those of the stomach and those of the heart, are evinced in many diseases. First, many people are occasionally affected with an intermission 211 SECT. XXVI. GLANDS AND MEMBRANES. intermission of their pulse for a few days, which then ceases again. In this case there is a stop of the motion of the heart, and at the same time a tendency to eructation from the stomach. As soon as the patient feels a tendency to the intermission of the motion of his heart, if he voluntarily brings up wind from his stomach, the stop of the heart does not occur. From hence I conclude, that the stop of digestion is the primary disease; and that air is instantly generated from the aliment, which begins to ferment, if the digestive process is impeded for a moment, (see Sect. XXIII. 4.) and that the stop of the heart is in con- sequence of the association of the motions of these viscera, as explained in Sect. XXXV. 1. 4. but if the little air, which is instantly generated during the temporary torpor of the stomach, be evacuated, the digestion recommences, and the temporary torpor of the heart does not follow. One patient, whom I lately saw, and who had been for five or six days much trou- bled with this intermission of a pulsation of his heart, and who had hemicrania, with some fever, was immediately relieved from them all by losing ten ounces of blood, which had what is term- ed an inflammatory crust on it. Another instance of this association between the motions of the stomach and heart is evinced, by the exhibition of an overdose of foxglove, which induces an incessant vomiting, which is attended with very stow, and sometimes intermitting pulse; which continues, in spite of the exhibition of wine and opium, for two or three days. To the same association must be a- scribed the weak pulse, which constantly attends the exhibition of emetics during their operation. And also the sudden deaths, which have been occasioned in boxing by a blow on the sto- mach; and lastly, the sudden death of those who have been long debilitated by the gout, from the torpor of the stomach. See Sect. XXV. 1. 4. SECT. XXVI. OF THE CAPILLARY GLANDS AND MEMBRANES. I. 1. The capillary vessels are glands. 2. Their excretory ducts. Experiments on the mucus of the intestines, ab- domen, cellular membrane, and on the humours of the eye. 3. Scurf on the head, cough, catarrh, diarrhœa, gonorrhœa. 4. Rheumatism. Gout. Leprosy. II. 1. The most minute membranes are unorganized. 2. Lar- ger membranes are composed of the ducts of the capilla- F f - ries, 212 GLANDS AND MEMBRANES. Sect. XXVI. r. ries, and the mouths of the absorbents. 3. Mucilaginous fluid is secreted on their surfaces. III. Three kinds of rheumatism. I. 1. THE capillary vessels are like all the other glands except the absorbent system, inasmuch as they receive blood from the arteries, separate a fluid from it, and return the re- mainder by the veins. 2. This series of glands is of the most extensive use, as their excretory ducts open on the whole external skin, forming its perspirative pores, and on the internal surfaces of every cavity of the body. Their secretion on the skin is termed in- sensible perspiration, which in health is in part reabsorbed by the mouths of the lymphatics, and in part evaporated in the air: the secretion on the membranes, which line the larger cavities of the body, which have external openings, as the mouth and intestinal canal, is termed mucus, but is not how- ever coagulable by heat; and the secretion on the membranes of those cavities of the body, which have no external open- ings, is called lymph, or water, as in the cavities of the cellu- lar membrane, and of the abdomen: this lymph, however, is coagulable by the heat of boiling water. Some mucus, nearly as viscid as the white of egg, which was discharged by stool, did not coagulate, though I evaporated it to one fourth of the quantity; nor did the aqueous and vitreous humours of a sheep's eye coagulate by the like experiment: but the serosity from an anasarcous leg, and that from the abdomen of a drop- sical person, and the crystalline humour of a sheep's eye, co- agulated in the same heat. 3. When any of these capillary glands are stimulated into greater irritative actions than is natural, they secrete a more copious material; and as the mouths of the absorbent system, which open in their vicinity, are at the same time stimulated into greater action, the thinner and more saline part of the se- creted fluid is taken up again; and the remainder is not only more copious, but also more viscid than natural. This is more or less troublesome, or noxious, according to the importance of the functions of the part affected: on the skin and bronchiæ, where this secretion ought naturally to evaporate, it becomes so viscid as to adhere to the membrane; on the tongue it forms a pellicle, which can with difficulty be scraped off; produces the scurf on the heads of many people; and the mucus, which is spit up by others in coughing. On the nostrils and fauces, when the secretion of these capillary glands is increased, it is termed simple catarrh; when in the intestines, a mucus diarr- hœa; 213 SECT. XXVI. 2. GLANDS AND MEMBRANES. hœa; and in the urethra, or vagina, it has the name of go- norrhœa, or fluor albus. 4. When these capillary glands become inflamed, a still more viscid, or even cretaceous humour is produced upon the surface of the membranes, which is the cause or the effect of rheumatism, gout, leprosy, and of hard tumours of the legs, which are generally termed scorbutic; all which will be treat- ed of hereafter. II. 1. The whole surface of the body, with all its cavities and contents, is covered with membrane. It lines every ves- sel, forms every cell, and binds together all the muscular and perhaps osseous fibres of the body; and is itself therefore pro- bably a simpler substance than those fibres. And as the con- taining vessels of the body, from the largest to the least, are thus lined and connected with membranes, it follows, that these mem- branes themselves consisted of unorganized materials. For however small we may conceive the diameters of the minutest vessels of the body, which escape our eyes and glasses, yet these vessels must consist of coats or sides, which are made up of an unorganized material, and which are probably pro- duced from a gluten, which hardens after its production, like the silk or web of caterpillars and spiders. Of this material consist the membranes, which line the shells of eggs, and the shell itself; both which are unorganized, and are formed from mucus, which hardens after it is formed, either by the absorp- tion of its more fluid part, or by its uniting with some part of the atmosphere. Such is also the production of the shells of snails, and of shell-fish, and I suppose of the enamel of the teeth. 2. But though the membranes that compose the sides of the most minute vessels, are, in truth, unorganized materials; yet the larger membranes, which are perceptible to the eye, seem to be composed of an intertexture of the mouths of the ab- sorbent system, and of the excretory ducts of the capillaries, with their concomitant arteries, veins, and nerves: and from this construction it is evident, that these membranes must possess great irritability to peculiar stimuli, though they are incapable of any motions that are visible to the naked eye: and daily ex- perience shews us, that in their inflamed date they have the greatest sensibility to pain, as in the pleurisy and paronychia. 3. On all these membranes a mucilaginous or aqueous fluid is secreted, which moistens and lubricates their surfaces, as was explained in Section XXIII. 2. Some have doubted, whether this mucus is separated from the blood by an appropriated set of glands, or exudes through the membranes, or is an abra- sion or destruction of the surface of the membrane itself, which is 214 OF HÆMORRHAGES. SECT. XXVII. is continually repaired on the other side of it; but the great ana- logy between the capillary vessels, and the other glands, coun- tenances the former opinion, and evinces, that these capilla- ries are the glands that secrete it; to which we must add, that the blood, in passing these capillary vessels, undergoes a change in its colour, from florid to purple, and gives out a quantity of heat; from whence, as in other glands, we must conclude that something is secreted from it. III. The feat of rheumatism is in the membranes, or upon them; but there are three very distinct diseases, which com- monly are confounded under this name. First, when a mem- brane becomes affected with torpor, or inactivity of the ves- sels which compose it, pain and coldness succeed, as in the hemicrania, and other head-achs, which are generally termed nervous rheumatism; they exist whether the part be at rest or in motion, and are generally attended with other marks of de- bility. Another rheumatism is said to exist, when inflammation and swelling, as well as pain, affect some of the membranes of the joints, as of the ancles, wrists, knees, elbows, and sometimes of the ribs. This is accompanied with fever, is analogous to pleurisy, and other inflammations, and is termed the acute rheumatism. A third disease is called chronic rheumatism, which is dis- tinguished from that first mentioned, as in this the pain only affects the patient during the motion of the part, and from the second kind of rheumatism above described, as it is not attend- ed with quick pulse Or inflammation. It is generally believed to succeed the acute rheumatism of the same part, and that some coagulable lymph, or cretaceous, or calculous material, has been left on the membrane; which gives pain, when the muscles move over it as some extraneous body would do, which was too insoluble to be absorbed. Hence there is aq analogy between this chronic rheumatism and the diseases which produce gravel or gout-stones; and it may perhaps re- ceive relief from the same remedies, such as aerated sal soda. SECT. XXVII. OF HÆMORRHAGES. I. The veins are absorbent vessels. 1. Hæmorrhages from inflammation. Case of hæmorrhage from the kidney cur- ed by cold bathing. Case of hæmorrhage from the nose cured by cold immersion. II. Hæmorrhage from venous paralysis. 215 SECT. XXVII. 1. OF HÆMORRHAGES. paralysis. Of Piles. Black stools. Petechiæ. Consump- tion. Scurvey of the lungs. Blackness of the face and eyes in epileptic fits. Curt of hæmorrhages from venous inability. I. AS the imbibing mouths of the absorbent system already described open on the surface, and into the larger cavities of the body, so there is another system of absorbent vessels, which are not commonly esteemed such; I mean the veins, which take up the blood from the various glands and capillaries, after their proper fluids or secretions have been separated from it. The veins resemble the other absorbent vessels; as the pro- gression of their contents is carried on in the same manner in both, they alike absorb their appropriated fluids, and have valves to prevent its regurgitation by the accidents of mecha- nical violence. This appears, first, because there is no pulsa- tion in the very beginnings of the veins, as is seen by micro- scopes; which must happen, if the blood was carried into them by the action of the arteries. For though the con- currence of various venous dreams of blood from different distances must prevent any pulsation in the larger branches, yet, in the very beginnings of all these branches, a pulsation must unavoidably exist, if the circulation in them was owing to the intermitted force of the arteries. Secondly, the venous absorption of blood from the penis, and from the teats of fe- male animals after their erection, is still more similar to the lymphatic absorption, as it is previously poured into cells, where all arterial impulse must cease. There is an experiment, which seems to evince this venous absorption, which consists in the external application of a stimu- lus to the lips, as of vinegar, by which they become instantly pale; that is, the bibulous mouths of the veins by this stimu- lus are excited to absorb the blood faster than it can be sup- plied by the usual arterial exertion. See Sect. XXIII. 5. There are two kinds of hæmorrhages frequent in diseases; one is where the glandular or capillary action is too power- fully exerted, and propels the blood forwards more hastily than the veins can absorb it; and the other, is, where the ab- sorbent power of the veins is diminished, or a branch of them is become totally paralytic. The former of these cases is known by the heat of the part, arid the general fever, or inflammation that accompanies the hæmorrhage. An hæmorrhage from the nose or from the lungs is sometimes a crisis of inflammatory diseases, as of the hepati- tis and gout, and generally ceases spontaneously, when the ves- sels 216 OF HÆMORRHAGES. SECT. XXVII. 2. sels are considerably emptied. Sometimes the hæmorrhage re- curs by daily periods, accompanying the hot fits of fever, and ceasing in the cold fits, or in the intermissions. This is to be cur- ed by removing the febrile paroxysms, which will be treated of in their place. Otherwise it is cured by venesection, by the internal or external preparations of lead, or by the applica- tion of cold, with an abstemious diet and diluting liquids, like other inflammations; which, by inducing a quiescence on those glandular parts that are affected, prevents a greater quan- tity of blood from being protruded forwards than the veins are capable of absorbing. Mr. B- had an hæmorrhage from his kidney, and parted with not less than a pint of blood a day (by conjecture) along with his urine, for above a fortnight: venesections, mucilages, balsams, preparations of lead, the bark, alum, and dragon's blood, opiates, with a large blister on his loins, were separately tried, in large doses, to no purpose. He was then directed to bathe in a cold spring up to the middle of his body only, the upper part being covered, and the hæmorrhage diminished at the first, and ceased at the second immersion. In this case the external capillaries were rendered quiescent by the coldness of the water, and thence a less quantity of blood was circulated through them; and the internal capillaries, or other glands, became quiescent from their irritative associations with the external ones; and the hæmorrhage was stopped a sufficient time for the ruptured vessels to contract their aper- tures, or for the blood in those apertures to coagulate. Mrs. K ------ had a continued hæmorrhage from her nose for some days; the ruptured vessel was not to be reached by plugs up the nostrils, and the sensibility of her sauces was such that nothing could be borne behind the uvula. After repeated venesection, and other common applications, she was directed to immerse her whole head into a pail of water, which was made colder by the addition of several handfulls of salt, and the hæmorrhage immediately ceased, and returned no more; but her pulse continued hard; and she was necessiated to lose blood from the arm on the succeeding day. Query. Might not the cold bath instantly stop hæmorrhages from the lungs in inflammatory cases? for the shortness of breath of those, who go suddenly into cold water, is not owing to the accumulation of blood in the lungs, but to the of the quiescence of the pulmonary capillaries from association, as explained in Section XXXII. 3. 2. II. The other kind of hæmorrhage is known from its being attended with a weak pulse, and other symptoms of general de- bility, 217 SECT. XXVII. 2. HÆMORRHAGES. bility, and very frequently occurs in those who have diseased livers, owing to intemperance in the use of fermented liquors. These constitutions are shewn to be liable to paralysis of the lymphatic absorbents, producing the various kinds of dropsies in Section XXIX.5. Now, if any branch of the venous system loses its power of absorption, the part swells, and at length bursts and discharges the blood, which the capillaries or other glands circulate through them. It sometimes happens that the large external veins of the legs burst, and effuse their blood; but this occurs most frequently in the veins of the intestines, as the vena portarum is liable to suffer from a schirus of the liver opposing the progression of the blood, which is absorbed from the intestines. Hence the piles are a symptom of hepatic obstruction; and hence the copious dischar- ges, downwards or upwards, of a black material, which has been called melancholia, or black bile; but is no other than the blood which is probably discharged from the veins of the intestines. J. F. Meckel, in his Experimenta de Finibus Vasorum, published at Berlin, 1772, mentions his discovery of a com- munication of a lymphatic vessel with the gastric branch of the vena portarum. It is possible, that when the motion of the lym- phatic becomes retrograde in some diseases, that blood may ob- tain a passage into it, where it anastomoses with the vein, and thus be poured into the intestines. A discharge of blood with the urine sometimes attends diabetes, and may have its source in the same manner. Mr. A ---- , who had been a hard drinker, and had the gutta rosacea on his face and breast, after a stroke of the palsy, voided near a quart of a black viscid material by stool; on dilut- ing it with water it did not become yellow, as it must have done if it had been inspissated bile, but continued black like the grounds of coffee. But any other part of the venous system may become quie- scent, or totally paralytic, as well as the veins of the intestines; all which occur more frequently in those who have diseased livers, than in any other. Hence troublesome bleedings of the nose, or from the lungs with a weak pulse; hence hæmorrha- ges from the kidneys, too great menstruation; and hence the oozing of blood from every part of the body, and the petechiæ in those fevers, which are termed putrid, and which is errone- ously ascribed to the thinness of the blood: for the blood in in- flammatory diseases is equally fluid before it coagulates in the cold air. Is not that hereditary consumption, which occurs chiefly in dark-eyed people about the age of twenty, and commences with slight 218 HÆMORRHAGES. SECT. XXVII. 2. slight pulmonary hæmorrhages without fever, a disease of this kind?—These hæmorrhages frequently begin during sleep, when the irritability of the lungs is not sufficient in these pa- tients to carry on the circulation without the assistance of voli- tion; for in our waking hours, the motions of the lungs are in part voluntary, especially if any difficulty of breathing renders the efforts of volition necessary. See Class I. 2. 1. 2. and Class III. 2. 1. 10. Another species of pulmonary consumption, which seems more certainly of scrophulous origin, is described in the next Section, No. 2. I have seen two cases of women, of about forty years of age, both of whom were seized with quick weak pulse, with diffi- cult respiration, and who spit up, by coughing, much viscid mu- cus mixed with dark coloured blood. They had both large vibices on their limbs, and petechiæ; in one the feet were in danger of mortification, in the other the legs were œdematous To relieve the difficult respiration, about six ounces of blood were taken from one of them, which, to my surprise, was sizy, like inflamed blood: they had both palpitations or unequal pul- sations of the heart. They continued four or five weeks with pale and bloated countenances, and did not cease spitting phlegm mixed with black blood, and the pulse seldom flower than 130 or 135 in a minute. This blood, from its dark colour, and from the many vibices and petechiæ, seems to have been ve- nous blood; the quickness of the pulse, and the irregularity of the motion of the heart, are to be ascribed to debility of that part of the system; as the extravasation of blood originated from the defect of venous absorption. The approximation of these two cases to sea-scurvy is peculiar, and may allow them to be called scorbutus pulmonalis. Had these been younger subjects, and the paralysis of the veins had only affected the lungs, it is probable the disease would have been a pulmonary consumption. Last week I saw a gentleman of Birmingham, who had for ten days laboured under great palpitation of his heart, which was so distinctly felt by the hand, as to discountenance the idea of there being a fluid in the pericardium. He frequently spit up mucus, stained with dark coloured blood ; his pulse very une- qual and very weak, with cold hands and nose. He could not lie down at all, and for about ten days past could not sleep a minute together, but waked perpetually with great uneasiness. Could those symptoms be owing to very extensive adhesions of the lungs? or is this a scorbutus pulmonalis? After a few days he suddenly got so much better as to be able to sleep many hours at a time, by the use of one grain of powder of foxglove twice a day, and a grain of opium at night. After a few days longer, the 219 SECT. XXVIII. 1. ABSORBENT SYSTEM. the bark was exhibited, and the opium continued with some wine; and the palpitations of his heart became much relieved, and he recovered his usual degree of health. In epileptic fits the patients frequently become black in the face, from the temporary paralysis of the venous system of this part. I have known two instances where the blackness has continued many days. M. P —, who had drank intem- perately, was seized with the epilepsy when he was in his for- tieth year; in one of these fits the white part of his eyes was left totally black with effused blood; which was attended with no pain or heat, and was in a few weeks gradually absorbed, changing colour as is usual with vibices from bruises. The hæmorrhage produced from the inability of the veins to absorb the refluent blood, is cured by opium, the preparations of steel, lead, the bark, vitriolic acid, and blisters; but these have the effect with much more certainty, if a venesection to a few ounces, and a moderate cathartic, with four or six grains of calomel, be premised, where the patient is not already too much dibilitated; as one great means of promoting the absorption of any fluid consists in previously emptying the vessels which are to receive it. SECT. XXVIII. OF THE PARALYSIS OF THE ABSORBENT SYSTEM. I. Paralysis of the lacteals, atrophy. Distaste to animal food. II. Cause of dropsy. Cause of herpes. Mesenteric con- sumption. Pulmonary consumption. Why ulcers in the lungs are so difficult to heal. THE term paralysis has generally been used to express the loss of voluntary motion, as in the hemiplagia, but may with equal propriety be applied to express the disobediency of the muscular fibres to the other kinds of stimulus; as to those of irritation or sensation. I. There is a species of atrophy, which has not been well understood: when the absorbent vessels of the stomach and intestines have been long inured to the stimulus of too much spi- rituous liquor, they at length, either by the too sudden omission of fermented or spirituous potation, or from the gradual decay of nature, become in a certain degree paralytic: now, it is ob- served in the larger muscles of the body, when one side is pa- ralytic, the other is more frequently in motion, owing to the less expenditure of sensorial power in the paralytic limbs; so, in this case, the other part of the absorbent system acts with greater G g force, 220 PARALYSIS OF SECT. XXVIII. 2. force, or with greater perseverance, in consequence of the pa- ralysis of the lacteals; and the body becomes greatly emaciated in a small time. I have seen several patients in this disease, of which the fol- lowing are the circumstances. 1. They were men about fifty years of age, and had lived freely in respect to fermented li- quors. 2. They lost their appetite to animal food. 3. They became suddenly emaciated to a great degree. 4. Their skins were dry and rough. 5. They coughed and expectorated with difficulty a viscid phlegm. 6. The membrane of the tongue was dry and red, and liable to become ulcerous. The inability to digest animal food, and the consequent dist- taste to it, generally precedes the dropsy, and other diseases, which originate from spirituous potation. I suppose, when the stomach becomes inirritable, that there is at the same time a de- ficiency of gastric acid; hence milk seldom agrees with these pa- tients, unless it be previously curdled, as they have not sufficient. gastric acid to curdle it; and hence vegetable food, which is it- self acescent, will agree with their stomachs longer than animal food, which requires more of the gastric acid for its digestion. In this disease the skin is dry from the increased absorption of the cutaneous lymphatics, the fat is absorbed from the in- creased absorption of the cellular lymphatics, the mucus of the lungs is too viscid to be easily spit up by the increased ab- sorption of the thinner parts of it, the membrana sneideriana becomes dry, covered with hardened mucus, and at length be- comes inflamed and full of apthæ, and either these sloughs, or pulmonary ulcers, terminate the scene. II. The immediate cause of dropsy is the paralysis of some other branches of the absorbent system, which are called lym- phatics, and which open into the larger cavities of the body, or into the cells of the cellular membrane; whence those cavities or m cells become distended with the fluid, which is hourly secreted into them for the purpose of lubricating their surfaces, as is more fully explained in No. 5. of the next Section. As those lymphatic vessels consist generally of a long neck or mouth, which drinks up its appropiated fluid, and of a conglo- bate gland, in which this fluid undergoes some change, it hap- pens, that sometimes the mouth of the lymphatic, and sometimes the belly or glandular part of it, becomes totally or partially paralytic. In the former case, where the mouths of the cuta- neous lymphatics become torpid or quiescent, the fluid secreted on the skin ceases to be absorbed, and erodes the skin by its sa- line acrimony, and produces eruptions, termed herpes, the discharge from which is as salt as the tears, which are secret- ed 221 SECT. XXVIII. 2. ABSORBENT SYSTEM. ed too fast to be reabsorbed, as in grief, or when the puncta lacrymalia are obstructed, and which, running down the cheek, redden and inflame the skin. When the mouths of the lymphatics, which open on the mucus membrane of the nostrils, become torpid, as on walk- ing into the air in a frosty morning, the mucus, which con- tinues to be secreted, has not its aqueous and saline part reab- forbed, which, running over the upper lip, inflames it, and has a salt taste, if it falls on the tongue. When the belly or glandular part of these lymphatics be- comes torpid, the fluid absorbed by its mouth stagnates, and forms a tumour in the gland. This disease is called the scro- phula. If these glands suppurate externally, they gradually heal, as those of the neck; if they suppurate without an open- ing on the external habit, as the mesenteric glands, a hectic fever ensues, which destroys the patient; if they suppurate in the lungs, a pulmonary consumption ensues, which is believed thus to differ from that described in the preceding Section, in respect to its seat or proximate cause. It is remarkable, that matter, produced by suppuration, will lie concealed in the body many weeks, or even months, with- out producing hectic fever; but as soon as the wound is open- ed, so as to admit air to the surface of the ulcer, a hectic fe- ver supervenes, even in very few hours, which is probably owing to the azotic part of the atmosphere rather than to the oxygene; because those medicines which contain much oxy- gene, as the calces or oxydes of metals, externally applied, greatly contribute to heal ulcers: of these are the solutions of lead and mercury, and copper in acids, or their precipitates. Hence, when ulcers are to be healed by the first intention, as It is called, it is necessary carefully to exclude the air from them. Hence we have one cause, which prevents pulmonary ulcers from healing, which is their being perpetually exposed to the air. Both the dark-eyed patients, which are affected with pul- monary ulcers from deficient venous absorption, as described in Sect. XXVII. 2. and the light-eyed patients from deficient lymphatic absorption, which we are now treating of, have generally large apertures of the iris: these large pupils of the eyes are a common mark of want of irritability; and it gene- rally happens, that an increase of sensibility, that is, of motions, in consequence of sensation, attends these constitutions. See Sect. XXXI. 2. Whence inflammations may occur in these from stagnated fluids more frequently than in those constitu- tions which possess more irritability and less sensibility. Great 222 RETROGRADE ABSORBENTS. SECT. XXIX. Great expectations, in respect to the cure of consumptions, as well as of many other diseases, are produced by the very ingenious exertions of Dr. BEDDOES; who has established an apparatus for breathing various mixtures of airs or gasses, at the hot-wells near Bristol, which well deserves the attention of the public. Dr. BEDDOES very ingeniously concludes, from the florid colour of the blood of consumptive patients, that it abounds In oxygene; and that the redness of their tongues, and lips, and the fine blush of their cheeks, shew the presence of the same principle, like flesh reddened by nitre. And adds, that the circumstance of the consumptions of pregnant women be- ing stopped in their progress during pregnancy, at which time their blood may be supposed to be in part deprived of its oxy- gene, by oxygenating the blood of the fœtus, is a forcible argument in favour of this theory; which must soon be con- firmed or confuted by his experiments. See Essay on Scurvy, Consumption, &c. by Dr. Beddoes. Murray. London. Also Letter to Dr. Darwin, by the same. Murray. London. SECT. XXIX. ON THE RETROGRADE MOTIONS OF THE ABSOR- BENT SYSTEM. I. Account of the absorbent system. II. The valves of the absorbent vessels may suffer their fluids to regurgitate in some diseases. III. Communication from the alimentary canal to the bladder by means of the absorbent vessels. IV. The phenomena of diabetes explained. V. 1. The phenomena of dropsies explained. 2. Cases of the use of foxglove. VI. Of cold sweats. VII. Translations of matter, of chyle, of milk, of urine. Operations of purg- ing drugs applied externally. VIII. Circumstances by which the fluids, that are effused by the retrograde mo- tions of the absorbent vessels, are distinguished. IX. Retrograde motions of vegetable juices. X. Objections answered. XI. The causes which induce the retrograde motions of animal vessels, and the medicines by which the natural motions are restored. N. B. The following Section is a translation of a part of a Latin thesis, written by the late Mr. Charles Darwin which was printed with his prize-dissertation on a crite- rion between matter and mucus, in 1780. Sold by Cadell, London. I. Account 223 SECT. XXIX. 1. RETROGRADE ABSORBENTS. I. Account as the absorbent system. 1. THE absorbent system of vessels in animal bodies consists of several branches, differing in respect to their situations, and to the fluids which they absorb. The intestinal absorbents open their mouths on the internal surfaces of the intestines; their office is to drink up the chyle and the other fluids from the alimentary canal; and they are termed lacteals, to distinguish them from the other absorbent vessels, which have been termed lymphatics. Those, whose mouths are dispersed on the external skin, imbibe a great quantity of water from the atmosphere, and a part of the perspirable matter, which does not evaporate, and are termed cutaneous absorbents. Those, which arise from the internal surface of the bron- chia, and which imbibe moisture from the atmosphere, and a part of the bronchial mucus, are called pulmonary absorbents. Those, which open their innumerable mouths into the cells of the whole cellular membrane, and whose use is to take up the fluid, which is poured into those cells, after it has done its office there, may be called cellular absorbents. Those, which arise from the internal surfaces of the mem- branes, which line the larger cavities of the body, as the tho- rax, abdomen, serotum, pericardium, take up the mucus pour- ed into those cavities; and are distinguished by the names of their respective cavities. Whilst those, which arise from the internal surfaces of the urinary bladder, gall-bladder, salivary ducts, or other recep- tacles of secreted fluids, may take their names from those flu- ids, the thinner parts of which it is their office to absorb; as urinary, bilious, or salivary absorbents. 2. Many of these absorbent vessels, both lacteals and lym- phatics, like some of the veins, are replete with valves; which seem designed to assist the progress of their fluids, or at least so prevent their regurgitation, where they are subjected to the intermitted pressure of the muscular, or arterial actions in their neighbourhood. These valves do not, however, appear to be necessary to all the absorbents, any more than to all the veins; since they are not found to exist in the absorbent system of fish, according to the discoveries of the ingenious and much lamented Mr. Hewson. Philos. Trans. v. 59. Enquiries into the Lymph. Syst. p. 94. 3. These absorbent vessels are also furnished with glands, which are called conglobate glands; whose use is not at pre- sent 224 RETROGRADE ABSORBENTS. SECT. XXIX. 2. sent diffidently investigated; but it is probable that they re- semble the conglomerate glands, both in structure and in use, except that their absorbent mouths are, for the conveniency of situation, placed at a greater distance from the body of the gland. The conglomerate glands open their mouths immedi- ately into the sanguiferous vessels which bring the blood, from whence they absorb their respective fluids, quite up to the gland: but these conglobate glands collect their adapted fluids from ve- ry distant membranes, or cysts, by means of mouths furnished with long necks for this purpose, and which are called lacteals, or lymphatics. 4. The fluids, thus collected from various parts of the body, pass by means of the thoracic duct into the left subclavian near the jugular vein; except, indeed, that those collected from the right side of the head and neck, and from the right arm, are car- ried into the right subclavian vein: and sometimes even the lym- phatics from the right side of the lungs are inserted into the right subclavian vein; whilst those of the left side of the head open but just into the summit of the thoracic duct. 5. In the absorbent system there are many anastomoses of the vessels, which seem of great consequence to the preservation of health. These anastomoses are discovered by dissection to be very frequent between the intestinal and urinary lymphatics, as mentioned by Mr. Hewson, (Phil. Trans. v. 58.) 6. Nor do ah the intestinal absorbents seem to terminate in the thoracic duct, as appears from some curious experiments of D. Monro, who gave madder to some animals, having previous- ly put a ligature on the thoracic duct, and found their bones and the serum of their blood, coloured red. II. The Valves of the Absorbent System may suffer their Fluids to regurgitate in some Diseases. 1. The many valves, which occur in the progress of the lym- phatics and lacteal vessels, would seem insuperable obstacles to the regurgitation of their contents. But as these valves are plac- ed in vessels which are indued with life, and are themselves en- dued with life also, and are very irritable into those natural mo- tions which absorb, or propel the fluids they contain; it is possible, in some diseases, where these valves or vessels are stimulated into unnatural exertions, or are become paralytic, that during the diastole of the part of the vessel to which the valve is attached, the valve may not so completely close as to prevent the relapse of the lymph or chyle. This is rendered more probable, by the experi- ments of injecting mercury, or water, or suet, or by blowing air down these vessels; all which pass the valves very easily, contrary to 225 SECT. XXIX. 2. RETROGRADE ABSORBENTS. to the natural course of their fluids, when the vessels are thus a little forcibly dilated, as mentioned by Dr. Haller. Elem. Physiol. T. iii. s. 4. " The valves of the thoracic duct are few; some assert they are not more than twelve, and that they do not very accurately perform their office, as they do not close the whole area of the duct, and thence may permit chyle to repass them downwards. In living animals, however, though not always, yet more fre- quently than in the dead, they prevent the chyle from returning. The principal of these valves is that which presides over the in- sertion of the thoracic duct, into the subclavian vein: many have believed this also to perform the office of a valve, both to admit the chyle into the vein, and to preclude the blood from entering the duct; but in my opinion it is scarcely sufficient for this pur- pose." Haller, Elem. Phys. T. vii. p. 226. 2. The mouths of the lymphatics seem to admit water to pass through them after death, the inverted way, easier than the natural one; since an inverted bladder readily lets out the wa- ter with which it is filled; whence it may be inferred, that there is no obstacle at the mouths of these vessels to prevent the re- gurgitation of their contained fluids. I was induced to repeat this experiment; and having accu- rately tied the ureters and neck of a fresh ox's bladder, I made an opening at the fundus of it; and then, having turned it in- side outwards, filled it half full with water, and was surprised to see it empty itself so hastily. I thought the experiment more apposite to my purpose, by suspending the bladder wish its neck downwards, as the lymphatics are chiefly spread upon this part of it; as shewn by Dr. Watson, Philos. Trans. v. 59. p. 392. 3. In some diseases, as in the diabetes and scrophula, it is probable the valves themselves are diseased, and are thence in- capable of preventing the return of the fluids they should support. Thus the valves of the aorta itself have frequently been found schirrous, according to the dissections of Mons. Lieu- taud, and have given rise to an interrupted pulse, and labori- ous palpitations, by suffering a return of part of the blood into the heart. Nor are any parts of the body so liable to schir- rosity, as the lymphatic glands and vessels, insomuch, that their schirrosities have acquired a distinct name, and been termed schrophula. 4. There are valves in other parts of the body, analogous to those of the absorbent system, and which are liable, when diseased, to regurgitate their contents: thus the upper and lower orifices of the stomach are closed by valves, which, when too great quantities of warm water have been drank, with 226 RETROGRADE ABSORBENTS. Sect. XXIX. 2. with a design to promote vomiting, have sometimes resisted the utmost efforts of the abdominal muscles and diaphragm : yet, at other times, the upper valve, or cardia, easily permits the evacuation of the contents of the stomach, whilst the infe- rior valve, or pylorus, permits the bile, and other contents of the duodenum, to regurgitate into she stomach. 5. The valve of the colon is well adapted to prevent the retro- grade motion of the excrements ; yet, as this valve is possessed of a living power, in the iliac passion, either from spasm, or other unnatural exertions, it keeps itself open, and either suf- fers or promotes the retrograde movements of the contents of the intestines below ; as in ruminating animals, the mouth of the first stomach seems to be so constructed, as to facilitate or assist the regurgitation of the food ; the rings of the œsopha- gus afterwards contracting themselves in inverted order. De Haen, by means of a syringe, forced so much water into the rectum intestinum of a dog, that he vomited it in a full dream from his mouth ; and in the iliac passion above-mentioned, excrements and clyster are often evacuated by the mouth. See Section XXV. 15. 6. The puncta lacrymalia, with the lacrymal sack and nasal duct, compose a complete gland, and much resemble the intes- tinal canal ; the puncta lacrymalia are absorbent mouths, that take up the tears from the eye, when they have done their of- fice there, and convey them into the nostrils ; but when the nasal duct is obstructed, and the lacrymal sack distended with its fluid, on pressure with the finger, the mouths of this gland, (puncta lacrymalia) will readily disgorge the fluid they had previously absorbed back into the eye. 7. As the capillary vessels receive blood from the arteries, and separating the mucus, or perspirable matter from it, con- vey the remainder back by the veins ; these capillary vessels are a set of glands, in every respect similar to the secretory ves- sels of the liver, or other large congeries of glands. The be- ginnings of these capillary vessels have frequent anastomoses into each other, in which circumstance they are resembled by the lacteals ; and, like the mouths or beginnings of other glands, they are a set of absorbent vessels, which drink up the blood which is brought to them by the arteries, as the chyle is drank up by the lacteals : for the circulation of the blood through the capillaries is proved to be independent of arterial impulse ; since, in the blush of shame, and in partial inflammations, their action is increased, without any increase of the motion of the heart. 8. Yet not only the months, or beginnings of these anasto- mosing 227 SECT. XXIX. 3. RETROGRADE ABSORBENTS. mosing capillaries are frequently seen, by microscopes, to re- gurgitate some particles of blood, during the druggies of the animal; but retrograde motion of the blood, in the veins of those animals, from the very heart to the extremity of the limbs, is observable, by intervals, during the distresses of the dying creature. Haller, Elem. Physiol. T. i. p. 216. Now, as the veins have perhaps all of them a valve, somewhere between their extremities and the heart, here is ocular demonstration of the fluids in this diseased condition of the animal, repassing through venous valves: and it is hence highly probable, from the strictest analogy, that if the course of the fluids, in the lym- phatic vessels, could be subjected to microscopic observation, they would also, in the diseased state of the animal, be seen to repass the valves, and the mouths of those vessels which had pre- viously absorbed them, or promoted their progression. III. Communication from the Alimentary Canal to the Blad- der, by means of the Absorbent Vessels. Many medical philosophers, both ancient and modern, have suspected that there was a nearer communication between the stomach and the urinary bladder than that of the circulation : they were led into this opinion from the great expedition with which cold water, when drank to excess, passes off by the bladder: and from the similarity of the urine, when produced in this hasty manner, with the material that was drank. The former of these circumstances happens perpetually to those who drink abundance of cold water when they are much heated by exercise, and to many at the beginning of intoxication. Of the latter many instances are recorded by Etmuller, T. xi. p. 716. where simple water, wine, and wine with sugar, and emulsions, were returned by urine unchanged. There are other experiments, that seem to demonstrate the existence of another passage to the bladder besides that through the kidneys. Thus Dr. Kratzenstein put ligatures on the ure- ters of a dog, and then emptied the bladder by a catheter; yet in a little time the dog drank greedily, and made a quantity of water. (Disputat. Moibor. Halleri. T. iv. p. 63.) A simi- lar experiment is related in the Philosophical Transactions, with the same event. (No. 65, 67, for the year 1670.) Add to this, that in some morbid cases the urine has continu- ed to pass, after the supuration or total destruction of the kid- neys; of which many instances are referred to in the Elem. Physiol. T. vii. p. 379, of Dr. Haller. From all which it must be concluded, that some fluids have passed from the stomach, or abdomen, without having gone Hh through 228 RETROGRADE ABSORBENTS. SECT. XXIX. 3. through the sanguiferous circulation: and as the bladder is sup- plied with many lymphatics, as described by Dr. Watson, in the Philos. Trans. v. 59. p. 392. and as no other vessels open into it besides these and the ureters, it seems evident, that the unnatural urine, produced as above described, when the ureters were tied, or the kidneys obliterated, was carried into the blad- der by the retrograde motions of the urinary branch of the lymphatic system. The more certainly to ascertain the existence of another communication between the stomach and bladder, besides that of the circulation, the following experiment was made, to which I must beg your patient attention: A friend of mine (June 14, 1772,) on drinking repeatedly of told small punch, till he began to be intoxicated, made a quantity of colourless urine. He then drank about two drams of nitre, dissolved in some of the punch, and cut about twenty stalks of boiled aspa- ragus: on continuing to drink more of the punch, the next urine that he made was quite clear, and without smell; but in a little time another quantity was made, which was not quite so colour- less, and had a strong smell of the asparagus: he then lost about four ounces of blood from the arm. The smell of the asparagus was not at all perceptible in the blood, neither when fresh taken, nor the next morning, as my- self and two others accurately attended to; yet this smell was strongly perceived in the urine which was made just before the blood was taken from his arm. Some bibulous paper, moistened in the serum of this blood, and differed to dry, shewed no signs of nitre by its manner of burning. But some of the same paper, moistened in the urine, and dried, on being ignited, evidently shewed, the presence of nitre. This blood and the urine stood some days exposed to the sun in the open air, till they were evaporated to about a fourth of their original quantity, and began to stink; the paper, which was then moistened with the concentrated urine, shewed the presence of much nitre by its manner of burning; whilst that moistened with the blood shewed no such appearance at all. Hence it appears, that certain fluids, at the beginning of in- toxication, find another passage to the bladder besides the long course of the arterial circulation; and as the intestinal absor- bents are joined with the urinary lymphatics by frequent anas- tomoses, as Hewson has demonstrated; and as there is no other road, we may justly conclude, that these fluids pass into the bladder by the urinary branch of the lymphatics, which has its motions inverted during the diseased state of the animal. A gentleman, who had been some weeks affected with jaun- dice, 229 SECT. XXIX. 4. RETROGRADE ABSORBENTS. dice, and whose urine was, in consequence, of a very deep yellow, took some cold small punch, in which was dissolved about a dram of nitre; he then took repeated draughts of the punch, and kept himself in a cool room, till on the approach of slight intoxication he made a large quantity of water; this water had a slight yellow tinge, as might be expected from a small admix- ture of bile secreted from the kidneys; but if the whole of it had passed through the sanguiferous vessels, which were now replete with bile (his whole skin being as yellow as gold) would not this urine also, as well as that he had made for weeks be- fore, have been of a deep yellow? Paper dipped in this water, and dryed, and ignited, shewed evident marks of the presence of nitre, when the flame was blown out. IV. The Phenomena of the Diabetes explained, and of some Diarrhœas. The phenomena of many diseases are only explicable from the retrograde motions of some of the branches of the lympha- tic system; as the great and immediate flow of pale urine in the beginning of drunkenness; in hysteric paroxysms; from being exposed to cold air, or to the influence of fear or anxiety. Before we endeavour to illustrate this doctrine, by describing the phenomena of these diseases, we must premise one circum- stance; that all the branches of the lymphatic system have a certain sympathy with each other, insomuch, that when one branch is stimulated into unusual kinds or quantities of motion, some other branch has its motions either increased, or decreas- ed, or inverted at the same time. This kind of sympathy can only be proved by the concurrent testimony of numerous facts, which will be related in the course of the work, I shall only add here, that it is probable, that this sympathy does not de- pend on any communication of nervous filaments, but on ha- bit, owing to the various branches of this system having fre- quently been stimulated into action at the same time. There are a thousand instances of involuntary motions asso- ciated in this manner; as in the act of vomiting, while the motions of the stomach and œsophagus are inverted, the pulsa- tions of the arterial system, by a certain sympathy, become weaker; and when the bowels or kidneys, are stimulated by poison, a done, or inflammation, into more violent action the stomach and œsophagus, by sympathy, invert their motions. 1. When any one drinks a moderate quantity of vinous spi- rit, the whole system acts with more energy by consent with the stomach and intestines, as is seen from the glow on the skin. and the increase of strength and activity; but when a greater quantity 230 RETROGRADE ABSORBENTS. SECT. XXIX. 4. quantity of this inebriating material is drank, at the same time that the lacteals are excited into greater action to absorb it, it frequently happens, that the urinary branch of absorbents, which is connected with the lacteals by many anastomoses, inverts its motions, and a great quantity of pale unanimalized urine is discharged. By this wife contrivance too much of an unne- cessary fluid is prevented from entering the circulation. This may be called the drunken diabetes, to distinguish it from the ether temporary diabetes, which occur in hysteric diseases, and from continued fear or anxiety. 2. If this idle ingurgitation of too much vinous spirit be daily practised. the urinary branch of absorbents at length gains an habit of inverting its motions, whenever the lacteals are much stimulated: and the whole, or a great part of the chyle is thus daily carried to the bladder, without entering the circu- lation, and the body becomes emaciated. This is one kind of chronic diabetes, and may be distinguished from the others by the taste and appearance of the urine; which is sweet, and the colour of whey, and may be termed the chyliferous diabetes. 3. Many children have a similar deposition of chyle in their urine, from the irritation of worms in their intestines, which stimulating the mouths of the lacteals into unnatural action, the urinary branch of the absorbents becomes inverted, and carries part of the chyle to the bladder: part of the chyle also has been carried to the iliac and lumber glands, of which in stances are recorded by Haller, T. vii. 225. and which can be explained on no other theory; but the dissections of the lym- phatic system of the human body, which have yet been publish- ed, are not sufficiently extensive for our purpose; yet if we may reason from comparative anatomy, this translation of chyle to the bladder is much illustrated by the account given of this system of vessels in a turtle, by Mr. Hewson, who observed, "That the lacteals near the root of the mesentery anastomose, so as to form a net-work, from which several large branches go into some considerable lymphatics lying near the spine; and which can be traced almost to the anus, and particularly to the kidneys." Philos. Trans. v. 59. p. 199.—Enquiries, p. 74. 4. At the same time that the urinary blanch of absorbents, in the beginning of diabetes, is excited into inverted action, the cellular branch is excited by the sympathy above mention- ed, into more energetic action; and the fat, that was before deposited, is reabsorbed and thrown into the blood vessels, where it floats, and was mistaken for chyle, till the late experiments of the ingenious Mr. Hewson demonstrated it to be fat. This appearance of what was mistaken for chyle in the blood which 231 SECT. XXIX. 4. RETROGRADE ABSORBENTS. which was drawn from these patients, and the obstructed liver, which very frequently accompanies this disease, seems to have led Dr. Mead to suspect the diabetes was owing to a defect of sanguification; and that the schirrous of the liver was the ori- ginal cause of it: but as the schirrous of the liver is most fre- quently owing to the same causes that produce the diabetes and dropsies, namely, the great use of fermented liquors, there is no wonder they should exist together, without being the con- sequence of each other. 5. If the cutaneous branch of absorbents gains a habit of being excited into stronger action, and imbibes greater quan- tities of moisture from the atmosphere, at the same time that the urinary branch has its motions inverted, another kind of diabe- tes is formed, which may be termed the aqueous diabetes. In this diabetes the cutaneous absorbents frequently imbibe an amazing quantity of atmospheric moisture; insomuch that there are authentic histories, where many gallons a day, for many weeks together, above the quantity that has been drank, have been discharged by urine. Dr. Keil, in his Medicina Statica, found that he gained eighteen ounces from the moist air of one night; and Dr. Per- cival affirms, that one of his hands imbibed, after being well chased, near an ounce and half of water, in a quarter of an hour. (Transact. of the College, London, vol. ii. p. 102.) Home's Medic. Facts, p. 2. sect. 3. The pale urine in hysterical women, or which is produced by fear or anxiety, is a temporary complaint of this kind: and it would in reality be the same disease, if it was confirmed by habit. 6. The purging stools, and pale urine, occasioned by expos- ing the naked body to cold air, or Sprinkling it with cold wa- ter, originate from a similar cause; for the mouths of the cu- taneous lymphatics being suddenly exposed to cold, become tor- pid, and cease, or nearly cease to act; whilst, by the sympathy above described, not only the lymphatics of the bladder and intestines cease also to absorb the more aqueous and saline part of the fluids secreted into them; but it is probable that these lymphatics invert their motions, and return the fluids, which were previously absorbed, into the intestines and bladder. At the very instant that the body is exposed naked to the cold air, an unusual movement is felt in the bowels; as is experienced by boys going into the cold bath: this could not occur from an obstruction of the perspirable matter, since there is not time for that to be returned to the bowels by the course of the circulation There is also a chronic aqueous diarrhœa, in which the at- mospheric moisture, drank up by the cutaneous and pulmonary lymphatics, 232 RETROGRADE ABSORBENTS. SECT. XXIX. 4. lymphatics, is poured into the intestines, by the retrograde motions of the lacteals. This disease is most similar to the aqueous diabetes, and is frequently exchanged for it: a distinct instance of this is recorded by Benningerus, Cent. v. Obs. 98, in which an aqueous diarrhœa succeeded an aqueous diabetes, and destroyed the patient. There is a curious example of this described by Sympson (De Re Medica) —" A young man (says he) was seized with a fever, upon which a diarrhœa came on, with great stupor, and he refused to drink any thing, though he was parched up with excessive heat: the better to supply him with moisture, I directed his feet to be immersed in cold water; immediately I observed a wonderful decrease of water in the vessel, and then an impetuous stream of a fluid, scarcely co- loured, was discharged by stool, like a cataract." 7. There is another kind of diarrhœa which has been called cæliaca; in this disease the chyle, drank up by the lacteals of the small intestines, is probably poured into the large intestines by the retrograde motions of their lacteals; as in the chylife- rous diabetes the chyle, is poured into the bladder by the retro- grade motions of the urinary branch of absorbents. The chyliferous diabetes, like this chyleferous diarrhœa, pro- duces sudden atrophy; since the nourishment, which ought to supply the hourly waste of the body, is expelled by the bladder, or rectum: whilst the aqueous diabetes, and the aqueous diarr- hœa produce excessive third; because the moisture, which is obtained from the atmosphere, is not conveyed to the thora- cic receptacle as it ought to be, but to the bladder, or lower intestines; whence the chyle, blood, and whole system of glands are robbed of their proportion of humidity. 8. There is a third species of diabetes, in which the urine is mucilaginous, and appears ropy in pouring it from one vessel into another; and will sometimes coagulate over the fire. This disease appears by intervals, and ceases again, and seems to be occasioned by a previous dropsy in some part of the bo- dy. When such a collection is reabsorbed, it is not always returned into the circulation; but the same irritation that stimu- lutes one lymphatic branch to reabsorb the deposited fluid, in- verts the urinary branch, and pours it into the bladder. Hence this mucilaginous diabetes is a cure, or the consequence of a cure, of a worse disease, rather than a disease itself. Dr. Cotunnius gave half an ounce of cream of tartar, eve- ry morning, to a patient who had the anasarca; and he voided a great quantity of urine; a part of which, put over the fire, coagulated, on the evaporation of half of it, so as to look like the white of an egg. De Ischiade Nervos. This 233 SECT. XXIX. 4. RETROGRADE ABSORBENTS. This kind of diabetes frequently precedes a dropsy; and has this remarkable circumstance attending it, that it generally hap- pens in the night; as during the recumbent state of the body, the fluid, that was accumulated in the cellular membrane, or in the lungs, is more readily absorbed, as it is less impeded by its gravity. I have seen more than one instance of this disease. Mr. D. a man in the decline of life, who had long accustom- ed himself to spirituous liquor, had swelled legs, and other symp- toms of approaching anasarca; about once in a week, or ten days, for several months, he was seized, on going to bed, with great general uneasiness, which his attendants resembled to an hysteric fit, and which terminated in a great discharge of vi- scid urine; his legs became less swelled, and he continued in better health for some days afterwards. I had not the oppor- tunity to try if this urine would coagulate over the fire, when part of it was evaporated, which I imagine would be the cri- terion of this kind of diabetes, as the mucilaginous fluid depo- sited in the cells and cysts of the body, which have no commu- nication with the external air, seems to acquire, by stagnation, this property of coagulation by heat, which the secreted mu- cus of the intestines and bladder do not appear to possess, as I have found by experiment; and if any one should suppose this coagulable urine was separated from the blood by the kidneys, he may recollect, that in the most inflammatory diseases, in which the blood is most replete, or mod ready to part with the coagulable lymph, none of this appears in the urine. 9. Different kinds of diabetes require different methods of cure. For the first kind, or chyliferous diabetes, after clear- ing the stomach and intestines, by ipecacuanha and rhubarb, to evacuate any acid material, which may too powerfully sti- mulate the mouths of the lacteals, repeated and large doses of tincture of cantharides have been much recommended. The specific stimulus of this medicine on the neck of the bladder, is likely to excite the numerous absorbent vessels, which are spread on that part, into stronger natural actions, and by that means prevent their retrograde ones; till, by persisting in the use of the medicine, their natural habits of motions might again be established. Another indication of cure requires such medi- cines as, by lining the intestines with mucilaginous substances, or with such as consist of smooth particles, or which chemi- cally destroy the acrimony of their contents, may prevent the too great action of the intestinal absorbents. For this purpose I have found the earth precipitated from a solution of alum, by Means of fixed alcali, given in the dose of half a dram every six hours, of great advantage, with a few grains of rhubarb, so as to procure a daily evacuation. The 234 RETROGRADE ABSORBENTS. SECT. XXIX. 4. The food should consist of materials that have the least sti- mulus, with calcareous water, as of Bristol and Matlock; that the mouths of the lacteals may be as little stimulated as is ne- cessary for their proper absorption; lest with their greater ex- ertions should be connected by sympathy the inverted motions of the urinary lymphatics. The same method may be employed, with equal advantage, in the aqueous diabetes, so great is the sympathy between the skin and the stomach. To which, however, some application to the skin might be usefully added; as rubbing the patient all over with oil, to prevent the too great action of the cutane- ous absorbents. I knew an experiment of this kind made upon one patient with apparent advantage. The mucilaginous diabetes will require the same treatment, which is most efficacious in the dropsy, and will be described below. I must add, that the diet and medicines above mention- ed, are strongly recommended by various authors, as by Mor- gan, Willis, Harris, and Etmuller; but more histories of the successful treatment of these diseases are wanting to fully afcer- tain the most efficacious methods of cure. In a letter from Mr. Charles Darwin, dated April 24, 1778, Edinburgh, is the subsequent passages:—" A man who long laboured under a diabetes died yesterday in the clinical ward. He had for some time drank four, and passed twelve pounds of fluid daily; each pound of urine contained an ounce of sugar. He took, without considerable relief, gum kino, sanguis dra- conis melted with alum, tincture of cantharides, isinglass, gum arabic, crabs eyes, spirit of hartshorn, and eat ten or fifteen oysters thrice a day. Dr. Home, having read my thefts, bled him, and found that neither the fresh blood nor the serum tasted sweet. His body was opened this morning—every viscus ap- peared in a sound and natural state, except that the left kidney had a very small pelvis, and that there was a considerable en- largement of most of the mesenteric lymphatic glands. I in- tend to insert this in my thesis, as it coincides with the ex- periment, where some asparagus was eaten at the beginning of intoxication, and its smell perceived in the urine, though not in the blood." The following case of chyliferous diabetes is extracted from some letters of Mr. Hughs, to whose unremitted care the in- firmary at Stafford for many years was much indebted, dated October 10, 1778. Richard Davis, aged 33, a whitesmith by trade, had drank hard by intervals; was much troubled with sweating of his hands, which incommoded him in his occupation, but which ceased 235 SECT. XXIX. 4. RETROGRADE ABSORBENTS. ceased on his frequently dipping them in lime. About seven months ago he began to make large quantities of water; his legs are œdematous, his belly tense, and he complains of a ris- ing in his throat, like the globus histericus: he eats twice as much as other people, drinks about fourteen pints of small beer a day, besides a pint of ale, some milk-porridge, and a bason of broth, and he makes about eighteen pints of water a day. He tried alum, dragon's blood, steel, blue vitriol, and can- tharides in large quantities, and duly repeated, under the care of Dr. Underhill, but without any effect; except that on the day after he omitted the cantharides, he made but twelve pints of water; but on the next day this good effect ceased again. November 21 .—He made eighteen pints of water, and he now, at Dr. Darwin's request, took a grain of opium every four hours; and five grains of aloes at night; and had a flannel shirt given him. 22.—Made sixteen pints. 23.—Thirteen pints: drinks less. 24.—Increased the opium to a grain and a quarter every four hours: he made twelve pints. 25.—Increased the opium to a grain and half: he now makes ten pints, and drinks eight pints in a day. The opium was gradually increased during the next fort- night, till he took three grains every four hours, but without any further diminution of his water. During the use of the opium he sweat much in the nights, so as to have large drops stand on his face and all over him. The quantity of opium was then gradually decreased, but not totally omitted, as he continued to take about a grain morning and evening. January 17.—He makes fourteen pints of water a day. Dr. Underhill now directed him two scruples of common rosin tri- turated with as much sugar, every six hours, and three grains of opium every night. 19.—Makes fifteen pints of Water: sweats at night. 21 .—Makes seventeen pints of water; has twitchings of his limbs in a morning, and pains of his legs: he now takes a dram of rosin for a dose, and continues the opium. 23.—Water more coloured, and reduced to sixteen pints, and he thinks has a brackish taste. 26.— Water reduced to fourteen pints. 28.—Water thirteen pints: he continues the opium, and takes four scruples of the rosin for a dose. February 1. —Water twelve pints. 4.— Water eleven pints; twitchings less: takes five scruples for a dose. I i 8.—Water 236 RETROGRADE ABSORBENTS. SECT. XXIX. 4. 8.—Water ten pints: has had many stools. 12.—Appetite less: purges very much. After this the rosin either purged him, or would not stay on his stomach; and he gradually relapsed nearly to his former condition, and in a few months sunk under the disease. October 3.—Mr. Hughes evaporated two quarts of the water, and obtained from it four ounces and half of a hard and brit- tle saccharine mass, like treacle which had been some time boiled. Four ounces of blood, which he took from his arm with design to examine it, had the common appearances, ex- cept that the serum resembled cheese-whey; and that on the evidence of four persons, two of whom did not know what it was they tasted, the serum had a saltish taste. From hence it appears, that the saccharine matter, with which the urine of these patients so much abounds, does not enter the blood vessels like the nitre and asparagus mentioned above; but that the process of digestion resembles the process of the germination of vegetables, or of making barley into malt; as the vast quantity of sugar found in the urine must be made from the food which he took (which was double that taken by others), and from the; fourteen pints of small beer which he drank. And, secondly, as the serum of the blood was not sweet, the chyle appears to have been conveyed to the bladder without entering the circulation of the blood, since so large a quantity of sugar, as was found in the urine, namely, twenty ounces a day, could not have previously existed in the blood without being perceptible to the taste. November 1.—Mr. Hughes dissolved two drams of nitre in a pint of a decoction of the roots of asparagus, and added to it two ounces of tincture of rhubarb: the patient took a fourth part of this mixture every five minutes, till he had taken the whole.—In about half an hour he made eighteen ounces of water, which was very manifestly tinged with the rhubarb; the smell of asparagus was doubtful. He then lost four ounces of blood, the serum of which was not so opake as that drawn before, but of a yellowish cast, as the serum of the blood usually appears. Paper, dipped three or four times in the tinged urine, and dried again, did not scintillate when it was set on fire; but when the flame was blown out, the fire ran along the paper for half an inch; which, when the same paper was unimpregnated, it would not do, nor when the same paper was dipped in urine made before he took the nitre, and dried in the same manner. Paper, clipped in the serum of the blood, and dried in the same manner as in the urine, did not scintillate when the flame was blown 237 SECT. XXIX. 5. RETROGRADE ABSORBENTS. blown out, but burnt exactly in the same manner as the same paper dipped in the serum of blood drawn from another person. This experiment, which is copied from a letter of Mr. Hughes, as well as the former, seems to evince the existence of another passage from the intestines to the bladder, in this disease, besides that of the sanguiferous system; and coincides with the curious experiment related in section the third, ex- cept that the smell of the asparagus was not here perceived, owing perhaps to the roots having been made use of instead of the heads. The rising in the throat of this patient, and the twitchings of his limbs, seem to indicate some similarity between the dia- betes and the hysteric disease, besides the great flow of pale urine, which is common to them both. Perhaps, if the mesenteric glands were nicely inspected in the dissections of these patients, and if the thoracic duct, and the larger branches of the lacteals, and if the lymphatics which arise from the bladder, were well examined by injection, or by the knife, the cause of diabetes might be more certainly understood. The opium alone, and the opium with the rosin, seem much to have served this patient, and might probably have effected a cure, if the disease had been slighter, or the medicine had been exhibited before it had been confirmed by habit during the seven months it had continued. The increase of the quan- tity of water on beginning the large doses of rosin, was proba- bly owing to his omitting the morning doses of opium. V. The Phenomena of Dropsies explained. 1. Some inebriates have their paroxysms of inebriety termi- nated by much pale urine, or profuse sweats, or vomiting, or stools; others have their paroxysms terminated by stupor, or deep, without the above evacuations. The former kind of these inebriates have been observed to be more liable to diabetes and dropsy; and the latter to gout, gra- vel and leprosy. Evoe! attend ye bacchanalians! start at this dark train of evils, and, amid your immodest jests, and ideot laughter, recollect, Quem Deus vult perdere, prius dementat. In those who are subject to diabetes and dropsy, the absor- bent vessels are naturally more irritable than the latter; and by being frequently disturbed, or inverted by violent stimulus, and by their too great sympathy with each other, they become at length either entirely paralytic, or are only susceptible of mo- tion 238 RETROGRADE ABSORBENTS. SECT. XXIX. 5. tion from the stimulus of very acrid materials; as every part of the body, after having been used to great irritations, be- comes less affected by smaller ones. Thus we cannot distin- guish objects in the night, for some time after we come out of a strong light, though the iris is presently dilated: and the air of a summer evening appears cold, after we have been ex- posed to the heat of the day. There are no cells in the body, where dropsy may not be produced, if the lymphatics cease to absorb that mucilaginous fluid, which is perpetually deposited in them, for the purpose of lubricating their surfaces. If the lymphatic branch, which opens into the cellular membrane, either does its office imperfectly, or not at all; these cells become replete with a mucilaginous fluid, which, af- ter it has stagnated some time in the cells, will coagulate over the fire; and is erroneously called water. Wherever the seat of this disease is, (unless in the lungs or other pendent viscera) the mucilaginous liquid above mentioned will subside to the most depending parts of the body, as the feet and legs, when those are lower than the head and trunk; for all these cells have communications with each other. When the cellular absorbents are become insensible to their usual irritations, it most frequently happens, but not always, that the cutaneous branch of absorbents, which is strictly as- sociated with them, differs the like inability. And then, as no water is absorbed from the atmosphere, the urine is not only less diluted at the time of its secretion, and consequently in less quantity and higher coloured; but great thirst is at the same time induced, for as no water is absorbed from the atmos- phere to dilute the chyle and blood, the lacteals and other ab- sorbent vessels, which have not lost their powers, are excited into more constant or more violent action, to supply this defi- ciency; whence the urine becomes still less in quantity, and of a deeper colour, and turbid, like the yolk of an egg, owing to a greater absorption of its thinner parts. From this stronger action of those absorbents, which still retain their irritabi- lity, the fat is also absorbed, and the whole body becomes ema- ciated. This increased exertion of some branches of the lym- phatics, while others are totally or partially paralytic, is re- sembled by what constantly occurs in the hemiplagia; when the patient has lost the use of his limbs on one side, he is in- cessantly moving those of the other: for the moving power, not having access to the paralytic limbs, becomes redundant in those which are not diseased. The paucity of urine and third cannot be explained from a greater 239 SECT. XXIX. 5. RETROGRADE ABSORBENTS. greater quantity of mucilaginous fluid being deposited in the cellular membrane: for though these symptoms have continu- ed many weeks, or even months, this collection frequently does not amount to more than very few pints. Hence also the difficulty of promoting copious sweats in anasarca is account- ed for, as well as the great thirst, paucity of urine, and loss of fat; since, when the cutaneous branch of absorbents is pa- ralytic, or nearly so, there is already too small a quantity of aqueous fluid in the blood: nor can these torpid. cutaneous lymphatics be readily excited into retrograde motions. Hence, likewise, we understand why, in the ascites and some other dropsies, there is often no thirst, and no paucity of urine; in these cases the cutaneous absorbents continue to do their office. Some have believed, that dropsies were occasioned by the in- ability of the kidneys, from having only observed the paucity of urine; and have thence laboured much to obtain diuretic medicines; but it is daily observable, that those who die of a total inability to make water, do not become dropsical in con- sequence of it: Fernelius mentions one, who laboured under a perfect suppression of urine during twenty days before his death, and yet had no symptoms of dropsy. Pathol. l. vi. c. 8. From the same idea many physicians have restrained their pa- tients from drinking, though their thirst has been very urgent; and some cases have been published, where this cruel regimen has been thought advantageous; but others of nicer observa- tion are of opinion, that it has always aggravated the distresses of the patient; and though it has abated his swellings, yet, by inducing a fever, it has hastened his dissolution. See Transactions of the College, London, vol. ii. p. 235. Cases of Dropsy, by Dr. G. Baker. The cure of anasarca, so far as respects the evacuation of the accumulated fluid, coincides with the idea of the retrograde action of the lymphatic system. It is well known that vomits, and other drugs, which induce sickness or nausea, at the same time that they evacuate the stomach, produce a great absorp- tion of the lymph accumulated in the cellular membrane. In the operation of a vomit, not only the motions of the stomach and duodenum become inverted, but also those of the lympha- tics and lacteals, which belong to them; whence a great quan- tity of chyle and lymph is perpetually poured into the stomach and intestines, during the operation, and evacuated by the mouth. Now, at the same time, other branches of the lym- phatic system, viz. those which open on the cellular membrane, are brought into more energetic action, by the sympathy above mentioned, and an increase of their absorption is produced. Hence, 240 RETROGRADE ABSORBENTS. SECT. XXIX. 5. Hence, repeated vomits, and cupreous salts, and small doses of squill or foxglove, are so efficacious in this disease. And as drastic purges act also by inverting the motions of the lacteals, and thence the other branches of lymphatics are induced into more powerful natural action, by sympathy, and drink up the fluids from all the cells of the body; and by their anastomoses, pour them into the lacteal branches; which, by their inverted actions, return them into the intestines; and they are thus eva- cuated from the body. These purges also are used with success in discharging the accumulated fluid in anasarca. II. The following cases are related with design to ascertain the particular kinds of dropsy in which the digitalis purpurea, or common foxglove, is preferable to squill, or other evacu- ants, and were first published in 1780, in a pamphlet entitled Experiments on mucilaginous and purulent Matter, &c. Cadell. London. Other cases of dropsy, treated with digitalis, were afterwards published by Dr. Darwin, in the Medical Transac- tions, vol. iii. in which there is a mistake in respect to the dose of the powder of foxglove, which should have been from five grains to one, instead of from five grains to ten. Anasarca of the Lungs. 1. A lady, between forty and fifty years of age, had been indisposed some time, was then seized with cough and fever, and afterwards expectorated much digested mucus. This ex- pectoration suddenly ceased, and a considerable difficulty of breathing supervened, with a pulse very irregular both in velocity and strength; she was much distrssed at first lying down, and at first rising; but after a minute or two, bore either of those attitudes with ease. She had no pain or numbness in her arms; she had no hectic fever, nor any cold shiverings, and the urine. was in due quantity, and of the natural colour. The difficulty of breathing was twice considerably relieved by small doses of ipecacuanha, which operated upwards and down- wards, but recurred in a few days: she was then directed a de- coction of foxglove, (digitalis purpurea) prepared by boiling four ounces of the fresh leaves from two pints of water to one pint; to which was added two ounces of vinous spirit: she took three large spoonfuls of this mixture every two hours, till she had taken it four times; a continued sickness supervened, with frequent vomiting, and a copious flow of urine: these evacuations continued, at intervals, for two or three days, and relieved the difficulty of breathing. She had some relapses af- terwards, which were again relieved by the repetition of the decoction of foxglove. 2. A 241 SECT. XXIX. 5. RETROGRADE ABSORBENTS. 2. A gentleman, about sixty years of age, who had been addicted to an immoderate use of fermented liquors, and had been very corpulent, gradually lost his strength and flesh, had great difficulty of breathing, with legs somewhat swelled, and a very irregular pulse. He was very much distressed at first lying down, and at first rising from his bed; yet in a minute or two was easy in both those attitudes. He made draw-coloured urine in due quantity, and had no pain or numbness of his arms. He took a large spoonful of the decoction of foxglove, as above, every hour, for ten or twelve successive hours; had in- cessant sickness for about two days, and passed a large quantity of urine; upon which his breath became quite easy, and the swelling of his legs subsided; but as his whole constitution was already sinking from the previous intemperance of his life, he did not survive more than three or four months. Hydrops Pericardii. 3. A gentleman of temperate life and sedulous application to business, between thirty and forty years of age, had long been subject, at intervals, to an irregular pulse: a few months ago he became weak, with difficulty of breathing, and dry cough. In this situation a physician of eminence directed him to abstain from all animal food and fermented liquor, during which regimen all his complaints increased; he now became emaci- ated, and totally lost his appetite; his pulse very irregular, both in velocity and strength; with great difficulty of breathing, and some swelling of his legs; yet he could lie down horizon- tally in his bed, though he got little sleep, and passed a due quantity of urine, and of the natural colour: no fullness or hardness could be perceived about the region of the liver; and he had no pain or numbness in his arm. One night he had a most profuse sweat all over his body and limbs, which quite deluged his bed, and for a day or two some- what relieved his difficulty of breathing, and his pulse became less irregular: this copious sweat recurred three or four times at the intervals of five or six days, and repeatedly alleviated his symptoms. He was directed one large spoonful of the above decoction of foxglove every hour, till it procured some considerable eva- cuation: after he had taken it eleven successive hours, he had a few liquid stools, attended with a great flow of urine, which last had a dark tinge, as if mixed with a few drops of blood: he continued sick at intervals for two days, but his breath be- came quite easy, and his pulse quite regular; the swelling of his legs disappeared, and his appetite and sleep returned. He 242 RETROGRADE ABSORBENTS. SECT. XXIX. 5 He then took three grains of white vitriol twice a day, with some bitter medicines, and a grain of opium, with five grains of rhubarb, every night; was advised to eat flesh meat, and spice, as his stomach would bear it, with small beer, and a few glasses of wine; and had issues made in his thighs; and has suffered no ralapse. 4. A lady, about fifty years of age, had for some weeks great difficulty of breathing, with very irregular pulse, and considerable general debility: she could lie down in bed, and the urine was in due quantity and of the natural colour, and she had no pain or numbness of her arms. She took one large spoonful of the above decoction of fox- glove every hour, for ten or twelve successive hours; was sick, and made a quantity of pale urine for about two days, and was quite relieved, both of the difficulty of breathing, and the irre- gularity of her pulse. She then took a grain of opium, and five grains of rhubarb, every night, for many weeks, with some slight chalybeate and bitter medicines, and has differed no relapse. Hydrops Thorasis. 5. A tradesman, about fifty years of age, became weak and short of breath, especially on increase of motion, with pain in one arm, about the insertion of the biceps muscle. He observed he sometimes in the night made an unusual quantity of pale water. He took calomel, alum, and Peruvian bark, and all his symptoms increased: his legs began to swell consi- derably; his breath became more difficult, and he could not lie down in bed; but all this time he made a due quantity of straw-coloured water. The decoction of foxglove was given as in the preceding cases, which operated chiefly by purging, and seemed to re- lieve his breath for a day or two, but also seemed to contribute to weaken him. He became, after some weeks, universally dropsical, and died comatous. 6. A young lady of delicate constitution, with light eyes and hair, and who had perhaps lived too abstemiously, both in respect to the quantity and quality of what she eat and drank, was seized with great difficulty of breathing, so as to threaten immediate death. Her extremities were quite cold, and her breath felt cold to the back of ones hand. She had no sweat, nor could lie down for a single moment; and had previously, and at present, complained of great weakness and pain, and numbness of both her arms; had no swelling of her legs, no third, water in due quantity and colour. Her sister, about a year before, was afflicted with similar symptoms, was repeat- edly blooded, and died universally dropsical. A grain 243 SECT. XXIX. 5. RETROGRADE ABSORBENTS. A grain of opium was given immediately, and repeated eve- ry six hours with evident and amazing advantage; afterwards a blister, with chalybeates, bitters, and essential oils, were exhibit- ed, but nothing had such eminent effect in relieving the difficulty of breathing and coldness of her extremities as opium; by the use of which, in a few weeks, she perfectly regained her health and has suffered no relapse. Ascites. 7. A young lady, of delicate constitution, having been expos- ed to great fear, cold, and fatigue, by the overturn of a chaise in the night, began with pain and tumour in the right hypochon- drium: in a few months a fluctuation was felt throughout the whole abdomen, more distinctly perceptible indeed about the region of the stomach; since the integuments of the lower part of the abdomen generally become thickened in this disease by a degree of anasarca. Her legs were not swelled, no thirst, wa- ter in due quantity and colour.—She took the foxglove so as to induce sickness and stools, but without abating the swelling, and was obliged, at length, to submit to the operation of tapping. 8. A man about sixty-seven, who had long been accustomed to spirituous potation, had some time laboured under ascites; his legs somewhat swelled; his breath easy in all attitudes; no appetite; great third; urine in exceedingly small quantity, very deep coloured, and turbid; pulse equal. He took the foxglove in such quantity as vomited him, and induced sickness for two days; but procured no flow of urine, or diminution of his swel- ling; but was thought to leave him considerably weaker. 9. A corpulent man, accustomed to large potation of fer- mented liquors, had vehement cough, difficult breathing, ana- sarca of his legs, thighs and hands, and considerable tumour, with evident fluctuation of his abdomen; his pulse was equal; his urine in small quantity, of deep colour, and turbid. These swellings had been twice considerably abated by drastic cathar- tics. He took three ounces of a decoction of foxglove (made by boiling one ounce of the fresh leaves in a pint of water) every three hours, for two whose days; it then began to vomit and purge him violently, and promoted a great flow of urine; he was by these evacuations completely emptied in twelve hours. After two or three months all these symptoms returned, and were again relieved by the use of the foxglove; and thus, in the space of about three years, he was about ten times evacuated, and continued all that time his usual potations: excepting at first, the medicine operated only by urine, and did not appear considerably to weaken him. The last time he took it, it had K k no 244 RETROGRADE ABSORBENTS. SECT. XXIX. 5. no effect; and a few weeks afterwards he vomited a great quantity of blood, and expired. QUERIES. 1. As the first six of these patients had a due discharge of urine, and of the natural colour, was not the seat of the disease confined to some part of the thorax, and the swelling of the legs rather a symptom of the obstructed circulation of the blood, than of a paralysis of the cellular lymphatics of those parts? 2. When the original disease is a general anasarca, do not the cutaneous lymphatics always become paralytic at the same time with the cellular ones, by their greater sympathy with each other; and hence the paucity of urine, and the great thirst distinguish this kind of dropsy? 3. In the anasarca of the lungs, when the disease is not very great, though the patients have considerable difficulty of breath- ing at their first lying down, yet after a minute or two their breath becomes easy again; and the same occurs at their first rising. Is not this owing to the time necessary for the fluid in the cells of the lungs to change its place, so as the least to incommode respiration in the new attitude? 4. In the dropsy of the pericardium, does not the patient bear the horizontal or perpendicular attitude with equal case? Does this circumstance distinguish the dropsy of the pericardi- um from that of the lungs and of the thorax? 5. Do the universal sweats distinguish the dropsy of the pe- ricardium, or of the thorax? and those, which cover the upper parts of the body only, the anasarca of the lungs? 6. When, in the dropsy of the thorax, the patient endeavours to lie down, does not the extravasated fluid compress the upper parts of the bronchia, and totally preclude the access of air to every part of the lungs, whilst in the perpendicular attitude the inferior parts of the lungs only are compressed? Does not something similar to this occur in the anasarca of the lungs when the disease is very great, and thus prevent those patients also from lying down? 7. As a principal branch of the fourth cervical nerve of the left side, after having joined a branch of the third and of the se- cond cervical nerves, descending between the subclavian vein and artery, is received in a groove formed for it in the pericar- dium, and is obliged to make a considerable turn outwards to go over the prominent part of it, where the point of the head is lodged, in its course to the diaphragm; and as the other phre- nic nerve of the right side has a straight course to the diaphragm; and as many other considerable branches of this fourth pair of cervical 245 SECT. XXIX. 6. RETROGRADE ABSORBENTS. cervical nerves are spread on the arms; does not a pain in the left arm distinguish a disease of the pericardium, as in the agina pectoris, or in the dropsy of the pericardium? and does not a pain or weakness in both arms distinguish the dropsy of the tho- rax? 8. Do not the dropsies of the thorax and pericardium fre- quently exist together, and thus add to the uncertainty and fa- tality of the disease? 9. Might not the foxglove he serviceable in hydrocephalus internus, in hydrocele, and in white swellings of the joints? VI. Of Cold Sweats. There have been histories given of chronical immoderate sweatings, which bear some analogy to the diabetes. Dr. Wil- lis mentions a lady, then living, whose sweats were, for many years, so profuse, that all her bed-clothes were not only mois- tened, but deluged with them every night; and that many oun- ces, and sometimes pints, of this sweat, were received in vessels properly placed, as it trickled down her body. He adds, that she had great third, had taken many medicines, and submitted to various rules of life, and changes of climate, but dill continued to have these immoderate sweats. Pharmac. ration, de sudore anglico. Dr. Willis has also observed, that the sudor angllcanus which appeared in England in 1483, and continued till 1551, was, in some respects, similar to the diabetes; and, as Dr. Caius, who saw this disease, mentions the viscidity, as well as the quantity of these sweats, and adds, that the extremities were often cold when the internal parts were burnt up with heat and thirst, with great and speedy emaciation and debility, there is great reason to believe, that the fluids were absorbed from the cells of the body by the cellular and cystic branches of the lymphatics, and poured on the skin by the retrograde motions of the cutaneous ones. Sydenham has recorded, in the stationary fever of the year 1655, the viscid sweats flowing from the head, which were probably from the same source as those in the sweating plague above mentioned. It is very common, in dropsies of the chest or lungs, to have the difficulty of breathing relieved by copious sweats, flowing from the head and neck. Mr. P------, about fifty years of age, had, for many weeks, been afflicted with anasarca of his legs and thighs, attended with difficulty of breathing; and had re- peatedly been relieved by squill, other bitters, and chalybeates. One night the difficulty of breathing became so great, that it was thought he must have expired; but so copious a sweat came out of 246 RETROGRADE ABSORBENTS. SECT. XXIX. 6. of his head and neck, that in a few hours some pints, by esti- mation, were wiped off from those parts, and his breath was for a time relieved. This dyspnœa and these sweats recurred at intervals, and after some weeks he ceased to exist. The skin of his head and neck felt cold to the hand, and appeared pale at the time these sweats flowed so abundantly; which is a proof, that they were produced by an inverted motion of the absorbents of those parts: for sweats, which are the conse- quence of an increased action of the sanguiferous system, are always attended with a warmth of the skin, greater than is natural, and a more florid colour; as the sweats from exer- cise, or those that succeed the cold fits of agues. Can any one explain how these partial sweats should relieve the difficul- ty of breathing in anasarca, brat by supposing that the pulmo- nary branch of absorbents drank up the fluid in the cavity of the thorax, or in the cells of the lungs, and threw it on the skin, by the retrograde motions of the cutaneous branch? for, if we could suppose that the increased action of the cutane- ous glands or capillaries poured upon the skin this fluid, pre- viously absorbed from the lungs; why is not the whole surface of the body covered with sweat? why is not the skin warm? Add to this, that the sweats above mentioned were clammy or glutinous, which the condensed perspirable matter is not; whence it would seem to have been a different fluid from that of common perspiration. Dr. Dobson, of Liverpool, has given a very ingenious ex- planation of the acid sweats, which he observed in a diabetic patient—he thinks part of the chyle is secreted by the skin, and afterwards undergoes an acetous fermentation.—Can the chyle get thither, but by an inverted motion of the cutaneous lymphatics, in the same manner as it is carried to the bladder, by the inverted motions of the urinary lymphatics? Medic. Observat. and Enq. London, vol. 5. Are not the cold sweats in some fainting fits, and in dying people, owing to an inverted motion of the cutaneous lympha- tics? for in these there can be no increased arterial or glandu- lar action. Is the difficulty of breathing, arising from anasarca of the lungs, relieved by sweats from the head and neck, whilst that difficulty of breathing, which arises from a dropsy of the tho- rax, or pericardium, is never attended with these sweats of the head? and thence can these diseases be distinguished from each other? Do the periodic returns of nocturnal asthma rise from a temporary dropsy of the lungs, collected during their more torpid state in sound sleep, and then re-absorbed by the vehe- ment 247 SECT. XXIX. 7. RETROGRADE ABSORBENTS. ment efforts of the disordered organs of respiration, and carri- ed off by the copious sweats about the head and neck? More extensive and accurate dissections of the lymphatic sys- tem are wanting to enable us to unravel these knots of science. VII. Translations of Matter, of Chyle, of Milk, of Urine. Operation of purging Drugs applied externally. 1. The translations of matter from one part of the body to another, can only receive an explanation from the doctrine of the occasional retrograde motions of some branches of the lymphatic system: for how can matter, absorbed and mixed with the whole mass of blood, be so hastily collected again in any one part? and is it not an immutable law, in animal bo- dies, that each gland can secrete no other but its own proper fluid? which is, in part, fabricated, in the very gland by an animal process, which it there undergoes: of these purulent translations innumerable and very remarkable instances are recorded. 2. The chyle, which is seen among the materials thrown up by violent vomiting, or in purging stools, can only come thither by its having been poured into the bowels by the invert- ed motions of the lacteals: for our aliment is not converted into chyle in the stomach or intestines by a chemical process, but is made in the very mouths of the lacteals; or in the me- senteric glands; in the same manner as other secreted fluids are made by an animal process in their adapted glands. Here a curious phenomenon in the exhibition of mercury is worth explaining:—If a moderate dose of calomel, as six or ten grains, be swallowed, and within one or two days a cathar- tic is given, a salivation is prevented: but after three or four days, a salivation having come on, repeated purges every day, for a week or two, are required to eliminate the mercury from the constitution. For this acrid metallic preparation, being absorbed by the mouths of the lacteals, continues, for a time, arrested by the mesenteric glands, (as the variolous or vene- real poisons swell the subaxillar or inguinal glands:) which, during the operation of a cathartic, is returned into the intes- tines by the inverted action of the lacteals, and thus carried out of the system. Hence we understand the use of vomits or purges, to those who have swallowed either contagious or poisonous materials, even though exhibited a day, or even two days, after such acci- dents; namely, that by the retrograde motions of the lacteals and lymphatics, the material still arrested in the mesenteric, or other glands, may be eliminated from the body. 3. Many 248 RETROGRADE ABSORBENTS. SECT. XXIX. 7. 3. Many instances of milk and chyle found in ulcers, are given by Haller, El. Physiol. T. vii. p. 12,23. which admit of no other explanation than by supposing that the chyle, imbibed by one branch of the absorbent system, was carried to the ulcer by the inverted motions of another branch of the same system. 4. Mrs. P. on the second day after delivery, was seized with a violent purging, in which, though opiates, mucilages, the bark, and testacea were profusely used, continued many days, till at length she recovered. During the time of this purging, no milk could be drawn from her breads; but the stools ap- peared like the curd of milk broken into small pieces. In this case, was not the milk taken up from the follicles of the pecto- ral glands, and thrown on the intestines, by a retrogression of the intestinal absorbents? for how can we for a moment sus- pect that the mucous glands of the intestines could separate pure milk from the blood? Doctor Smelly has observed, that loose stools, mixed with milk, which is curdled in the intestines, frequently relieves the turgescency of the breads of those who studiously repel their milk. Cases in Midwifery, 43, No. 2. 1. 5. J. F. Meckel observed in a patient whose urine was in small quantity and high coloured, that a copious sweat under the arm-pits, of a perfectly urinous smell, stained the linen; which ceased again when the usual quantity of urine was dis- charged by the urethra. Here we must believe, from analogy, that the urine was first secreted in the kidneys, then re-absor- bed by the increased action of the urinary lymphatics, and last- ly carried to the axillæ by the retrograde motions of the lym- phatic branches of those parts. As in the jaundice it is neces- sary that the bile should first be secreted by the liver, and re- absorbed into the circulation, to produce the yellowness of the skin; as was formerly demonstrated by the late Dr. Monro, (Edin. Medical Essays) and if in this patient the urine had been re-absorbed into the mass of blood, as the bile in the jaun- dice, why was it not detected in other parts of the body as well as in the arm-pits? 6. Cathartic and vermifuge medicines, applied externally to the abdomen, seem to be taken up by the cutaneous branch of lymphatics, and poured on the intestines by the retrograde mo- tions of the lacteals, without having passed the circulation. For, when the drastic purges are taken by the mouth, they excite the lacteals of the intestines into retrograde motions, as appears from the chyle, which is found coagulated among the fæces, as was shewn above, (sect. 2 and 4.) And as the cutaneous lymphatics are joined with the lacteals of the intestines, by fre- quent anastomoses, it would be more extraordinary, when a strong 249 SECT. XXIX. 8. RETROGRADE ABSORBENTS. strong purging drug, absorbed by the skin, is carried to the anastomosing branches of the lacteals unchanged, if it should not excite them into retrograde action as efficaciously as if it was taken by the mouth, and mixed with the food of the stomach. VIII. Circumstances by which the Fluids that are effused by the retrograde Motions of the absorbent Vessels are distinguished. 1. We frequently observe an unusual quantity of mucus or other fluids in some diseases, although the action of the glands, by which those fluids are separated from the blood, is not unusu- ally increased, but when the power of absorption alone is di- minished. Thus the catarrhal humour from the nostrils of some who ride in frosty weather, and the tears which run down the cheeks of those who have an obstruction of the puncta lacry- malia, and the ichor of those phagedenic ulcers, which are not attended with inflammation, are all instances of this cir- cumstance. These fluids, however, are easily distinguished from others, by their abounding in ammoniacal or muriatic salts; whence they inflame the circumjacent skin: thus in the catarrh the upper lip becomes red, and swelled from the acrimony of the mucus, and patients complain of the saltness of its taste. The eyes and cheeks are red with the corrosive tears, and the ichor of some herpetic eruptions erodes far and wide the contiguous parts, and is pungently salt to the taste, as some patients have in- formed me. Whilst, on the contrary, those fluids which are effused by the retrograde action of the lymphatics, are for the most part mild and innocent; as water, chyle, and the natural mucus: or they take their properties from the materials previously absorbed, as in the coloured or vinous urine, or that scented with asparagus, described before. 2. Whenever the secretion of any fluid is increased, there is, at the same time, an increased heat in the part; for the se- creted fluid, as the bile, did not previously exist in the mass of blood, but a new combination is produced in the gland Now, as solutions are attended with cold, so combinations are attended with heat; and it is probable the sum of the heat given out by all the secreted fluids of animal bodies, may be the cause of their general heat above that of the atmosphere. Hence the fluids derived from increased secretions are readi- ly distinguished from those originating from the retrograde mo- tions of the lymphatics: thus an increase of heat, either in the diseased parts, or diffused over the whole body, is perceptible, when 250 RETROGRADE ABSORBENTS. SECT. XXIX. 9. when copious bilious stools are consequent to an inflamed liver, or a copious mucous salivation from the inflammatory angina. 3. When any secreted fluid is produced in an unusual quan- tity, and at the same time the power of absorption is increased in equal proportion, not only the heat of the gland becomes more intense, but the secreted fluid becomes thicker and milder, its thinner and saline parts being re-absorbed: and these are dis- tinguishable both by their greater consistence, and by their heat from the fluids, which are effused by the retrograde motions of the lymphatics; as is observable towards the termination of gonorrhœa, catarrh, chincough, and in those ulcers which are said to abound with laudable pus. 4. When chyle is observed in stools, or among the materi- als ejected by vomit, we may be confident it must have been brought thither by the retrograde motions of the lacteals; for chyle does not previously exist amid the contents of the intes- tines, but is made in the very mouths of the lacteals, as was before explained. 5. When chyle, milk, or other extraneous fluids are found in the urinary bladder, or in any other excretory receptacle of a gland; no one can for a moment believe, that these have been collected from the mass of blood by a morbid secretion, as it contradicts all analogy. ----- Aurea duræ Mala ferant quereus? Narcisco floreat alnus? Pinguia corticious sudent electra myricæ? VIRG. IX. Retrograde Motions of Vegetable Juices. There are besides some motions of the sap in vegetables, which bear analogy to our present subject; and as the vege- table tribes are by many philosophers held to be inferior ani- mals, it may be a matter of curiosity at least to observe, that their absorbent vessels seem evidently, at times, to be capable of a retrograde motion. Mr. Perault cut off a forked branch of a tree, with the leaves on; and inverting one of the forks into a vessel of water, observed, that the leaves on the other branch continued green much longer than those of a similar branch, cut off from the same tree; which shews, that the water from the vessel was carried up one part of the forked branch, by the retrograde motion of its vessels, and supplied nutriment some time to the other part of the branch, which was out of the water. And the celebrated Dr. Hales found, by numerous very accurate experiments, that the sap of trees role upwards during the warmer hours of the day, and in part descended again during the cooler ones. Vegetable Statics. It 251 SECT. XXIX. 10. RETROGRADE ABSORBENTS. It is well known that the branches of willows, and of many other trees, will either take root in the earth, or engraft on other trees, so as to have their natural direction inverted, and yet flourish with vigour. Dr. Hope has also made this pleasing experiment, after the manner of Hales—he has placed a forked branch, cut from one tree, erect between two others; then cutting off a part of the bark from one fork, applied it to a similar branch of one of the trees in its vicinity, and the same of the other fork; so that a tree is seen to grow suspended in the air, between two other trees, which supply their softer friend with due nourishment. Miranturque novas frondes, et non sua poma. All these experiments clearly evince, that the juices of ve- getables can occasionally pass either upwards or downwards in their absorbent system of vessels. X. Objections answered. The following experiment, at first view, would seem to in validate this opinion of the retrograde motions of the lympha- tic vessels in some diseases. About a gallon of milk having been given to an hungry swine, he was differed to live about an hour, and was then killed by a stroke or two on his head, with an axe. On open- ing his belly, the lacteals were seen well filled with chyle; on irritating many of the branches of them with a knife, they did not appear to empty themselves hastily; but they did however carry forwards their contents in a little time. I then passed a ligature round several branches of lacteals, and irritated them much with a knife beneath the ligature, but could not make them regurgitate their contained fluid into the bowels. I am not indeed certain that the nerve was not at the same time included in the ligature, and thus the lymphatic rendered unirritable or lifeless; but this however is certain, that it is not any quantity of any stimulus, which induces the vessels of animal bodies to revert their motions; but a certain quantity of a certain stimulus, as appears from wounds in the stomach, which do not produce vomiting; and wounds of the intestines, which do not produce the cholera morbus. At Nottingham, a few years ago, two shoemakers quarrelled, and one of them, with a knife which they use in their occupa- tion, stabbed his companion about the region of the stomach. On opening the abdomen of the wounded man after his death, the food and medicines he had taken were in part found in the L l cavity 252 RETROGRADE ABSORBENTS. SECT. XXIX. 11. cavity of the belly, on the outside of the bowels; and there was a wound about half an inch long at the bottom of the sto- mach; which I suppose was distended with liquor and food at the time of the accident, and thence was more liable to be in- jured at its bottom: but during the whole time he lived, which was about ten days, he had no efforts to vomit, nor ever even complained of being sick at the stomach! Other cases, similar to this, are mentioned in the Philosophical Transactions. Thus, if you vellicate the throat with a feather, nausea is produced; if you wound it with a pen-knife, pain is induced, but not sickness. So if the soles of the feet of children or their arm-pits are tickled, convulsive laughter is excited, which ceases the moment the hand is applied, so as to rub them more forcibly. The experiment, therefore, above related upon the lacteals of a dead pig, which were included in a strict ligature, proves nothing; as it is not the quantity, but the kind of stimulus, which excites the lymphatic vessels into retrograde motion. XI. The Causes which induce the Retrograde Motions of animal Vessels, and the Medicines by which the natural Motions are restored. 1. Such is the construction of animal bodies, that all their parts, which are subjected to less stimuli than nature designed, perform their functions with less accuracy: thus, when too watery or too acescent food is taken into the stomach, indiges- tion, and flatulency, and heartburn succeed. 2. Another law of irritation, connate with our existence, is, that all those parts of the body which have previously been exposed to too great a quantity of such stimuli as strongly af- fect them, become for some time afterwards disobedient to the natural quantity of their adapted stimuli.—Thus the eye is in- capable of seeing objects in an obscure room, though the iris is quite dilated, after having been exposed to the meridian sun. 3. There is a third law of irritation, that all the parts of our bodies, which have been lately subjected to less stimulus than they have been accustomed to when they are exposed to their usual quantity of stimulus, are excited into more energe- tic motions: thus, when we come from a dusky cavern into the glare of day-light, our eyes are dazzled; and after emerging from the cold bath, the skin becomes warm and red. There is a fourth law of irritation, that all the parts of our bodies, which are subjected to still stronger stimuli for a length of time, become torpid, and refuse to obey even these stronger stimuli; and thence do their offices very imperfectly.—Thus, if 253 SECT. XXIX. 11. RETROGRADE ABSORBENTS. if any one looks earnestly for some minutes on an area, an inch diameter, of red silk, placed on a sheet of white paper, the image of the silk will gradually become pale, and at length totally vanish. 5. Nor is it the nerves of sense alone, as the optic and audi- tory nerves, that thus become torpid when the stimulus is with drawn, or their irritability decreased; but the motive muscles, when they are deprived of their natural stimuli, or of their irri- tability, become torpid and paralytic; as is seen in the tremu- lous hand of a drunkard in the morning, and in the awkward step of age. The hollow muscles also, of which the various vessels of the body are constructed, when they are deprived of their natural stimuli, or of their due degree of irritability, not only become tremulous as the arterial pulsations of dying people, but also frequently invert their motions, as in vomiting, in hysteric suf- focations, and diabetes above described. I must beg your patient attention, for a few moments, whilst I endeavour to explain, how the retrograde actions of our hollow muscles are the consequence of their debility; as the tremulous actions of the solid muscles are the consequence of their debility. When, through fatigue, a muscle can act no longer, the antagonist muscles, either by their inanimate elas- ticity, or by their animal action, draw the limb into a contrary direction: in the solid muscles, as those of locomotion, their actions are associated in tribes, which have been accustomed to synchronous action only; hence, when they are fatigued, only a single contrary effort takes place; which is either tre- mulous, when the fatigued muscles are again immediately brought into action; or it is a pendiculation, or stretching, where they are not immediately again brought into action. Now, the motions of the hollow muscles, as they in general propel a fluid along their cavities, are associated in trains, which have been accustomed to successive actions; hence, when one ring of such a muscle is fatigued from its too great debility, and is brought into retrograde action, the next ring from its asso- ciation falls successively into retrograde action; and so on throughout the whole canal. See Sect. XXV. 6. 6. But as the retrograde motions of the stomach, œsopha- gus, and sauces in vomiting, are, as it were, apparent to the eye, we shall consider this operation more minutely, that the similar operations in the more recondite parts of our system may be easier understood. From certain nauseous ideas of the mind, from an ungrate- ful taste in the mouth, or from fœtid smells, vomiting is some- times 254 RETROGRADE ABSORBENTS. SECT. XXIX. 11 times instantly excited; or even from a stroke on the head; or from the vibratory motions of a ship; all which originate from association, or sympathy. See Sect. XX. on Vertigo. But when the stomach is subjected to a less stimulus than is natural, according to the first law of irritation mentioned above, its motions become disturbed, as in hunger; first, pain is pro- duced, then sickness, and, at length, vain efforts to vomit, as many authors inform us. But when a great quantity of wine, or of opium, is swallowed, the retrograde motions of the stomach do not occur till after several minutes, or even hours; for when the power of so strong a stimulus ceases, according to the second law of ir- ritation, mentioned above, the peristaltic motions become tre- mulous, and at length retrograde; as is well known to the drunkard, who, on the next morning, has sickness and vomitings. When a still greater quantity of wine, or of opium, or when nauseous vegetables, or strong bitters, or metallic salts, are taken into the stomach, they quickly induce vomiting; though all these, in less doses, excite the stomach into more energetic action, and strengthen the digestion; as the flowers of cha- momile, and the vitriol of zine: for, according to the fourth law of irritation, the stomach will not long be obedient to a stimulus so much greater than is natural; but its action be- comes first tremulous, and then retrograde. 7. When the motions of any vessels become retrograde, less heat of the body is produced; for in paroxysms of vomiting, of hysteric affections, of diabetes, of asthma, the extremities of the body are cold: hence we may conclude, that these symptoms arise from the debility of the parts in action; for an increase of muscular action is always attended with increase of heat. 8. But as animal debility is owing to defect of stimulus, or to defect of irritability, as shewn above, the method of cure is easily deduced: when the vascular muscles are not excited into their due action by the natural stimuli, we should exhibit those medicines which possess a still greater degree of stimu- lus; amongst these are the fœtids, the volatiles, aromatics, bitters, metallic salts, opiates, wine, which indeed should be given in small doses, and frequently repeated. To these should be added constant, but moderate exercise, cheerfulness of mind, and change of country to a warmer climate; and perhaps oc- casionally the external stimulus of blisters. It is also frequently useful to diminish the quantity of natural stimulus for a short time, by which afterwards the irritability of the system becomes increased, according to the third law of irritation above mentioned. Hence the use of baths somewhat colder than animal heat, and of equitation in the open air. The 255 SECT. XXX. 1. PARALYSIS OF THE LIVER. The catalogue of diseases, owing to the retrograde motions of lymphatics, is here omitted, as it will appear in the second volume of this work. The following is the conclusion to this thesis of Mr. CHARLES DARWIN. Thus have I endeavoured, in a concise manner, to explain the numerous diseases which deduce their origin from the invert- ed motions of the hollow muscles of our bodies: and it is pro- bable, that Stint Vitus's dance, and the stammering of speech, originate from a similar inverted order of the associated mo- tions of some of the solid muscles, which, as it is foreign to my present purpose, I shall not here discuss. I beg, illustrious professors, and ingenious fellow-students, that you will recollect how difficult a talk I have attempted, to evince the retrograde motions of the lymphatic vessels, when the vessels themselves, for so many ages, escaped the eyes and glasses of philosophers: and if you are not yet convinced of the truth of this theory, hold, I entreat you, your minds in suspence, till ANATOMY draws her sword with happier omens, cuts asunder the knots which entangle PHYSIOLOGY; and, like an augur, inspecting the immolated victim, announces to mankind the wisdom of HEAVEN. SECT. XXX. PARALYSIS OF THE LIVER AND KIDNEYS. I. 1. Bile-ducts less irritable after having been stimulated much. 2. Jaundice from paralysis of the bile-ducts cured by electric shocks. 3. From bile-stones. Experiments on bile-stones. Oil-vomit. 4. Palsy of the liver, two cases. 5. Schirrosity of the liver. 6. Large livers of geese. II. Paralyfis of the kidneys. III. Story of Prometheus. I. 1. FROM the ingurgitation of spirituous liquors into the stomach and duodenum, the termination of the common bile duct in that bowel becomes stimulated into unnatural action, and a greater quantity of bile is produced from all the secretory vessels of the liver, by the association of their motions with those of their excretory ducts; as has been explained in Sec- tion XXIV. and XXV. but as all parts of the body that have been affected with stronger stimuli for any length of time, be- come less susceptible of motion, from their natural weaker sti- muli, it follows, that the motions of the secretory vessels, and in consequence the secretion of bile, is less than is natural dur- ing the intervals of sobriety. 2. If this ingurgitation of spiri- tuous 256 PARALYSIS OF THE LIVER. SECT. XXX. 1. tuous liquors has been daily continued in considerable quanti- ty, and is then suddenly intermitted, a languor or paralysis of the common bile-duct is induced; the bile is prevented from being poured into the intestines; and as the bilious absorbents are stimulated into stronger action by its accumulation, and by the acrimony or viscidity which it acquires by delay, it is ab- sorbed, and carried to the receptacle of the chyle; or otherwise the secretory vessels of the liver, by the above-mentioned stimulus, invert their motions, and regurgitate their contents into the blood, as sometimes happens to the tears in the lachry- mal sack, see Sect. XXIV. 2. 7. and one kind of jaundice is brought on. There is reason to believe, that the bile is most frequently returned into the circulation by the inverted motions of these hepatic glands, for the bile does not seem liable to be absorbed by the lymphatics, for it soaks through the gall-ducts, and is frequently found in the cellular membrane. This kind is jaun- dice, is not generally attended with pain, neither at the extre- mity of bile-duct, where it enters the duodenum, nor on the region of the gall-bladder. Mr. S. a gentleman between 40 and 50 years of age, had had the jaundice about six weeks, without pain, sickness, or fever; and had taken emetics, cathartics, mercurials, bitters, chalybeates, essential oil, and æther, without apparent advan- tage. On a supposition that the obstruction of the bile might be owing to the paralysis, or torpid action of the common bile-duct, and the stimulants taken into the stomach seeming to have no effect, I directed half a score smart electric shocks from a coated bottle, which held about a quart, to be passed through the liver, and along the course of the common gall- duct, as near as could be guessed, and on that very day the stools became yellow; he continued the electric shocks a few days more, and his skin gradually became clear. 3. The bilious vomiting and purging that affects some peo- ple by intervals of a few weeks, is a less degree of this disease: the bile-duct is less irritable than natural; and hence the bile becomes accumulated in the gall-bladder and hepatic-ducts, till by its quantity, acrimony, or viscidity, a greater degree of irrita- tion is produced, and it is suddenly evacuated; or, lastly, from the absorption of the more liquid parts of the bile, the remainder becomes inspissated, and chrystallizes into masses too large to pass, and forms another kind of jaundice, where the bile-duct is not quite paralytic, or has regained its irritability. This disease is attended with much pain, which at first is felt at the pit of the stomach, exactly in the center of the body, where 257 SECT. XXX. 1. PARALYSIS OF THE LIVER. where the bile-duct enters the duodenum: afterwards, when the size of the bile-stones increase, it is also felt on the right side, where the gall-bladder is situated. The former pain at the pit of the stomach recurs by intervals, as the bile-done is pushed against the neck of the duct; like the paroxysms of the stone in the urinary bladder, the other is a more dull and constant pain. Where these bile-stones are too large to pass, and the bile- ducts possess their sensibility, this becomes a very painful and hopeless disease. I made the following experiments with a view to their chemical solution. Some fragments of the same bile-done were put into the weak spirit of marine salt, which is sold in the shops, and into a solution of mild alcali, and into a solution of caustic alcali, and into oil of turpentine, without their being dissolved. All these mixtures were, after some time, put into a heat of boiling water, and then the oil of turpentine dissolved its fragments of bile- stone; but no alteration was produced upon those in the other liquids, except some change of their colour. Some fragments of the same bile-stone were put into vitriolic æther, and were quickly dissolved without additional heat. Might not æther, mixed with yolk of egg, or with honey, be given advantageously in bilious concretions? I have, in two instances, seen from thirty to fifty bile-stones come away by stool, about the size of large pease, after having given six grains of calomel in the evening, and four ounces of oil of almonds or olives on the succeeding morning. I have also given half a pint of good olive or almond oil, as an emetic, dur- ing the painful fit, and repeated it in half an hour, if the first did not operate, with frequent good effect. 4. Another disease of the liver, which I have several times observed, consists in the inability, or paralysis of the secretory vessels. This disease has generally the same cause as the pre- ceding one,—the too frequent potation of spirituous liquors, or the too sudden omission of them after the habit is confined; and is greater or less, in proportion as the whole or a part of the liver is affected, and as the inability or paralysis is more or less complete. This palsy of the liver is known from these symptoms: The patients have generally passed the meridian of life, have drank fermented liquors daily, but perhaps not been opprobrious drunkards; they lose their appetite, then their flesh and strength diminish in consequence; there appears no bile in their stools, nor in their urine; nor is any hardness or swelling perceptible on the region of the liver. But what is peculiar to this disease, and distinguishes it from all others at the first glance of the eye, is the 258 PARALYSIS OF THE LIVER. SECT. XXX. 1. the bombycinous colour of the skin, which, like that of full- grown silk-worms, has a degree or transparency, with a yellow tint, not greater than is natural to the serum of the blood. Mr. C. and Mr. B. both very strong men, between fifty and sixty years of age, who had drank ale at their meals instead of small beer, but were not reputed hard-drinkers, suddenly became weak, lost their appetite, flesh and strength, with all the symp- toms above enumerated, and died in about two months from the beginning of their malady. Mr. C. became anasarcous a few days before his death; and Mr. B. had frequent and great hæmorrhages from an issue, and some parts of his mouth, a few days before his death. In both these cases calomel, bitters and chalybeates were repeatedly used without effect. One of the patients described above, Mr. C. was by trade a plumber; both of them could digest no food, and died appa- rently for want of blood. Might not the transfusion of blood be used in these cases with advantage? 5. When the paralysis of the hepatic glands is less complete, or less universal, a schirrosity of some part of the liver is induced; for the secretory vessels, retaining some of their living power, take up a fluid from the circulation, without being sufficiently irritable to carry it forwards to their excretory ducts, hence the body, or receptacle of each gland, becomes inflated; and this distention increases, till, by its very great stimulus, inflammation is produced, or till those parts of the viscus become totally pa- ralytic. This disease is distinguishable from the foregoing by the palpable hardness or largeness of the liver; and as the heap- tic glands are not totally paralytic, or the whole liver not af- fected, some bile continues to be made. The inflammations of this viscus, consequent to the schirrosity of it, belong to the dis- eases of the sensitive motions, and will be treated of hereafter. 6. The ancients are said to have possessed an art of increasing the livers of geese to a size greater than the remainder of the goose. Martial. I. 13. epig. 58. This is said to have been done by fat and figs, Horace, 1. 2. fat. 8.—Juvenal sets these large livers before an epicure as a great rarity. Sat. 5. l. 114; and Persius, sat. 6. I. 71. Pliny says these large goose-livers were soaked in mulled milk, that is, I suppose, milk mixed with honey and wine; and adds, "that it is uncertain whether Scipio Me- tellus, of consular dignity, or M. Sestius, a Roman knight, was the great discoverer of this excellent dish." A modern travel- ler, I believe Mr. Brydone, asserts that the art of enlarging the livers of geese dill exists in Sicily; and it is to be lament- ed that he did not import it into his native country, as some method of affecting the human liver might, perhaps, have been collected 259 SECT. XXX. 2, 3. PARALYSIS OF THE LIVER. collected from it; besides, the honour he might have acquired in improving our giblet pies. Our wiser caupones, I am told, know how to fatten their fowls, as well as their geese, for the London markets, by mixing gin instead of figs and fat with their food; by which they are said to become sleepy, and to fatten apace, and pro- bably acquire enlarged livers, as the swine are asserted to do, which are fed on the sediments of barrels in the distilleries; and which so frequently obtains in those who ingurgitate much ale, or wine, or drams. II. The irritative diseases of the kidneys, pancreas, spleen, and other glands, are analogous to those of the liver above described, differing only in the consequences attending their in ability to action. For instance, when the secretory vessels of the kidneys become disobedient to the stimulus of the passing current of blood, no urine is separated or produced by them their excretory mouths become filled with concreted mucus, or calculus matter, and in eight or ten days stupor, and death su- pervenes in consequence of the retention of the feculent part of the blood. This disease, in a slighter degree, or when only a part of the kidney is affected, is succeeded by partial inflammation of the kidney, in consequence of previous torpor. In that case, greater actions of the secretory vessels occur, and the nucleus of gravel is formed by the inflamed mucous membranes of the tubuli uriniferi, as farther explained in its place. This torpor, or paralysis of the secretory vessels of the kid- neys, like that of the liver owes its origin to their being pre- viously habituated to too great stimulus; which, in this coun- try, is generally owing to the alcohol contained in ale or wine; and hence must be registered amongst the diseases owing to in- ebriety; though it may be caused by whatever occasionally in flames the kidney; as too violent riding on horseback, or the cold from a damp bed, or by sleeping on the cold ground or per- haps by drinking in general too little aqueous fluids. III. I shall conclude this section on the diseases of the liver induced by spirituous liquors, with the well known story of Prometheus, which seems indeed to have been invented by phy- sicians in those ancient times, when all things were clothed in hieroglyphic, or in sable. Prometheus was painted as dealing fire from heaven, which might well represent the inflammable spirit produced by fermentation, which may be said to animate or enliven the man of clay: whence the conquests of Bacchus, as well as the temporary mirth and noise of his devotees. But the after punishment of those who deal this accursed fire, is a M m vulture 260 OF TEMPERAMENTS. SECT. XXXL vulture gnawing the liver; and well allegorises the poor inebri- ate lingering for years under painful hepatic diseases. When the expediency of laying a further tax on the distillation of spirituous liquors from grain was canvassed before the House of Commons some years ago, it was said of the distillers, with great truth, " They take the bread from the people, and con- vert it into poison!" Yet is this manufactory of disease per- mitted to continue, as appears by its paying into the treasury above 900,000l. near a million of money annually. And thus, under the names of rum, brandy, gin, whisky, usquebaugh, wine, cyder, beer, and porter, alcohol is become the bane of the Christian world, as opium of the Mahometan. Evoe! parce, liber? Parce, gravi metuende thirso! HOR. SECT. XXXI. OF TEMPERAMENTS. I. The temperament of decreased irritability known by weak pulse, large pupils of the eyes, cold extremities. Are gene- rally supposed to be too irritable. Bear pain better than labour. Natives of North America contrasted wish those upon the coast of Africa. Narrow and broad-shouldered people. Irritable constitutions bear labour better than pain. II. Temperament of increased sensibility. Liable to intoxication, to inflammation, hœmoptoe, gutta serena, enthusiasm, delirium, reverie. These constitutions are in- dolent to voluntary exertions, and dull to irritations. The natives of South- America and brute animals of this tem- perament. III. Of increased voluntarity: these are sub- ject to locked jaw, convulsions, epilepsy, mania. Are very active; bear cold, hunger, fatigue. Are suited to great exertions. This temperament distinguishes mankind from other animals. IV. Of increased association. These have great memories, are liable to quartan agues, and stronger sympathies of parts with each other. V. Change of tem- peraments into one another. ANCIENT writers have spoken much of temperaments, but without sufficient precision. By temperament of the system should be meant a permanent predisposition to certain classes of diseases: without this definition a temporary predisposition to every distinct malady might be termed a temperament. There are four kinds of constitution, which permanently deviate from good 261 SECT. XXXI. 1. OF TEMPERAMENTS. good health, and are perhaps sufficiently marked to be distin- guished from each other, and constitute the temperaments or predispositions to the irritative, sensitive, voluntary, and asso- ciate classes of diseases. I. The Temperament of decreased Irritability. The diseases, which are caused by irritation, must frequently originate from the defect of it; for those which are immediately owing to the excess of it, as the hot fits of fever, are generally occasioned by an accumulation of sensorial power, in conse- quence of a previous defect of irritation, as in the preceding cold fits of fever. Whereas the diseases which are caused by sensation and volition, must frequently originate from the ex- cess of those sensorial powers, as will be explained below. The temperament of decreased irritability appears from the following circumstances, which shew, that the muscular fibres or organs of sense are liable to become torpid or quiescent, from less defect of stimulation than is productive of torpor or quie- scence in other constitutions. 1. The first is the weak pulse, which, in some constitu- tions, is, at the same time, quick. 2. The next most marked criterion of this temperament is the largeness of the aperture of the iris, or pupil of the eye, which has been reckoned by some a beautiful feature in the female countenance, as an in- dication of delicacy; but to an experienced observer, it is an indication of debility, and is therefore a defect, not an excel- lence. The third most marked circumstance in this constitu- tion is, that the extremities, as the hands and feet, or nose and ears, are liable to become cold and pale in situations in respect to warmth, where those of greater strength are not affected. Those of this temperament are subject to hysteric affections, nervous fevers, hydrocephalus, scrophula, and consumption, and to all other diseases of debility. Those who possess this kind of constitution are popularly supposed to be more irritable than is natural, but are in reality less so. This mistake has arisen from their generally having a greater quickness of pulse, as explained in Sect. XII. 1. 4. XII. 3. 3. ; but this frequency of pulse is not necessary to the temperament, like the debility of it. Persons of this temperament are frequently found amongst the softer sex, and amongst narrow-shouldered men, who are said to bear labour worse, and pain better than others. This last circumstance is supposed to have prevented the natives of North- America from having been made slaves of by the Europeans. They are a narrow-shouldered race of people, and 262 OF TEMPERAMENTS. SECT. XXXI. 2. and will rather expire under the lash, than be made to la- bour. Some nations of Asia have small hands, as may be seen by the handles of their scymetars; which, with their nar- row shoulders, shew, that they have not been accustomed to so great labour with their hands and arms, as the European na- tions in agriculture, and those on the coasts of Africa in swim- ming and rowing. Dr. Maningham, a popular accoucheur, in the beginning of this century, observes in his Aporisms, that broad-shouldered men procreate broad-shouldered children. Now, as labour strengthens the muscles employed, and in- creases their bulk, it would seem that a few generations of la- bour or of indolence, may, in this respect, change the form and temperament of the body. On the contrary, those who are happily possessed of a great degree of irritability, bear labour better than pain, and are strong, active, and ingenious. But there is not properly a temperament of increased irritability tending to disease, because an increased quantity of irritative motions generally induces an increase of pleasure or pain, as in intoxication, or inflammation; and then the new motions are the immediate consequences of increased sensation, not of increased irritation; which have hence been so perpetually confounded with each other. II. Temperament of Sensibility. There is not properly a temperament pr predisposition, to disease, from decreased sensibility, since irritability and not sen- sibility is immediately necessary to bodily health. Hence it is the excess of sensation alone, as it is the defect of irritation, that most frequently produces disease. This temperament of increase- ed sensibility is known from the increased activity of all those motions of the organs of sense and muscles, which are exert- ed in consequence of pleasure or pain, as in the beginning of drunkenness, and in inflammatory fever. Hence those of this constitution are liable to inflammatory diseases, as hepatitis; and to that kind of consumption which is hereditary, and com- mences with slight repeated hœmoptoe. They have high-co- loured lips, frequently dark hair and dark eyes, with large pu- pils, and are in that case subject to gutta serena. They are liable to enthusiasm, delirium, and reverie. In this last cir- cumstance they are liable to start at the clapping of a door; because the more intent any one is on the passing current of his ideas, the greater surprise he experiences on their being disse- vered by some external violence, as explained in Sect. XIX, on Reverie. As 263 SECT. XXXI. 3. OF TEMPERAMENTS. As in these constitutions more than the natural quantities of sensitive motions are produced by the increased quantity of sen- sation existing in the habit, it follows, that the irritative mo- tions will be performed in some degree with less energy, ow- ing to the great expenditure of sensorial power on the sensitive ones. Hence those of this temperament do not attend to slight stimulations, as explained in Sect. XIX. But when a stimulus is so great as to excite sensation, it produces greater sensitive actions of the system than in others; such as delirium or inflame- mation. Hence they are liable to be absent in company; sit or lie long in one posture; and in winter have the skin of their legs burnt into various colours by the fire. Hence also they are fearful of pain; covet music and sleep; and delight in poetry and romance. As the motions in consequence of sensation are more than natural, it also happens, from the greater expenditure of senso- rial power on them that the voluntary motions are less easily exerted. Hence the subjects of this temperament are indolent in respect to all voluntary exertions, whether of mind or body. A race of people of this description seems to have been found by the Spaniards in the islands of America, where they first landed, ten of whom are said not to have consumed more food than one Spaniard, nor to have been capable of more than one tenth of the exertion of a Spaniard. Robertson's History. In a state similar to this the greatest part of the animal world pass their lives, between deep or inactive reverie, except when they are excited by the call of hunger. III. The Temperament of increased Voluntarity. Those of this constitution differ from both the last mentioned in this, that the pain, which gradually subsides in the first, and is productive of inflammation or delirium in the second, is in this succeeded by the exertion of the muscles or ideas, which are most frequently connected with volition; and they are thence subject to locked jaw, convulsions, epilepsy, and mania, as ex- plained in Sect. XXXIV. Those of this temperament attend to the slightest irritations or sensations, and immediately exert themselves to obtain or avoid the objects of them; they can at the same time bear cold and hunger better than others, of which Charles the Twelfth of Sweden was an instance. They are suited, and generally prompted to all great exertions of genius or labour, as their desires are more extensive and more vehement, and their powers of attention and of labour greater. It is this facility of voluntary exertion which distinguishes men from brutes, and which has made them lords of the creation. IV. The 264 OF TEMPERAMENTS. SECT. XXXI. 4,5. IV. The Temperament of increased Association. This constitution consists in the too great facility, with which the fibrous motions acquire habits of association, and by which these associations become proportionably stronger than in those of the other temperaments. Those of this tem- perament are slow in voluntary exertions, or in those depend- ent on sensation, or on irritation. Hence great memories have been said to be attended with less sense and less imagination, from Aristotle down to the present time; for by the word me- mory these writers only understood the unmeaning repetition of words or numbers in the order they were received, without any voluntary efforts of the mind. In this temperament those associations of motions, which are commonly termed sympathies, of with greater certainty and energy, as those between disturbed vision and the inversion of the motion of the stomach, as in sea-sickness, and the pains in the shoulder from hepatic inflammation. Add to this, that the catenated circles of actions are of greater-extent than in the other constitutions. Thus, if a strong vomit or cathartic be exhibited in this temperament, a smaller quantity will produce as great an effect, if it be given some weeks afterwards; whereas in other temperaments this is only to be expected, if it be exhibited in a few days after the first dose. Hence quartan agues are formed in those, of this temperament, as explained in Section XXXII. on diseases from irritation; and other intermittents are liable to recur from slight causes many weeks after they have been cured by the bark. V. The first of these temperaments differs from the standard of health from defect, and the others from excess of sensorial power; but it sometimes happens that the same individual, from the changes introduced into his habit by the different sea- sons of the year, modes or periods of life, or by accidental dis- eases, passes from one of these temperaments to another. Thus a long use of too much fermented liquor produces the tempera- ment of increased sensibility; great indolence and solitude, that of decreased irritability; and want of the necessaries of life, that of increased voluntarity. SECT. 265 SECT. XXXII. 1. DISEASES OF IRRITATION. SECT. XXXII. DISEASES OF IRRITATION. I. Irritative fevers with strong pulse. With weak pulse. Symptoms of fever. Their source. II. 1. Quick pulse is owing to decreased irritability. 2. Not in sleep or in apo- plexy. 3. From inanition. Owing to deficiency of sensorial power. III. 1. Causes of fever. From defect of heat. Heat from secretions. Pain of cold in the loins and fore- head. 2. Great expense of sensorial power in the Vital motions. Immersion in cold water. Succeeding glow of heat. Difficult respiration in cold bathing explained. Why the old bath invigorates. Bracing and relaxation are mechanical terms. 3. Uses of cold air in fevers. 4. Ague-fits from cold air. Whence their periodical returns. IV. Defect of distention a cause of fever. Deficiency of blood. Transfusion of blood. V. 1. Defect of momentum of the blood from mechanic stimuli. 2. Air injected into the blood-vessels. 3. Exercise increases the momentum of the blood. 4. Sometimes bleeding increases the momentum of it. VI. Influence of the sun and moon on diseases. The chemical stimulus of the blood. Menstruation obeys the lunations. Queries. VII. Quiescence of large glands a cause of fever. Swelling of the precordia. VIII. Other causes of quiescence, as hunger, bad air, fear, anxiety. IX. 1. Symptoms of the cold fit. 2. Of the hot fit. 3. Se- cond cold fit why. 4. Inflammation introduced, or deli- rium, or stupor. X. Recapitulation. Fever not an effort of nature to relieve herself. Doctrine of Spasm. 1. WHEN the contractile sides of the heart and arteries perform a greater number of pulsations in a given time, and move through a greater area at each pulsation, whether these motions are occasioned by the stimulus of the acrimony, or quantity of the blood, or by their association with other irrita- tive motions, or by the increased irritability of the arterial sys- tem; that is, by an increased quantity of sensorial power, one kind of fever is produced; which may be called Synocha irri- tativa, or Febris irritativa pulsu forti, or irritative fever with strong pulse. When the contractile sides of the heart and arteries perform a greater number of pulsations in a given time, but move through a much less area at each pulsation, whether these mo- tions are occasioned by defect of their natural stimuli, or by the defect 266 DISEASES OF IRRITATION. SECT. XXXII. 2. defect of other irritative motions with which they are associ- ated, or from the inirritability of the arterial system; that is, from a decreased quantity of sensorial power, another kind of fever arises; which may be termed, Typhus irritativus, or Fe- bris irritativa pursu debili, or irritative fever with weak pulse. The former of these fevers is the synocha or nosologists; and the latter, the typhus mitior, or nervous fever. In the former, there appears to be an increase of sensorial power; in the lat- ter, a deficiency of it; which is shewn to be the immediate cause of strength and weakness, as defined in Sect. XII. 1. 3. It should be added, that a temporary quantity of strength or debility may be induced by the defect or excess of stimulus above what is natural; and that in the same fever debility al- ways exists during the cold fit, though strength does not al- ways exist during the hot fit. These fevers are always connected with, and generally in- duced by, the disordered irritative motions of the organs of sense, or of the intestinal canal, or of the glandular system, or of the absorbent system; and hence are always complicated with some or many of these disordered motions, which are termed the symptoms of the fever, and which compose the great variety in these diseases. The irritative fevers, both with strong and with weak pulse, as well as the sensitive fevers with strong and with weak pulse, which are to be described in the next section, are liable to pe- riodical remissions, and then they take the name of intermittent fevers, and are distinguished by the periodical times of their access. II. For the better illustration of the phenomena of irritative fevers we must refer the reader to the circumstances of irrita- tion, explained in Sect. XII. and shall commence this intricate subject by speaking of the quick pulse, and proceed by consi- dering many of the causes which either separately or in com- bination most frequently produce the cold fits of fevers. 1. If the arteries are dilated but to half their usual diameters, though they contract twice as frequently in a given time, they will circulate only half their usual quantity of blood; for as they are cylinders, the blood which they contain must be as the squares of their diameters. Hence, when the pulse becomes quicker and smaller in the same proportion, the heart and arte- ries act with less eneregy than in their natural date. See Sect. XII. 1. 4. That this quick small pulse is owing to want of irritability, appears, first, because it attends other symptoms of want of ir- ritability; and, secondly, because, on the application of a sti- mulus 267 SECT. XXXII. 2. DISEASES OF IRRITATION. mulus greater than usual, it becomes dower and larger. Thus, in cold fits of agues, in hysteric palpitations of the heart, and when the body is much exhausted by hæmorrhages, or by fa- tigue, as well as in nervous fevers, the pulse becomes quick and small; and, secondly, in all those cases, if an increase of stimulus be added, by giving a little wine or opium, the quick small pulse becomes dower and larger, as any one may easily experience on himself, by counting his pulse after drinking one or two glasses of wine, when he is faint from hunger or fatigue. Now, nothing can so strongly evince that this quick small pulse is owing to defect of irritability, than that an additional stimulus, above what is natural, makes it become dower and larger immediately: for what is meant by a defect of irritabi- lity, but that the arteries and heart are not excited into their usual exertions by their usual quantity of stimulus? But if you increase the quantity of stimulus, and they immediately act with their usual energy, this proves their previous want of their natural degree of irritability. Thus the trembling hands of drunkards in a morning become steady, and acquire strength to perform their usual offices, by the accustomed stimulus of a glass or two of brandy; 2. In sleep and in apoplexy the pulse becomes slower, which is not owing to defect of irritability, for it is at the same time larger; arid thence the quantity of the circulation is ra- ther increased than diminished. In these cases the organs of sense are closed, and the voluntary power is suspended; while the motions dependent on internal irritations, as those of diges- tion and secretion, are carried on with more than their usual vigour; which has led superficial observers to confound these cases with those arising from want of irritability. Thus if you lift up the eye-lid of an apoplectic patient, who is not actually dying, the iris will, as usual, contract itself, as this motion is associated with the stimulus of light; but it is not so in the last stages of nervous fevers, where the pupil of the eye continues expanded in the broad day-light: in the former case there is a want of voluntary power; in the latter, a want of irritability. Hence also those constitutions which are deficient in quantity of irritability, and which possess too great sensibility, as during the pain of hunger, of hysteric spasms, or nervous head-achs, are generally supposed to have too much irritability; and opium, which in its due dose is a most powerful stimulant, is erroneously called a sedative; because, by increasing the irritative motions, it decreases the pains arising from defect of them. Why the pulse should become quicker both from an increase of irritation, as in the synocha irritativa, or irritative fever with N n strong 268 DISEASES OF IRRITATION. SECT. XXXIT. 3 strong pulse; and from the decrease of it, as in the typhus irri- tativus, or irritative fever with weak pulse; seems paradoxical. The former circumstance needs no illustration; since, if the sti- mulus of the blood, or the irritability of the sanguiferous system, be increased, and the strength of the patient not diminished, it is plain that the motions must be performed quicker and stronger. In the latter circumstance, the weakness of the muscular power of the heart is soon over-balanced by the elasticity of the coats of the arteries, which they possess besides a muscu- lar power of contraction; and hence the arteries are distended to less than their usual diameters. The heart being thus stopped when it is but half emptied, begins sooner to dilate again; and the arteries being dilated to less than their usual diameters, begin so much sooner to contract themselves; in somuch, that in the last stages of fevers, with weakness, the fre- quency of pulsation of the heart and arteries becomes doubled; which, however, is never the case in fevers with strength, in which they seldom exceed 118 or 120 pulsations in a minute. It must be added, that in these cases, while the pulse is very small and very quick, the heart often feels large, and labour- ing to one's hand; which coincides with the above explana- tion, shewing that it does not completely empty itself. 3. In cases however of debility from paucity of Wood, as in animals which are bleeding to death in the slaughter-house, the quick pulsations of the heart and arteries may be owing to their not being distended to move than half their usual diastole; and in consequence they must contract sooner, or more frequently, in a given time. As weak people are liable to a deficient quan- tity of blood, this cause may occasionally contribute to quicken the pulse in fevers with debility, which may be known by applying one's hand upon the heart as above; but the prin- cipal cause I suppose to consist in the diminution of sensorial power. When a muscle contains, or is supplied with but lit- tle sensorial power, its contraction soon ceases, and in conse- quence may soon recur, as is seen in the trembling hands of people weakened by age or by drunkenness. See Sect. XII. 1. 4. XII. 3. 4. It may, nevertheless, frequently happen, that both the defi- ciency of stimulus, as where the quantity of Wood is lessened, (as described in No. 4. of this section,) and the deficiency of sensorial power, as in those of the temperament of inirritability, described in Sect. XXXI. occur at the same time; which will. thus add to the quickness of the pulse, and to the danger of the disease. III. 1. A certain degree of heat is necessary to muscular motion, 269 SECT. XXXII. 3. DISEASES OF IRRITATION. motion, and is, in consequence, essential to life. This is ob- served in those animals and infects which pass the cold season in a torpid state, and which revive on being warmed by the fire. This necessary stimulus of heat has two sources; one from the fluid atmosphere of heat, in which all things are im- mersed, and the other from the internal combinations of the par- ticles, which form the various fluids, which are produced in the extensive systems of the gland. When either the external heat, which surrounds us, or the internal production of it be- comes lessened to a certain degree, the pain at cold is perceived. This pain of cold is experienced most sensibly by our teeth, when ice is held in the mouth, or by our whole system after having been previously accustomed to much warmth. It is probable, that this pain does not arise from the mechanical or chemical effects of a deficiency of heat; but that, like the or- gans of sense by which we perceive hunger and thirst, this sense of heat differs pain, when the stimulus of its object is wanting to excite the irritative motions of the organ; that is, when the sensorial power becomes too much accumulated in the quie- scent fibres. See Section XII. 5. 3. For as the peristaltic mo- tions of the stomach are lessened, when the pain of hunger is great, so the action of the cutaneous capillaries are lessened dur- ing the pain of cold; as appears by the paleness of the skin, as explained in Sect. XIV. 6. on the production of ideas. The pain in the small of the back and forehead in the cold fits of the ague, in nervous hemicrania, and in hysteric parox- ysms, when all the irritative motions are much impaired, seems to arise from this cause; the vessels of these membranes or mus- cles become torpid by their irritative associations with other parts of the body, and thence produce less of their accustomed secretions, and in consequence less heat is evolved, and they experience the pain of cold; which coldness may often be felt by the hand applied upon the affected part. 2. The importance of a greater or less deduction of heat from the system will be more easy to comprehend, if we first consider the great expense of sensorial power used in carrying on the vital motions; that is, which circulates, absorbs, se- cretes, ærates, and elaborates the whole mass of fluids with unceasing assiduity. The sensorial power, or spirit of anima- tion, used in giving perpetual and strong motion to the heart, which overcomes the elasticity and vis inertiæ of the whole ar- terial system; next the expense of sensorial power in moving with great force and velocity the innumerable trunks and rami- fications of the arterial system; the expense of sensorial power in circulating the whole mass of blood through the long and intricate 270 DISEASES OF IRRITATION. SECT. XXXII. 3. intricate intortions of the very fine vessels, which compose the glands and capillaries; then the expense of sensorial power in the exertions of the absorbent extremities of all the lacteals, and of all the lymphatics, which open their mouths on the exter- nal surface of the skin, and on the internal surfaces of every cell or interstice of the body; then the expense of sensorial power in the venous absorption, by which the Wood is received from the capillary vessels, or glands, where the arterial power ceafes and is drank up, and returned to the heart; next the expense of sensorial power used by the muscles of respiration in their office of perpetually expanding the bronchia, or air-ves- sels, of the lungs; and lastly, in the unceasing peristaltic motions of the stomach and whole system of intestines, and in all the secretions of bile, gastric juice, mucus, perspirable matter, and the various excretions from the system. If we consider the ceaseless expense of sensorial power thus perpetually employed, it will appear to be much greater in a day than all the volun- tary exertions of our muscles and organs of sense consume in a week; and all this without any sensible fatigue! Now, if but a part of these vital motions are impeded, or totally stopped for but a short time, we gain an idea, that there must be a great ac- cumulation of sensorial power; as its production in these or- gans, which are subject to perpetual activity, is continued during their quiescence, and is in consequence accumulated. While, on the contrary, where those vital organs act too forcibly by increase of stimulus without a proportionally in creased production of sensorial power in the brain, it is evident, that a great deficiency of action, that is, torpor, must soon fol- low, as in fevers; whereas the locomotive muscles, which act only by intervals, are neither liable to so great accumulation of sensorial power during their times of inactivity, nor to so great an exhaustion of it during their times of action. Thus, on going into a very cold bath, suppose at 33 degrees of heat on Fahrenheit's scale, the action of the subcutaneous capillaries or glands, and of the mouths of the cutaneous absor- bents, is diminished, or ceases for a time. Hence less or no blood passes these capillaries, and paleness succeeds. but soon after emerging from the bath, a more florid colour and a greater degree of heat is generated on the skin than was possessed before immersion; for the capillary glands, after this quiescent state, occasioned by the want of stimulus, become more irrita- ble than usual to their natural stimuli, owing to the accumula- tion of sensorial power, and hence a greater quantity of blood is transmitted through them, and a greater secretion of perspira- ble matter; and, in consequence, a greater degree of heat suc- ceeds. 271 SECT. XXXII. 3. DISEASES OF IRRITATION. ceeds. During the continuance in cold water the breath is cold, and the act of respiration quick and laborious; which have ge- nerally been ascribed to the obstruction of the circulating fluid by a spasm of the cutaneous vessels, and by a consequent accu- mulation of blood in the lungs, occasioned by the pressure as well as by the coldness of the water. This is not a satisfactory account of this curious phenomenon, since, at this time, the whole circulation is less, as appears from the smallness of the pulse, and coldness of the breath; which shew that less blood pas- ses through the lungs in a given time. The same laborious breath- ing immediately occurs when the paleness of the skin is produced by fear, where no external cold or pressure is applied. The minute vessels of the bronchia, through which the blood passes from the arterial to the venal system, and which corres- pond with the cutaneous capillaries, have frequently been expos- ed to cold air, and become quiescent along with those of the skin; and hence their motions are so associated together, that when one is affected either with quiescence or exertion, the other sympathizes with it, according to the laws of irritative association. See Sect. XXVII. 1. on Hæmorrhages. Besides the quiescence of the minute vessels of the lungs, there are many other systems of vessels which become torpid from their irritative associations with those of the skin, as the absorbents of the bladder and intestines; whence an evacuation of pale urine occurs, when the naked skin is exposed only to the coldness of the atmosphere; and sprinkling the naked body with cold water is known to remove even pertinacious constipation of the bowels. From the quiescence of such extensive systems of vessels as the glands and capillaries of the skin, and the minute vessels of the lungs, with their various absorbent series of vessels, a great accumulation of sensorial powers is occasioned; part of which is again expended in the increased exertion of all these vessels, with an universal glow of heat in consequence of this exertion, and the remainder of it adds vigour to both the vital and voluntary exertions of the whole day. If the activity of the subcutaneous vessels, and of those with which their actions are associated, was too great before cold immersion, as in the hot days of summer, and by that means the sensorial power was previously diminished, we see the cause why the cold bath gives such present strength; namely, by stop- ping the unnecessary activity of the subcutaneous vessels, and thus preventing the too great exhaustion of sensorial power; which, in metaphorical language, has been called bracing the system; which is, however, a mechanical term, only applica- ble to drums, or musical strings: as, on the contrary, the word relaxation, 272 DISEASES OF IRRITATION. SECT. XXXII. 3. relaxation, when applied to living animal bodies, can only mean too small a quantity of stimulus, or too small a quantity of sensorial power; as explained in Sect. XII. 1. 3. This experiment of cold bathing presents us with a simple fever-fit; for the pulse is weak, small and quick during the cold immersion, and becomes strong, full and quick during the subsequent glow of heat; till, in a few minutes, these symptoms subside, and the temporary fever ceases. In those constitutions where the degree of inirritability, or of debility, is greater than natural, the coldness and paleness of the skin, with quick and weak pulse, continue a long time after the patient leaves the bath; and the subsequent heat approaches by unequal flushings, and he feels himself disordered for many hours. Hence the bathing in a cold spring of water, where the heat is but forty-eight degrees on Fahrenheit's thermometer, much disagrees with those of weak or inirritable habits of body, who possess so little sensorial power, that they cannot, without Injury, bear to have it diminished even for a short time; but who can nevertheless bear the more temperate coldness of Buxton bath, which is about eighty degrees of heat, and which strength- ens them, and makes them by habit less liable to great quie- scence from small variations of cold, and thence less liable to be disordered by the unavoidable accidents of life. Hence it ap- pears, why people of these inirritable constitutions, which is an- other expression for sensorial deficiency, are often much injured by bathing in a cold spring of water ; and why they should continue but a very short time in baths, which are colder than their bodies; and should gradually increase both the degree of coldness of the water, and the time of their continuance in it, if they would obtain salutary effects from cold immersions.— See Sect. XII. 2. 1. On the other hand, in all cases where the heat of the external surface of the body, or of the internal surface of the lungs, is greater than natural, the use of exposure to cool air may be de- duced. In fever-fits, attended with strength, that is, with great quantity of sensorial power, it removes the additional stimulus of heat from the surfaces above mentioned, and thus prevents their excess of useless motion; and in fever-fits, attended with debility, that is, with a deficiency of the quantity of sensorial power, it pervents the great and dangerous waste of sensorial power expended in the unnecessary increase of the actions of the glands and capillaries of the skin and lungs. 4. In the same manner, when any one is long exposed to very cold air, a quiescence is produced of the cutaneous and pulmonary capillaries and absorbents, owing to the deficiency of 273 SECT. XXXII. 4. DISEASES OF IRRITATION. of their usual stimulus of heat: and this quiescence of so great a quantity of vessels affects, by irritative association, the whole absorbent and glandular system, which becomes in a greater or less degree quiescent, and a cold fit of fever is produced. If the deficiency of the stimulus of heat is very great, the quiescence becomes so general as to extinguish life, as in those. who are frozen to death. If the deficiency of heat be in less degree, but yet so great as in some measure to disorder the system, and should occur the succeeding day, it will induce a greater degree of quiescence than before, from its acting in concurrence with the period of the diurnal circle of actions, explained in Sect. XXXVI.— Hence, from a small beginning a greater and greater degree of quiescence may be induced, till a complete fever-fit is formed; and which will continue to recur at the periods by which it was produced. See Sect. XVII. 3. 6. If the degree of quiescence occasioned by defect of the stimulus of heat be very great, it will recur a second time by a slighter cause than that which first induced it. If the cause which in- duces the second fit of quiescence recurs the succeeding day, the quotidian fever is produced, if not till the alternate day, the ter- tian fever; and if not till after seventy-two hours from the first fit of quiescence, the quartan fever is formed.. This last kind of fever recurs less frequently than the other, as it is a disease only of those of the temperament of associability, as mentioned. in Sect. XXXI. for in other constitutions the capability of forming a habit ceases, before the new cause of quiescence is again applied, if that does not occur sooner than in seventy- two hours. And hence those fevers, whose cause is from cold air of the night or morning, are more liable to observe the solar day in their periods; while those from other causes frequently observe the lunar day in their periods, their paroxysms returning near an hour later every day, as explained in Sect. XXXVI. IV. Another frequent cause of the cold fits of fever is the defect of the stimulus of distention. The whole arterial sys- tem would appear, by the experiments of Haller, to be irrita- ble by no other stimulus; and the motions of the heart and ali- mentry canal are certainly in some measure dependent on the same cause. See Sect. XIV. 7. Hence there can be no won- der, that the diminution of distention should frequently induce the quiescence, which constitutes the beginning of fever-fits. Monsieur Lieutaud has judiciously mentioned the deficiency of the quantity of blood amongst the causes of diseases, which he says is frequently evident in dissections: fevers are hence brought 274 DISEASES OF IRRITATION. SECT. XXXII. 5. brought on by great hæmorrhages, diarrhœas, or other evacua- tions; or from the continued use of diet, which contains but little nourishment; or from the exhaustion occasioned by vio- lent fatigue, or by those chronic diseases in which the digestion is much impaired; as where the stomach has been long effect- ed with the gout or schirrus; or in the paralysis of the liver, as described in Sect. XXX. Hence a paroxysm of gout is liable to recur on bleeding Or purging; as the torpor of some viscus, which precedes the inflammation of the foot, is thus induced by the want of the stimulus of distention. And hence the extre- mities of the body, as the nose and fingers, are more liable to become cold, when we have long abstained from food; and hence the pulse is increased, both in strength and velocity, above the natural standard, after a full meal, by the stimulus of disten- tion. However, this stimulus of distention, like the stimulus of heat above described, though it contributes much to the due ac- tion not only of the heart, arteries, and alimentary canal, but seems necessary to the proper secretion of all the various glands; yet, perhaps it is not the sole cause of any of these numerous motions; for as the lacteals, cutaneous absorbents, and the va- rious glands appear to be stimulated into action by the peculiar pungency of the fluids they absorb; so in the intestinal canal the pungency of the digesting aliment, or the acrimony of the fæces, seem to contribute, as well as their bulk, to promote the peristaltic motions; and in the arterial system, the momentum of the particles of the circulating blood, and their acrimony, sti- mulate the arteries, as well as the distention occasioned by it. Where the pulse is small. this defect of distention is present, and contributes much to produce the febris irritativa pulsu debili, or irritative fever with weak pulse, called by modern writers, nervous fever, as a predisponent cause. See Sect. XII. 1. 4. Might not the transfusion of blood, suppose of four ounces daily from a strong man, or other healthful animal, as a sheep or an ass, be used in the early date of nervous or putrid fevers with great prospect of success? V. The defect of the momentum of the particles of the circu- lating blood is another cause of the quiescence, with which the cold fits of fever commence. This stimulus of the momentum of the progressive particles of the blood does not act over the whole body like those of heat and distention above described, but is confined to the arteral system, and differs from the stimu- lus of the distention of the blood as much as the vibration of the air does from the currents of it. Thus are the different organs of our bodies stimulated by four different mechanic pro- perties. 275 SECT. XXXII. 5. DISEASES OF IRRITATION. perties of the external world: the sense of touch by the pres- sure of solid bodies, so as to distinguish their figure, the muscu- lar system by the distention which they occasion; the inter- nal surface of the arteries, by the momentum of their moving particles; and the auditory nerves, by the vibration of them; and these four mechanic properties are as different from each other as the various chemical ones, which are adapted to the numerous glands, and to the other organs of sense. 2. The momentum of the progessive particles of blood is compounded of their velocity and their quantity of matter: hence, whatever circumstances diminish either of these without proportionally increasing the other, and without superadding either of the general, stimuli of heat or distention, will tend to produce a quiescence of the arterial system, and from thence of all the other irritative motions which are connected with it. Hence, in all those constitutions or diseases where the blood contains a greater proportion of serum, which is the lighted part of its composition, the pulsations of the arteries are weaker, as in nervous fevers, chlorosis, and hysteric complaints; for in these cases the momentum of the progressive particles of blood is less: and hence, where the denier parts of its compo- sition abound, as the red part of it, or the coagulable lymph, the arterial pulsations are stronger; as in those of robust health, and in inflammatory diseases. That this stimulus of the momentum of the particles of the circulating fluid is of the greatest consequence to the arterial action, appears from the experiment of injecting air into the blood vessels, which seems to destroy animal life from the want of this stimulus of momentum; for the distention of the ar- teries is not diminished by it; it possesses no corrosive acrimony, and is less liable to repass the valves than the blood itself; since air-valves in all machinary require much less accuracy of construction than those which are opposed to water. 3. One method of increasing the velocity of the blood, and in consequence the momentum of its particles, is by the exercise of the body, or by the friction of its surface: so, on the contrary, too great indolence contributes to decrease this sti- mulus of the momentum of the particles of the circulating blood, and thus tends to induce quiescence; as is seen in hysteric ea- ses, and chlorosis, and the other diseases of sedentary people. 4. The velocity of the particles of the blood in certain cir- cumstances, is increased by venesection, which, by removing a part of it, diminishes the resistance to the motion of the other part, and hence the momentum of the particles of it is in- creased. This may be easily understood by considering it in O o the 276 DISEASES OF IRRITATION. SECT. XXXII. 6. the extreme, since, if the rest dance was greatly increased, so as to overcome the propelling power, there could be no velo- city, and in consequence no momentum at all. From this cir- cumstance arises that curious phenomenon, the truth of which I have been more than once witness to, that venesection will often instantaneously relieve those nervous pains, which attend the cold periods of hysteric asthmatic, or epileptic diseases; and that even where large doses of opium have been in vain ex- hibited. In these cases, the pulse becomes stronger after the bleeding, and the extremities regain their natural warmth; and an opiate then given, acts with much more certain effect. VI. There is another cause, which seems occasionally to induce quiescence into some part of our system; I mean the influence of the sun and moon: the attraction of these lumi- naries, by decreasing the gravity of the particles of the blood, cannot affect their momentum, as their vis inertiæ remains the same; but it may, nevertheless, produce some chemical change in them, because whatever affects the general attract- tions of the particles of matter, may be supposed from analogy to affect their specific attractions or affinities: and thus the stimulus of the particles of blood may be diminished, though not their momentum. As the tides of the sea obey the south- ing and northing of the moon, (allowing for the time necessary for their motion, and the obstructions of the shores,) it is pro- bable, that there are also atmospheric tides on both sides of the earth, which, to the inhabitants of another planet, might so de- flect the light as to resemble the ring of Saturn. Now, as these tides of water, or of air, are raised by the diminution of their gravity, it follows, that their pressure on the surface of the earth is no greater than the pressure of the other parts of the ocean, or of the atmosphere, where no such tides exist; and therefore, that they cannot affect the mercury in the ba- rometer. In the same manner the gravity of all other terres- trial bodies is diminished at the times of the southing and northing of the moon, and that in a greater degree when this coincides with the southing and northing of the sun, and this in a still greater degree about the times of the equinoxes. This decrease of the gravity of all bodies during the time the moon passes our zenith or nadir, might possibly be shewn by the flower vibrations of a pendulum, compared with a spring clock, or with astronomical observation: since a pendulum of a certain length moves slower at the line than near the poles, because the gravity being diminished, and the vis inertiæ continuing the same, the motive power is less, but the resistance to be overcome con- tinues the same. The combined powers of the lunar and solar attraction 277 SECT. XXXII. 6. DISEASES OF IRRITATION. attraction is estimated, by Sir Isaac Newton, not to exceed one 7,868,850th part of the power of gravitation, which seems in- deed but a small circumstance to produce any considerable ef- fect on the weight of sublunary bodies, and yet this is sufficient to raise the tides at the equator above ten feet high; and if it be considered, what small impulses of other bodies produce their effects on the organs of sense adapted to the perception of them, as of vibration on the auditory nerves, we shall cease to be sur- prised, that so minute a diminution in the gravity of the parti- cles of blood should so far affect their chemical changes, or their stimulating quality, as, joined with other causes, some times to produce the beginnings of diseases. Add to this, that if the lunar influence produces a very small degree of quiescence at first, and if that recurs at certain pe- riods, even with less power to produce quiescence than at first, yet the quiescence will daily increase by the acquired habit act- ing, at the same time, till, at length, so great a degree of quie- scence is induced as to produce phrensy, canine madness, epi- lepsy, hysteric pains, or cold fits of fever; instances of many of which are to be found in Dr. Mead's work on this subject. The solar influence also appears daily in several diseases; but as darkness, silence, sleep, and our periodical meals, mark the parts of the solar circle of actions, it is sometimes dubious to which of these the periodical returns of these diseases are to be ascribed. As far as I have been able to observe, the periods of inflam- matory diseases observe the solar day; as the gout and rheuma- tism have their greatest quiescence about noon and midnight, and their exacerbations some hours after; as they have more frequently their immediate cause from cold air, inanition, or fatigue, than from the effects of lunations; whilst the cold fits of hysteric patients, and those in nervous fevers, more fre- quently occur twice a day, later by near half an hour each time, according to the lunar day; whilst some fits of intermittents, which are undisturbed by medicines, return at regular solar pe- riods, and others at lunar ones; which may probably be owing to the difference of the periods of those external circumstances of cold, inanition, or lunation, which immediately caused them. We must, however, observe, that the periods of quiescence and exacerbation in diseases do not always commence at the times of the syzygies or quadratures of the moon and sun, or at the times of their passing the zenith or nadir; but as it is proba- ble, that the stimulus of the particles of the circumfluent blood is gradually diminished from the time of the quadratures to that of the syzygies, the quiesence may commence at any hour, when, co-operating 278 DISEASES OF IRRITATION. SECT. XXXII. 6. co-operating with other causes of quiescence, it becomes great enough to produce a disease: afterwards it will continue to recur at the same period of the lunar or solar influence; the same cause operating conjointly with the acquired habit, that is, with the catenation of this new motion with the dissevered links of the lunar or solar circles of animal action. In this manner, the periods of menstruation obey the lunar month with great exactness in healthy patients, (and perhaps the venereal orgasm in brute animals does the same) yet these periods do not commence, either at the syzygies or quadra- tures of the lunations; but at whatever time of the lunar pe- riods they begin, they observe the same in their returns till some greater cause disturbs them. Hence, though the best way to calculate the time of the ex- pected returns of the paroxysms of periodical diseases is to count the number of hours between the commencement of the two preceding fits, yet the following observations may be worth attending to, when we endeavour to prevent the returns of ma- niacal or epileptic diseases; whose periods (at he beginning of them especially) frequently observe the syzygies of the moon and sun, and particularly about the equinox. The greatest of the two tides happening in every revolution of the moon, is that when the moon approaches nearest to the zenith or nadir; for this reason, while the sun is in the northern signs, that is, during the vernal and summer months, the greater of the two diurnal tides in our latitude is that when the moon is above the horizon; and when the sun is in the southern signs, or during the autumnal and winter months, the greater tide is that which arises when the moon is below the horizon: and as the sun approaches somewhat nearer the earth in win- ter than in summer, the greatest equinoxial tides are observed to be a little before the vernal equinox, and a little after the autumnal one. Do not the cold periods of lunar diseases commence a few hours before the southing of the moon during the vernal and summer months, and before the northing of the moon during the autumnal and winter months? Do not palsies and apoplex- ies, which occur about the equinoxes, happen a few days be- fore the vernal equinoctial lunation, and after the autumnal one? Are not the periods of those diurnal diseases more obsti- nate, that commence many hours before the southing or north- ing of the moon, than of those which commence at those times? Are not those palsies and apoplexies more dangerous which commence many days before the syzygies of the moon, than those which happen at those times? See Sect. XXXVI. on the Periods of Diseases. VII. Another 279 SECT. XXXII. 7, 8. DISEASES OF IRRITATION. VII. Another very frequent cause of the cold fit of fever is the quiescence of some of those large congeries of glands, which compose the liver, spleen, or pancreas; one or more of which are frequently so enlarged in the autumnal intermittents as to be perceptible to the touch externally, and are called by the vulgar ague-cakes. As these glands are stimulated into action by the specific pungency of the fluids which they absorb, the general cause of their quiescence seems to be the too great insipidity of the fluids of the body, co-operating perhaps at the same time with other general causes of quiescence. Hence, in marshy countries at cold seasons, which have suc- ceeded hot ones, and amongst those who have lived on innu- tritious and unstimulating diet, these agues are most frequent. The enlargement of these quiescent viscera, and the swelling of the præcordia in many other fevers, is most probably owing to the same cause; which may consist in a general deficiency of the production of sensorial power, as well as the diminished sti- mulation of the fluids; and when the quiescence of so great a number of glands as constitute one of those large viscera com- mences, all the other irritative motions are affected by their con- nection with it, and the cold fit of fever is produced. VIII. There are many other causes which produce quie- scence of some part of the animal system, as fatigue, hunger, thirst, bad diet, disappointed love, unwholesome air, exhaust- tion from evacuations, and many others; but the last cause that we shall mention, as frequently productive of cold fits of fever, is fear or anxiety of mind. The pains which we are first and most generally acquainted with, have been produced by defect of some stimulus: thus, soon after our nativity we be- come acquainted with the pain from the coldness of the air, from the want of respiration, and from the want of food. Now, all these pains occasioned by defect of stimulus are attended with quiescence of the organ, and at the same time with a greater or less degree of quiescence of other parts of the system: thus, if we even endure the pain of hunger so as to miss one meal instead of our daily habit of repletion, not only the pe- ristaltic motions of the stomach and bowels are diminished, but we are more liable to coldness of our extremities, as of our no- ses, and ears, and feet, than at other times. Now, as fear is originally excited by our having experienced pain, and is itself a painful affection, the same quiescence of other fibrous motions accompany it, as have been most frequent- ly connected with this kind of pain, as explained in Sect. XVI. 8. 1. as the coldness and paleness of the skin, trembling, diffi- cult respiration, indigestion, and other symptoms which contri- bute 280 DISEASES OF IRRITATION. SECT. XXXII. 9. bute to form the cold fit of fevers. Anxiety is fear continued through a longer time, and, by producing chronical torpor of the system, extinguishes life slowly, by what is commonly termed a broken heart. IX. I. We now step forwards to consider the other symp- toms in consequence of the quiescence which begins the fits of fever. If, by any of the circumstances before described, or by two or more of them acting at the same time, a great degree of quiescence is induced on any considerable part of the circle of irritative motions, the whole class of them is more or less dis- turbed by their irritative associations. If this torpor be occa- sioned by a deficient supply of sensorial power, and happens to any of those parts of the system which are accustomed to per- petual activity, as the vital motions, the torpor increases rapid- ly, because of the great expenditure of sensorial power by the incessant activity of those parts of the system, as shewn in No. 3. 2. of this section. Hence a deficiency of all the secretions succeeds; and as animal heat is produced in proportion to the quantity of those secretions, the coldness of the skin is the first circumstance which is attended to. Dr. Martin asserts, that some parts of his body were warmer than natural in the cold fit of fever; but it is certain, that those which are uncovered, as the fingers, and nose, and ears, are much colder to the touch, and paler in appearance. It is possible, that his experiments were made at the beginning of the subsequent hot fits; which commence with partial distributions of heat, owing to some parts of the body regaining their natural irritability sooner than others. From the quiescence of the anastomosing capillaries a pale- ness of the skin succeeds, and a less secretion of the perspirable matter; from the quiescence of the pulmonary capillaries a dif- ficulty of respiration arises; and from the quiescence of the other glands less bile, less gastric and pancreatic juice, are secret- ed into the stomach and intestines, and less mucus and saliva are poured into the mouth; whence arises the dry tongue, cos- tiveness, dry ulcers, and paucity of urine. From the quiescence of the absorbent system arises the great thirst, as less moisture is absorbed from the atmosphere. The absorption from the at- mosphere was observed, by Dr. Lyster, to amount to eighteen ounces in one night, above what he had at the same time insen- sibly perspired. See Langrish. On the same account the urine is pale, though in small quantity, for the thinner part is not ab- sorbed from it; and when repeated ague fits continue long, the legs swell from the diminished absorption of the cellular absor- bents. From 281 SECT. XXXII. 9. DISEASES OF IRRITATION. From the quiescence of the intestinal canal a loss of appetite and flatulencies proceed. From the partial quiescence of the glandular viscera a swelling and tension about the præcordia become sensible to the touch; which is occasioned by the de- lay of the fluids from the defect of venous or lymphatic absorp- tion. The pain of the forehead, and of the limbs, and of the small of the back, arises from the quiescence of the membranous fascia, or muscles of those parts, in the same manner as the skin becomes painful, when the vessels, of which it is composed, be- come quiescent from cold. The trembling in consequence of the pain of coldness, the restlessness, and the yawning, and stretching of the limbs, together with the shuddering, or rigours, are convulsive motions; and will be explained amongst the dis- eases of volition, Sect. XXXIV. Sickness and vomiting is a frequent symptom in the begin- nings of fever-fits: the muscular fibres of the stomach share the general torpor and debility of the system; their motions become first lessened, and then flop, and then become retrograde; for the act of vomiting, like the globus hystericus and the borbo- rigmi of hypocondriasis, is always a symptom of debility, either from want of stimulus, as in hunger; or from want of sensorial power, as after intoxication; or from sympathy, with some other torpid irritative motions, as in the cold fits of ague. See Sect. XII. 5. 5. XXIX. 11. and XXXV. 1. 3. where this act of vomiting is further explained. The small pulse, which is said by some writers to be slow at the commencement of ague-fits, and which is frequently trem- bling and intermittent, is owing to the quiescence of the heart and arterial system, and to the resistance opposed to the circulat- ing fluid from the inactivity of all the glands and capillaries. The great weakness and inability to voluntary motions, with the insensibility of the extremities, are owing to the general quiescence of the whole moving system; or, perhaps, simply to the deficient production of sensorial power. If all these symptoms are further increased, the quiescence of all the muscles, including the heart and arteries, becomes com- plete, and death ensues. This is most probably the case of those who are starved to death with cold, and of those who are said to die in Holland from long skaiting on their frozen canals. 2. As soon as this general quiescence of the system ceases, either by the diminution of the cause, or by the accumulation of sensorial power, (as in syncope, Sect. XII. 7. 1.) which is the natural consequence of previous quiescence, the hot fit com- mences. Every gland of the body is now stimulated into stronger action than is natural, as its irritability is increased by accu- mulation 282 DISEASES OF IRRITATION. SECT. XXXII. 9. mulation of sensorial power during its late quiescence; super- abundance of all the secretions is produced, and an increase of heat in consequence of the increase of these secretions. The skin becomes red, and the perspiration great, owing to the increased action of the capillaries during the hot part of the paroxysm. The secretion of perspirable matter is perhaps greater during the hot fit than in the sweating fit which follows; but as the absorption of it also is greater, it does not stand on the skin in visible drops: add to this, that the evaporation of it also is greater, from the increased heat of the skin. But at the decline of the hot fit, as the mouths of the absorbents of the skin are exposed to the cooler air, or bed-clothes, these vessels sooner lose their increased activity, and cease to absorb more than their natural quantity: but the secerning vessels, for some time longer, being kept warm by the circulating blood, continue to pour out an increased quantity of perspirable matter, which now stands on the skin in large visible drops; the exhalation of it also being lessened by the greater coolness of the skin, as well as its absorption by the di- minished action of the lymphatics. See Class I. 1. 2. 3. The increased secretion of bile and of other fluids poured in to the intestines frequently induces a purging at the decline of the hot fit; for as the external absorbent vessels have their mouths exposed to the cold air, as above mentioned, they cease to be excited into unnatural activity sooner than the secretory vessels, whose mouths are exposed to the warmth of the blood: now, as the internal absorbents sympathize with the external ones, these also, which during the hot fit drank up the thin- ner part of the bile, or of other secreted fluids, lose their increase- ed activity before the gland loses its increased activity, at the de- cline of the hot fit: and the loose dejections are produced from the same cause, that the increased perspiration stands on the sur- face of the skin, from the increased absorption ceasing sooner than the increased secretion. The urine during the cold fit is in small quantity and pale, both from a deficiency of the secretion and a deficiency of the absorption. During the hot fit it is in its usual quantity, but very high coloured and turbid, because a greater quantity had been secreted by the increased action of the kidnies, and also a greater quantity of its more aqueous part had been absorbed from it in the bladder by the increased action of the absorbents; and lastly, at the decline of the hot fit it is in lets coloured large quantity and or turbid, because the absorbent vessels of the bladder, as observed above, lose their increased action by sym- pathy with the cutaneous ones sooner than the secretory ves- sels of the kidnies, lose their increased activity. Hence, the quan- tity 283 SECT. XXXII. 9. DISEASES OF IRRITATION. tity of the sediment, and the colour of the urine, in fevers, de- pend much on the quantity secreted by the kidnies, and the quantity absorbed from it again in the bladder: the kinds of sedi- ment, as the lateritious, purulent, mucous, or bloody sedi- ments, depend on other causes. It should be observed, that if the sweating be increased by the heat of the room, or of the bed clothes, that a paucity of turbid urine will continue to be pro- duced, as the absorbents of the bladder will have their activity increased by their sympathy with the vessels of the skin, for the purpose of supplying the fluid expended in perspiration. The pulse becomes strong and full, owing to the increased irritability of the heart and arteries, from the accumulation of sensorial power during their quiescence, and to the quickness of the return of the blood from the various glands and capillaries. This increased action of all the secretory vessels does not oc- cur very suddenly; nor universally at the same time. The heat seems to begin about the center, and to be diffused from thence irregularly to the other parts of the system. This may be owing to the situation of the parts which first became quie- scent, and caused the fever-fit, especially when a hardness of tumour about the præcordia can be felt by the hand; and hence this part, in whatever viscus it is seated, might be the first to regain its natural or increased irritability. 3. It must be here noted, that by the increased quantity of heat, and of the impluse of the blood, at the commencement of the hot fit, a great increase of stimulus is induced, and is now added to the increased irritability of the system, which was oc- casioned by its previous quiescence. This additional stimulus of heat and momentum of the Wood, augments the violence of the movements of the arterial and glandular system in an in- creasing ratio. These violent exertions still producing more heat and greater momentum of the moving fluids, till, at length, the sensorial power becomes wasted by this great stimulus be- neath its natural quantity, and predisposes the system to a se- cond cold fit. At length all these unnatural exertions spontaneously sub- side with the increased irritability that produced them; and which was itself produced by the preceding quiescence, in the same manner as the eye, on coming from darkness into day light, in a little time ceases to be dazzled and pained, and gra- dually recovers its natural degree of irritability 4 But if the increase of irritability, and the consequent in- crease of the stimulus of heat and momentum, produce more violent exertions than those above described, great pain arises in some part of the moving system, as in the membranes of the P P brain, 284 DISEASES OF IRRITATION. SECT. XXXII. 10. brain, pleura, or joints; and new motions of the vessels are produced in consequence of this pain, which are called in- flammation; or delirium, or stupor arises; as explained in Sect. XXI. and XXXIII. for the immediate effect is the same, whether the great energy of the moving organs arises from an increase of stimulus, or an increase of irritability; though in the former case the waste of sensorial power leads to debility, and in the latter, to health. Recapitulation. X. Those muscles, which are less frequently exerted, and whose actions are interrupted by sleep, acquire less accumulation of sensorial power during their quiescent state, as the muscles of locomotion. In these muscles, after great exertion, that is, after great exhaustion of sensorial power, the pain of fatigue ensues; and during rest there is a renovation of the natural quantity of sensorial power; but where the rest, or quiescence of the muscle, is long continued, a quantity of sensorial power becomes accumulated beyond what is necessary; as appears by the un- easiness occasioned by want of exercise; and which in young animals is one cause exciting them into action, as is seen in the play of puppies and kittens. But when those muscles, which are habituated to perpetual action, as those of the stomach by the stimulus of food, those of the vessels of the skin by the stimulus of heat, and those which constitute the arteries and glands by the stimulus of the blood, become for a time quiescent, from the want of their appropri- ated stimuli, or by their associations with other quiescent parts of the system; a greater accumulation of sensorial power is ac- quired during their quiescence, and a greater or quicker exhaust- tion of it is produced during their increased action. This accumulation of sensorial power from deficient action, if it happens to the stomach from want of food, occasions the pain of hunger; it it happens to the vessels of the skin from want of heat, it occasions the pain of cold; and if to the arterial system from the want of its adapted stimuli, many disagreeable sensations are occasioned, such as are experienced in the cold fits of intermittent fevers, and are as various as there are glands or membranes in the system, and are generally term- ed universal uneasiness. When the quiescence of the arterial system is not owing to defect of stimulus as above, but to the defective quantity of sensorial power, as in the commencement of nervous fever, or irritative fever with weak pulse, a great torpor of this system is quickly induced, because both the irritation from the stimulus of 285 SECT. XXXII. 10. DISEASES OF IRRITATION. of the blood, and the association of the vascular motions with each other, continue to excite the arteries into action, and thence quickly exhaust the ill-supplied vascular muscles; for to rest is death; and therefore those vascular muscles continue to proceed, though with feebler action, to the extreme of weariness or faint- ness; while nothing similar to this affects the locomotive mus- cles, whose actions are generally caused by volition, and not much subject either to irritation or to other kinds of associations besides the voluntary ones, except indeed when they are excited by the lash of slavery. In these vascular muscles, which are subject to perpetual ac- tion, and thence liable to great accumulation of sensorial power during their quiescence from want of stimulus, a great increase of activity occurs, either from the renewal of their accustomed stimulus, or even from much less quantities of stimulus than usual. This increase of action constitutes the hot fit of fever, which is attended with various increased secretions, with great conco- mitant heat, and general uneasiness. The uneasiness attending this hot paroxysm of fever, or fit of exertion, is very different from that which attends the previous cold fit, or fit of quie- scence, and is frequently the cause of inflammation, as in pleurisy, which is treated of in the next section. A similar effect occurs after the quiescence of our organs of sense; those which are not subject to perpetual action, as the taste and smell, are less liable to an exuberant accumulation of sensorial power after their having for a time been inactive; but the eye, which is in perpetual action during the day, becomes dazzled, and liable to inflammation after a temporary quiescence. Where the previous quiescence has been owing to a defect of sensorial power, and not to a defect of stimulus, as in the irri- tative fever with weak pulse, a similar increase of activity of the arterial system succeeds, either from the usual stimulus of the blood, or from a stimulus less than usual; but as there is, in general, in these cases of fever with weak pulse, a deficiency of the quantity of the blood, the pulse in the hot fit is weaker than in health, though it is stronger than in the cold fit, as explained in No. 2. of this section. But at the same time, in those fevers where the defect of irritation is owing to the defect of the quan- tity of sensorial power, as well as to the defect of stimulus, ano- ther circumstance occurs, which consists in the partial distribu- tion of it, as appears in partial flushings, as of the face or bosom, while the extremities are cold; and in the increase of particular secretions, as of bile, saliva, insensible perspiration, with great heat of the skin, or with partial sweats, or diarrhœa. There are also many uneasy sensations attending these increas- ed 286 DISEASES OF SENSATION. SECT. XXXIII. ed actions, which, like those belonging to the hot fit of fever with strong pulse, are frequently followed by inflammation, as in scarlet fever; which inflammation is nevertheless accompanied with a pulse weaker, though quicker, than the pulse during the remission or intermission of the paroxysms, though stronger than that of the previous cold fit. From hence I conclude, that both the cold and hot fits of fever are necessary consequences of the perpetual and incessant action of the arterial and glandular system; since those mus- cular fibres and those organs of sense, which are most frequently exerted, become necessarily moll affected both with defect and accumulation of sensorial power: and that hence fever-fits are not an effort of nature to relieve herself, and that therefore they should always be prevented or diminished as much as pos- sible, by any means which decrease the general or partial vas- cular actions when they are greater, or by increasing them when they are less than in health, as described in Sect. XII. 6. 1. Thus have I endeavoured to explain, and I hope to the sa- tisfaction of the candid and patient reader, the principal symp- toms or circumstances of fever, without the introduction of the supernatural power of spasm. To the arguments in favour of the doctrine of spasm it may be sufficient to reply, that in the evolution of medical as well as of dramatic catastrophe, Nec Deus intersit, nisi dignus vindice nodus incident. HOR. SECT. XXXIII. DISEASES OF SENSATION. I. 1. Motions excited by sensation. Digestion. Generation. Pleasure of existence. Hypochondriacism. 2. Pain in- troduced. Sensitive fevers of two kinds. 3. Two senso- rial powers exerted in sensitive fevers. Size of the blood. Nervous fevers distinguished from putrid ones. The sep- tic and antiseptic theory. 4. Two kinds of delirium. 5. Other animals are less liable to delirium, cannot receive our contagious diseases, and are less liable to madness. II. 1. Sensitive motions generated. 2. Inflammation explain- ed. 3. Its remote causes from excess of irritation, or of irritability, not from those pains which are owing to de- fect of irritation. New vessels produced, and much heat. 4. Purulent matter secreted. 5. Contagion explained. 6. Received but once. 7. If common matter be contagious? 8. Why some contagions are received but once. 9. Why others 287 SECT. XXXIII. 1. DISEASES OF SENSATION. others may be received frequently. Contagions of small- pox and measles do not act at the same time. Two cases of such patients. 10. The blood from patients in the small- pox will not infect others. Cases of children thus inocu- lated. The variolous contagion is not received into the blood. It acts by sensitive association between the stomach and skin. III. 1. Absorption of solids and fluids. 2. Art of healing ulcers. 3. Mortification attended with less pain in weak people. I. 1. AS many motions of the body are excited and continu- ed by irritations, so others require, either conjunctly with these or separately, the pleasureable or painful sensations, for the pur- pose of producing them with due energy. Amongst these the business of digestion supplies us with an instance: if the food which we swallow is not attended with agreeable sensation, it digests less perfectly; and if very disagreeable sensation accom- panies it, such as a nauseous idea, or very disgustful taste, the digestion becomes impeded; or retrograde motions of the sto- mach and œsophagus succeed, and the food is ejected. The business of generation depends so much on agreeable sensation, that, where the object is disgustful, neither voluntary exertion nor irritation can effect the purpose; which is also lia- ble to be interrupted by the pain of tear or bashfulness. Besides the pleasure which attends the irritations produced by the objects of lust and hunger, there seems to be a sum of plea- sureable affection, accompanying the various secretions of the numerous glands, which constitutes the pleasure of life, in con- tradistinction to the tedium vitæ. This quantity, or sum of pleasureable affection, seems to contribute to the due or energetic performance of the whole moveable system, as well that of the heart and arteries, as of digestion and of absorption; since, with- out the due quantity of pleasureable sensation, flatulency and hypochondriacism affect the intestines, and a languor seizes the arterial pulsations and secretions; as occurs in great and con- tinued anxiety of the mind. 2. Besides the febrile motions occasioned by irritation, de- scribed in Sect. XXXII. and termed irritative fever, it frequent- ly happens that pain is excited by the violence of the fibrous contractions; and other new motions are then superadded, in Consequence of sensation, which we shall term febris sensitiva, or sensitive fever. It must be observed, that most irritative fe- vers begin with a decreased exertion of irritation, owing to de- fect of stimulus; but that, on the contrary, the sensitive fevers, or inflammations, generally begin with the increased exertion of 288 DISEASES OF SENSATION. SECT. XXXIII. 1. of sensation, as mentioned in Sect. XXXI. on temperaments: for though the cold fit, which introduces inflammation, com- mences with decreased irritation, yet the inflammation itself commences in the hot fit during the increase of sensation. Thus a common pustule, or phlegmon, in a part of little sensibi- lity, does not excite an inflammatory fever; but if the stomach, intestines, or the tender substance beneath the nails, be injured, great sensation is produced, and the whole system is thrown into that kind of exertion which constitutes inflammation. These sensitive fevers, like the irritative ones, resolve them- selves into those with arterial strength, and those with arterial debility; that is, with excess or defect of sensorial power: these may be termed the febris sensitiva pulsu forti, sensitive fever with strong pulse, which is the synocha, or inflammatory fever; and the febris sensitiva pulsu debili, sensitive fever with weak pulse, which is the typhus gravior, or putrid fever of some writers. 3. The inflammatory fevers, which are here termed sensitive fevers with strong pulse, are generally attended with some topi- cal inflammation, as pleurisy, peripneumony, or rheumatism, which distinguishes them from irritative fevers with strong pulse. The pulse is strong, quick, and full; for in this fever there is great irritation, as well as great sensation, employed in moving the arterial system. The size, or coagulable lymph, which ap- pears on the blood, is probably an increased secretion from the inflamed internal lining of the whole arterial system, the thinner part being taken away by the increased absorption of the in- flamed lymphatics. The sensitive fevers with weak pulse, which are termed pu- trid or malignant fevers, are distinguished from irritative fevers with weak pulse, called nervous fevers, described in the last sec- tion, as the former consists of inflammation joined with debility, and the latter of debility alone. Hence there is greater heat and more florid colour of the skin in the former, with petechiæ, or purple spots, and apthæ, or sloughs in the throat, and gene- rally with previous contagion. When animal matter dies, as a slough in the throat, or the mortified part of a carbunkle, if it be kept moist and warm, as during its adhesion to a living body, it will soon putrify. This, and the origin of contagion, from putrid animal substances, seem to have given rise to the septic and antiseptic theory of these fevers. The matter in pustules and ulcers is thus liable to become putrid, and to produce microscopic animalcula; the urine, if too long retained, may also gain a putrescent smell, as well as the alvine feces; but some writers have gone so far as to be- lieve, 289 SECT. XXXIII. 1. DISEASES OF SENSATION. lieve, that the blood itself in these fevers has smelt putrid, when drawn from the arm of the patient: but this seems not well founded; since a single particle of putrid matter taken into the blood can produce fever, how can we conceive that the whole mass could continue a minute in a putrid state without destroying life? Add to this, that putrid animal substances give up air, as in gangrenes; and that hence, if the blood was putrid, air should be given out, which, in the blood vessels is known to occasion immediate death. In these sensitive fevers with strong pulse, (or inflamma- tions) there are too sensorial faculties concerned in producing die disease, viz. irritation and sensation; and hence, as their combined action is more violent, the general quantity of sen- sorial power becomes further exhausted during the exacerba- tion, and the system more rapidly weakened than in irritative fever with strong pulse; where the spirit of animation is weak- ened by but one mode of its exertion: so that this febris sensitiva pulsu forti (or inflammatory fever,) may be considered as the febris irritativa pulsu forti, with the addition of inflammation; and the febris sensitiva pulsu debili (or malignant fever) may be considered as the febris irritativa pulsu debili, (or nervous fever,) with the addition of inflammation. 4. In these putrid or malignant fevers a deficiency of irrita- bility accompanies the increase of sensibility; and by this waste of sensorial power by the excess of sensation, which was al- ready too small, arises the delirium and stupor which so perpe- tually attend these inflammatory fevers with arterial debility. In these cases, the voluntary power first ceases to act from deficiency of sensorial spirit; and the stimuli from external bo- dies have no effect on the exhausted sensorial power, and a de- lirium like a dream is the consequence. At length, the inter- nal stimuli cease to excite sufficient irritation, and the secretions are either not produced at all, or two parsimonious in quantity. Amongst these, the secretion of the brain, or production of the sensorial power, becomes deficient, till at last all sensorial power ceases, except what is just necessary to perform the vital motions, and a stupor succeeds; which is thus owing to the same cause as the preceding delirium exerted in a greater degree. This kind of delirium is owing to a suspension of volition, and to the disobedience of the senses to external stimuli, and is always occasioned by great debility, or paucity of sensorial power; it is therefore a bad sign at the end of inflammatory fevers, which had previous arterial strength, as rheumatism or pleurisy, as it shews the presence of great exhaustion of sensorial power in a system, which having lately been exposed to great excitement, 290 DISEASES OF SENSATION. SECT. XXXIII. 1. excitement, is not so liable to be stimulated into its healthy ac- tion, either by additional stimulus of food and medicines, or by the accumulation of sensorial power during its present torpor. In inflammatory fevers with debility, as those termed putrid fe- vers, delirium is sometimes, as well as stupor, rather a favour- able sign; as less sensorial power is wasted during its continu- ance (see Class II. 1. 6. 8.); and the constitution not having been previously exposed to excess of stimulation, is more liable to be excited after previous quiescence. When the sum of general pleasureable sensation becomes too great, another kind of delirium supervenes, and the ideas thus excited are mistaken for the irritations of external objects: such a delirium is produced for a time by intoxicating drugs, as fer- mented liquors, or opium: a permanent delirium of this kind is sometimes induced by the pleasures of inordinate vanity, or by the enthusiastic hopes of heaven. In these cases, the power of volition is incapable of exertion, and in a great degree, the ex- ternal senses become incapable of perceiving their adapted sti- muli, because the whole sensorial power is employed or ex- pended on the ideas excited by pleasureable sensation. This kind of delirium is distinguished from that which at- tends the fevers above mentioned, from its not being accom- panied with general debility, but simply with excess of plea- sureable sensation; and is, therefore, in some measure, allied to madness or to reverie: it differs from the delirium of dreams, as in this the power of volition is not totally suspended, nor are the senses precluded from external stimulation; there is, therefore, a degree of consistency in this kind of delirium, and a degree of attention to external objects, neither of which exist in the delirium of fevers or in dreams. 5. It would appear, that the vascular systems of other animals are less liable to be put into action by their general sum of plea- sureable or painful sensation; and that the trains of their ideas, and the muscular motions usually associated with them, are less powerfully connected than in the human system. For other animals neither weep, nor smile, nor laugh; and are hence seldom subject to delirium, as treated of in Sect. XVI. on In- stinct. Now, as our epidemic and contagious diseases are pro- bably produced by disagreeable sensation, and not simply by ir- ritation, there appears a reason why brute animals are less liable to epidemic or contagious diseases; and secondly, why none of our contagions, as the small-pox or meazles, can be commu- nicated to them, though one of theirs, viz. the hydrophobia, as well as many of their poisons, as those of snakes and of insects, communicate their deleterious or painful effects to mankind. Where 291 SECT. XXXIII. 2. DISEASES OF SENSATION. Where the quantity of general painful sensation is too great in the system, inordinate voluntary exertions are produced either of our ideas, as in melancholy and madness, or of our muscles, as in convulsion. From these maladies also brute animals are much more exempt than mankind, owing to their greater inaptitude to Voluntary exertion, as mentioned in Sect. XVI. on Instinct. II. 1. When any moving organ is excited into such violent motions, that a quantity of pleasureable or painful sensation is produced, it frequently happens (but not always) that new mo- tions of the affected organ are generated in consequence of the pain or pleasure, which are termed inflammation. These new motions are of a peculiar kind, tending to distend the old, and to produce new fibres, and thence to elongate the straight muscles, which serve locomotion, and to form new vessels at the extremities or sides of the vascular muscles. 2. Thus the pleasureable sensations produce an enlargement of the nipples of nurses, of the pallæ of the tongue, of the penis, and probably produce the growth of the body from its embryon dstte to its maturity; whilst the new motions, in Consequence of painful sensation, with the growth of the fibres or vessels, which they occasion, are termed inflammation. Hence, when the straight muscles are inflamed, part of their tendons at each extremity gain new life and sensibility, and thus the muscle is for a time elongated; and the inflamed bones become soft, vascular, and sensible. Thus, new vessels shoot over the cornea of inflamed eyes, and into schirrous tumours, when they become inflamed: and hence, all inflamed parts grow together by intermixture, and inosculation of the new and old vessels. The heat is occasioned from the increased secretions either of mucus, or of the fibres, which produce or elongate the ves- sels. The red colour is owing to the pellucidity of the newly formed vessels, as the arterial parts of them ate probably formed before their correspondent venous parts. 3. These new motions are excited either from the increased quantity of sensation, in consequence of greater fibrous con- tractions, or from increased sensibility, that is, from the increased quantity of sensorial power in the moving organ. Hence they are induced by great external stimuli, as by wounds, broken bones; and by acrid or infectious materials; or by common stimuli on those organs which have been some time quiescent; as the usual light of the day inflames the eyes of those who have been confined in dungeons, and the warmth of a com- mon fire inflames those who have been previously exposed to much cold. Q q But 292 DISEASES OF SENSATION. SECT. XXXIII. 2. But these new motions are never generated by that pain which arises from defect of stimulus, as from hunger, thirst, cold, or inanition, with all those pains which are termed nervous. Where these pains exist, the motions of the affected part are lessened; and if inflammation succeeds, it is in some distant parts; as coughs are caused by coldness and moisture being long ap- plied to the feet; or, it is in consequence of the renewal of the stimulus, as of heat or food, which excites our organs into stronger action after their temporary quiescence; as kibed heels after walking in snow. 4. But when these new motions of the vascular muscles are exerted with greater violence, and these vessels are either elon- gated too much or too hastily, a new material is secreted from their extremities, which is of various kinds, according to the peculiar animal motions of this new kind of gland, which se- cretes it; such is the pus laudabile, or common matter, the va- riolous matter, venereal matter, catarrhous matter, and many others. 5. These matters are the product of an animal process; they are secreted or produced from the blood by certain diseas- ed motions of the extremities of the blood-vessels, and are, on that account, all of them contagious; for if a portion of any of these matters is transmitted into the circulation, or perhaps only inserted into the skin, or beneath the cuticle of an healthy person, its stimulus, in a certain time, produces the same kind of morbid motions by which itself was produced; and hence a similar matter is generated. See Sect. XXXIX. 6. 1. 6. It is remarkable, that many of these contagious matters are capable of producing a similar disease but once, as. the small-pox and measles; and I suppose this is true of all those contagious diseases which are spontaneously cured by nature in a certain time; for if the body was capable of receiving the dis- ease a second time, the patient must perpetually infect himself by the very matter which he has himself produced, and is lodged about him; and hence he could never become free from the dis- ease. Something similar to this is seen in the secondary fever of the confluent small-pox: there is a great absorption of vario- lous matter, a very minute part of which would give the genuine small-pox to another person; but here it only stimulates the sys- tem into common fever, like that which common pus, or any other acrid material might occasion. 7. In the pulmonary consumption, where common matter is daily absorbed, an irritative fever only, not an inflammatory one, is produced; which is terminated like other irritative fe- vers, by sweats or loose stools. Hence it does not appear, that this 293 SECT. XXXIII. 2. DISEASES OF SENSATION. this absorbed matter always acts as a contagious material, pro- ducing fresh inflammation or new abscesses. Though there is reason to believe, that the first time any common matter is ab- sorbed, it has this effect, but not the second time, like the va- riolous matter above mentioned. This accounts for the opinion that the pulmonary consump- tion is sometimes infectious, which opinion was held by the an- cients, and continues in Italy at present; and I have myself seen three or four instances, where a husband and wife, who have slept together, and have thus much received each other's breath, who have infected each other, and both died in consequence of the original taint of only one of them. This also accounts for the abscesses in various parts of the body, that are sometimes produced after the inoculated small-pox is terminated; for this second absorption of variolous matter acts like common matter, and produces only irritative fever in those children whose con- stitutions have already experienced the absorption of common matter; and inflammation, with a tendency to produce new abscesses in those whose constitutions have not experienced the absorptions of common matter. It is probable, that more certain proofs might have been found to shew, that common matter is infectious the first time it is absorbed, tending to produce similar abscesses, but not the second time of its absorption, if this subject had been attended to. 8. These contagious diseases are very numerous, as the plague, small-pox, chicken-pox, measles, scarlet-fever, pemphigus, ca- tarrh, chincough, venereal disease, itch, trichoma, tinea. The infectious material does not seem to be dissolved by the air, but only mixed with it perhaps in fine powder, which soon subsides; since many of these contagions can only be received by actual contact; and others of them only at small distances from the infected person; as is evident from many persons having been near patients of the small-pox without acquiring the disease. The reason why many of these diseases are received but once, and others repeatedly, is not well understood; it appears to me, that the constitution becomes so accustomed to the stimuli of these infectious materials, by having once experienced them, that though irritative motions, as hectic fevers, may again be produced by them, yet no sensation, and in consequence no ge- neral inflammation succeeds; as disagreeable smells or tastes by habit cease to be perceived; they continue indeed to excite irri- tative ideas on the organs of sense, but these are not succeeded by sensation. There are many irritative motions, which were at first suc- ceeded by sensation, but which by frequent repetition cease to ex- cite 294 DISEASES OF SENSATION. SECT. XXXIII. 2. cite sensation, as explained in Sect. XX. on Vertigo. And that this circumstance exists in respect to infectious matter appears from a known fact; that nurses, who have had the small-pox, are liable to experience small ulcers on their arms by the contact of variolous matter in lifting their patients; and that when pa- tients, who have formerly had the small-pox, have been inocu- lated in the arm, a phlegmon, or inflamed fore, has succeeded, but no subsequent fever. Which shews, that the contagious matter of the small-pox has not lost its power of stimulating the part it is applied to, but that the general system is not affected in consequence. See Section XII. 7. 6. XIX. 10. 9. From the accounts of the plague, virulent catarrh, and pu- trid dysentery, it seems uncertain whether these diseases are ex- perienced more than once; but the venereal disease and itch are doubtless repeatedly infectious; and as these diseases are never cured spontaneously, but require medicines, which act without apparent operation, some have suspected, that the contagious material produces similar matter rather by a chemical change of the fluids, than by an animal process; and that the specific medicines destroy their virus by chemically combining with it. This opinion is successfully combated by Mr. Hunter, in his Treatise on Venereal Disease, Part I. c. i. But this opinion wants the support of analogy, as there is no known process in animal bodies, which is purely chemical, not even digestion; nor can any of these matters be produced by chemical processes. Add to this, that it is probable that the infects observed in the pustules of the itch, and in the stools of dysenteric patients, are the consequences, and not the causes of these diseases. And that the specific medicines, which cure the itch and lues venerea, as brimstone and mercury, act only by increasing the absorption of the matter in the ulcuscles of those diseases, and thence disposing them to heal, which would otherwise continue to spread. Why the venereal disease, and itch, and tenia, or scald head, are repeatedly contagious, while those contagions, attended with fever, can be received but once, seems to depend on their being rather local diseases than universal ones, and are hence not at- tended with fever, except the purulent fever in their last stages, when the patient is destroyed by them. On this account the whole of the system does not become habituated to these morbid actions, so as to cease to be affected with sensation, by a repe- tition of the contagion. Thus the contagious matter of the ve- nereal disease, and of the tenia, affects the lymphatic glands, as the inquinal glands, and those about the roots of the hair and neck, where it is arrested, but does not seem to affect the blood vessels, since no fever ensues. Hence 295 SECT. XXXIII. 2. DISEASES OF SENSATION. Hence it would appear, that these kinds of contagion are pro- pagated not by means of the circulation, but by sympathy of dis- tant parts with, each other; since, if a distant part, as the palate, should be excited by sensitive association into the same kind of motions as the parts originally affected by the contact of in- fectious matter, that distant part will produce the same kind of infectious matter; for every secretion from the blood is formed from it by the peculiar motions of the fine extremities of the gland which secretes it; the various secreted fluids, as the bile, saliva, gastric juice, not previously existing, as such, in the blood-vessels. And this peculiar sympathy between the genitals and the threat, owing to sensitive association, appears not only in the production of venereal ulcers in the throat, but in variety of other instances, as in the mumps, in the hydrophobia, some coughs, strangulation, the production of the beard, change of voice at puberty. Which are further described in Class IV. 2. 1.7. To evince that the production of such large quantities of contagious matter as are seen in some variolous patients, so as to cover the whole skin almost with pustules, does not arise from any chemical fermentation in the blood, but that it is ow- ing to morbid motions of the fine extremities of the capillaries or glands, whether these be ruptured or not, appears from the quantity of this matter always corresponding with the quantity of the fever; that is, with the violent exertions of those glands and capillaries which are the terminations of the arterial system. The truth of this theory is evinced further by a circumstance observed by Mr. J. Hunter, in his Treatise on Venereal Disease; that in a patient who was inoculated for the small-pox, and who appeared afterwards to have been previously infected with the measles, the progress of the small-pox was delayed till the measles had run their course, and that then the small-pox went through its usual periods. Two similar cases fell under my care, which I shall here re- late, as it confirms that of Mr. Hunter, and contributes to illus- trate this part of the theory of contagious diseases. I have transcribed the particulars from a letter of Mr. Lightwood, of Yoxal, the surgeon who daily attended them, and, at my request, after I had seen them, kept a kind of journal of their cases. Miss H. and Miss L. two sisters, the one about four and the other about three years old, were inoculated Feb. 7, 1791. On the 10th there was a redness on both arms discernible by a glass. On the 11th their arms were so much inflamed as to leave no doubt of the infection having taken place. On the 12th less appearance of inflammation on their arms. In the evening Miss 296 DISEASES OF SENSATION. SECT. XXXIII. 2. Miss L. had an eruption which resembled the measles. On the 13th the eruption on Miss L. was very full on the face and breast, like the measles, with considerable fever. It was now known, that the measles were in a farm-house in the neighbour- hood. Miss H.'s arm less inflamed than yesterday. On the 14th Miss L.'s fever great, and the eruption universal. The arm appears to be healed. Miss H.'s arm somewhat redder. They were now put into separate rooms. On the 15th Miss L.'s arms as yesterday. Eruption continues. Miss H.'s arms have varied but little. 16th, the eruptions on Miss L. are dy- ing away; her fever gone. Begins to have a little redness in one arm at the place of inoculation. Miss H.'s arms get redder, but she has no appearance of complaint. 20th, Miss L.'s arms have advanced slowly till this day, and now a few pustules ap- pear. Miss H.'s arm has made little progress from the 16th to this day, and now she has some fever. 21st, Miss L. as yes- terday. Miss H. has much inflammation, and an increase of the red circle on one arm to the size of half a crown, and had much fever at night, with fetid breath. 22d, Miss L.'s pustules continue advancing. Miss H.'s inflammation of her arm and red circle increases. A few red spots appear in different parts, with some degree of fever this morning. 23d, Miss L. has a larger crop of pustules. Miss H. has small pustules and great inflammation of her arms, with but one pustule like to suppu- rate. After this day they gradually got well, and the pustules disappeared. In one of these cases the measles went through their com- mon course with milder symptoms that usual, and in the other, the measly contagion seemed just sufficient to stop the progress of variolous contagion, but without itself throwing the consti- tution into any disorder. At the same time both the measles and small-pox seem to have been rendered milder. Does not this give an idea, that if they were both inoculated at the same time, that neither of them might affect the patient? From these cases I contend, that the contagious matter of these diseases does not affect the constitution by a fermenta- tion, or chemical change of the blood, because then they must have proceeded together, and have produced a third something, not exactly similar to either of them; but that they produce new motions of the cutaneous terminations of the blood vessels, which, for a time, proceed daily with increasing activity, like some paroxysms of fever, till they at length secrete or form a similar poison by these unnatural actions. Now, as in the measles one kind of unnatural motion takes place, and in the small-pox another kind, it is easy to conceive, 297 SECT. XXXIII. 2. DISEASES OF SENSATION. conceive, that these different kinds of morbid motions cannot exist together; and, therefore, that that which has first begun will continue till the system becomes habituated to the stimu- lus which occasions it, and has ceased to be thrown into ac- tion by it; and then the other kind of stimulus will, in its turn, produce fever, and new kinds of motions peculiar to itself. 10. On further considering the action of contagious mat- ter, since the former part of this work was sent to the press, where I have asserted, in Sect. XII. 3. 6. that it is probable that the variolous matter is diffused through the blood; I pre- vailed on my friend Mr. Power, surgeon at Bosworth, in Lei- cester shire, to try whether the small-pox could be inoculated by using the blood of a variolous patient, instead of the mat- ter from the pustules; as I thought such an experiment might throw some light, at least, on this interesting subject. The fol- lowing is an extract from his letter:— " March 11, 1793. I inoculated two children, who had not had the small-pox, with blood which was taken from a pa- tient on the second day after the eruption commenced, and be- fore it was completed. And at the same time I inoculated my- self with blood from the same person, in order to compare the appearances which might arise in a person liable to receive the in section, and in one not liable to receive it. On the same day I inoculated four other children, liable to receive the in- fection, with blood taken from another person on the fourth day after the commencement of the eruption. The patients from whom the blood was taken had the disease mildly, but had the most pustules of any I could select from twenty in- oculated patients; and as much of the blood was insinuated un- der the cuticle as I could introduce by elevating the skin without drawing blood ; and three or four such punctures were made in each of their arms, and the blood was used in its fluid state. " As the appearances in all these patients, as well as in my- self, were similar, I shall only mention them in general terms. March 13. A slight subcuticular discoloration, with rather a livid appearance, without soreness or pain, was visible in them all, as well as in my own hand. 15. The discoloration some what less, without pain or soreness. Some patients inoculated on the same day with variolous matter have considerable in- flammation. 17. The discoloration is quite gone in them all, and from my own hand, a dry mark only remaining. And they were all inoculated on the 18th, with variolous matter, which produced the disease in them all." Mr. Power afterwards observes, that, as the patients from whom the blood was taken had the disease mildly, it may be supposed, 298 DISEASES OF SENSATION. SECT. XXXIII. 2. supposed, that though the contagious matter might be mixed with the blood, it might still be in too dilute a date to convey the infection; but adds at the same time, that he has diluted re- cent matter with at least five times its quantity of water, and which has still given the infection; though he has sometimes diluted it so far as to fail. The following experiments were instituted at my request by my friend Mr. Hadley, surgeon in Derby, to ascertain whether the blood of a person in the small-pox be capable of communi- cating the disease. " Experiment 1st. October 18th, I took 1793. some blood from a vein in the arm of a person who had the small-pox, on the second day of the eruption, and introduc- ed a small quantity of it immediately with the point of a lan- cet, between the scarf and true skin of the right arm of a boy nine years old, in two or three different places; the other arm was inoculated with variolous matter at the same time. " 19th. The punctured parts of the right arm were surrounded with some degree of subcuticular inflammation. 20th. The inflammation more considerable, with a slight degree of itching, but no pain upon pressure. 21st. Upon examining the arm this day with a lens, I found the inflammation less extensive, and the redness changing to a deep yellow or orange-colour. 22d. In- flammation nearly gone. 23d. Nothing remained, except a slight discoloration and a little scurfy appearance on the punctures. At the same time the inflammation of the arm inoculated with variolous matter was increasing fast, and he had the disease mildly at the usual time. " Experiment 2d. I inoculated another child at the same tune and in the same manner, with blood taken on the first day of the eruption; but as the appearance and effects were similar to those in the preceding experiment, I shall not relate them minutely. " Experiment 3d. October 20th. Blood was taken from a person who had the small-pox, on the third day of the erup- tion, and on the sixth from the commencement of the erup- tive fever. I introduced some of it in its fluid state into both arms of a boy seven years old. 21st. There appeared to be some inflammation under the cuticle, where the punctures were made 22d. Inflammation more considerable. 23d. On this day the inflammation was somewhat greater, and the cuticle rather elevated. 24th. Inflammation much less, and only a brown or orange colour remained. 25th. Scarcely any dis- coloration less. On this day he was inoculated with variolous matter; the progress of the infection went on in the usual way, and he had the small-pox very favourably. " At 299 SECT. XXXIII. 2. DISEASES OF SENSATION. " At this time I was requested to inoculate a young person, who was thought to have had the small-pox, but his parents were not quite certain; in one arm I introduced variolous mat- ter, and in the other blood, taken as in experiment 3d. On the second day after the operation, the punctured parts were inflamed, though I think the and in which I had inferred va- riolous matter was rather more so than the other. On the third the inflammation was increased, and looked much the same as in the preceding experiment. 4th. The inflammation was much diminished, and on the 5th almost gone. He was ex- posed at the same time to the natural infection, but has con- tinued perfectly well. " I have frequently observed (and believe most practiti- oners have done the same), that if variolous matter be inserted in the arm of a person who has previously had the small-pox, that the inflammation on the second or third days is much greater than if they had not had the disease, but on the fourth or fifth it disappears. " On the 23d I introduced blood into the arms of three more children, taken on the third and fourth days of the erup- tion. The appearances were much the same as mentioned in experiments first and third. They were afterwards inoculated with variolous matter, and had the disease in the regular way. " The above experiments were made with blood taken from a small vein in the hand or foot of three or four different pa- tients, whom I had at that time under inoculation. They were selected from 160, as having the greatest number of pustules. The part was washed with warm water before the blood was taken, to prevent the possibility of any matter being mixed with it from the surface." Shall we conclude from hence, that the variolous matter never enters the blood-vessels? but that the morbid motions of the vessels of the skin around the insertion of it continue to in- crease in a larger and larger circle for fix or seven days; that then their quantity of morbid action becomes great enough to produce a fever -fit. and to affect the stomach by association of motions? and finally, that a second association of motions is produced between the stomach and the other parts of the skin, inducing them into morbid actions similar to those of the circle round the insertion of the variolous matter? Many more expe- riments and observations are required before this important question can be satisfactorily answered. It may be adduced, that as the matter inferred into the skin Of the arm frequently swells the lymphatic in the axilla, that in that circumstance it seems to be there arrested in its progress, R r and 300 DISEASES OF SENSATION. SECT. XXXIII. 2. and cannot be imagined to enter the blood by that lymphatic gland till the swelling of it subsides. Some other phenomena of the disease are more easy reconcileable to this theory of sym- pathetic motions than to that of absorption; as the time taken up between the insertion of the matter, and the operation of it on the system, as mentioned above. For the circle around the insertion is seen to increase, and to inflame; and I believe, un- dergoes a kind of diurnal paroxysm of torpor and paleness, with a succeeding increase of action and colour, like a topical fever- fit. Whereas, if the matter is conceived to circulate for six or seven days with the blood, without producing disorder, it ought to be rendered milder, or the blood-vessels more familiarized to its acrimony. It is much easier to conceive, from this doctrine of associated or sympathetic motions of distant parts of the system, how it happens, that the variolous infection can be received but once, as before explained, than by supposing, that a change is effect- ed in the mass of blood by any kind of fermentative process. The curious circumstance of the two contagions of small- pox and measles not acting at the same time, but one of them resting or suspending its action till that of the other ceases, may be much easier explained from sympathetic or associated actions of the infected part with other parts of the system, than it can from supposing the two contagions to enter the circulation. The skin of the face is subject to more frequent vicissitudes of heat and cold, from its exposure to the open air, and is in consequence more liable to sensitive association with the stomach than any other part of the surface of the body, because their ac- tions have been more frequently thus associated. Thus, in a surfeit from drinking cold water, when a person is very hot and fatigued, an eruption is liable to appear on the face in conse- quence of this sympathy. In the same manner the rosy erup- tion on the faces of drunkards more probably arises from the sympathy of the face with the stomach, rather than between the face and the liver, as is generally supposed. This sympathy between the stomach and the skin of the face is apparent in the eruption of the small-pox: since, where the disease is in considerable quantity, the eruption on the face first succeeds the sickness of the stomach. In the natural disease the stomach seems to be frequently primarily affected, either alone or along with the tonsils, as the matter seems to be only diffused in the air, and by being mixed with the saliva, or mucus of the tonsils, to be swallowed into the stomach. After some days the irritative circles of motions become dis- ordered by this new stimulus, which acts upon the mucous lining of 301 SECT. XXXIII. 3. DISEASES OF SENSATION. of the stomach; and sickness, vertigo, and a diurnal fever suc- ceed. These disordered irritative motions become daily increased for two or three days, and then, by their increased action, cer- tain sensitive motions, or inflammation, is produced; and at the next cold fit of fever, when the stomach recovers from its torpor, an inflammation of the external skin is formed in points (which afterwards suppurate), by sensitive association, in the same man- ner as a cough is produced in consequence of exposing the feet to cold, as described in Sect. XXV. 1. 1. and Class IV. 2. 2. 4. If the inoculated skin of the arm, as far as it appears inflam- ed, was to be cut out, or destroyed by caustic, before the fe- ver commenced, as suppose on the fourth day after inoculation, would this prevent the disease? as it is supposed to prevent the hydrophobia. III. 1. Where the new vessels, and enlarged old ones, which constitute inflammation, are not so hastily distended as to burst, and form a new kind of gland for the secretion of matter, as above mentioned; if such circumstances happen as diminish the painful sensation, the tendency to growth ceases, and by and by an absorption commences, not only of the superabundant quan- tity of fluids deposited in the inflamed part, but of the solids like- wise, and this even of the hardest kind. Thus, during the growth of the second set of teeth in chil- dren, the roots of the first set are totally absorbed, till at length nothing of them remains but the crown; though a few weeks before, if they are drawn immaturely, their roots are found com- plete. Similar to this Mr. Hunter has observed, that where a dead piece of bone is to exfoliate, or to separate from a living one, that the dead part does not putrify, but remains perfectly sound; while the surface of the living part of the bone, which is in contact with the dead part, becomes absorbed, and thus effects its separation. Med. Comment. Edinb. v. i. 425. In the same manner the calcareous matter of gouty concretions, the coagu- lable lymph deposited on inflamed membranes in rheumatism and extravasated blood, become absorbed; which are all as solid and as indissoluble materials as the new vessels produced in in- flammation. This absorption of the new vessels and deposited fluids of in- flamed parts is called resolution: it is produced by first using such internal means as decrease the pain of the part, and, in consequence, its new motions, as repeated bleeding, cathartics, diluent potations, and warm bath. After the vessels are thus emptied, and the absorption of the new vessels and deposited fluids is evidently begun, it is much promoted by stimulating the part externally by solutions of lead or 302 DISEASES OF SENSATION. SECT.XXXIII.3. or other metals, and internally by the bark and small doses of opium. Hence, when an ophthalmy begins to become paler, any acrid eye-water, as a solution of six grains of white vitriol in an ounce of water, hastens the absorption, and clears the eye in a very short time. But the same application used a few days sooner would have increased the inflammation. Hence, after evacuation, opium in small doses may contribute to promote the absorption of fluids deposited on the brain, as observed by Mr. Bromfield, in his Treatise of Surgery. 2. Where an abscess is formed by the rupture of these new vessels, the violence of inflammation ceases, and a new gland separates a material called pus: at the same time a less degree of inflammation produces new vessels, called vulgarly proud flesh; which, if no bandage confines its growth, nor any other circumstance promotes absorption in the wound, would rise to a great height above the usual size of the part. Hence the art of healing ulcers consists in producing ten- dency to absorption in the wound, greater than the deposition. Thus, when an ill-conditioned ulcer separates a copious and thin discharge, by the use of any stimulus, as of salts of lead, or mercury, or copper externally applied, the discharge becomes diminished in quantity, and becomes thicker as the thinner parts are first absorbed. But nothing so much contributes to increase the absorption in a wound, as covering the whole limb above the sore with a bandage, which should be spread with some plaster, as with emplastrum de minio, to prevent it from slipping. By this arti- ficial tightness of the skin, the arterial pulsations act with double their usual power in promoting the ascending current of the fluid in the valvular lymphatics. Internally the absorption from ulcers should be promoted first by evacuation, then by opium, bark, mercury, steel. 3. Where the inflammation proceeds with greater violence or rapidity, that is, when, by the painful sensation, a more in- ordinate activity of the organ is produced, and, by this great activity, an additional quantity of painful sensation follows in an increasing ratio, till the whole of the sensorial power, or spirit of animation, in the part becomes exhausted, a mortifica- tion ensues, as in a carbuncle, in inflammations of the bowels, in the extremities of old people, or in the limbs of those who are brought near a fire after having been much benumbed with cold. And from hence it appears, why weak people are more subject to mortification than strong ones, and why, in weak persons, less pain will produce mortification, namely, because the sensorial power is sooner exhausted by an excess of activity. I re- 303 SECT. XXXIII. 4. DISEASES OF SENSATION. I remember seeing a gentleman who had the preceding day tra- velled two stages in a chaise, with what he termed a bearable pain in his bowels, which, when I saw him, had ceased rather suddenly, and without a passage through him: his pulse was then weak, though not very quick; but as nothing which he swallowed would continue in his stomach many minutes, I concluded that the bowel was mortified: he died on the next day. It is usual for patients sinking under the small-pox, with mortified pustules, and with purple spots intermixed, to complain of no pain, but to say they are pretty well to the last moment. Recapitulation. IV. When the motions of any part of the system, in conse- quence of previous torpor, are performed with more energy than in the irritative fevers, a disagreeable sensation is produced, and new actions of some part of the system commence in con- sequence of this sensation, conjointly with the irritation; which motions constitute inflammation. If the fever be attended with a strong pulse, as in pleurisy or rheumatism, it is termed synocha sensitiva, or sensitive fever with strong pulse; which is usually termed inflammatory fever. If it be attended with weak pulse, it is termed typhus sensitivus, or sensitive fever with weak pulse; or typhus gravior, or putrid malignant fever. The synocha sensitiva, or sensitive fever with strong pulse, is generally attended with some topical inflammation, as in pe- ripneumony, hepatitis, and is accompanied with much coagu- lable lymph, or size; which rises to the surface of the blood, when taken into a bason, as it cools; and which is believed to be the increased mucous secretion from the coats of the arteries, inspissated by a greater absorption of its aqueous and saline part, and perhaps changed by its delay in the circulation. The typhus sensitivus, or sensitive fever with weak pulse, is frequently attended with delirium, which is caused by the defi- ciency of the quantity of sensorial power, and with variety of cutaneous eruptions. Inflammation is caused by the pains occasioned by excess of action, and not by those pains which are occasioned by defect of action. These morbid actions, which are thus produced by two sensorial powers, viz. by irritation and sensation, se- crete new living fibres, which elongate the old vessels, or form new ones, and, at the same time, much heat is evolved from these combinations. By the rupture of these vessels, or by a new construction of their apertures, purulent matters are secreted of various kinds; which are infectious the first time they are ap- plied to the skin beneath the cuticle, or swallowed with the sa- liva 304 DISEASES OF SENSATION. SECT. XXXIII. 4. liva into the stomach. This contagion acts not by its being absorbed into the circulation, but by the sympathies, or associ- ated actions, between the part first stimulated by the contagious matter and the other parts of the system. Thus, in the natural small-pox the contagion is swallowed with the saliva, and by its stimulus inflames the stomach: this variolous inflammation. of the stomach increases every day, like the circle round the puncture of an inoculated arm, till it becomes great enough to disorder the circles of irritative and sensitive motions, and thus produces fever-fits, with sickness and vomiting. Lastly, after the cold paroxysm, or fit of torpor, of the stomach has in- creased for two or three successive days, an inflammation of the skin commences in points; which generally first appear upon the face, as the associated actions between the skin of the face and that of the stomach have been more frequently exerted to- gether than those of any other parts of the external surface. Contagious matters, as those of the measles and small-pox, do not act upon the system at the same time; but the progress of that which was last received is delayed, till the action of the former infection ceases. All kinds of matter, even that from common ulcers, are probably contagious the first time they are inserted beneath the cuticle, or swallowed into the stomach; that is, as they were formed by certain morbid actions of the extre- mities of the vessels, they have the power to excite similar mor- bid actions in the extremities of other vessels, to which they are applied; and these by sympathy, or associations of motion, ex- cite similar morbid actions in distant parts of the system, with out entering the circulation; and hence the blood of a patient in the small-pox will not give that disease by inoculation to others. When the new fibres or vessels become again absorbed into the circulation, the inflammation ceases; which is promoted after diffident evacuations, by external stimulants and banda- ges: but where the action of the vessels is very great, a morti- fication of the part is liable to ensue, owing to the exhaustion of sensorial power; which, however, occurs in weak people without much pain, and without very violent previous inflam- mation; and, like partial paralysis, may be esteemed one mode of natural death of old people, a part dying before the whole. SECT. 305 SECT. XXXIV. 1. DISEASES OF VOLITION. SECT. XXXIV. DISEASES OF VOLITION. I. 1. Volition defined. Motions termed involuntary are caused by volition. Desires opposed to each other. Deli- beration. Ass between two hay-cocks. Saliva swallowed against one 's desire. Voluntary motions distinguished from those associated with sensitive motions. 2. Pains from ex- cess, and from defect of motion. No pain is felt during vehement voluntary exertion; as in cold fits of ague, la- bour-pains, stranguary, tenesmus, vomiting, restlessness in fevers, convulsion of a wounded muscle. 3. Of holding the breath and screaming in pain: why swine and dogs cry out in pain, and not sheep and horses. Of grinning and biting in pain: why mad animals bite others. 4. Epileptic convulsions explained: why the fits begin with quivering of the under jaw, biting the tongue, and fitting the teeth: why the convulsive motions are alternately re- laxed. The phenomenon of laughter explained. Why children cannot tickle themselves. How some have died from immoderate laughter. 5. Of cataleptic spasms, of the locked jaw, of painful cramps, 6. Syncope explained. Why no external objects are perceived in syncope. 7. Of palsy and apoplexy from violent exertions. Case of Mrs. Scot. From dancing, scating, swimming. Case of Mr. Nairn. Why palsies are not always immediately preceded by violent exertions. Palsy and epilepsy from diseased livers. Why the right arm more frequently paralytic than the left. How paralytic limbs regain their motions. II. Diseases of the sensual motions from excess or defect of voluntary exertion. 1. Madness. 2. Distinguished from delirium. 3. Why mankind more liable to insanity than brutes. 4. Suspicion. Want of shame and of cleanliness. 5. They bear cold, hunger and fatigue. Charles XII. of Sweden. 6. Pleasureable delirium, and insanity. Child riding on stick. Pains of martyrdom not felt. 7. Dropsy. 8. Inflammation cured by insanity. III. 1. Pain relieved by reverie. Reverie is an exertion of voluntary and sen- sitive motions. 2. Case of reverie. 3. Lady supposed to have two fouls. 4. Methods of relieving pain. I. 1. BEFORE we commence this Section on Diseased Voluntary Motions, it may be necessary to premise, that the word volition is not used in this work exactly in its common acceptation. 306 DISEASES OF VOLITION. SECT. XXXIV. 1. acceptation. Volition is said, in Section V. to bear the same, analogy to desire and aversion, which sensation does to pleasure; and pain. And hence, that when desire or aversion produces any action of the muscular fibres, or of the organs of sense, they are termed volition; and the actions produced in conse- quence are termed voluntary actions. Whence it appears, that motions of our muscles or ideas may be produced in consequence of desire or aversion, without our having the power to prevent them; and yet these motions may be termed voluntary, accord- ing to our definition of the word; though, in common lan- guage, they would be called involuntary. The objects of desire and aversion are generally at a distance, whereas those of pleasure and pain are immediately acting upon our organs. Hence, before desire or aversion is exerted, so as to cause any actions, there is generally time for deliberation; which consists in discovering the means to obtain the object of desire, or to avoid the object of aversion, or in examining the good or bad consequences which may result from them. In this case it is evident that we have a power to delay the pro- posed action, or to perform it; and this power of choosing, whether we shall act or not, is, in common language, expressed by the word volition, or will. Whereas, in this work the word volition means simply the active date of the sensorial fa- culty in producing motion in consequence of desire or aversion, whether we have the power of restraining that action or not; that is, whether we exert any actions in consequence of oppo- site desires or aversions, or not. For if the objects of desire or aversion are present, there is no necessity to investigate or compare the means of obtaining. them, nor do we always deliberate about their consequences; that is, no deliberation necessarily intervenes, and, in conse- quence, the power of choosing to act or not is not exerted. It is probable, that this two-fold use of the word volition in all languages, has confounded the metaphysicians, who have dis- puted about free will and necessity. Whereas, from the above analysis, it would appear, that during our sleep we use no vo- luntary exertions at all; and in our waking hours, that they are the consequence of desire or aversion. To will, is to act in consequence of desire; but to desire, means to desire something, even if that something be only to become free from the pain which causes the desire; for to desire nothing, is not to desire: the word desire, therefore, includes both the action and the object or motive; for the object and motive of desire are the same thing. Hence, to desire without an object, that is, without a motive, is a solecism in language. As 307 SECT. XXXIV. 1. DISEASES OF VOLITION. As if one should ask, if you could eat without food, or breathe without air. From this account of volition it appears, that convulsions of the muscles, as in epileptic fits, may, in the common sense of that word, be termed involuntary; because no deliberation is in- terposed between the desire or aversion and the consequent ac- tion; but in the sense of the word, as above defined, they belong to the class of voluntary motions, as delivered in Vol. ii. Class III. If this use of the word be discordant to the ear of the rea- der, the term morbid voluntary motions, or motions in conse- quence of aversion, may be substituted in its stead. If a person has a desire to be cured of the ague, arid has at the same time an aversion (or contrary desire) to swallowing an ounce of Peruvian bark, he balances desire against desire, or aversion against aversion; and thus he acquires the power of choosing, which is the common acceptation of the word wil- ling. But in the cold fit of ague, after having discovered that the act of shuddering, Or exerting the subcutaneous muscles, re- lieves the pain of cold, he immediately exerts this act of voli- tion, and shudders, as soon as the pain and Consequent aversion return, without any deliberation intervening: yet is this act, as well as that of swallowing an ounce of the bark, caused by volition; and that even though he endeavours in vain to prevent it by a weaker contrary volition. This recalls to our minds the story of the hungry ass between two hay-stacks, where the two desires are supposed so exactly to counteract each other, that he goes to neither of the stacks, but perishes by want. Now, as two equal and opposite desires are thus supposed to balance each other, and prevent all action, it follows, that if one of these hay-stacks was suddenly removed, that the ass would irresistibly be hurried to the other, which, in the common use of the word, might be called an involuntary act; but which, in our acceptation of it, would be classed amongst voluntary ac- tions, as above explained. Hence, to deliberate is to compare opposing desires or aver- sions, and that which is the most interesting at length prevails, and produces action. Similar to this, where two pains oppose each other, the stronger or more interesting one produces ac- tion; as in pleurisy the pain from suffocation would produce expansion of the lungs, but the pain occasioned by extending the inflamed membrane, which lines the chest, opposes this ex- pansion, and one or the other alternately prevails. When any one moves his hand quickly near another person's eyes, the eye-lids instantly close: this act, in common language, is termed involuntary, as we have not time to deliberate or to S s exert 308 DISEASES OF VOLITION. SECT. XXXIV. 1. exert any contrary desire or aversion; but in this work it would be termed a voluntary act, because it is caused by the faculty of volition, and after a few trials the nectitation can be pre- vented by a contrary or opposing volition. The power of opposing volitions is best exemplified in the story of Mutius Scævola, who is said to have thrust his hand into the fire before Porcenna, and to have suffered it to be con- sumed for having failed him in his attempt on the life of that ge- neral. Here the aversion for the loss of same, or the unsatisfi- ed desire to serve his country, the two prevalent enthusiasms at that time, were more powerful than the desire of withdrawing his hand, which must be occasioned by the pain of combustion; of these opposing volitions Vincet amor patriæ, laudumque immensa cupido. If any one is told not to swallow his saliva for a minute, he soon swallows it contrary to his will, in the common sense of that word; but this also is a voluntary action, as it is perform- ed by the faculty of volition, and is thus to be understood. When the power of volition is exerted on any of our senses, they become more acute, as in our attempts to hear small noises in the night; as explained in Section XIX. 6. Hence, by our attention to the fauces, from our desire not to swallow our saliva, the fauces becomes more sensible; and the stimulus of the saliva is followed by greater sensation, and consequent de- sire of swallowing it. So that the desire or volition, in conse- quence of the increased sensation of the saliva, is more power- ful than the previous desire not to swallow it. See vol. ii. Deglutitio invita. In the same manner, if a modest man wishes not to want to make water, when he is confined with ladies in a coach or an assembly-room, that very act of volition in- duces the circumstance which he wishes to avoid, as above explained; insomuch, that I once saw a partial insanity, which might be called a voluntary diabetes, which was occasioned by the fear (and consequent aversion) of not being able to make water at all. It is further necessary to observe here, to prevent any con- fusion of voluntary with sensitive, or associate motions, that in all the instances of violent efforts to relieve pain, those ef- forts are at first voluntary exertions; but after they have been frequently repeated for the purpose of relieving certain pains, they become associated with those pains, and cease, at those times, to be subservient to the will; as in coughing, sneezing, and strangury. Of these motions those which contribute to remove or dislodge the offending cause, as the actions of the abdominal 309 SECT. XXXIV. 1. DISEASES OF VOLITION. abdominal muscles in parturition, or in vomiting, though they were originally excited by volition, are in this work termed sen- fitive motions; but those actions of the muscles or organs of sense, which do not contribute to remove the offending cause, as in general convulsions or in madness, are in this work term- ed voluntary motions, or motions in consequence of aversion, though, in common language, they are called involuntary ones. Those sensitive unrestrainable actions which contribute to re- move the cause of pain, are uniformly and invariably exerted, as in coughing or sneezing; but those motions which are ex- erted in consequence of aversion without contributing to re- move the painful cause, but only to prevent the sensation of it, as in epileptic or cataleptic fits, are not uniformly and invari- ably exerted, but change from one set of muscles to another, as will be further explained; and may, by this criterion also, be distinguished from the former. At the same time those motions which are excited by per- petual stimulus, or by association with each other, or imme- diately by pleasureable or painful sensation, may properly be termed involuntary motions, as those of the heart and arteries; as the faculty of volition seldom affects those, except when it exists in unnatural quantity, as in maniacal people. 2. It was observed in Section XIV. on the Production of Ideas, that those parts of the system which are usually termed the organs of sense, are liable to be excited into pain by the ex- cess of the stimulus of those objects which are, by nature, adapted to affect them; as of too great light, sound, or pres- sure. But that these organs receive no pain from the defect or absence of these stimuli, as in darkness or silence. But that our other organs of perception, which have generally been called appetites, as of hunger, third, want of heat, want of fresh air, are liable to be affected with pain by the defect, as well as by the excess of their appropriated stimuli. This excess or defect of stimulus is, however, to be consider- ed only as the remote cause of the pain, the immediate cause being the excess or defect of the natural action of the affected part, according to Sect. IV. 5. Hence all the pains of the body may be divided into those from excess of motion, and those from defect of motion; which distinction is of great importance in the knowledge and cure of many diseases. For as the pains from excess of motion either gradually subside, or are in gene- ral succeeded by inflammation; so those from defect of motion either gradually subside, or are in general succeeded by convul- sion or madness. These pains are easily distinguishable from each other by this circumstance, that the former are attended with 310 DISEASES OF VOLITION. SECT. XXXIV. 1. with heat of the pained part, or of the whole body; whereas the latter exists without increase of heat in the pained part, and is generally attended with coldness of the extremities of the bo- dy; which is the true criterion of what have been called ner- vous pains. Thus, when any acrid material, as snuff or lime, falls into the eye, pain, and inflammation, and heat, are produced from the excess of stimulus; but violent hunger, hemicrania, or the cla- vus hystericus, are attended with coldness of the extremities, and defect of circulation. When we are exposed to great cold, the pain we experience from the deficiency of heat is at- tended with a quiescence of the motions of the vascular system; so that no inflammation is produced, but a great desire of heat, and a tremulous motion of the subcutaneous muscles, which is properly a convulsion in consequence of this pain from defect of the stimulus of heat. It was before mentioned, that as sensation consists in certain movements of the sensorium, beginning at some of the extremi- ties of it, and propagated to the central parts of it; so volition consists of certain other movements of the sensorium, com- mencing in the central parts of it, and propagated to some of its extremities. This idea of these two great powers of motion in the animal machine is confirmed from observing, that they ne- ver exist in a great degree or universally at the same time; for while we strongly exert our voluntary motions, we cease to feel the pains or uneasinesses which occasioned us to exert them. Hence, during the time of fighting with fists or (words no pain is felt by the conbatants, till they cease to exert themselves. Thus, in the beginning of ague-fits, the painful sensation of cold is diminished, while the patient exerts himself in the shivering and gnashing of his teeth. He then ceases to exert himself, and the pain of cold returns; and he is thus perpetually induced to reiterate these exertions, from which he experiences a tempo- rary relief. The same occurs in labour-pains; the exertion of; the parturient Woman relieves the violence of the pains for a time, which recur again soon after she has ceased to use those exertions. The same is true in many other painful diseases, as in the strangury, tenesmus, and the efforts of vomiting; all these disagreeable sensations are diminished or removed for a time the various exertions by they occasion, and recur alternately with those exertions. The restlessness in some fevers is an almost perpetual exer- tion of this kind, excited to relieve some disagreeable sensa- tions; the reciprocal opposite exertions of a wounded worm, the alternate emprosthotonos and opisthotonos of some spasmodic diseases, 311 SECT. XXXIV. 1. DISEASES OF VOLITION. diseases, and the intervals of all convulsions, from whatever cause, seem to be owing to this circumstance of the laws of ani- mation; that great or universal exertion cannot exist at the same time with great or universal sensation, though they can exist reciprocally; which is probably resolvable into the more general law, that the whole sensorial power being expanded in one mode of exertion, there is none to spare for any other. Whence syn- cope, or temporary apoplexy, succeeds to epileptic convulsions. 3. Hence, when any violent pain afflicts us, of which we can neither avoid nor remove the cause, we soon learn to en- deavour to alleviate it, by exerting some violent voluntary effort, as mentioned above; and are naturally induced to use those muscles for this purpose, which have been, in the early periods of our lives, most frequently or most powerfully exerted. Now, the first muscles which infants use most frequently, are those of respiration; and, on this account, we gain a habit of holding our breath, at the same time that we use great efforts to exclude it, for the purpose of alleviating unavoidable pain; or we press out our breath through a small aperture of the la- rynx, and scream violently, when the pain is greater than is believable by the former mode of exertion. Thus children scream to relieve any pain either of body or mind, as from an- ger, or fear of being beaten. Hence it is curious to observe, that those animals who have more frequently exerted their muscles of respiration violently, as in talking, barking, or grunting, as children, dogs, hogs, scream much more, when they are in pain, than those other animals who use little or no language in their common modes of life, as horses, sheep, and cows. The next most frequent or most powerful efforts which in- fants are first tempted to produce, are those with the muscles in biting hard substances: indeed, the exertion of these muscles is very powerful in common mastication, as appears from the pain we receive, if a bit of bone is unexpectedly found amongst our softer food; and further appears from their acting to so great mechanical disadvantage, particularly when we bite with the incisores, or canine teeth; which are first formed, and thence are first used to violent exertion. Hence, when a person is in great pain, the cause of which he cannot remove, he sets his teeth firmly together, or bites some substance between them with great vehemence, as another mode of violent exertion to produce a temporary relief. Thus we have a proverb, where no help can be had in pain, " to grin and abide;" and the tortures of hell are said to be attended with " gnashing of teeth." Hence, 312 DISEASES OF VOLITION. SECT. XXXIV. 1. Hence, in violent spasmodic pains, I have seen people bite not only their tongues, but their arms or fingers, or those of the attendants, or any object which was near them; and also strike, pinch, or tear others or themselves, particularly the part of their own body which is painful at the time. Soldiers who die of painful wounds in battle, are said by Homer to bite the ground. Thus, also, in the bellon, or colica saturnina, the patients are said to bite their own flesh, and dogs in this disease to bite up the ground they lie upon. It is probable that the great endea- vours to bite in mad dogs, and the violence of other mad ani- mals, is owing to the same cause. 4. If the efforts of our voluntary motions are exerted with still greater energy for the relief of some disagreeable sensation, convulsions are produced; as the various kinds of epilepsy, and in some hysteric paroxysms. In all these diseases a pain or dis- agreeable sensation is produced, frequently by worms, or acidity in the bowels, or by a diseased nerve in the side or head, or by the pain of a diseased liver. In some constitutions a more intolerable degree of pain is produced, in some part, at a distance from the cause, by sensitive association, as before explained: these pains, in such constitu- tions, arise to so great a degree, that I verily believe no artificial i tortures could equal some which I have witnessed; and am confident life would not have long been preserved, unless they had been soon diminished or removed by the universal convul- sion of the voluntary motions, or by temporary madness. In some of the unfortunate patients I have observed, the pain has risen to an inexpressible degree, as above described, before the convulsions have supervened, and which were preceded by screaming and grinning: in others, as in the common epilepsy, the convulsion has immediately succeeded the commencement of the disagreeable sensations; and as a stupor frequently suc- ceeds the convulsions, they only seemed to remember that a pain at the stomach preceded the fit, or some other uneasy feel; or more frequently retained no memory at all of the immediate cause of the paroxysm. But even in this kind of epilepsy, where the patient does not recollect any preceding pain, the paroxysms generally are preceded by a quivering motion of the under jaw, with a biting of the tongue: the teeth afterwards become pressed together with vehemence, and the eyes are then convulsed, be- fore the commencement of the universal convulsion, which are all efforts to relieve pain. The reason why these convulsive motions are alternately ex- erted and remitted was mentioned above, and in Sect. XII. 1.3. when the exertions are such as give a temporary relief to pain, which 313 SECT. XXXIV. 1. DISEASES OF VOLITION. which excites them, they cease for a time, till the pain is again perceived; and then new exertions are produced for its relief. We see daily examples of this in the loud reiterated laughter of some people: the pleasureable sensation which excites this laughter arises, for a time, so high as to change its name and become painful: the convulsive motions of the respiratory mus- cles relieve the pain for a time: we are, however, unwilling to lose the pleasure, and presently put a slop to this exertion, and immediately the pleasure recurs, and again as instantly rises into pain. All of us have felt the pain of immoderate laughter; children have been tickled into convulsions of the whole body, and others have died in the aa of laughing, probably from a paralysis succeeding the long-continued actions of the muscles of respiration. Hence we learn the reason why children, who are so easily excited to laugh by the tickling of other people's fingers, can- not tickle themselves into laughter. The exertion of their hands in the endeavour to tickle themselves prevents the neces- sity of any exertion of the respiratory muscles to relieve the excess of pleasureable affection. See Sect. XVII. 3. 5. Chrysippus is recorded to have died laughing, when an ass was invited to dip with him. The same is related of one of the popes, who, when he was ill, saw a tame monkey at his bedside put on the holy thiara. Hall. Phys. T. iii. p. 306. There are instances of epilepsy being produced by laughing, recorded by Van Swieton, T. iii. 402 and 308. And it is well known, that many people have died instantaneously from the painful excess of joy, which probably might have been pre- vented by the exertions of laughter. Every combination of ideas which we attend to, occasions pain or pleasure: those which occasion pleasure, furnish either social or selfish pleasure—either malicious or friendly, or la- scivious, or sublime pleasure; that is, they give us pleasure, mixed with other emotions, or they give us unmixed pleasure, without occasioning any other emotions or exertions at the same time. This unmixed pleasure, if it be great, becomes painful, like all other animal motions, from stimuli of every kind; and if no other exertions are occasioned at the same time, we use the exertion of laughter to relieve this pain. Hence laughter is occasioned by such wit as excites simple pleasure without any other emotion, such as pity, love, reve- rence: for sublime ideas are mixed with admiration, beautiful ones with love, new ones with surprise; and these exertions of our ideas prevent the action of laughter from being necessary to relieve the painful pleasure above described. Whence laugh- able 314 DISEASES OF VOLITION. SECT. XXXIV. 1. able wit consists of frivolous ideas, without connections of any consequence, such as puns on words, or on phrases, incon- gruous junctions of ideas; on which account laughter is so frequent in children. Unmixed pleasure less than that which causes laughter, causes sleep, as in singing children to sleep, or in slight intoxication from wine or food. See Sect. XVIII. 12. If the pains, or disagreeable sensations above described, do not obtain a temporary relief from these convulsive exertions of the muscles, those convulsive exertions continue without remission, and one kind of catalepsy is produced. Thus, when a nerve or tendon produces great pain by its being inflamed or wounded, the patient sets his teeth firmly together, and grins violently, to diminish the pain; and if the pain is not relieved by this exertion, no relaxation of the maxillary muscles takes place, as in the convulsions above described, but the jaws re- main firmly fixed together. This locked jaw is the most fre- quent instance of cataleptic spasm, because we are more in- clined to exert the muscles subservient to mastication from their early obedience to violent efforts of volition. But in the case related in Sect. XIX. on Reverie, the cata- leptic lady had pain in her upper teeth; and pressing one of her hands vehemently against her cheek-bone to diminish this pain, it remained in that attitude for about half an hour twice a day, till the painful paroxysm was over. I have this very day seen a young lady in this disease (with which she has frequently been afflicted); she began to-day with violent pain shooting from one side of the forehead to the occiput, and after various druggies lay on the bed with her fingers and wrists bent and stiff for about two hours; in other respects she seemed in a syncope with a natural pulse. She then had inter- vals of pain and of spasm, and took three grains of opium every hour till she had taken nine grains, before the pains and spasm ceased. There is, however, another species of fixed spasm, which differs from the former, as the pain exists in the contracted muscle, and would seem rather to be the consequence than the cause of the contraction, as in the cramp in the calf of the leg, and in many other parts of the body. In these spasms it should seem, that the muscle itself is first thrown into contraction by some disagreeable sensation, as of cold; and that then the violent pain is produced by the great contraction of the muscular fibres extending its own tendons, which are said to be sensible to extension only: and is further explained in Sect. XVIII. 15. 6. Many 315 SECT. XXXIV. 1. DISEASES OF VOLITION. 6. Many instances have been given in this work, where, after violent motions, excited by irritation, the organ has become quiescent to less, and even to the great irritation, which induced it into violent motion; as after looking long at the sun or any bright colour, they cease to be seen; and after removing from bright day-light into a gloomy room, the eye cannot at first per- ceive the objects which stimulate it less. Similar to this is the syncope, which succeeds after the violent exertions of our volun- tary motions, as after epileptic fits; for the power of volition acts in this case as the stimulus in the other. This syncope is a temporary palsy, or apoplexy, which ceases after a time, the muscles recovering their power of being excited into action by the efforts of volition; as the eye, in the circumstance above mentioned, recovers in a little time us power of seeing objects in a gloomy room, which were invisible immediately after com- ing out of a stronger light. This is owing to an accumula- tion of sensorial power during the inaction of those fibres which were before accustomed to perpetual exertions, as explained in Sect. XII. 7. 1. A slighter degree of this disease is experienced by every one after great fatigue, when the muscles gain such inability to further action, that we are obliged to rest them for a while, or to summon a greater power of volition to continue their motions. In all the syncopes which I have seen induced after convul- sive fits, the pulse has continued natural, though the organs of sense, as well as the locomotive muscles, have ceased to perform their functions; for it is necessary for the perception of objects, that the external organs of sense should be properly excited by the voluntary power, as the eye-lids must be open, and perhaps the muscles of the eye put into action to distend, and thence give greater pellucidity to the cornea, which in syncope, as in death, appears flat and less transparent. The tympanum of the ear also seems to require a voluntary exertion of its muscles, to gain its due tension; and it is probable the other external organs of sense require a similar voluntary exertion to adapt them to the distinct perception of objects. Hence, in syncope, as in sleep as the power of volition is suspended, no external objects are perceived. Sec Sect. XVIII. 5. During the time which the patient lies in a fainting fit, the spirit of animation becomes ac- cumulated; and hence the muscles in a while become irritable bv their usual stimulation, and the fainting fit ceases. See Sect. XII. 7. 1. 7. If the exertion of the voluntary motions has been still more energetic, the quiescence which succeeds, is so complete, that they cannot again be excited into action by the efforts of T t the 316 DISEASES OF VOLITION SECT. XXXIV. 1 the will. In this manner the palsy and apoplexy (which is an universal palsy) are frequently produced after convulsions, or other violent exertions: of this I shall add a few instances. Piaternus mentions some who have died apoplectic from violent exertions in dancing; and Dr. Mead, in his Essay on Poisons, records a patient in the hydrophobia, who at one ef- fort broke the cords which bound him, and at the same instant expired. And it is probable, that those who have expired from immoderate laughter, have died from this paralysis consequent to violent exertion. Mrs. Scott, of Stafford, was walking in her garden in perfect health, with her neighbour Mrs. ---; the latter accidentally fell into a muddy rivulet, and tried in vain to disengage herself by the assistance of Mrs. Scott's hand. Mrs. Scott exerted her utmost power for many minutes, first to assist her friend, and next to prevent herself from being pulled into the morass, as her distressed companion would not disengage her hand. After other assistance was procured by their united screams, Mrs. Scott walked to a chair about twenty yards from the brook, and was seized with an apoplectic stroke; which continued many days, and terminated in a total loss of her right arm, and her speech; neither of which she ever after perfectly recovered. It is said, that many people in Holland have died after skat- ing too long or too violently on their frozen canals; it is pro- bable the death of these, and of others, who have died sudden- ly in swimming, has been owing to this great quiescence or pa- ralysis; which has succeeded very violent exertions, added to the concomitant cold, which has had greater effect after the suf- ferers had been heated and exhausted by previous exercise. I remember a young man of the name of Nairne, at Cam- bridge, who, walking on the edge of a barge, fell into the river. His cousin and fellow-student of the same name, knowing the other could not swim, plunged into the water after him, caught him by his clothes, and, approaching the bank, by a vehement exertion propelled him safe to the land; but that instant, seized, as was supposed, by the cramp, or paralysis, sunk to rise no more. The reason why the cramp of the muscles, which com- pose the calf of the leg, is so liable to affect swimmers, is, be- cause these muscles have very weak antagonists, and are in walking generally elongated again after their contraction by the weight of the body on the ball of the toe, which is very much greater than the resistance of the water in swimming. See Section XVIII. 15. It does not follow, that every apoplectic or paralytic attack is immediately preceded by vehement exertion; the quiescence, which 317 SECT. XXXIV. 1. DISEASES OF VOLITION. which succeeds exertion, and which is not so great as to be termed paralysis, frequently recurs afterwards at certain periods; and by other causes of quiescence, occurring with those peri- ods, as was explained in treating of the paroxysms of intermit- ting fevers; the quiescence at length becomes so great as to be incapable of again being removed by the efforts of volition, and complete paralysis is formed. See Section XXXII. 3. 2. Many of the paralytic patients, whom I have seen, have evidently had diseased livers from the too frequent potation of spirituous liquors; some of them have had the gutta rosea on their faces and breasts; which has, in some degree, receded either spontaneously, or by the use of external remedies, and the paralytic stroke has succeeded; and as in several persons, who have drank much vinous spirits, I have observed epileptic fits to commence at about forty or fifty years of age, without any hereditary taint, from the stimulus, as I believed, of a dis- eased liver: I was induced to ascribe many paralytic cases to the same source, which were not evidently the effect of age, or of unacquired debility. And the account given before of dropsies, which very frequently are owing to a paralysis of the absorbent system, and are generally attendant on free drinkers of spirituous liquors, confirmed me in this opinion. The disagreeable irritation of a diseased liver produces exer- tions and consequent quiescence; these, by the accidental con- currence of other causes of quiescence, as cold, solar or lunar periods, inanition, the want of their usual portion of spirit of wine, at length produces paralysis. This is further confirmed by observing, that the muscles we most frequently or most powerfully exert, are most liable to palsy, as those of the voice and of articulation; and of those paralytics which I have seen, a much greater proportion have lost the use of their right arm, which is so much more general- ly exerted than the left. I cannot dismiss this subject without observing, that after a paralytic stroke, if the vital powers are not much injured, that the patient has all the movements of the affected limb to learn over again, just as in early infancy: the limb is first moved by the irritation of its muscles, as in stretching, (of which a case was related in Section VII. 1, 3.) or by the electric concussion; afterwards it becomes obedient to sensation, as in violent dan- ger or fear; and lastly, the muscles become again associated with volition, and gradually acquire their usual habits of act- ing together. Another phenomenon in palsies is, that when the limbs of one side are disabled those of the other are in a perpetual motion. This 318 DISEASES OF VOLITION. SECT. XXXIV. 2, This can only be explained from conceiving that the power of motion, whatever it is, or wherever it resides, and which is capa- ble of being exhausted by fatigue, and accumulated in rest, is now less expended, whilst one half of the body is incapable of receiving its usual proportion of it, and is hence derived with greater ease, or in greater abundance, into the limbs, which remain unaffected. II. 1. The excess or defect of voluntary exertion produces similar effects upon the sensual motions, or ideas of the mind, as those already mentioned upon the muscular fibres. Thus, when any violent pain, arising from the defect of some pecu- liar stimulus, exists either in the muscular or sensual systems of fibres, and which cannot be removed by acquiring the de- fective stimulus; as in some constitutions convulsions of the muscles are produced to procure a temporary relief, so in other constitutions vehement voluntary exertions of the ideas of the mind are produced tor the same purpose; for during this ex- ertion, like that of the muscles, the pain either vanishes or is diminished: this violent exertion constitutes madness; and in many cases I have seen the madness take place, and the convul- sions cease, and reciprocally the madness cease, and the convul- sions supervene. See Section III. 5. 8. 2. Madness is distinguishable from delirium, as in the latter the patient knows not the place where he resides, nor the persons of his friends or attendants, nor is conscious of any external ob- jects, except when spoken to with a louder voice, or stimulated with unusual force, and even then he soon relapses into a state of inattention to every thing about him: Whilst in the former he is perfectly sensible to every thing external, but has the volun- tary powers of his mind intensely exerted on some particular object of his desire or aversion; he harbours in his thoughts a suspicion of all mankind, left they should counteract his designs; and while he keeps his intentions, and the motives of his actions profoundly secret, he is perpetually studying the means of ac- quiring the object of his wish, or of preventing or revenging the injuries he suspects. 3. A late French philosopher, Mr. Helvetius, has deduced almost all our actions from this principle of their relieving us from the ennui or tædium vitæ; and true it is, that our desires or aversions are the motives or all our voluntary actions; and human nature seems to excel other animals in the more facile use of this voluntary power, and on that account is more liable to insanity than other animals. But in mania this violent exertion or volition is expended on mistaken objects, and would not be relieved, though we were to gain or escape the objects that ex- cite 319 SECT. XXXIV. 2. DISEASES OF VOLITION. cite it. Thus I have seen two instances of madmen, who con- ceived that they had the itch, and several have believed they had the venereal infection, without in reality having a symptom of either of them. They have been perpetually thinking upon this subject, and some of them were in vain salivated with de- sign of convincing them to the contrary. 4. In the minds of mad people those volition's alone exist, which are unmixed with sensation; immoderate suspicion is generally the first symptom, and want of shame, and want of delicacy about cleanliness. Suspicion is a voluntary exertion of the mind arising from the pain of tear, which it is exerted to re- lieve: shame is the name of a peculiar disagreeable sensation, see Fable of the Bees; and delicacy about cleanliness arises from another disagreeable sensation: and therefore are not found in the minds of maniacs, which are employed solely in voluntary exertions. Hence the most; modest women in this disease walk naked amongst men without any kind of concern, use obscene discourse, and have no delicacy about their natural evacuations. 5. Nor are maniacal people more attentive to their natural appetites, or to the irritations which surround them, except as far as may respect their suspicions or designs; for the violent and perpetual exertions of their voluntary powers of mind pre- vents their perception of almost every other object, either of irritation or of sensation. Hence it is that they bear cold, hun- ger, and fatigue, with much greater pertinacity that in their sober hours, and are less injured by them in that respect to their general health. Thus it is asserted by historians, that Charles the Twelfth of Sweden slept on the snow, wrapped only in his cloak, at the siege of Frederickstad, and bore extremes of cold, and hunger, and fatigue, under which numbers of his soldiers perished; because the king was insane with ambition, but the soldier had no such powerful stimulus to preserve his system from debility and death. 6. Besides the insanities arising from exertions in consequence of pain, there is also a pleasureable insanity, as well as a plea- sureble delirium; as the insanity of personal vanity, and that of religious fanaticism. When agreeable ideas excite into mo- tion the sensorial power of sensation, and this again causes other trains of agreeable ideas, a constant stream of pleasureable ideas succeeds, and produces pleasureable delirium. So when the sensorial power of volition excites agreeable ideas, and the plea- sure thus produced excites more volition in its turn, a constant flow of agreeable voluntary ideas succeeds; which, when thus exerted in the extreme, constitutes insanity. Thus, when our muscular actions are excited by our sensations of 320 DISEASES OF VOLITION. SECT. XXXIV. 2. of pleasure, it is termed play; when they are excited by our vo- lition, it is termed work; and the former of these is attended with less fatigue, because the muscular actions in play produce in their turn more pleasureable sensation; which again has the property of producing more muscular action. An agreeable instance of this I saw this morning. A little boy, who was tired with walking, begged of his papa to carry him. " Here," says the reverend doctor, " ride upon my gold-headed cane;" and the pleased child, putting it between his legs, gallopped away with delight, and complained no more of his fatigue. Here the aid of another sensorial power, that of pleasureable sensation, superadded vigour to; the exertions of exhausted volition; which could otherwise only have been excited by additional pain, as by the lash of slavery. On this account, where the whole sensorial power has been exerted on the contemplation of the promised joys of heaven, the faints of all persecuted reli- gions have borne the tortures of martyrdom with otherwise un- accountable firmness. 7. There are some diseases, which obtain at least a temporary relief from the exertions of insanity; many instances of dropsies being thus for a time cured are recorded. An elderly woman labouring with ascites, I twice saw relieved, for some weeks, by insanity; the dropsy ceased for several weeks, and recurred again, alternating with the insanity. A man afflicted with difficult respiration on lying down, with very irregular pulse, and œde- matous legs, whom I saw this day, has for above a week been much relieved in respect to all those symptoms by the accession of insanity, which is shewn by inordinate suspicion, and great anger. In cases of common temporary anger the increased action of the arterial system is seen by the red skin, and increased pulse, with the immediate increase of muscular activity. A friend of mine, when he was painfully fatigued by riding on horseback, was accustomed to call up ideas into his mind, which used to excite his anger or indignation, and thus for a time at lead re- lieved the pain of fatigue. By this temporary insanity, the effect of the voluntary power upon the whole of his system was in- creased; as in cases of dropsy above mentioned, it would appear that the increased action of the voluntary faculty of the senso- rium affected the absorbent system, as well as the secerning one. 8. In respect to relieving inflammatory pains, and removing fever, I have seen many instances, as mentioned in Sect. XII. 2. 4. One lady whom I attended, had twice, at some years interval, a locked jaw, which relieved a pain on her sternum with peripneumony. Two other ladies I saw, who, towards the 321 SECT. XXXIV. 3. DISEASES OF VOLITION. the end of violent peripneumony, in which they frequently lost blood, were at length cured by insanity supervening. In the for- mer the increased voluntary exertion of the muscles of the jaw in the latter that of the organs of sense, removed the disease; that is, the disagreeable sensation which had produced the in- flammation, now excited the voluntary power, and these new voluntary exertions employed or expended the superabundant sensorial power, which had previously been exerted on the arterial system, and caused inflammation. Another case, which I think worth relating, was of a young man about twenty; he had laboured under an irritative fever, with debility, for three or four weeks, with very quick and very feeble pulse, and other usual symptoms of that species of typhus; but at this time complained much, and frequently of pain of his legs and feet. When those who attended him were nearly in despair of his recovery, I observed with pleasure an insanity of mind supervene; which was totally different from delirium, as he knew his friends, calling there by their names, and the room in which he lay, but became violently suspicious of his attendants, and calumniated with vehement oaths his tender mother, who fat weeping by his bed. On this his pulse became slower and firmer, but the quickness did not for some time entirely cease, and he gradually recovered. In this case the introduction of an increased quantity of the power of vo- lition gave vigour to those movements of the system, which are generally only actuated by the power of irritation, and of as- sociation. Another case I recollect of a young man, about twenty- five, who bad the scarlet fever, with very quick pulse, and an universal eruption on his skin, and was not without reason esteemed to be in great danger of his life. After a few days an insanity supervened, which his friends mistook for delirium, and he gradually recovered, and the cuticle peeled off. From these and a few other cases I have always esteemed insanity to be a favourable sign in fevers, and have cautiously distinguished it from delirium. III. Another mode of mental exertion to relieve pain, is by producing a train of ideas not only by the efforts of volition, as in insanity, but by those of sensation likewise, as in delirium and sleep. This mental effort is termed reverie, or somnam- bulation, and is described more at large in Sect. XIX. on that subject. But I shall here relate another case of that wonder- ful disease, which fell yesterday under my eye, and to which I have seen many analogous alienations of mind, though not ex- actly similar in ail circumstances. But as all of them either began 322 DISEASES OF VOLITION. SECT. XXXIV. 3. began or terminated with pain or convulsion, there can be no doubt but that they are of epileptic origin, and constitute ano- ther mode of mental exertion to relieve some painful sensation. 1. Master A. about nine years old, had been seized at seven every morning for ten days with uncommon fits, and had slight returns in the afternoon. They were supposed to originate from worms, and had been in vain attempted to be removed by vermifuge purges. As his fit was expected at seven yesterday morning, I saw him before that hour; he was asleep, seemed free from pain, and his pulse natural. About seven he began to complain of pain about his navel, or more to the left side, and in a few minutes had exertions of his arms and legs like swimming. He then for half an hour hunted a pack of hounds; as appeared by his hallooing, and calling the dogs by their names, and discoursing with the attendants of the chase, describ- ing exactly a day of hunting, which (I was informed) he had witnessed a year before, going through all the most minute cir- cumstances of it; calling to people, who were then present, and lamenting the absence of others, who were then also ab- sent. After this scene he imitated, as he lay in bed, some of the plays of boys, as swimming and jumping. He then sung an English and then an Italian song; part of which with his eyes open, and part with them closed, but could not be awakened or excited by any violence which it was proper to use. After about an hour he came suddenly to himself with ap- parent surprise, and seemed quite ignorant of any part of what had passed; and after being apparently well for half an hour, he suddenly fell into a great stupor, with slower pulse than na- tural, and a slow moaning respiration, in which he continued about another half hour, and then recovered. The sequel of this disease was favourable; he was directed one grain of opium at six every morning, and then to rise out of bed; at half past fix he was directed fifteen drops of lauda- num in a glass of wine and water. The first day the paroxysm became shorter, and less violent. The dose of opium was in- creased to one-half more, and in three or four days the fits left him. The bark and filings of iron were also exhibited twice a day; and I believe the complaint returned no more. 2. In this paroxysm it must be observed, that he began with pain, and ended with stupor, in both circumstances resembling a fit of epilepsy. And that therefore the exertions both of mind and body, both the voluntary ones, and those immediately excit- ed by pleasureable sensation, were exertions to relieve pain. The hunting scene appeared to be rather an act of memory than of imagination, and was therefore rather a voluntary ex- ertion, 323 SECT. XXXIV. 3. DISEASES OF VOLITION. ertion, though attended with the pleasureable eagerness which was the consequence of those ideas recalled by recollection, and not the cause of them. These ideas thus voluntarily recollected were succeeded by sensations of pleasure, though his senses were unaffected by the stimuli of visible or audible objects; or so weakly excited by them as not to produce sensation or attention. And the pleasure thus excited by volition produced other ideas and other motions in consequence of the sensorial power of sensation. Whence the mixed catenations of voluntary and sensitive ideas and muscular motions in reverie; which, like every other kind of vehement exertion, contribute to relieve pain, by expend- ing a large quantity of sensorial power. Those fits generally commence during sleep, from whence I suppose they have been thought to have some connection with sleep, and have thence been termed Somnambalism; but their commencement, during sleep, is owing to our increased excitability by internal sensations at that time, as explained in Sect. XVIII. 14. and 15. and not to any similitude between reverie and sleep. 3. I was once concerned for a very elegent and ingenious young lady, who had a reverie on alternate days, which con- tinued nearly the whole day; and as in her days of disease she took up the same kind of ideas which she had conversed about on the alternate day before, and could recollect nothing of them on her well-day, she appeared to her friends to possess two minds. This case also was of epileptic kind, and was cured, with some relapses, by opium administered before the com- mencement of the paroxysm. 4. Whence it appears, that the method of relieving in- flammatory pains, is by removing all stimulus, as by venesec- tion, cool air, mucilaginous diet, aqueous potation, silence, darkness. The method of relieving pain from defect of stimulus is by supplying the peculiar stimulus required, as of food or warmth. And the general method of relieving pain is by exciting into action some great part of the system, for the purpose of expend- ing a part of the sensorial power. This is done either by ex- ertion of the voluntary ideas and muscles, as in insanity and convulsions; or by exerting both voluntary and sensitive mo- tions, as in reverie; or by exciting the irritative motions by wine or opium internally, and by the warm bath or blisters externally; or lastly, by exciting the sensitive ideas by good news, affecting stories, or agreeable passions. U u SECT. 324 DISEASES OF ASSOCIATION. SECT. XXXV. 1. SECT. XXXV. DISEASES OF ASSOCIATION. I. 1. Sympathy or consent of parts. Primary and secondary parts of an associated train of motions reciprocally affect each other. Parts of irritative trains of motion affect each other in four ways. Sympathies of the skin and sto- mach. Flushing of the face after a meal. Eruption of the small-pox on the face. Chilness after a meal. 2. Vertigo from intoxication. 3. Absorption from the lungs and peri- cardium by emetics. In vomiting the actions of the stomach are decreased, not increased. Digestion strengthened after an emetic. Vomiting from deficiency of sensorial power. 4. Dyspnœa from cold bathing. Slow pulse from digitalis. Death from gout in the stomach. II. I. Primary and se- condary parts of sensitive associations affect each other Pain from gall-stone; from urinary stone. Hemicrania. Painful epilepsy. 2. Gout and red face from inflamed liver. Shingles from inflamed kidney. 3. Coryza front cold applied to the feet. Pleurisy. Hepatitis. 4. Pain of shoulders from inflamed liver. III. Diseases from, the associations of ideas. I. 1. MANY synchronous and successive motions of our muscular fibres, and of our organs of sense, or ideas, become associated so as to form indissoluble tribes or trains of action, as shewn in Section X. on Associate Motions. Some constitu- tions more easily establish these associations, whether by vo- luntary, sensitive, or irritative repetitions, and some more easily lose them again, as shewn in Section XXXI. on Tempera- ments. When the beginning of such a train of actions becomes by any mean disordered, the succeeding part is liable to become disturbed in consequence, and this is commonly termed sympa- thy or consent of parts, by the writers of medicines. For the more clear understanding of these sympathies, we must consi- der a tribe or train of actions as divided into two parts, and call one of them the primary or original motions, and the other the secondary or sympathetic ones. The primary and secondary parts of a train of irritative ac- tions may reciprocally affect each other in four different man- ners. 1. They may both be exerted with greater energy than natural. 2. The former may act with greater, and the latter with less energy. 3. The former may act with less, and the latter 325 SECT. XXXV. 1. DISEASES OF ASSOCIATION. latter with greater energy. 4. They may both act with less energy than natural. I shall now give an example of each kind of these modes of action, and endeavour to shew, that though the primary and secondary parts of these trains or tribes of motion are connected by irritative association, or their pre- vious habits of acting together, as described in Sect. XX. on Vertigo. Yet, that their acting with similar or dissimilar de- grees of energy, depends on the greater or less quantity of sen- sorial power, which the primary part of the train expends in its exertions. The actions of the stomach constitute so important a part of the associations of both irritative and sensitive motions, that it is said to sympathize with almost, every part of the body: the first example which I shall adduce to shew, that both the pri- mary and secondary parts of a train of irritative associations of motion act with increased energy, is taken from the consent of the skin with this organ. When the action of the fibres of the stomach is increased, as by the stimulus of a full meal, the ex- ertions of the cutaneous arteries of the face become increased by their irritative associations with those of the stomach, and a glow or flushing of the face succeeds. For the small vessels of the skin of the face having been more accustomed to the varie- ties of action, from their frequent exposure to various degrees of cold and heat, become more easily excited into increased action, than those of the covered parts of our bodies, and thus act with more energy from their irritative or sensitive asso- ciations with the stomach. On this account, in small-pox, the eruption, in consequence of the previous affection of the sto- mach, breaks out a day sooner on the face than on the hands, and two days sooner than on the trunk, and recedes in similar times after maturation. But, secondly, in weaker constitutions, that is, in those who possess less sensorial power, so much of it is expended in the increased actions of the fibres of the stomach, excited by the stimulus of a meal, that a sense of chilness succeeds instead of the universal glow above mentioned; and thus the secondary part of the associated train of motions is diminished in energy in consequence of the increased activity of the primary part of it. 2. Another instance of a similar kind, where the secondary part of the train acts with less energy in consequence of the greater exertions of the primary part, is the vertigo attending intoxication: in this circumstance so much sensorial power is expended on the stomach, and on its nearest or more strongly associated motions, as those of the subcutaneous vessels, and probably of the membranes of some internal viscera, that the irritative 326 DISEASES OF ASSOCIATION. SECT. XXXV. 1. irritative motions of the retina become imperfectly exerted from deficiency of sensorial power, as explained in Sect. XX. and XXI. on Vertigo and on Drunkenness, and hence the stagger- Ing inebriate cannot completely balance himself by such indis- tinct vision. 3. An instance of the third circumstance, where the pri- mary part of a train of irritative motions acts with less, and the secondary part with greater energy, may be observed by making the following experiment. If a person lies with his arms and shoulders out of bed till they become cold, a tem- porary coryza or catarrh is produced, so that the passage of the nostrils becomes totally obstructed; at least this happens to many people; and then, on covering the arms and shoulders, till they become warm, the passage of the nostrils ceases again to be obstructed, and a quantity of mucus is discharged from them. In this case the quiescence of the vessels of the skin of the arms and shoulders, occasioned by exposure to cold air, produces, by irritative association, an increased action of the ves- sels of the membrane of the nostrils; and the accumulation of sensorial power, during die torpor of the arms and shoulders, is thus expended in producing a temporary coryza or catarrh. Another instance may be adduced from the sympathy or con- sent of the motions of the stomach with other more distant links of the very extensive tribes or trains of irritative motions associated with them, described in Sect. XX. on Vertigo. When the actions of the fibres of the stomach are diminished or in- verted, the actions of the absorbent vessels, which take up the mucus from the lungs, pericardium, and other cells of the body, become increased, and absorb the fluids accumulated in them with greater avidity, as appears from the exhibition of foxglove, antimony, or other emetics, in cases of anasarca, attended with, unequal pulse and difficult respiration. That the act of nausea and vomiting is a decreased exertion of the fibres of the stomach may be thus deduced: when an emetic medicine is administered, it produces the pain of sick- ness as a disagreeable taste in the mouth produces the pain of nausea; these pain, like that of hunger, or of cold, or like those which are usually termed nervous, as the head-ach, or hemicrania, do not excite the organ into greater action; but in this case I imagine the pains of sickness or of nausea coun- teract or destroy the pleasureable sensation which seems ne- cessary to digestion, as shewn in Sect. XXIII. I. 1. The peristaltic motions of the fibres of the stomach become enfeebled by the want of this stimulus of pleasureable sensation, and, in consequence, stop for a time, and then become inverted; for they 327 SECT. XXXV. 2. DISEASES OF ASSOCIATION. they cannot become inverted without being previously stopped. Now, that this inversion of the trains of motion of the fibres of the stomach is owing to the deficiency of pleasureable sensa- tion, is evinced from this circumstance, that a nauseous idea excited by words, will produce vomiting as effectually as a nauseous drug. Hence it appears, that the act of nausea or vomiting expends less sensorial power than the usual peristaltic motions of the stomach in the digestion of our aliment; and that hence there is a greater quantity of sensorial power becomes accumulated in the fibres of the stomach, and more of it, in consequence, to spare for the action of those parts of the system which are thus associated with the stomach, as of the whole absorbent series of vessels, and which are at the same time excited by their usual stimuli. From this we can understand how, after the operation of an emetic, the stomach becomes more irritable and sensible to the stimulus and the pleasure of food; since, as the sensorial power becomes accumulated during the nausea and vomiting, the di- gestive power is afterwards exerted more forcibly for a time. It should, however, be here remarked, that though vomiting is in general produced by the defect of this stimulus of pleasure- able sensation, as when a nauseous drug is administered; yet, in long-continued vomiting, as in sea-sickness, or from habitual dram-drinking, it arises from deficiency of sensorial power, which, in the former case, is exhausted by the increased exer- tion of the irritative ideas of vision, and in the latter, by the frequent application of an unnatural stimulus. 4. An example of the fourth circumstance above mentioned, where both the primary and secondary parts of a train of mo- tions proceed with energy less than natural, may be observed in the dyspnœa, which occurs in going into a very cold bath, and which has been described and explained in Sect. XXXII. 3. 2. And by the increased debility of the pulsations of the heart and arteries during the operation of an emetic. Secondly, from the slowness and intermission of the pulsations of the heart from the incessant efforts to vomit, occasioned by an overdose of di- gitalis. And thirdly, from the total stoppage of the motions of the heart, or death, in consequence of the torpor of the sto- mach, when affected with the commencement or cold parox- ysm of the gout. See Sect. XXV. 17. II. 1. The primary and secondary parts of the trains of sen- sitive association reciprocally affect each other In different manners. 1. The increased sensation of the primary part may cease, when that of the secondary part commences. 2. The increased 328 DISEASES OF ASSOCIATION. SECT. XXXV. 2. increased action of the primary part may cease, when that of the secondary part commences. 3. The primary part may have increased sensation, and the secondary part increased ac- tion. 4. The primary part may have increased action, and the secondary part increased sensation. Examples of the first mode, where the increased sensation of the primary part of a train of sensitive associations ceases, when that of the secondary part commences, are not unfrequent; as this is the general origin of those pains which continue some time without being attended with inflammation, such as the pain at the pit of the stomach from a stone at the neck of the gall-bladder, and the pain of strangury in the glans penis from a stone at the neck of the urinary bladder. In both these cases, the part which is affected secondarily, is believed to be much more sensible than the part primarily affected, as described in the Catalogue of Diseases, Class II. I. 1. 10. and IV. 2. 1. 1. and IV. 2. 1.2. The hemicrania, or nervous head-ach, as it is called, when it originates from a decaying tooth, is another disease of this kind; as the pain of the carious tooth always ceases when the pain over one eye and temple commences. And it is probable, that the violent pains which induce convulsions in painful epi- lepsies, are produced in the same manner, from a more sensible part sympathizing with a diseased one of less sensibility. See Catalogue of Diseases, Class IV. 2. 1. 5. and III. 1. 1. 7. The last tooth, or dens sapientiæ, of the upper jaw, most frequently decays first, and is liable to produce pain over the eye and temple of that side. The last tooth of the under jaw is also liable to produce a similar hemicrania, when it begins to decay. When a tooth in the upper jaw is the cause of the head-ach, a slighter pain is sometimes perceived on the cheek- bone: and when a tooth in the lower jaw is the cause of head-ach, a pain sometimes affects the tendons of the muscles of the neck, which are attached near the jaws. But the clavus hystericus, or pain about the middle of the parietal bone on one side of the head, I have seen produced by the second of the mo- lares, or grinders, of the under jaw, of which I shall relate the following case. See Class II. 1. 1. 4. and IV. 2. 1.5. Mrs. -----, about thirty years of age, was seized with great pain about the middle of the right parietal bone, which had con- tinued a whole day before I saw her, and was so violent as to threaten to occasion convulsions. Not being able to detect a decaying tooth, or a tender one, by examination with my eye, or by striking them with a tea-spoon, and fearing bad conse- quences from her tendency to convulsion, I advised her to ex- tract 329 SECT. XXXV. 2. DISEASES OF ASSOCIATION. tract the last tooth of the under-jaw on the affected side; which was done without any good effect. She was then directed to lose blood, and to take a brisk cathartic; and after that had operated, about 60 drops of laudanum were given her, with large doses of bark; by which the pain was removed. In about a fortnight she took a cathartic medicine by ill advice, and the pain returned with greater violence in the same place; and, before I could arrive, as she lived 30 miles from me, she suffered a paralytic stroke; which affected her limbs and her face on one side, and relieved the pain of her head. About a year afterwards I was again called to her on ac- count of a pain as violent as before exactly on the same part of the other parietal bone. On examining her mouth, I found the second molaris of the under jaw, on the side before affected, was now decayed, and concluded, that this tooth had occa- sioned the stroke of the palsy by the pain and consequent exer- tion it had caused. On this account I earnestly intreated her to allow the sound molaris of the same jaw opposite to the de- cayed one to be extracted; which was forthwith done, and the pain of her head immediately ceased, to the astonishment of her attendants. In the cases above related of the pain existing in a part dis- tant from the seat of the disease, the pain is owing to defect of the usual motions of the painful part. This appears from the coldness, paleness, and emptiness of the affected vessels, or of the extremities of the body in general, and from there being no tendency to inflammation. The increased action of the primary part of these associated motions, as of the hepatic termination of the bile-duct from the stimulus of a gall-stone, or of the interior termination of the urethra from the stimulus of a stone in the bladder, or lastly, of a decayed tooth in hemicrania, deprives the secondary part of these associated motions, name- ly, the exterior terminations of the bile-duct or urethra, or the pained membranes of the head in hemicrania, of their natural share of sensorial power; and hence the secondary parts of these sensitive trains of association become pained from the de- ficiency of their usual motions, which is accompanied with de- ficiency of secretions and of heat. See Sect. IV. 5. XII. 5. 3. XXXIV. 1. Why does the pain of the primary part of the association cease, when that of the secondary part commences? This is a question of intricacy, but perhaps not inexplicable. The pain of the primary part of these associated trains of motion was owing to too great stimulus, as of the stone at the neck of the bladder, and was consequently caused by too great action of the 330 DISEASES OF ASSOCIATION. SECT. XXXV. 2. the pained part. This greater action than natural of the pri- mary part of these associated motions, by employing or ex- pending the sensorial power of irritation belonging to the whole associated train of motions, occasioned torpor, and consequent pain, in the secondary part of the associated train; which was possessed of greater sensibility than the primary part of it. Now, the great pain of the secondary part of the train as soon as it commences, employs or expends the sensorial power of sensa- tion belonging to the whole associated train of motions; and in consequence the motions of the primary part, though in creased by the stimulus of an extraneous body, cease to be ac- companied with pain or sensation. If this mode of reasoning be just, it explains a curious fact, why, when two parts of the body are strongly stimulated, the pain is felt only in one of them, though it is possible, by volun- tary attention, it may be alternately perceived in them both. In the same manner, when two new ideas are presented to us from the stimulus of external bodies, we attend to but one of them at a time. In other words, when one set of fibres, whether of the muscles or organs of sense, contract so strongly as to excite much sensation, another set of fibres, contracting more weakly, do not excite sensation at all, because the sensorial power of sensation is pre-occupied by the first set of fibres. So we cannot will more than one effect at once, though, by associations pre- viously formed, we can move many fibres in combination. Thus, in the instances above related, the termination of the bile-duct in the duodenum, and the exterior extremity of the urethra, are more sensible than their other terminations. When these parts are deprived of their usual motions, by defi- ciency of the sensorial power of irritation, they become pain- ful, according to law the fifth in Section IV. and the less pain originally excited by the stimulus of concreted bile, or of a stone at their other extremities ceases to be perceived. After wards, however, when the concretions of bile, or the stone on the urinary bladder, become more numerous or larger, the pain from their increased stimulus becomes greater than the as- sociated pain; and is then felt at the neck of the gall bladder or urinary bladder; and the pain of the glans penis, or at the pit of the stomach, ceases to be perceived. 2. Examples of the second mode, where the increased action of the primary part of a train of sensitive association ceases, when that of the secondary part commences, are also not un- frequent; as this is the usual manner of the translation of in- flammations from internal to external parts of the system, such as when an inflammation of the liver or stomach is translated to 331 SECT. XXXV. 2. DISEASES OF ASSOCIATION. to the membranes of the foot, and forms the gout; or to the skin of the face, and forms the rosy drop; or when an inflamma- tion of the membranes of the kidneys is translated to the skin of the loins, and forms one kind of herpes, called shingles: in these cases, by whatever cause the original inflammation may have been produced, as the secondary part of the train of sensi- tive association is more sensible, it becomes exerted with greater violence than the first part of it; and by both its increased pain, and the increased motion of its fibres, so far diminishes or ex- hausts the sensorial power of sensation, that the primary part of the train being less sensible, ceases both to feel pain and to act with unnatural energy. 3. Examples of the third mode, where the primary part of a train of sensitive association of motions may experience increase- ed sensation, and the secondary part increased action, are like- wise not unfrequent; as it is in this manner that mod inflamma- tions commence, Thus, after standing some time in snow, the feet become affected with the pain of cold, and a common co- ryza, or inflammation of the membrane of the nostrils succeeds. It is probable that the internal inflammations, as pleurisies, or hepatitis, which are produced after the cold paroxysm of fever, originate in the same manner from the sympathy of those parts with some others, which were previously pained from quie- scence; as happens to various parts of the system during the cold fits of fevers. In these cases it would seem that the sensorial power of sensation becomes accumulated during the pain of cold, as the torpor of the vessels occasioned by the defect of heat contributes to the increase or accumulation of the sensorial power of irritation, and that both these become exerted on some inter- nal part, which was not rendered torpid by the cold which af- fected the external parts, nor by its association with them; or which sooner recovered its sensibility. 4. An example of the fourth mode, or where the primary part of a sensitive association of motions may have increased action, and the secondary part increased sensation, may be taken from the pain of the shoulder, which attends inflammation of the membranes of the liver. See Hepatitis, Class IV. 2.1.6. In this circumstance so much sensorial power seems to be expended in the violent actions and sensations of the inflamed membranes of the liver, that the membranes associated with them become quiescent to their usual stimuli, and painful in consequence. There may be other modes in which the primary and second- ary parts of the trains of associated sensitive motions may reci- procally affect each other, as may be seen by looking over Class IV. in the Catalogue of Diseases; all which may probably be X x resolved 332 PERIODS OF DISEASES. SECT. XXXVI. 1. resolved into the plus and minus of sensorial power; but we have not yet had sufficient observations made upon them with a view to this doctrine. III. The associated trains of our ideas may have sympathies, and their primary and secondary parts affect each other in some manner similar to those above described; and may thus occasion various curious phenomena not yet adverted to, besides those explained in the sections on dreams, reveries, vertigo, and drun- kenness; and may thus disturb the deductions of our reason- ings, as well as the dreams of our imaginations present us with false degrees of fear, attach unfounded value to trivial circum- stances, give occasion to our early prejudices and antipathies, and thus embarrass the happiness of our lives. A copious and curious harvest might be reaped from this province of science; in which, however, I shall not at present wield my sickle. SECT. XXXVI. OF THE PERIODS OF DISEASES. 1. Muscles excited by volition soon cease to contract, or by sensation, or by irritation, owing to the exhaustion of sen- sorial power. Muscles subjected to less stimulus have their sensorial power accumulated. Hence the periods of some fevers. Want of irritability after intoxication. II. 1. Natural actions catenated with daily habits of life. 2. With solar periods. Periods of sleep. Of evacuating the bowels. 3. Natural actions catenated with lunar periods. Menstruation. Venereal orgasm of animals. Barrenness. III. Periods of diseased animal actions from stated returns of nocturnal cold; from solar and lunar influence. Periods of diurnal fever, hectic fever, quotidian, tertian, quartan fever. Periods of gout, pleurisy, of fevers with arterial debility, and with arterial strength. Periods of rhapha- nia, of nervous cough, hemicrania, arterial hæmorrhages, hæmorrhoids, hæmoptoe, epilepsy, palsy, apoplexy, mad- ness. IV. Critical days depend on lunar periods. Lunar periods in the small-pox. I. IF any of our muscles be made to contract violently by the power of volition, as those of the fingers, when any one hangs by his hands on a swing, fatigue soon ensues, and the muscles cease to act, owing to the temporary exhaustion of the spirit of animation: as soon as this is again accumulated in the muscles, they are ready to contract again by the efforts of volition. Those 333 SECT. XXXVI. 1. PERIODS OF DISEASES. Those violent muscular actions induced by pain become, in the same manner, intermitted and recurrent; as in labour-pains, vomiting, tenesmus, strangury; owing, likewise, to the tempo- rary exhaustion of the spirit of animation, as above mentioned. When any stimulus continues long to act with unnatural violence, so as to produce too energetic action of any of our moving organs, those motions soon cease, though the stimulus continues to act; as in looking long on a bright object, as on an inch-square of red silk laid on white paper in the sunshine. See Plate I. in Sect. III. 1. On the contrary, where less of the stimulus of volition, sen- sation, or irritation, has been applied to a muscle than usual, there appears to be an accumulation of the spirit of animation in the moving organ, by which it is liable to act with greater energy from less quantity of stimulus than was previously ne- cessary to excite it into so great action; as, after having been immersed in snow, the cutaneous vessels of our hands are ex- cited into stronger action by the stimulus of a less degree of heat than would previously have produced that effect. From hence the periods of some fever-fits may take their ori- gin, either simply, or by their accidental coincidence with lunar and solar periods, or with the diurnal periods of heat and cold to be treated of below; for, during the cold fit at the commencement of a fever, from whatever cause that cold fit may have been in- duced, it follows, 1. That the spirit of animation must become accumulated in the parts which exert, during this cold fit, less than their natural quantity of action. 2. If the, cause produc- ing the cold fit does not increase, or becomes diminished, the parts before benumbed or inactive become now excitable by smaller stimulus, and are thence thrown into more violent ac- tion than is natural; that is, a hot fit succeeds the cold one. 3. By the energetic action of the system during the hot fit, if it continues long, an exhaustion of the spirit of animation takes place, and another cold fit is liable to succeed, from the mov- ing system not being excitable into action from its usual stimu- lus. This inirritability of the system from a too great previous stimulus, and consequent exhaustion of sensorial power, is the cause of the general debility, and sickness, and head-ach, some hours after intoxication. And hence we see one of the causes of the periods of fever-fits; which, however, are frequently combined with the periods of our diurnal habits, or of heat and cold, or of solar or lunar periods. When, besides the tendency to quiescence occasioned by the expenditure of sensorial power during the hot fit of fever, some other cause of torpor, as the solar or lunar periods, is necessary to 334 PERIODS OF DISEASES. SECT. XXXVI. 2 to the introduction of a second cold fit, the fever becomes of the intermittent kind; that is, there is a space of time intervenes between the end of the hot fit, and the commencement of the next cold one. But where no exterior cause is necessary to the introduction of the second cold fit, no such interval of health in- tervenes; but the second cold fit commences as soon as the sen- sorial power is sufficiently exhausted by the hot fit, and the fever becomes continual. II. 1. The following are natural animal actions, which are frequently catenated with our daily habits of life, as well as ex- cited by their natural irritations. The periods of hunger and thirst become catenated with certain portions of time, or degrees of exhaustion, or other diurnal habits of life. And if the pain of hunger be not relieved by taking food at the usual time, it is liable to cease till the next period of time or other habits recur: this is not only true in respect to our general desire of food, but the kinds of it also are governed by this periodical habit; insomuch, that beer taken to breakfast will disturb the digestion of those who have been accustomed to tea; and tea taken at din- ner will disagree with those who have been accustomed to beer. Whence it happens, that those who have weak stomachs will be able to digest more food, if they take their meals at regular hours; because they have both the stimulus of the aliment they take, and the periodical habit, to assist their digestion. The periods of emptying the bladder are not only dependent on the acrimony or distention of the water in it, but are fre- quently catenated with the external cold applied to the skin, as in cold bathing, or washing the hands; or with other habits of life, as many are accustomed to empty the bladder before going to bed, or into the house after a journey, and this whether it be full or not. Our times of respiration are not only governed by the stimu- lus of the blood in the lungs, or our desire of fresh air, but also by our attention to the hourly objects before us. Hence, when a person is earnestly contemplating an idea of grief, he forgets to breathe, till the sensation in his lungs becomes very urgent; and then a sigh succeeds for the purpose of more forcibly push- ing forwards the blood which is accumulated in the lungs. Our times of respiration are also frequently governed in part by our want of a steady support for the actions of our arms and hands, as in threading a needle, or hewing wood, or in swimming: when we are intent upon these objects, we breathe at the intervals of the exertion of the pectoral muscles. 2. The following natural animal action are influenced by solar period. The periods of sleep and of waking depend much 335 SECT. XXXVI. 3. PERIODS OF DISEASES. much on the solar period; for we are inclined to sleep at a cer- tain hour, and to awake at a certain hour, whether we have had more or less fatigue during the day, if within certain li- mits; and are liable to wake at a certain hour, whether we went to bed earlier or later within certain limits. Hence it ap pears, that those who complain of want of sleep, will be liable to sleep better or longer, if they accustom themselves to go to rest and to rise at certain hours. The periods of evacuating the bowels are generally connect- ed with some part of the solar day, as well as with the acri- mony or distention occasioned by the fæces. Hence, one me- thod of correcting costiveness is by endeavouring to establish a habit of evacuation at a certain hour of the day, as recommended by Mr. Locke, winch may be accomplished by using daily voluntary efforts, at those times, joined with the usual stimulus of the material to be evacuated. 3. The following natural animal actions are connected with lunar periods. I. The periods of female menstruation are connected with lunar periods to great exactness, in some in- stances even to a few hours. These do not commence or ter- minate at the full or change, or at any other particular part of the lunation; but after they, have commenced at any part of it, they continue to recur at that part with great regularity, unless disturbed by some violent circumstance, as explained in Section XXXII. No. 6. Their return is immediately caused by defi- cient venous absorption, which is owing to the want of the sti- mulus, designed by nature, of amatorial copulation, or of the growing fœtus. When the catamenia returns sooner than the period of lunation, it shews a tendency of the constitution to inirritability; that is, to debility, or deficiency of sensorial power, and is to be relieved by small doses of steel and opium. The venereal orgasm of birds and quadrupeds seems to com- mence or return about the most powerful lunations at the vernal or autumnal equinoxes; but if it be disappointed of its object, it is said to recur at monthly periods; in this respect resembling the female catamenia. Whence it is believed, that women are more liable to become pregnant at or about the time of their catamenia, than at the intermediate times; and on this account they are seldom much mistaken in their reckoning of nine lunar periods from the last menstruation: the inattention to this may sometimes have been the cause of supposed barrenness, and is therefore worth the observation of those who wish to have children. III. We now come to the periods of diseased animal actions. The periods of fever-fits, which depend on the stated returns of 336 PERIODS OF DISEASES. SECT. XXXVI. 3. of nocturnal cold, are discussed in Sect. XXXII. 3. Those which originate or recur at solar or lunar periods, are also ex- plained in Section XXXII. 6. These we shall here enume- rate; observing, however, that it is not more surprizing, that the influence of the varying attractions of the sun and moon should raise the ocean into mountains, than that it should af- fect the nice sensibilities of animal bodies; though the manner of its operation on them is difficult to be understood. It is probable, however, that as this influence gradually lessens dur- ing the course of the day, or of the lunation, or of the year, some actions of our system become less and less, till at length a total quiescence of some part is induced; which is the com- mencement of the paroxysms of fever, of menstruation, of pain, with decreased action of the affected organ, and of con- sequent convulsion. 1. A diurnal fever, in some weak people, is distinctly ob- served to come on towards evening, and to cease with a moist skin early in the morning, obeying the solar periods. Persons of weak constitutions are liable to get into better spirits at the access of the hot fit of this evening fever, and are thence in- clined to sit up late, which, by further enfeebling them, increases the disease; whence they lose their strength and their colour. 2. The periods of hectic fever, supposed to arise from ab- sorption of matter, obey the diurnal periods like the above, having the exacerbescence towards evening, and its remission early in the morning, with sweats, or diarrhœa, or urine with white sediment. The periods of quotidian fever are either catenated with so- lar time, and return at the intervals of twenty-four hours, or with lunar time, recurring at the intervals of about twenty-five hours. There is great use in knowing with what circumstances the periodical return of new morbid motions are conjoined, as the most effectual times of exhibiting the proper medicines are thus determined. So, if the torpor which ushers in an ague fit is catenated with the lunar day, it is known when the bark or opium must be given, so as to exert its principal effect about the time of the expected return. Solid opium should be given about an hour before the expected cold fit; liquid opium and wine about half an hour; the bark repeatedly for six or eight hours previous to the expected return. 4. The periods of tertian fevers, reckoned from the com- mencement of one cold fit to the commencement of the next cold fit, recur with solar intervals of forty-eight hours, or with lunar ones of about fifty hours. When these times of recur- rence begin one or two hours earlier than the solar periods, it shews, 337 SECT. XXXVI. 3. PERIODS OF DISEASES. shews, that the torpor or cold fit is produced by less external influence; and, therefore, that it is more liable to degenerate into a fever with only remissions: so, when menstruation recurs sooner than the period of lunation, it shews a tendency of the habit to torpor or inirritability. 5. The periods of quartan fevers return at solar intervals of seventy-two hours, or at lunar ones of about seventy-four hours and an half. This kind of ague appears most in moist cold au- tumns, and in cold countries replete with marshes. It is at- tended with greater debility, and its cold access more difficult to prevent. For, where there is previously a deficiency of senso- rial power, the constitution is liable to run into greater torpor from any further diminution of it: two ounces of bark and some steel should be given on the day before the return of the cold paroxysm, and a pint of wine, by degrees, a few hours be- fore its return, and thirty drops of laudanum one hour before the expected cold fit. 6. The periods of the gout generally commence about an hour before sun-rise, which is usually the coldest part of the twenty-four hours. The greater periods of the gout seem also to observe the solar influence, returning about the same season of the year. 7. The periods of the pleurisy recur with exacerbation of the pain and fever about sun-set, at which time venesection is of most service. The same may be observed of the inflammatory rheu- matism, and other fevers with arterial strength, which seem to obey solar periods; and those with debility seem to obey lunar ones. 8. The periods of fevers with arterial debility seem to obey the lunar day, having their access daily nearly an hour later; and have sometimes two accesses in a day, resembling the lunar ef- fects upon the tides. 9. The periods of rhaphania, or convulsions of the limbs from rheumatic pains, seem to be connected with solar influ- ence, returning at nearly the same hour for weeks together, un- less disturbed by the exhibition of powerful doses of opium. So the periods of Tussis ferina, or violent cough with slow pulse, called nervous cough, recurs by solar periods. Five grains of opium, given at the time the cough commenced, dis- turbed the period, from seven in the evening to eleven, at which time it regularly returned for some days, during which time the opium was gradually omitted. Then 120 drops of laudanum were given an hour before the access of the cough, and it totally ceased. The laudanum was continued a fortnight, and then gradually discontinued. 10. The 338 PERIODS OF DISEASES. SECT. XXXVI. 4. 10. The periods of hemicrania, and of painful epilepsy, are liable to obey lunar periods, both in their diurnal returns and in their greater periods of weeks; but are also induced by other ex- citing causes. 11. The periods of arterial hæmorrhages seem to return at solar periods, about the same hour of the evening or morning. Perhaps the venous hæmorrhages obey the lunar periods, as the catamenia and hæmorrhoids. 12. The periods of the hæmorrhoids, or piles, in some, re- cur monthly, in others only at the greater lunar influence about the equinoxes. 13. The periods of hæmoptoe sometimes obey solar influ- ence, recurring early in the morning for several days; and sometimes lunar periods, recurring monthly; and sometimes depend on our hours of sleep. See Class I. 2. 1. 9. 14. Many of the first periods of epileptic fits obey the monthly lunation with some degree of accuracy; others recur only at the most powerful lunations before the vernal equinox, and after the autumnal one; but when the constitution has gained a habit of relieving disagreeable sensations by this kind of exertion, the fit recurs from any slight cause. 15. The attack of palsy and apoplexy is known to recur with great frequency about the equinoxes. 16. There are numerous instances of the effect of the luna- tions upon the periods of insanity; whence the name of lunatic has been given to those afflicted with this disease. IV. The critical days, in which fevers are supposed to ter- minate, have employed the attention of medical philosophers from the days of Hippocrates to the present time. In whatever part of a lunation a fever commences, which owes either its whole cause to solar and lunar influence, or to this in con- junction with other causes, it would seem, that the effect would he the greatest at the full and new moon, as the tides rise highest at those times, and would be the least at the quad- ratures: thus, if a fever-fit should commence at the new or full moon, occasioned by the solar and lunar attraction, dimi- nishing some chemical affinity of the particles of blood, and thence decreasing their stimulus on our sanguiferous system, as mentioned in Sect. XXXII. 6. this effect will daily decrease for the first seven days, and will then increase till about the fourteenth day, and will again decrease till about the twenty- first day, and increase again till the end of the lunation. If a fever-fit from the above cause should commence on the seventh day after either lunation, the reverse of the above circumstances would happen. Now, it is probable, that those fevers, whose crisis 339 SECT. XXXVII. 1. DIGESTION, &c. crisis or terminations are influenced by lunations, may begin at one or other of the above times, namely, at the changes or quadratures; though sufficient observations have not been made to ascertain this circumstance. Hence I conclude, that the small-pox and measles have their critical days, not go- verned by the times required for certain chemical changes in the Wood, which affect or alter the stimulus of the contagious matter, but from the daily increasing or decreasing effect of this lunar link of catenation, as explained in Section XVII. 3. 3. And as other fevers terminate mod frequently about the seventh, fourteenth, twenty-first, or about the end of four weeks, when no medical assistance has disturbed their periods, I conclude, that these crises, or terminations are governed by periods of the lunations, though we are still ignorant of their manner of operation. In the distinct small-pox, the vestiges of lunation are very apparent: after inoculation, a quarter of a lunation precedes the commencement of the fever, another quarter terminates with the complete eruption, another quarter with the com- plete maturation, and another quarter terminates the complete absorption of a material now rendered inoffensive to the con- stitution. SECT. XXXVII. OF DIGESTION, SECRETION, NUTRITION. I. Crystals increase by the greater attraction of their sides. Accretion by chemical precipitations, by welding, by pres- sure, by agglutination. II. Hunger, digestion; why it cannot be imitated out of the body. Lacteals absorb by animal selection, or appotency. III. The glands and pores absorb nutritious particles by animal selection. Organic particles of Buffon. Nutrition applied at the time of elon- gation of fibres. Like inflammation. IV. It seems easier to have preserved animals than to re-produce them. Old age and death from inirritability. Three causes of this. Original fibres of the organs of sense and muscles un- changed. V. Art of producing long life. I. THE larger crystals of saline bodies may be conceived to arise from the combination of smaller crystals of the same form, owing to the greater attractions of their sides than of their angles. Thus, if four cubes were floating in a fluid, whose friction or resistance is nothing, it is certain the sides of Y y these 340 DIGESTION, &c. SECT. XXXVII.2. these cubes would attract each other stronger than their angles; and hence that these four smaller cubes would so arrange them- selves as to produce one larger one. There are other means of chemical accretion, such as the depositions of dissolved calcareous or siliceous particles, as are seen in the formation of the stalactites of limestone in Derby- shire, or of calcedone in Cornwall. Other means of adhesion are produced by heat and pressure, as in the welding of iron- bars; and other means, by simple pressure, as in forcing two pieces of caoutchou, or elastic gum, to adhere ; and, lastly, by the agglutination of a third substance penetrating the pores of the other two, as in the agglutination of wood by means of animal gluten. Though the ultimate particles of animal bo- dies are held together during life, as well as after death, by their specific attraction of cohesion, like all other matter; yet it does not appear, that their original organization was produced by chemical laws; and their production and increase must there- fore only be looked for from the laws of animation. II. When the pain of hunger requires relief, certain parts of the material world which surround us, when applied to our palates, excite into action the muscles of deglutition, and the material is swallowed into the stomach. Here the new aliment becomes mixed with certain animal fluids, and undergoes a che- mical process, termed digestion; which, however, chemistry has not yet learnt to imitate out of the bodies of living animals or vegetables. This process seems very similar to the saccha- rine process in the lobes of farinaceous feeds, as of barley, when it begins to germinate; except that, along with the sugar, oil and mucilage are also produced; which form the chyle of ani- mals, which is very similar to their milk. The reason, I imagine, why this chyle-making, or saccharine process, has not yet been imitated by chemical operations, is owing to the materials being in such a situation, in respect to warmth, moisture and motion, that they will immediately change into the vinous or acetous fermentation, except the new sugar be absorbed by the numerous lacteal or lymphatic vessels, as soon as it is produced, which is not easy to imitate in the laboratory. These lacteal vessels have months, which are irritated into action by the stimulus of the fluid which surrounds them; and by animal selection, or appetency, they absorb such part of the fluid as is agreeable to their palate; those parts, for instance, which are already converted into chyle, before they have time to undergo another change by a vinous or acetous fermenta- tion. This animal absorption of fluid is almost visible to the naked 341 SECT. XXXVII. 3. DIGESTION, &c. naked eye in the action of the puncta lacrymalia, which im- bibe the tears from the eye, and discharge them again into the nostrils. III. The arteries constitute another reservoir of a change- ful fluid; from which, after its recent oxygenation in the lungs, a further animal selection of various fluids is absorbed by the numerous glands: these select their respective fluids from the blood, which is perpetually undergoing a chemical change: but the selection by these glands, like that of the lacteals, which open their mouths into the digesting aliment in the stomach, is from animal appetency, not from chemical affinity; secretion cannot, therefore, be imitated in the laboratory, as it consists in a selection of part of a fluid during the chemical change of that fluid. The mouths of the lacteals and lymphatics, and the ulti- mate terminations of the glands, are finer than can easily be- conceived; yet, it is probable that the pores, or interstices of the parts, or coats, which constitute these ultimate vessels, may still have greater tenuity; and that these pores, from the above analogy, must possess a similar power of irritability, and ab- sorb, by their living energy, the particles of fluid adapted to their purposes, whether to replace the parts abraded or dissolve- ed, or to elongate and enlarge themselves. Not only every kind of gland is thus endued with its peculiar appetency, and selects the material agreeable to its taste from the blood, but every individual pore acquires, by animal selection, the mate- rial which it wants; and thus nutrition seems to be performed in a manner so similar to secretion, that they only differ in the one retaining, and the other parting again with the particles which they have selected from the blood. This way of accounting for nutrition from stimulus, and the consequent animal selection of particles, is much more ana- logous to other phenomena of the animal microcosm, than by having recourse to the microscopic animalcula, or organic par- ticles of Buffon and Needham; which, being already com- pounded, must themselves require nutritive particles to conti- nue their own existence; and must he liable to undergo a change by our digestive or secretory organs; otherwise mankind would soon resemble, by their theory, the animals which they feed upon. He, who is nourished by beef or venison, would in time become horned; and he, who feeds on pork or bacon, would gain a nose proper for rooting into the earth, as well as for the perception of odours. The whole animal system may be considered as consisting of the extremities of the nerves, or of having been produced from them; 342 DIGESTION, &c. SECT. XXXVII. 3. them; if we except perhaps the medullary part of the brain re- siding in the head and spine, and in the trunks of the nerves. These extremities of the nerves are either of those of locomotion, which are termed muscular fibres; or of those of sensation, which constitute the immediate organs of sense, and which have also their peculiar motions. Now, as the fibres which con- stitute the bones and membranes, possessed originally, sensation and motion, and are liable again to possess them, when they become inflamed; it follows, that those were, when first formed, appendages to the nerves of sensation or locomotion, or were formed from them: and that hence, all these solid parts of the body, as they have orginally consisted of extremities of nerves, require an apposition of nutritive particles of a similar kind, contrary to the opinion of Buffon and Needham above recited. Lastly, as all these filaments have possessed or do possess the power of contraction, and of consequent inertion or elongation, it seems probable that the nutritive particles are applied during their times of elongation, when their original constituent par- ticles are removed to a greater distance from each other. For each muscular or sensual fibre may be considered as a row or string of beads, which approach when in contraction, and recede during its red or elongation; and our daily experience shews us, that great action emaciates the system, and that it is repaired during rest. Something like this is seen out of the body; for if a hair, or a single Untwisted fibre of flax or silk, be soaked in water, it becomes longer and thicker by the water which is absorbed into its pores. Now, if a hair could be supposed to be thus im- mersed in a solution of particles similar to those which compose it, one may imagine that it might be thus increased in weight and magnitude; as the particles of oak-bark increase the sub- stance of the hides of beads in the process of making leather. I mention these not as philosophic analogies, but as similies to fa- cilitate our ideas, how an accretion of parts may be effected by animal appetences, or selections, in a manner somewhat similar to mechanical or chemical attractions. If those new particles of matter, previously prepared by di- gestion and sanguification, only supply the places of those which have been abraded by the actions of the system, it is properly termed nutrition. If they are applied to the extremities of the nervous fibrils, or in such quantity as to increase the length or crassitude of them, the body becomes at the same time enlarged, and its growth is increased as well as its deficiencies repaired. In this last case something more than a simple apposition or selection of particles seems to be necessary; as many parts of the 343 SECT. XXXVII. 4. DIGESTION, &c. the system, during its growth, are caused to recede from those with which they were before in contact; as the ends of the bones, or cartilages, recede from each other as their growth ad- vances: this process resembles inflammation, as appears in oph- thalmy, or in the production of new flesh in ulcers, where old vessels are enlarged and new ones produced; and, like that, is attended with sensation. In this situation the vessels become distended with blood, and acquire greater sensibility, and may thus be compared to the erection of the penis, or of the nipples of the breasts of women; while new particles become added at the same time, as in the process of nutrition above described. When only the natural growth of the various parts of the body is produced, a pleasureable sensation attends it, as in youth, and perhaps in those who are in the progress of becoming fat. When an unnatural growth is the consequence, as in inflame- matory diseases, a painful sensation attends the enlargement of the system. IV. This apposition of new parts, as the old ones disappear, selected from the aliment we take, first enlarges and strengthens our bodies for twenty years, for another twenty years it keeps us in health and vigour, and adds strength and solidity to the system, and then gradually ceases to nourish us properly, and for another twenty years we gradually sink into decay, and finally cease to act and to exist. On considering this subject, one should have imagined, at first view, that it might have been easier for nature to have sup- ported her progeny for ever in health and life, than to have perpetually re-produced them by the wonderful and mysterious process of generation. But it seems our bodies, by long habit, cease to obey the stimulus of the aliment which should support us. After we have acquired our height and solidity, we make no more new parts, and the system obeys the irritations, sen- sations, volitions, and associations, with less and less energy, till the whole sinks into inaction. Three causes may conspire to render our nerves less excitable, which have been already mentioned. 1. If a stimulus be greater than natural, it produces too great an exertion of the stimulated organ, and, in consequence, exhaust the spirit of animation; and the moving organ ceases to act, even though the stimulus be continued. And though rest will recruit this exhaustion, yet some degree of permanent injury remains, as is evident after exposing the eyes long to too strong alight. 2. If excitations weaker than natural be applied, so as not to excite the organ into action, (as when small doses of aloe or rhubarb are ex- hibited) they may be gradually increased, without exciting the organ 344 DIGESTION, &c. SECT. XXXVII. 5. organ into action, which will thus acquire a habit of disobe- dience to the stimulus: thus, by increasing the dose by degrees, great quantities of opium or wine may be taken without in- toxication. See Sect. XII. 3. 1. 3. Another mode, by which life is gradually undermined, is when irritative motions continue to be produced in consequence of stimulus, but are not succeeded by sensation: hence the sti- mulus of contagious matter is not capable of producing fever a second time, because it is not succeeded by sensation. See Sect. XII. 3. 6. And hence, owing to the want of the general pleasureable sensation which ought to attend digestion and glan- dular secretion, an irksomeness of life ensues; and, where this is in greater excess, the melancholy of old age occurs, with torpor or debility. From hence I conclude, that it is probable that the fibrillæ, or moving filaments at the extremities of the nerves of sense, and the fibres which constitute the muscles (which are, perhaps, the only parts of the system that are endued with contractile life) are not changed, as we advance in years, like the other parts of the body, but only enlarged or elongated with our growth; and, in consequence, they become less and less excit- able into action. Whence, instead of gradually changing the old animal, the generation of a totally new one becomes neces- sary, with undiminished excitability; which many years will continue to acquire new parts, or new solidity, and then, losing its excitability in time, perish like its parent. V. From this idea the art of preserving long health and life may be deduced, which must consist in using no greater stimu- lus, whether of the quantity or kind of our food and drink, or of external circumstances, such as heat, and exercise, and wake- fulness, than is sufficient to preserve us in vigour; and gradually, as we grow old, to increase the stimulus of our aliment, as the inirritability of our system increases. The debilitating effects ascribed, by the poet MARTERIAL, to the excessive use of warm bathing in Italy, may, with equal propriety, be applied to the warm rooms of England, which, with the general excessive stimulus of spirituous or fermented liquors, and, in some instances, of immoderate venery, contri- bute to shorten our lives. Balnea, vina, venus, corrumstunt corpora nostra, At saciunt vitam balnea, vina, venus! Wine, women, warmth, against our lives combine; But what is life without warmth, women, wine! SECT. 345 SECT. XXXVIII. 1. OXYGENATION, &c. SECT. XXXVIII. OF THE OXYGENATION OF THE BLOOD IN THE LUNGS, AND IN THE PLACENTA. I. Blood absorbs oxygene from the air, whence phosphoric acid, changes its colour, gives out heat, and some phlogistic material, and acquires an etherial spirit, which is dissi- pated in fibrous motion. II. The placenta is a pulmonary organ like the gills of fish. Oxygenation of the blood from air, from water, by lungs, by gills, by the placenta; neces- sity of this oxygenation to quadrupeds, to fish, to the fœtus in utero. Placental vessels inserted into the arteries of the mother. Use of cotyledons in cows. Why quadrupeds have not sanguiferous lochia. Oxygenation of the chick in the egg, of seeds. III. The liquor amnii is not excre- mentitious. It is nutritious. It is found in the œsophagus and stomach, and forms the meconium. Monstrous births without heads. Question of Dr. Hervey. I. FROM the recent discoveries of many ingenious philoso- phers it appears, that during respiration the blood imbibes the vital part of the air, called oxygene, through the membranes of the lungs; and that hence respiration may be aptly compared to a slow combustion. As in combustion the oxygene of the atmosphere unites with some phlogistic or inflammable body, and forms an acid (as in the production of vitriolic acid from sulphur, or carbonic acid from charcoal,) giving out at the same time a quantity of the matter of heat; so in respiration the oxygene of the air unites with the phlogistic part of the blood, and probably produces phosphoric or animal acid, changing the colour of the blood from a dark to a bright red; and proba- bly some of the matter of heat is, at the same time, given out, according to the theory of Dr. Crawford. But as the evolu- tion of heat attends almost all chemical combinations, it is pro- bable, that it also attends the secretions of the various fluids from the blood; and that the constant combinations or productions of new fluids, by means of the glands, constitute the more gene- ral source of animal heat: this seems evinced by the universal evolution of the matter of heat in the blush of shame or of an- ger; in which, at the same time, an increased secretion of the per- spirable matter occurs; and the partial evolution of it from to- pical inflammations, as in gout or rheumatism, in which there is a secretion of new blood-vessels. Some medical philosophers have ascribed the heat of animal bodies 346 OXYGENATION SECT. XXXVIII. 2. bodies to the friction of the particles of the blood against the sides of the vessels. But no perceptible heat has ever been produced by the agitation of water, or oil, or quick silver, or other fluids except those fluids have undergone, at the same time, some che- mical change, as in agitating milk or wine, till they become sour. Besides the supposed production of phosphoric acid, and change of colour of the blood, and the production of carbo- nic acid, there would appear to be something of a more subtile nature perpetually acquired from the atmosphere; which is too fine to be long contained in animal vessels, and therefore re- quires perpetual renovation; and without which life cannot continue longer than a minute or two: this ethereal fluid is pro- bably secreted from the blood by the brain, and perpetually dis- sipated in the actions of the muscles and organs of sense. That the blood acquires something from the air which is immediately necessary to life, appears from an experiment of Dr. Hare, (Philos. Transact. abridged, vol. iii. p. 239.) who found, " that birds, mice, &c. would live as long again in a vessel, where he had crowded in double the quantity of air by a condensing engine, than they did when confined in air of the common density." Whereas, if some kind of deleterious vapour only was exhaled from the blood in respiration, the air, when condensed into half its compass, could not be supposed to receive so much of it. II. Sir Edward Hulse, a physician of reputation at the begin- ning of the present century, was of opinion, that the placenta was a respiratory organ, like the gills of fish; and not an organ to supply nutriment to the fœtus, as mentioned in Derham's Physico-theology. Many other physicians seem to have es- poused the same opinion, as noticed by Haller. Elem. Physi- ologiæ, T. i. Dr. Gipson published a defence of this theory in the Medical Essays of Edinburgh, vol. i. and ii. which doc- trine is there controverted at large by the late Alexander Mon- ro; and since that time the general opinion has been, that the placenta is an organ of nutrition only, owing, perhaps, rather to the authority of so great a name, than to the validity of the arguments adduced in its support. The subject has lately been returned by Dr. James Jeffray and Dr. Forester French, in their inaugural dissertations, at Edinburgh and at Cambridge, who have defended the contrary opinion in an able and ingenious manner, and from whose Theses I have extracted many of the following remarks. First, by the late discoveries of Dr. Priestley, M. Lavoisier, and other philosophers, it appears, that the basis of atmospherical air, called oxygene, is received by the blood through the mem- branes 347 SECT. XXXVIII. 2. OF BLOOD. branes of the lungs; and that, by this addition, the colour of the blood is changed from a dark to a light red. Secondly, that water possesses oxygene also, as a part of its competition, and contains air likewise in its pores: whence the blood of fish re- ceives oxygene from the water, or from the air it contains, by means of their gills, in the same manner as the blood is oxygen- nated in the lungs of air-breathing animals: it changes its co- lour, at the same time, from a dark to a light red, in the vessels of their gills, which constitute a pulmonary organ, adapted to the medium in which they live. Thirdly, that the placenta consists of arteries carrying the blood to its extremities, and a vein bringing it back, resembling exactly, in structure, the lungs and gills above mentioned; and that the blood changes its colour, from a dark to a light red, in passing through these vessels. This analogy between the lungs and gills of animals, and the placenta of the fœtus, extends through a great variety of other circumstances: thus, air-breathing creatures and fish can live but a few minutes without air or water, or when they are con- fined in such air or water as has been spoiled by their own re- spiration: the same happens to the fœtus, which, as soon as the placenta is separated from the uterus, must either expand its lungs, and receive air, or die. Hence, from the structure, as well as the use of the placenta, it appears to be a respiratory organ, like the gills of fish, by which the blood in the fœtus becomes oxygenated. From the terminations of the placental vessels not being ob- served to bleed after being torn from the uterus, while those of the uterus effuse a great quantity of florid arterial blood, the terminations of the placental vessels would seem to be inserted into the arterial ones of the mother; and to receive oxygena- tion from the passing currents of her blood through their coats or membranes; which oxygenation is proved by the change of the colour of the blood from dark to light red, in its passage from the placental arteries to the placental vein. The curious structure of the cavities, or lacunae of the pla- centa, demonstrated by Mr. J. Hunter, explains this circum- stance. That ingenious philosopher has shewn, that there are numerous cavities or lacunae formed on that side of the pla- centa, which is in contact with the uterus; those cavities or cells are filled with blood from the maternal arteries which open into them; which blood is again taken up by the mater- nal veins, and is thus perpetually changed: while the termi- nations of the placental arteries and veins are spread in fine reticulation on the sides of these cells: and thus, as the grow- ing fœtus requires greater oxygenation, an apparatus is pro- duced resembling exactly the air-cells of the lungs. Z z In 348 OXYGENATION SECT. XXXVII. 3. In cows, and other ruminating animals, the internal surface of the uterus is unequal, like hollow cups, which have been called cotyledons; and into these cavities the prominencies of the numerous placentas with which the fœtus of those animals is furnished, are inserted, and strictly adhere; though they may be extracted without effusion of blood. These inequalities of the uterus, and the numerous placentas in consequence, seemed to be designed for the purpose of expanding a greater surface for the terminations of the placental vessels, for the purpose of re- receiving oxygenation from the uterine ones; as the progeny of this class of animals are more completely formed before their nativity, than that of the carnivorous classes, and must thence, in the latter weeks of pregnancy, require greater oxygenation. Thus calves and lambs can walk about in a few minutes after their birth; while puppies and kittens remain many days with- out opening their eyes. And though on the separation of the cotyledons of ruminating animals, no blood is effused, yet this is owing clearly to the greater power of contraction of their uterine lacunæ or alveoli. See Medical Essays, vol. v. page 144. And from the same cause they are not liable to a san- guiferous menstruation. The necessity of the oxygenation of the blood in the fœtus is farther illustrated by the analogy of the chick in the egg; which appears to have its blood oxygenated at the extremities of the vessels surrounding the yolk; which are spread on the air-bag at the broad end of the egg, and may absorb oxygene through that moist membrane from the air confined behind it; and which is shewn, by experiments, in the exhausted receiver, to be changeable through the shell. This analogy may even be extended to the growing seeds of vegetables; which were shewn, by Mr. Scheele, to require a re- novation of the air over the water in which they were con- fined. Many vegetable feeds are surrounded with air in their pods or receptacles, as peas, the fruit of staphylea, and lichnis vesicaria: but it is probable, that those seeds, after they are shed, as well as the spawn of fish, by the situation of the former on or near the moist and aerated surface of the earth, and of the latter in the ever-changing and ventilated water, may not be in need of an apparatus tor the oxygenation of their first blood, before the leaves of one and the gills of the other are produced for this purpose. III. 1. There are many arguments, besides the strict analogy between the liquor amnii and the albumen ovi, which shew the former to be a nutritive fluid; and that the fœtus, in the latter mouths of pregnancy, takes it into its stomach; and that, in consequence, 349 SECT. XXXVIII. 3. OF BLOOD. consequence, the placenta is produced for some other important purpose. First, that the liquor amnii is not an excrementitous fluid, is evinced, because it is found in greater quantity, when the fœtus is young, decreasing after a certain period till birth. Hal- ler asserts, " that in some animals, but a small quantity of this fluid remains at the birth. In the eggs of hens it is consumed on the eighteenth day, so that, at the exclusion of the chick, scarcely any remains. In rabbits, before birth, there is none." Elem. Physiol. Had this been an excrementitious fluid, the contrary would probably have occurred. Secondly, the skin of the fœtus is covered with a whitish crust or pellicle, which would seem to preclude any idea of the liquor amnii being produced by any exsudation of perspirable matter. And it cannot consist of urine, because, in brute animals, the urachus passes from the bladder to the alantois for the express purpose of carrying off that fluid; which, however, in the human fœtus, seems to be retained in the distended bladder, as the fæces are accumulated in the bowels of all animals. 2. The nutritious quality of the liquid which surrounds the fœtus, appears from the following considerations. 1. It is co agulable by heat, by nitrous acid, and by spirit of wine, like milk, serum of blood, and other fluids, which daily experience evinces to be nutritious. 2. It has a saltish taste, according to the accurate Baron Haller, not unlike the whey of milk, which it even resembles in smell. 3. The white of the egg, which constitutes the food of the chick, is shewn to be nutritious by our daily experience; besides the experiment of its nutritious effects, mentioned by Dr. Fordyce, in his late Treatise on Di- gestion, p. 178; who adds, that it much resembles the essential parts of the serum of blood. 3. A fluid, similar to the fluid with which the fœtus is sur- rounded, except what little change may be produced by a be- ginning digestion, is found in the stomach of the fœtus; and the white of the egg is found, in the same manner, in the sto- mach of the chick. Numerous hairs, similar to those of its skin, are perpetually found among the contents of the stomach in new-born calves; which must, therefore, have licked themselves before their na- tivity. Blasii Anatom. See Sect. XVI. 2. on Instinct. The chick in the egg is seen gently to move in its surround- ing fluid, and to open and shut its mouth alternately. The same has been observed in puppies. Haller's El. Phys. I. 8, p. 201. A column of ice has been seen to reach down the œsopha- gus, 350 OXYGENATION, &c. Sect. XXXVIII. 3. gus. from the mouth of the stomach, in a frozen fœtus; and this ice was the liquor amnii frozen. The meconium, or first fœces, in the bowels of new-horn infants, evince, that something has been digested; and what could this be but the liquor amnii, together with the recre- ments of the gastric juice and gall, which were necessary for its digestion? There have been recorded some monstrous births of animals without heads, and consequently without mouths, which seem to have been delivered on doubtful authority, or from inaccu- rate observation. There are two of such monstrous produc- tions, however, better attested; one of a human fœtus, men- tioned by Gipson, in the Scots Medical Essays; which, having the gula impervious, was furnished with an aperture into the wind-pipe, which communicated below into the gullet; by means of which the liquor amnii might be taken into the sto- mach, before nativity, without danger of suffocation, while the fœtus had no occasion to breathe. The other monstrous fœtus is described by Vander Wiel, who asserts, that he saw a mon- strous lamb, which had no mouth; but instead of it was fur- nished with an opening in the lower part of the neck into the stomach. Both these instances evidently favour the doctrine of the fœtus being nourished by the mouth; as otherwise there had been no necessity for new or unnatural apertures into the stomach, when the natural ones were deficient. From these facts and observations we may safely infer, that the fœtus in the womb is nourished by the fluid which surrounds it; which, during the first period of gestation, is absorbed by the naked lacteals; and is afterwards swallowed into the stomach and bowels, when these organs are perfected; and lastly, that the placenta is an organ for the purpose of giving due oxygena- tion to the blood of the fœtus; which is more necessary, or at least more frequently necessary, than even the supply of food. The question of the great Harvey becomes thus easily an- swered. " Why is not the fœtus in the womb suffocated for want of air, when it remains there even to the tenth month without respiration: yet, if it be born in the seventh or eighth month, and has once respired, it becomes immediately suffocat- ed for want of air, if its respiration be obstructed?" For further information on this subject, the reader is referred to the Tentamen Medicum of Dr. Jeffray, printed at Edinburgh in 1786. And it is hoped that Dr. French will some time give his theses on this subject to the public. SECT. 351 SECT. XXXIX. OF GENERATION. SECT. XXXIX. OF GENERATION. Felix, qui causas altâ œligine mersas Pandit, et evoivit tenuissima vincula rerum. ANON. I. Habits of acting and feeling of individuals attend the foul into a future life, and attend the new embryon at the time of its production. The new speck of entity absorbs nutriment, and receives oxygene. Spreads the terminations of its vessels on cells, which communicate with the arteries of the uterus; sometimes with those of the peritoneum. Afterwards it swallows the liquor amnii, which it produces by its irritation from the uterus, or peritoneum. Like infects in the heads of calves and sheep. Why the white of egg is of two consistencies. Why nothing is found in quadrupeds similar to the yolk, nor in most vegetable seeds. II. 1. Eggs of frogs and fish impregnated out of their bo- dies. Eggs of fowls which are not fecundated, contain only the nutriment for the embryon. The embryon is pro- duced by the male, and the nutriment by the female. Ani- malcula in semine. Profusion of nature's births. 2. Ve- getables viviparous. Buds and bulbs have each a father, but no mother. Vessels of the leaf and bud inosculate. The paternal offspring exactly resembles the parent. 3. Insects impregnated for six generations. Polypus branches like buds. Creeping roots. Viviparous flowers. Tænia, volvox. Eve from Adam's rib. Semen not a stimulus to the egg. III. 1. Embryons not originally created within other embryons. Organized matter is not so minute. 2. All the parts of the embryon are not formed in the male parent. Crabs produce their legs; worms produce their heads and tails. In wens, cancers and inflammations, new vessels are formed. Mules partake of the forms of both parents. Hair and nails grow by elongation, not by dis- tention. 3. Organic particles of Buffon. IV. 1. Rudi- ment of the embryon a simple living filament; becomes a living ring, and then a living tube. 2. It acquires new irritabilities, and sensibilities with new organizations, as in wounded snails, polypi, moths, gnats, tadpoles. Hence new parts are acquired by addition, not by distention. 3. All parts of the body grow, if not confined. 4. Fœtuses deficient at their extremities, or have a duplicature of parts. Monstrous births. Double parts of vegetables. 5. Mules 352 OF GENERATION. SECT. XXXIX. 1. 5. Mules cannot be formed by distention of the seminal ens. 6. Families of animals from a mixture of their orders. Mules imperfect. 7. Animal appetency like chemical af- finity. Vis fabricatrix and medicatrix of nature. 8. The changes of animals before and after nativity. Similarity of their structure. Changes in them from lust, hunger, and danger. All warm-blooded animals derived from one liv- ing filament. Cold-blooded animals, insects, worms, ve- getables, derived also from one living filament. Male animals have teats. Male pidgeon gives milk. The world itself generated. The cause of causes. A state of probation and responsibility. V. 1. Efficient cause of the colours of birds eggs, and of hair and feathers, which become white in snowy countries. Imagination of these male colours the egg. Ideas or motions of the retina imi- tated by the extremities of the nerves of touch, or rete mucosum. 2. Nutriment supplied by the female of three kinds. Her imagination can only affect the first kind. Mules how produced, and mulattoes. Organs of re-pro- duction why deficient in mules. Eggs with double yolks. VI. 1. Various secretions produced by the extremities of the vessels, as in the glands. Contagious matter. Many glands affected by pleasureable ideas, as those which se- crete the semen. 2. Snails and worms are hermaphrodite, yet cannot impregnate themselves. Final cause of this. 3. The imagination of the male forms the sex. Ideas, or motions of the nerves of vision or of touch, are imitated by the ultimate extremities of the glands of the testes, which mark the sex. This effect of the imagination belongs only to the male. The sex of the embryon is not owing to acci- dent. 4. Causes of the changes in animals from imagina- tion, as in monsters. From the male. From the female. 5. Miscarriages from fear. 6. Power of the imagination of the male over the colour, form, and sex of the progeny. An instance of it. 7. Act of generation accompanied with ideas of the male or female form. Art of begetting beau- tiful children of either sex. VII. Recapitulation. VIII. Conclusion. Of cause and effect. The atomic philosophy leads to a first cause. 1. THE ingenious Dr. Hartley, in his work on man, and some other philosophers, have been of opinion, that our immortal part acquires, during this life, certain habits of action or of sentiment, which become for ever in dissoluble, continuing after death in a future state of existence; and add, that if these, habits are of the malevolent 353 SECT. XXXIX. 1. OF GENERATION. malevolent kind, they must render the possessor miserable even in heaven. I would apply this ingenious idea to the generation or production of the embryon, or new animal, which partakes so much of the form and propensities of the parent. Owing to the imperfection of language the offspring is term- ed a new animal, but is in truth a branch or elongation of the parent; since a part of the embryon-animal is, or was, a part of the parent; and therefore, in strict language, it cannot be said to be entirely new at the time of its production; and therefore it may retain some of the habits of the parent-system. At the earliest period of its existence the embryon, as secret- ed from the blood of the male, would seem to consist of a living filament, with certain capabilities of irritation, sensation, voli- tion, and association; and also with some acquired habits or propensities peculiar to the parent: the former of these are in common with other animals; the latter seem to distinguish or produce the kind of animal, whether man or quadruped, with the similarity of feature or form to the parent. It is difficult to be conceived, that a living entity can be separated or produced from the blood by the action of a gland, and which shall after- wards become an animal similar to that in whose vessels it is formed; even though we should suppose, with some modern the- orists, that the blood is alive; yet every other hypothesis concern- ing genration rests on principles still more difficult to our com- prehension. At the time of procreation this speck of entity is received in to an appropriated nidus, in which it must acquire two circum- stances necessary to its life and growth; one of these is food or sustenance, which is to be received by the absorbent mouths of its vessels; and the other is that part of atmospherical air, or of water, which, by the new chemistry, is termed oxygene, and which affects the blood by passing through the coats of the ves- sels which contain it. The fluid surrounding the embryon in its new habitation, which is called liquor amnii, supplies it with nourishment; and as some air cannot but be introduced into the uterus along with the new embryon, it would seem that this same fluid would, for a short time, suppose for a few hours, sup- ply likewise a sufficient quantity of the oxygene for its immedi- ate existence. On this account the vegetable impregnation of aquatic plants is performed in the air; and it is probable that the honey-cup, or nectary of vegetables, requires to be open to the air, that the anthers and stigmas of the flower may have food of a more ox- ygenated kind than the common vegetable sap-juice. On the introduction of this primordium of entity into the ute- rus, 354 OF GENERATION. SECT. XXXIX. 1. rus, the irritation of the liquor amnii, which surrounds it, ex- cites the absorbent mouths of the new vessels into action; they drink up a part of it, and a pleasureable sensation accompanies this new action; at the same time the chemical affinity of the oxygene acts through the vessels of the rubescent blood; and a previous want, or disagreeable sensation, is relieved by this pro- cess. As the want of this oxygenation of the blood is perpetual, (as appears from the incessant necessity of breathing by lungs or gills) the vessels become extended by the efforts of pain or desire to seek this necessary object of oxygenation, and to re- move the disagreeable sensation which that want occasions. At the same tune new particles of matter are absorbed, or applied to these extended vessels, and they become permanently elongate- ed, as the fluid in contact with them soon loses the oxygenous part which it at first possessed, which was owing to the intro- duction of air along with the embryon. These new blood vessels approach the sides of the uterus, and penetrate, with their fine terminations, into the vessels of the mother, or adhere to them, acquiring oxygene, through their coats, from the pas- sing currents of the arterial blood of the mother. See Sect. XXXVIII. 2. This attachment of the placental vessels to the internal side of the uterus, by their own proper efforts, appears further illus- trated by the many instances of extra- uterine fœtuses which have thus attached or inferred their vessels into the peritoneum, or on the viscera, exactly in the same manner as they naturally insert or attach them to the uterus. The absorbent vessels of the embryon continue to drink up nourishment from the fluid in which they swim, or liquor am- nii; and which at first needs no previous digestive preparation; but which, when the whole apparatus of digestion becomes complete, is swallowed by the mouth into the stomach, and being mixed with saliva, gastric juice, bile, pancreatic juice, and mucus of the intestines, becomes digested, and leaves a re- crement, which produces the first fæces of the infant, called meconium. The liquor amnii is secreted into the uterus, as the fœtus re- quires it, and may probably be produced by the irritation of the fœtus, as an extraneous body; since a similar fluid is acquired from the peritoneum in cases of extra-uterine gestation. The young caterpillars of the gad-fly, placed in the skins of cows, and the young of the ichneumon-fly, placed in the backs of the caterpillars, on cabbages, seem to produce their nourishment by their irritating the sides of their nidus. A vegetable secretion and 355 SECT. XXXIX. 1. OF GENERATION. and concretion is thus produced on oak-leaves, by the gall-in- sect, and by the cynips in the bedeguar of the rose; and by the young grasshopper on many plants, by which the animal sur- rounds itself with froth. But in no circumstance is extra-ute- rine gestation so exactly resembled as by the eggs of a fly, which are deposited in the frontal sinus of sheep and calves. These eggs float in some ounces of fluid, collected in a thin pellicle or hydatide. This bag of fluid compresses the optic nerve on one side, by which the vision being less distinct in that eye, the animal turns, in perpetual circles, towards the side af- fected, in order to get a more accurate view of objects; for the same reason as in squinting the affected eye is turned away from the object contemplated. Sheep, in the warm months, keep their notes close to the ground, to prevent this fly from so rea- dily getting into their nostrils. The liquor amnii is secreted into the womb as it is required, hot only in respect to quantity, but, as the digestive powers of the fœtus become formed, this fluid becomes of a different con- fidence and quality, till it is exchanged for milk after nativity; Haller. Physiol. V. 1. In the egg the white part, which is analogous to the liquor amnii of quadrupeds, consists of two distinct parts; one of which is more viscid, and probably more difficult of digestion, and more nutritive than the other; and this latter is used in the last week of incubation. The yolk of the egg is a still stronger or more nutritive fluid, which is drawn up into the bowels of the chick, just at its exclusion front the shell, and serves it for nourishment for a day or two, till it is able to digest, and has learnt to chuse the harder seeds or grains, which are to afford it sustenance. Nothing analogous to this yolk is found in the fœtus of lactiferous animals, as the milk is another nutritive fluid ready prepared for the young progeny. The yolk, therefore, is not necessary to the spawn of fish, the eggs of insects, or for the seeds of vegetables; as their embry- ons have probably their food presented to them as soon as they are excluded from their shells, or have extended their roots. Whence it happens, that some infects produce a living progeny in the spring and summer, and eggs in the autumn; and some vegetables have living roots, or buds, produced in the place of seeds, as the polygonum viviparum, and magical onions. See Botanic Garden, P. II. art. anthoxanthum. There seems, however, to be a reservoir of nutriment prepar- ed for some seeds besides their cotyledons or seed-leave's, which may be supposed in some measure analogous to the yolk of the egg. Such are the saccharine juices of apples, grapes and other fruits, which supply nutrition to the seeds after they fall on the A a a ground. 356 OF GENERATION. SECT. XXXIX. 2. ground. And such is the milky juice in the centre of the co- coa-nut, and part of the kernel of it; the same I suppose of all other monocotyledon seeds, as of the palms, grasses, and lilies. II. 1. The process of generation is still involved in impene- trable obscurity; conjectures may nevertheless be formed con- cerning some of its circumstances. First, the eggs of fish and frogs are impregnated, after they leave the body of the female; because they are deposited in a fluid, and are not therefore co- vered with a hard shell. It is, however, remarkable, that nei- ther frogs nor fish will part with their spawn without the pre- sence of the male; on which account female carp and gold-fish in small ponds, where there are no males, frequently die from the distention of their growing spawn. 2. The eggs of fowls, which are laid without being impregnated, are seen to contain only the yolk and white, which are evidently the food or suste- nance for the future chick. 3. As the cicatricula of these eggs is given by the cock, and is evidently the rudiment of the new animal, we may conclude, that the embryon is produced by the male, and the proper food and nidus by the female. For if the female be supposed to form an equal part of the embryon, why should she form the whole of the apparatus for nutri- ment and for oxygenation? The male in many animals is lar- ger, stronger, and digests more food than the female, and there- fore should contribute as much or more towards the re-produc- tion of the species; but if he contributes only half the embryon, and none of the apparatus for sustenance and oxygenation, the division is unequal; the strength of the male and his con- sumption of food are too great for the effect, compared with that of the female, which is contrary to the usual course of nature. In objection to this theory of generation it may be said, if the animalcula in semine, as seen by the microscope, be all of them rudiments of homunculi, when but one of them can find a nidus, what a waste nature has made of her productions? I do not assert that these moving particles, visible by the mi- croscope, are homunciones; perhaps they may be the creatures of stagnation or putridity, or perhaps no creatures at all; but if they are supposed to be rudiments of homunculi, or embryons, such a profusion of them corresponds with the general efforts of nature to provide for the continuance of her species of ani- mals. Every individual tree produces innumerable seeds, and every individual fish innumerable spawn, in such inconceive- able abundance as would, in a short space of time, crowd the earth and ocean with inhabitants; and these are much more perfect animals than the animalcula in semine can be supposed to be, and 357 SECT. XXXIX. 2. OF GENERATION. and perish in uncounted millions. This argument only shews, that the productions of nature are governed by general laws; and that, by a wife superfluity of provision, she has ensured their continuance. 2. That the embryon is secreted or produced by the male, and not by the conjunction of fluids from both male and fe- male, appears from the analogy of vegetable seeds. In the large flowers, as the tulip, there is no similarity of apparatus between the anthers and the stigma; the seed is produced, according to the observations of Spallanzani, long before the flowers open, and, in consequence, long before it can be impregnated, like the egg in the pullet. And after the prolific dust is shed on the stigma, the seed becomes coagulated in one point first, like the cicatricula of the impregnated egg. See Botanic Garden, Part I. additional note 38. Now, in these simple products of na- ture, if the female contributed to produce the new embryon equally with the male, there would probably have been some visible similarity of parts for this purpose, besides those neces- sary for the nidus and sustenance of the new progeny. Besides, in many flowers the males are more numerous than the females, or than the separate uterine cells in their germs, which would shew that the office of the male was at least as important as that of the female; whereas, if the female, besides producing the egg or seed, was to produce an equal part of the embryon, the office of re-production would be unequally divided between them. Add to this, that, in the most simple kind of vegetable re- production, I mean the buds of trees, which are their vivipa- rous offspring, the leaf is evidently the parent of the bud, which rises in its bosom, according to the observation of Linnæus. This leaf consists of absorbent vessels, and pulmonary ones, to obtain its nutriment, and to impregnate it with oxygene. This simple piece of living organization is also furnished with a power of re-production; and as the new offspring is thus sup- ported, adhering to its father, it needs no mother to supply it with a nidus, and nutriment, and oxygenation; and hence no female leaf has existence. I conceive, that the vessels between the bud and the leaf communicate or inosculate; and that the bud is thus served with vegetable blood, that is, with both nutriment and oxygenation, till the death of the parent leaf in autumn: and in this respect it differs from the fœtus of viviparous animals. Secondly, that then the bark-vessels belonging to the dead-leaf, and in which suppose a kind of manna to have been deposited, become now the placental vessels, if they may be so called, of the new bud. From 358 OF GENERATION. SECT. XXXIX. 1. From the vernal sap, thus produced, of one sugar-maple-tree in New-York and in Pennsylvania, five or six pounds of good sugar may be made annually, without destroying the tree. Account of Maple-sugar, by B. Rush. London, Phillips. (See Botanic Garden, Part I. additional note on vegetable placenta- tion.) These vessels, when the warmth of the vernal sun hatches the young bud, serve it with a saccharine nutriment, till it ac- quires leaves of its own, and shoots a new system of absorbents down the bark and root of the tree, just as the farinaceous or oily matter in seeds, and the saccharine matter in fruits, serve their embryons with nutriment, till they acquire leaves and roots. This analogy is as forcible, in so obscure a subject, as it is curious; and may, in large buds, as of the horse-chesut, be almost seen by the naked eye, if, with a penknife, the remain- ing rudiment of the last year's leaf, and of the new bud in its bosom, be cut away, slice by slice. The seven ribs of the last year's leaf will be seen to have arisen, from the pith, in seven distinct points, making a curve; and the new bud to have been produced in their centre, and to have pierced the alburnum and cortex, and grown without the assistance of a mother. A similar process may be seen on dissecting a tulip-root in winter: the leaves which inclosed the last year's flower-stalk were not necessary for the flower; but each of these was the father of a new bud, which may be now found at its base, and which, as it adheres to the parent, requires no mother. This paternal offspring of vegetables, I mean their buds and bulbs, is attended with a very curious circumstance; and that is, that they exactly resemble their parents, as is observable in grafting fruit-trees, and in propagating flower-roots; whereas the seminal offspring of plants, being supplied with nutriment by the mother, is liable to perpetual variation. Thus, also, in the vegetable class dioicia, where the male flowers are produced on one tree and the female ones on another, the buds of the male trees uniformly produce either male flowers, or other buds similar to themselves, and the buds of the female trees produce either female flowers, or other buds similar to themselves; whereas the seeds of these trees produce either male or female plants. From this analogy of the production of vegetable buds without a mother, I contend, that the mother does not contri- bute to the formation of the living ens in animal generation, but is necessary only for supplying its nutriment and oxygena- tion. There is another vegetable fact published by M. Koelreuter, which he calls " a complete metamorphosis of one natural species 359 SECT. XXXIX. 2. OF GENERATION. species of plants into another," which shews, that in seeds as well as in buds, the embryon proceeds from the male parent, though the form of the subsequent mature plant is in part de- pendent on the female. M. Koelreuter impregnated a stigma of the nicotiana rustica with the farina of the nicotiana pani- culata, and obtained prolific seeds from it. With the plants which sprung from these seeds, he repeated the experiment, im- pregnating them with the farina of the nicotiana paniculata. As the mule plants which he thus produced were prolific, he continued to impregnate them, for many generations, with the farina of the nicotiana paniculata, and they became more and more like the male parent, till he at length obtained six plants in every respect perfectly similar to the nicotiana paniculata, and in no respect resembling their female parent the nicotiana rustica. Blumenbach on Generation. 3. It is probable that the infects which are said to require but one impregnation for six generations, as the aphis (see Amenit. Academ.) produce their progeny in the manner above described; that is, without a mother, and not without a father; and thus experience a lucina fine concubitu. Those who have attended to the habits of the polypus, which is found in the stagnant water of our ditches in July, affirm that the young ones branch out from the side of the parent like the buds of trees, and after a time separate themselves from them. This is so analogous to the manner in which the buds of trees ap- pear to be produced, that these polypi may be considered as all male animals, producing embryons, which require no mother to supply them with a nidus, or with nutriment, and oxygen- nation. This lateral or lineal generation of plants, not only obtains in the buds of trees, which continue to adhere to them, but is beautifully seen in the wires of knot-grass, polygonum avicu- lare, and in those of strawberries, fragaria vesca. In these an elongated creeping bud is protruded, and, where it touches the ground, takes root, and produces a new plant derived from its father, from which it acquires both nutriment and, oxygenation, and, in consequence, needs no maternal apparatus for these pur- poses. In viviparous flowers, as those of allium magicum, and polygonum viviparum, the anthers and the stigmas become ef- fete and perish; and the lateral or paternal offsping succeeds instead of seeds, which adhere till they are diffidently mature, and then fall upon the ground, and take root like other bulbs. The lateral production of plants by wires, while each new plant is thus chained to its parent, and continues to put forth another and another, as the wire creeps onward on the ground, is 360 OF GENERATION. SECT. XXXIX. 3. is exactly resembled by the tape-worm, or tænia, so often found in the bowels, stretching itself in a chain quite from the sto- mach to the rectum. Linnæus asserts, " that it grows old at one extremity, while it continues to generate young ones at the other, proceeding ad infinitum, like a root of grass. The se- parate joints are called gourd-worms, and propagate new joints, like the parent, without end; each joint being furnished with its proper mouth and organs of digestion." Systema Naturæ Vermes Tenia. In this animal there evidently appears a power of re-production, without any maternal apparatus for the pur- pose of supplying nutriment and oxygenation to the embryon, as it remains attached to its father till its maturity. The volvox globator, which is a transparent animal, is said, by Linnæus, to bear within it sons and grand-sons to the fifth generation. These are probably living fœtuses, produced by the father, of different degrees, of maturity, to be detruded at different periods of time, like the unimpregnated eggs, of various sizes, which are found in poultry; and, as they are produced without any known copulation, contribute to evince, that the living embryon in other orders of animals is formed by the male-parent, and not by the mother, as one parent has the power to produce it. This idea of the re-production of animals from a single liv- ing filament of their fathers, appears to have been shadowed. or allegorized in the curious account, in sacred writ, of the for- mation of Eve from a rib of Adam. From all these analogies I conclude, that the embryon is produced solely by the male, and that the female supplies it with a proper nidus, with sustenance, and with oxygenation; and that the idea of the semen of the male, constituting only a sti- mulus to the egg of the female, exciting it into life, (as held by some philosophers) has no support from experiment or analogy. III. 1. Many ingenious philosophers have found so great difficulty in conceiving the manner of the re-production of ani- mals, that they have supposed all the numerous progeny to have existed in miniature in the animal originally created; and that these infinitely minute forms are only evolved or distend- ed, as the embryon increases in the womb. This idea, besides its being unsupported by any analogy we are acquainted with, ascribes a greater tenuity to organized matter than we can readily admit; as these included embryons are supposed each of them to consist of the various and complicate parts of ani- mal bodies: they must possess a much greater degree of mi- nuteness, than that which was ascribed to the devils that tempt- ed St. Anthony; of whom 20,000 were said to have been able to dance a saraband on the point of the finest needle without incommoding each other. 2. Others 361 SECT. XXXIX. 3. OF GENERATION. 2. Others have supposed, that all the parts of the embryon are formed in the male, previous to its being deposited in the egg or uterus; and that it is then only to have its parts evolv- ed or distended, as mentioned above; but this is only to get rid of one difficulty by proposing another equally incomprehensi- ble: they found it difficult to conceive, how the embryon could be formed in the uterus or egg, and therefore wished it to be formed before it came thither. In answer to both these doc- trines it may be observed, 1st, that some animals, as the crab- fish, can re-produce a whole limb, as a leg which has been broken off; others, as worms and snails, can re-produce a head, or a tail, when either of them has been cut away; and that hence, in these animals, at lead a part can be formed anew, which cannot be supposed to have existed previously in miniature. Secondly, there are new parts, or new vessels, produced in many diseases, as on the cornea of the eye in ophthalmy, in wens and cancers, which cannot be supposed to have had a prototype or original miniature in the embryon. Thirdly, how could mule-animals be produced, which par- take of the forms of both the parents, if the original embryon was a miniature existing in the semen of the male parent? If an embryon of the male ass was only expanded, no resem- blance to the mare could exist in the mule. This mistaken idea of the extension of parts seems to have had its rise from the mature man, resembling the general form of the fœtus; and from thence it was believed, that the parts of the fœtus were distended into the man; whereas they have increased 100 times in weight, as well as 100 times in size: now, no one will call the additional 99 parts a distention of the original one part in respect to weight. Thus, the uterus, dur- ing pregnancy, is greatly enlarged in thickness and solidity, as well as in capacity, and hence must have acquired this addi- tional size by accretion of new parts, not by an extension of the old ones: the familiar act of blowing up the bladder of an animal recently slaughtered, has led our imaginations to apply this idea of distention to the increase of size from natural growth; which, however, must be owing to the apposition of new parts; as it is evinced, from the increase of weight, along with the increase of dimension, and is even visible to our eyes, in the elongation of our hair, from the colour of its ends; or, when it has been dyed on the head; and in the growth of our nails, from the specks sometimes observable on them; and in the increase of the white crescent at their roots; and in the growth of new flesh in wounds, which consists of new nerves as well as of new blood-vessels. 3. Lastly, 362 OF GENERATION. SECT. XXXIX. 4. 3. Lastly, Mr. Buffon has, with great ingenuity, imagined the existence of certain organic particles, which are supposed to be partly alive, and partly mechanic springs. The latter of these were discovered by Mr. Needham, in the milt or male Organ of a species of cuttle-fish, called calmar; the former, or living animalcula, are found in both male and female secretions, in the infusions of seeds, as of pepper, in the jelly of roasted veal, and in all other animal and vegetable substances. These organic particles he supposes to exist in the spermatic fluids of both sexes, and that they are derived thither from every part of the body, and must therefore resemble, as he supposes, the parts from whence they are derived. These organic particles he be- lieves to be in constant activity, till they become mixed in the womb, and then they instantly join and produce an embryon, or fœtus, similar to the two parents. Many objections might be adduced to this fanciful theory; I shall only mention two: First, that it is analogous to no known animal laws: And, secondly, that, as these fluids, replete with organic particles, derived both from the male and female organs, are supposed to be similar, there is no reason why the mother should not produce a female embryon without the assistance of the male, and realize the lucina sine concubitu. IV. 1. I conceive the primordium, or rudiment of the em- bryon, as secreted from the blood of the parent, to consist of a simple living filament, as a muscular fibre, which I suppose to be an extremity of a nerve of locomotion, as a fibre of the re- tina is an extremity of a nerve of sensation; as, for instance, one of the fibrils which compose the mouth of an absorbent ves- sel: I suppose this living filament, of whatever form it may be, whether sphere, cube, or cylinder, to be endued with the capa- bility of being excited into action by certain kinds of stimulus. By the stimulus of the surrounding fluid, in which it is received from the male, it may bend into a ring, and thus form the be- ginning of a tube. Such moving filaments, and such rings, are described by those who have attended to microscopic animalcula. This living ring may now embrace or absorb a nutritive particle of the fluid in which it swims, and, by drawing it into its pores, or joining it, by compression, to its extremities, may increase its own length or crassitude; and, by degrees, the living ring may become a living tube. 2. With this new organization, or accretion of parts, new kinds of irritability may commence; for so long as there was but one living organ, it could only be supposed to possess irrita- bility; since sensibility may be conceived to be an extension of the effect of irritability over the red of the system. These new kinds 363 SECT. XXXIX.4. OF GENERATION. kinds of irritability and of sensibility in consequence of new or- ganization, appear from variety of facts in the more mature animal; thus the formation of the testes, and consequent se- cretion of the semen, occasion the passion of lust; the lungs must be previously formed before their exertions to obtain fresh air can exist; the throat or œsophagus must be formed previ- ous to the sensation or appetites of hunger and thirst; one of which seems to reside at the upper end, and the other at the lower end of that canal. Thus also the glans penis, when it is distended with blood, acquires a new sensibility, and a new appetency. The same Occurs to the nipples of the breasts of female animals; when they are distended with blood, they acquire the new; appetency of giv- ing milk. So inflamed tendons and membranes, and even bones, acquire new sensations; and the parts of mutilated animals, as of wounded snails, and polypi, and crabs, are re-produced; and at the same time acquire sensations adapted to their situations. Thus, when the head of a snail is re-produced after decollation with a sharp razor, those curious telescopic eyes are also re-pro- duced, and acquire their sensibility to light, as well as their adapted muscles for retraction on the approach of injury. With every new change, therefore, of organic form, or ad- dition of organic parts, I suppose a new kind of irritability or of sensibility to be produced; such varieties of irritability or of sen- sibility exist in our adult date in the glands; every one of which is furnished with an irritability, or a taste, or appetency, and a Consequent mode of action peculiar to itself. In this manner I conceive the vessels of the jaws to produce those of the teeth, those of the fingers to produce the nails, those of the skin to produce the hair; in the same manner as after- wards, about the age of puberty the beard and other great changes in the form of the body, and disposition of the mind, are pro- duced in consequence of the new secretion of semen; for if the animal is deprived of this secretion, those changes do not take place. These changes I conceive to be formed not by elonga- tion or distention of primeval stamina, but by apposition of parts; as the mature crab-fish, when deprived of a limb, in a certain space of time has power to regenerate it; and the tad- pole puts forth its feet long after its exclusion from the spawn; and the caterpillar, in changing into a butterfly, acquires a new form, with new powers, new sensations, and new desires. The natural history of butterflies, and moths, and beetles, and gnats, is full of curiosity; some of them pass many months, and others even years, in their caterpillar or grub state; they then rest many weeks without food, suspended in the air, buried in B b b the 364 OF GENERATION. SECT. XXXIX. 4. the earth, or submersed in water; and change themselves, dur- ing this time, into an animal apparently of a different nature: the stomachs of some of them, which, before, digested vegetable leaves or roots, now only digest honey; they have acquired wings for the purpose of seeking this new food, and a long pro- boscis to collect it from flowers, and, I suppose, the sense of smell to detect the secret places in flowers, where it is formed. The moths, which fly by night, have a much longer proboscis rolled up under their chins like a watch spring, which they ex- tend to collect the honey from flowers in their sleeping state, when they are closed, and the nectaries in consequence more difficult to be plundered. The beetle kind are furnished with an external covering of a hard material to their wings, that they may occasionally again make holes in the earth, in which they passed the former date of their existence. But what most of all distinguishes these new animals is, that they are new furnished with the powers of re-production; and that they now differ from each other in sex, which does not appear in their caterpillar or grub state. In some of them, the change from a caterpillar into a butterfly, or moth, seems to be accomplished for the sole purpose of their propagation; since they immediately die after this is finished, and take no food in the interim, as the silk-worm in this climate; though it is possible, it might take honey as food, if it was presented to it. For, in general, it would seem, that food of a more sti- mulating kind, the honey of vegetables, instead of their leaves, was necessary for the purpose of the seminal re-production of these animals, exactly similar to what happens in vegetables; in these the juices of the earth are sufficient for their purpose of re-production by buds or bulbs; in which the new plant seems to be formed by irritative motions, like the growth of their other parts, as their leaves or roots; but, for the purpose of seminal or amatorial re-production, where sensation is required, a more stimulating food becomes necessary for the anther, and stigma; and this food is honey; as explained in Sect. XIll. on Vege- table Animation. The gnat and the tadpole resemble each other in their change from natant animals, with gills, into aerial animals with lungs, and in their change of the element in which they live, and pro- bably of the food with which they are supported; and, lastly, with their acquiring in their new date the difference of sex, and the organs of seminal or amatorial re-production. While the polypus, who is their companion in their former state of life, not being allowed to change his form and element, can only propagate, like vegetable buds, by the same kind of irrita- tive 365 SECT. XXXIX. 4. OF GENERATION. tive motions which produces the growth of his own body, without the seminal or amatorial propagation, which require sensation; and which, in gnats and tadpoles, seems to require a change both of food and of respiration. From hence I conclude, that, with the acquisition of new parts, new sensations, and new desires, as well as new powers, are produced; and this by accretion to the old ones, and not by distention of them. And, finally, that the most essential parts of the system, as the brain for the purpose of distributing the power of life, and the placenta for the purpose of oxygenating the blood, and the additional absorbent vessels for the purpose of acquiring aliment, are first formed by the irritations above mentioned, and by the pleasureable sensations attending those irritations, and by the exertions in consequence of painful sen- sations, similar to those of hunger and suffocation. After these an apparatus of limbs for future uses, or for the purpose of moving the body in its present natant state, and of lungs for future respiration, and of testes for future re-production, are formed by the irritations and sensations, and consequent exer- tions of the parts previously existing, and to which the new parts are to be attached. 3. In confirmation of these ideas, it may be observed, that all the parts of the body endeavour to grow, or to make additional parts to themselves, throughout our lives, but are restrained by the parts immediately containing them: thus, if the skin be taken away, the fleshy parts beneath soon shoot out new gra- nulations, called by the vulgar proud flesh. If the periosteum be removed, a similar growth commences from the bone. Now, in the case of the imperfect embryon, the containing or con- fining parts are not yet supposed to be formed, and hence there is nothing to restrain its growth. 4. By the parts of the embryon being thus produced by new appositions, many phenomena, both of animal and vegetable productions, receive an easier explanation; such as that many fœtuses are deficient at the extremities, as in a finger or a toe, or in the end of the tongue, or in what is called a hair-lip, with deficiency of the palate. For, if there should be a deficiency in the quantity of the first nutritive particles laid up in the egg for the reception of the first living filament, the extreme parts, as being last formed, must drew this deficiency, by their being imperfect. This idea of the growth of the embryon accords also with the production of some monstrous births, which consist of a duplicature of the limbs, as chickens with four legs; which could not occur, if the fœtus was formed by the distention of an 366 OF GENERATION. SECT. XXXIX. 4. an original stamen, or miniature. For, if there should be a superiority of the first nutritive particles laid up in the egg for the first living filament, it is easy to conceive, that a duplica- ture of some parts may be formed. And that such superflu- ous nourishment sometimes exists, is evinced by the double yolks in some eggs, which I suppose were thus formed previous to their impregnation by the exuberant nutriment of the hen. This idea is confirmed by the analogy of the monsters in the vegetable world also; in which a duplicate or triplicate produc- tion of various parts of the flower is observable, as a triple nec- tary in some columbines, and a triple petal in some primroses; and which are supposed to be produced by abundant nourish- ment. 3. If the embryon be received into a fluid, whose stimulus is different, in some degree, from the natural, as in the produc- tion of mule-animals, the new irritabilities or sensibilities ac- quired by the increasing or growing organized parts, may dif- fer, and thence produce parts not similar to the father, but of a kind belonging, in part, to the mother; and thus, though the original stamen, or living ens, was derived totally from the fa- ther, yet new irritabilities or sensibilities being excited, a change of form corresponding with them will be produced. Nor could the production of mules exist, if the stamen or miniature of all the parts of the embryon is previously formed in the male semen, and is only distended by nourishment in the female ute- rus. Whereas, this difficulty ceases, if the embryon be sup- posed to consist of a living filament, which acquires or makes new parts with new irritabilities, as it advances in its growth. The form, solidity, and colour of the particles of nutri- ment laid up for the reception of the first living filament, as well as their peculiar kind of stimulus, may contribute to pro- duce a difference in the form, solidity, and colour of the fœtus, so as to resemble the mother, as it advances in life. This also may especially happen during the first state of the existence of the embryon, before it has acquired organs, which can change these first nutritive particles, as explained in No. 5. 2. of this Section. And as these nutritive particles are supposed to be similar to those which are formed for her own nutrition, it follows that the fœtus should so far resemble the mother. This explains, why hereditary diseases may be derived either from the male or female parent, as well as the peculiar form of either of their bodies. Some of these hereditary diseases are simply owing to a deficient activity of a part of the system, as of the absorbent vessels, which open into the cells or cavities of the body, and thus occasion dropsies. Others are, at the same time, 367 SECT. XXXIX. 4. OF GENERATION. time, owing to an increase of sensation, as in scrophula and consumption; in these the obstruction of the fluids is first caused by the inirritability of the vessels; and the inflammation and ulcer which succeed, are caused by the consequent increase of sensation in the obstructed part. Other hereditary diseases, as the epilepsy, and other convulsions, consist in too great volun- tary exertions, in consequence of disagreeable sensation in some particular diseased part. Now, as the pains which occasion these convulsions are owing to defect of the action of the dis- eased part, as shewn in Sect. XXXIV. it is plain, that all these hereditary diseases may have their origin either from defective irritability, derived from the father, or from deficiency of the stimulus of the nutriment derived from the mother. In either case the effect would be similar; as a scrophulous race is fre- quently produced among the poor from the deficient stimulus of bad diet, or of hunger; and among the rich, by a deficient irri- tability, from their hiving been long accustomed to too great stimulus, as of vinous spirit. 6. From this account of re-production it appears, that all animals have a similar origin, viz. from a single living filament; and that the difference of their forms and qualities has arisen only from the different irritabilities and sensibilities, or volunta- rities, or associabilities, of this original living filament, and, per haps, in some degree, from the different forms of the particles of the fluids by which it has been at first stimulated into activity. And that from hence, as Linnaeus has conjectured in respect to the vegetable world, it is not impossible but the great variety of species of animals which now tenant the earth, may have had their origin from the mixture of a few natural orders: and that those animals and vegetable mules which could continue their species, have done so, and constitute the numerous families of animals and vegetables which now exist; and that those mules which were produced with imperfect organs of generation, pe- rished without re-production, according to the observation of Aristotle; and are the animals which we now call mules. See Botanic Garden, Part II. Note on Dianthus. Such a promiscuous intercourse of animals is said to exist at this day, in New South Wales, by Captain Hunter: and that not only amongst the quadrupeds and birds of different kinds, but even amongst the fish, and, as he believes, amongst the ve- getables. He speaks of an animal between the opossum and the kangaroo, from the size of a sheep to that of a rat. Many fish seemed to partake of the shark; some with a skait's head and shoulders, and the hind part of a shark; others with a shark's head, and the body of a mullet; and some with a shark's head, and 368 OF GENERATION. SECT. XXXIX. 4. and the flat body of a sting-ray. Many birds partake of the parrot; some have the head, neck, and bill of a parrot, with long straight feet and legs; others with legs and feet of a parrot, with head and neck of a sea-gull. Voyage to South Wales, by Captain John Hunter, p. 68. 7. All animals, therefore, I contend, have a similar cause of their organization, originating from a single living filament, endued, indeed, with different kinds of irritabilities and sensibi- lities, or of animal appetencies, which exist in every gland, and in every moving organ of the body, and are as essential to living organization, as chemical affinities are to certain combinations of inanimate matter. If I might be indulged to make a simile in a philosophical work, I should say, that the animal appetencies are not only perhaps less numerous originally than the chemical affinities but that, like these latter, they change with every new combi- nation; thus vital air and azote, when combined, produce ni- trous acid; which now acquires the property of dissolving silver: so, with every new additional part to the embryon, as of the throat or lungs, I suppose a new animal appetency to be pro- duced. In this early formation of the embryon from the irritabilities, sensibilities, and associabilities, and consequent appetencies, the faculty of volition can scarcely be supposed to have had its birth. For about what can the fœtus deliberate, when it has no choice of objects? But in the more advanced date of the fœtus, it evident- ly possesses volition; as it frequently changes its attitude, though it seems to sleep the greatest part of its time; and afterwards the power of volition contributes to change or alter many parts of the body during its growth to manhood, by our early modes of exertion in the various departments of life. All these faculties then constitute the vis fabricatrix, and the vis conservatrix, as well as the vis medicatrix of nature, so much spoken of, but so little understood by philosophers. 8. When we revolve in our minds, first, the great changes which we see naturally produced in animals after their nativity, as in the production of the butterfly with painted wings from the crawling caterpillar; or of the respiring frog from the subna- tant tadpole; from the feminine boy to the bearded man, and from the infant girl to the lactescent woman; both which changes may be prevented by certain mutilations of the glands necessary to re-production. Secondly, when we think over the great changes introduced into various animals by artificial or accidental cultivation, as in horses, which we have exercised for the different purposes of strength 369 SECT. XXXIX. 4. OF GENERATION. strength or swiftness, in carrying burthens, or in running races; or in dogs, which have been cultivated for strength and cou- rage, as me bull-dogs; or for acuteness of his sense of smell, as the hound and spaniel; or for the swiftness of his foot, as the greyhound; or for his swimming in the water, or for drawing snow sledges, as the rough-haired dogs of the north; or lastly, as a play-dog for children, as the lap-dog; with the changes of the forms of the cattle, which have been domesticated from the greatest antiquity, as camels, and sheep, which have undergone to total a transformation, that we are now ignorant from what species of wild animals they had their origin. Add to these the great changes of shape and colour which we daily see produced in smaller animals from our domestication of them, as rabits, or pidgeons; or from the difference of climates and even of sea- sons; thus the sheep of warm climates are covered with hair instead of wool; and the hares and partridges of the latitudes which are long buried in snow, become white during the win- ter months: add to these the various changes produced in the forms of mankind, by their early modes of exertion; or by the diseases, occasioned by their habits of life; both of which be- came hereditary, and that through many generations. Those who labour at the anvil, the oar, or the loom, as well as those who carry sedan-chairs, or who have been educated to dance upon the rope, are distinguishable by the shape of their limbs; and the diseases occasioned by intoxication deform the counte- nance with leprous eruptions, or the body with tumid viscera, or the joints with knots and distortions. Thirdly, when we enumerate the great changes produced in the species of animals before their nativity: these are such as re- semble the form or colour of their parents, which have been altered by the cultivation or accidents above related, and are thus continued to their posterity. Or they are changes pro- duced by the mixture of species, as in mules; or changes pro- duced probably by the exuberance of nourishment supplied to the fœtus, as in monstrous births with additional limbs: many of these enormities of shape are propagated, and continued as a variety at least, if not as a new species of animal. I have seen a breed of cats with an additional claw on every foot; of poultry also, with an additional claw, and with wings to their feet; and of others without rumps. Mr. Buffon mentions a breed of dogs without tails, which are common at Rome and at Naples, which he supposes to have been produced by a cus- tom, long established, of cutting their tails close off. There are many kinds of pigeons, admired for their peculiarities, which are monsters thus produced and propagated. And to these must be 370 OF GENERATION. SECT. XXXIX. 4. be added the changes produced by the imagination of the male parent, as will be treated of more at large in No. 6. of this Sect. When we consider all these changes of animal form, and innumerable others which may be collected from the books of natural history, we cannot but be convinced, that the fœtus, or embryon, is formed by apposition of new parts, and not by the distention of a primordial nest of germs, included one within another; like the cups of a conjurer. Fourthly, when we revolve in our minds the great similarity of structure which obtains in all the warm-blooded animals, as well quadrupeds, birds, and amphibious animals, as in man- kind; from the mouse and bat, to the elephant and whale; one is led to conclude, that they have alike been produced from a similar living filament. In some, this filament, in its advance to maturity, has acquired hands and fingers, with a fine sense of touch, as in mankind: in others it has acquired claws or ta- lons, as in tygers and eagles: in others, toes, with an interven- ing web, or membrane, as in seals and geese: in others a has acquired cloven hoots, as in cows and swine; and whole hoofs in others, as in the horse. While, in the bird kind, this original living filament has put forth wings instead of arms or legs, and feathers instead of hair. In some it has protruded horns on the forehead, instead of teeth in the fore part of the upper jaw: in others, tushes instead of horns; and in others, beaks instead of either. And all this exactly as is daily seen in the transmu- tations of the tadpole, which acquires legs and lungs when he wants them, and loses his tail when it is no longer of service to him. Fifthly, from their first rudiment, or primordium, to the ter- mination of their lives, all animals undergo perpetual transfor- mations, which are, in part, produced by their own exertions, in consequence of their desires and aversions, of their pleasures and their pains; or of irritations, or of associations; and many of these acquired forms or propensities are transmitted to their posterity. See Sect. XXXI. 1. As air and water are supplied to animals in sufficient profu- sion, the three great objects of desire, which have changed the forms of many animals by their exertions to gratify them, are those of lust, hunger, and security. A great want of one part of the animal world has confided in the desire of the exclusive possession of the females; and these have acquired weapons to combat each other for this purpose, as the very thick, shield- like, horny skin on the shoulder of the boar, is a defence only against animals of his own species, who strike obliquely up- wards; nor are his tushes for other purposes, except to defend himself, 371 SECT. XXXIX. 4. OF GENERATION. himself, as he is not naturally a carnivorous animal. So the horns of the stag are sharp, to offend his adversary; but are branched, for the purpose of parrying or receiving the thrusts of horns similar to his own, and have therefore been formed for the purpose of combating other stags for the exclusive pos- session of the females, who are observed, like the ladies in the times of chivalry, to attend the car of the victor. The birds which do not carry food to their young, and do not therefore marry, are armed with spurs for the purpose of fighting for the exclusive possession of the females, as cocks and quails. It is certain, that these weapons are not provided for their defence against other adversaries, because the females of these species are without this armour. The final cause of this contest amongst the males seems to be, that the strongest and most active animal should propagate the species, which should thence become improved. Another great want consists in the means of procuring food, which has diversified the forms of all species of animals. Thus, the nose of the swine has become hard, for the purpose of turn- ing up the soil in search of insects and of roots. The trunk of the elephant is an elongation of the nose, for the purpose of pulling down the branches of trees for his food, and for taking up water without bending his knees. Beads of prey have ac- quired strong jaws or talons. Cattle have acquired a rough tongue and a rough palate, to pull off the blades of grass, as cows and sheep. Some birds have acquired harder beaks to crack nuts, as the parrot: others have acquired beaks adapted to break the harder seeds, as sparrows: others, for the softer seeds of flowers, or the buds of trees, as the finches: other birds have acquired long beaks, to penetrate the moister soils in search of insects or roots, as woodcocks; and others, broad ones, to filtrate the water of lakes, and to retain aquatic insects. All which seem to have been gradually produced, during many generations, by the perpetual endeavour of the creatures to supply the want of food, and to have been delivered to their posterity, with constant improvement of them, for the purposes required. The third great want amongst animals is that of security, which seems much to have diversified the forms of their bodies, and the colour of them: these consist in the means of escaping other animals more powerful than themselves. Hence some animals have acquired wings instead of legs, as the smaller birds, for the purpose of escape: others, great length of fin, or of membrane, as the flying-fish and the bat: others, great swift- ness of foot, as the hare: others have acquired hard or armed shells, as the tortoise and the echinus marinus. C c c The 372 OF GENERATION. SECT. XXXIX. 4. The contrivances for the purposes of security extend even to vegetables, as is seen in the wonderful and various means of their concealing or defending their, honey from insects, and their seeds from birds. On the other hand, swiftness of wing has been ac- quired by hawks and swallows, to pursue their prey; and a proboscis, of admirable structure, has been acquired by the bee, the moth, and the humming-bird, for the purpose of plundering the nectaries of flowers. All which seem to have been formed by the original living filament, excited into action by the neces- sities of the creatures which possess them, and on which their existence depends. From thus meditating on the great similarity of the structure of the warm-blooded animals, and, at the same time, of the great changes they undergo, both before and after their nativity, and by considering in how minute a portion of time many of the changes of animals above described have been produced; would it be too bold to imagine, that, in the great length of time since the earth began to exist, perhaps millions of ages before the commencement of the history of mankind,—would it be too bold to imagine, that all warm-blooded animals have arisen from one living filament, which THE GREAT FIRST CAUSE endued with animality, with the power of acquiring new parts, attended with new propensities, directed by irritations, sensations, volitions, and associations; and thus possessing the faculty of continuing to improve by its own inherent activity, and of de- livering down those improvements, by generation, to its poste- rity, world without end! Sixthly, The cold-blooded animals, as the fish tribes, which are furnished with but one ventricle of the heart, and with gills instead of lungs, and with fins instead of feet or wings, bear a great similarity to each other; but they differ, nevertheless, so much in their general structure from the warm-blooded animals that it may not seem probable, at first view, that the same living filament could have given origin to this kingdom of animals, as to the former. Yet are there some creatures, which unite or partake of both these orders of animation, as the whales and seals; and more particularly the frog, who changes from an aquatic animal furnished with gills, to an aerial one furnished with lungs. The numerous tribes of infects without wings, from the spi- der to the scorpion, from the flea to the lobster; or with wings from the gnat and the ant to the wasp and the dragon-fly, dif- fer so totally from each other, and from the red-blooded classes above described, both in the forms of their bodies, and their modes of life; besides the organ of sense which they seem to pos- sess 373 SECT. XXXIX. 4. OF GENERATION. sess in their antennæ or horns, to which it has been thought by some naturalists, that other creatures have nothing similar; that it can scarcely be supposed that this nation of animals could have been produced by the same kind of living filament, as the red-blooded classes above mentioned. And yet the changes which many of them undergo in their early state to that of their maturity, are as different as one animal can be from another: as those of the gnat, which passes his early state in water, and then stretching out his new wings, and expanding his new lungs, rises in the air; as of the caterpillar, and bee-nymph, which feed on vegetable leaves or farina, and at length, bursting from their self-formed graves, become beautiful winged inhabitants of the skies, journeying from flower to flower, and nourished by the ambrosial food of honey. There is still another class of animals, which are termed ver- mes by Linnæus, which are without feet, or brain, and are hermaphrodites, as worms, leeches, snails, shell-fish, coralline insects, and sponges; which possess the simplest structure of all animals, and appear totally different from those already describ- ed. The simplicity of their structure, however, can afford no argument against their having been produced from a living filament as above contended. Last of all, the various tribes of vegetables are to be enume- rated amongst the inferior orders of animals. Of these the an- thers and stigmas have already been shewn to possess some or- gans of sense, to be nourished by honey, and to have the power of generation like insects, and have thence been announced amongst the animal kingdom in Sect. XIII. and to these must be added the buds and bulbs which constitute the viviparous off- spring of vegetation. The former I suppose to be beholden to a single living filament for their seminal or amatorial procrea- tion; and the latter to the same cause for their lateral or branch- ing generation, which they possess in common with the poly- pus, tænia, and volvox; and the simplicity of which is an ar- gument in favour of the similarity of its cause. Linnæus supposes, in the Introduction to his Natural Orders, that very few vegetables were at first created, and that their numbers were increased by their intermarriages, and adds, sua- dent hæc Creatoris leges a simplicibus ad composita. Many other changes seem to have arisen in them by their perpetual contest for light and air above ground, and for food or mois- ture beneath the soil: as noted in Botanic Garden, Part II. Note on Cuscuta. Other changes of vegetables from climate, or other causes, are remarked in the note on Curcuma in the same work. From these one might be led to imagine, that each plant 374 OF GENERATION. SECT. XXXIX. 4. plant at first consisted of a single bulb or flower to each root, as the gentianella and daisy; and that in the contest for air and light, new buds grew on the old decaying flower-stem, shout- ing down their elongated roots to the ground; and that in pro- cess of ages, tall trees were thus formed, and an individual bulb became a swarm of vegetables. Other plants, which, in this contest for light and air, were too slender to rise by their own strength, learned, by degrees, to adhere to their neighbours, ei- ther by putting forth roots like the ivy, or by tendrils like the vine, or by spiral contortions like the honey-suckle; or by growing upon them like the misleto, and taking nourishment from their barks; or by only lodging or adhering on them, and deriving nourishment from the air, as tillandsia. Shall we then say, that the vegetable living filament was ori- ginally different from that of each tribe of animals above de- scribed? And that the productive living filament of each of those tribes was different originally from the other? Or, as the earth and ocean were probably peopled with vegetable produc- tions long before the existence of animals, and many families of these animals long before other families of them, shall we conjecture, that one and the same kind of living filaments is, and has been the cause of all organtic life ? This idea of the gradual formation and improvement of the animal world, accords with the observations of some modern philosophers, who have supposed, that the continent of Ame- rica has been raised out of the, ocean at a later period of time than the other three quarters of the globe, which they deduce from the greater comparative heights of its mountains, and the consequent greater coldness of its respective climates, and from the less size and strength of its animals, as the tygers and alle- gators, compared with those of Asia or Africa. And lastly, from the less progress in the improvements of the mind of us inhabitants in respect to voluntary exertions. This idea of the gradual formation and improvement of the animal world, seems not to have been unknown to the ancient philosophers. Plato having probably observed the reciprocal generation of inferior animals, as snails and worms, was of opinion, that mankind, with all other animals, were originally hermaphrodites during the infancy of the world, and were, in process of time, separated into male and female. The breads and teats of all male quadrupeds, to which no use can be now assigned, adds, perhaps, some shadow of probability to this opi- nion. Linnæus excepts the horse from the male quadrupeds, who have teats; which might have shewn the earlier origin of his existence; but Mr. T. Hunter asserts, that he has disco- vered 375 SECT. XXXIX. 5. OF GENERATION. vered the vestiges of them on his sheath, and has, at the same time, enriched natural history with a very curious fact con- cerning the male pigeon; at the time of hatching the eggs, both the male and female pigeon undergo a great change in their crops, which thicken and become corrugated, and secrete a kind of milky fluid, which coagulates, and with which alone they, for a few days, feed their young, and afterwards feed them with this coagulated fluid mixed with other food. How this resemble; the breads of female quadrupeds after the production of their young! and how extraordinary that the male should at this time give milk as well as the female! See Botanic Gar- den, Part II. Note on Curcuma. The late Mr. David Hume, in his posthumous works, places the powers of generation much above those of our boasted rea- son; and adds, that reason can only make a machine, as a clock or a ship, but the power of generation makes the maker of the machine; and probably from having observed, that the greatest part of the earth has been formed out of organic recrements; as the immense beds of limestone, chalk, marble, from the shells of fish; and the extensive provinces of clay, sandstone, iron- stone, coals, from decomposed vegetables; all which have been first produced by generation, or by the secretions of organic life: he concludes, that the world itself might have been gene- rated rather than created; that is, it might have been gradually produced from very small beginnings, increasing by the activity of its inherent principles rather than by a sudden evolution of the whole by the Almighty fiat.—What a magnificent idea of the infinite power of THE GREAT ARCHITECT! THE CAUSE OF CAUSE! PARENT OF PARENTS! ENS EN- TIUM! For if we may compare infinities, it would seem to require a greater infinity of power to cause the causes of effects, than to cause the effects themselves. This idea is analogous to the improving excellence observable in every part of the creation; such as in the progressive increase of the solid or habitable parts of the earth from water, and in the progressive increase of the wisdom and happiness of its inhabitants; and is consonant to the idea of our present situation, being a state of probation, which, by our exertions, we may improve, and are consequent- ly responsible for our actions. V. 1. The efficient cause of the various colours of the eggs of birds, and of the hair and feathers of animals, is a subject so curious, that I shall beg to introduce it in this place. The colours of many animals seem adapted to their purposes of con- cealing themselves either to avoid danger, or to spring upon their 376 OF GENERATION. SECT. XXXIX. 5. their prey. Thus the snake, and wild-cat, and leopard, are so coloured as to resemble dark leaves and their lighter interstices; birds resemble the colour of the brown ground, or the green hedges which they frequent; and moths and butterflies are co- loured like the flowers which they rob of their honey. Many instances are mentioned of this kind in Botanic Garden, Part II. Note on Rubia. These colours have, however, in some instances, another use, as the black diverging area from the eyes of the swan; which, as his eyes are placed less prominent than those of other birds, for the convenience of putting down his head under water, prevents the rays of light from being reflected into his eye, and thus dazzling his sight, both in air and beneath the water, which must have happened if that surface had been white like the rest of his feathers. There is a still more wonderful thing concerning these co- lours, adapted to the purpose of concealment; which is, that the eggs of birds are so coloured as to resemble the colour of the adjacent objects and their interstices. The eggs of hedge-birds are greenish, with dark spots; those of crows and magpies, which are seen from beneath through wicker nests, are white, with dark spots; and those of larks and partridges are russet or brown, like their nests or situations. A thing still more astonishing is, that many animals, in coun- tries covered with snow, become white in winter, and are said to change their colour again in the warmer months, as bears, hares, and partridges. Our domesticated animals lose their na- tural colours, and break into great variety, as horses, dogs, pi- geons. The final cause of these colours is easily understood, as they serve some purposes of the animal; but the efficient cause would seem almost beyond conjecture. First, the choroid coat of the eye, on which the semi-trans- parent retina is expanded, is of different colour in different ani- mals: in those which feed on grass it is green; from hence there would appear some connection between the colour of the cho- roid coat and of that constantly painted on the retina by the green grass. Now, when the ground becomes covered with snow, it would seem, that that action of the retina which is called whiteness, being constantly excited in the eye, may be gradually imitated by the extremities of the nerves of touch, or rete mucosum of the skin. And if it be supposed, that the ac- tion of the retina, in producing the perception of any colour, consists in so disposing its own fibres or surface as to reflect those coloured rays only, and transmit the others like soap-bub- bles, then that part of the retina which gives us the perception of 377 SECT. XXXIX. 5. OF GENERATION. of snow, must, at that time, be white; and that which gives us the perception of grass, must be green. Then, if, by the laws of imitation, as explained in Sect. XII. 33. and XXXIX. 6. the extremities of the nerves of touch, in the rete mucosum, be induced into similar action, the skin, or feathers, or hair may, in like manner, so dispose their extreme fibres, as to reflect white; for it is evident, that all these parts were originally obedient to irritative motions during their growth, and probably continue to be so; that those irritative motions are not liable, in a healthy state, to be succeeded by sensation; which, however, is no uncommon thing in their dis- eased state, or in their infant state, as in plica polonica, and in very young pen-feathers, which are still full of blood. It was shewn in Sea. XV. on the Production of Ideas, that the moving organ of sense, in some circumstances, resembled the object which produced that motion. Hence it may be con- ceived, that the rete mucosum, which is the extremity of the nerves of touch, may, by imitating the motions of the retina, become coloured. And thus, like the fable of the cameleon, all animals may possess a tendency to be coloured somewhat like the colours they most frequently inspect; and finally, that co- lours may be thus given to the egg-shell by the imagination of the female parent; which shell is previously a mucous mem- brane, endued with irritability, without which it could not cir- culate its fluids, and increase in its bulk. Nor is this more wonderful than that a single idea of imagination should, in an instant, colour the whole surface of the body of a bright scarlet, as in the blush of shame, though by a very different process. In this intricate subject, nothing but loose analogical conjectures can be had, which may, however, lead to future discoveries; but certain it is, that both the change of the colour of ani- mals to white in the winters of snowy countries, and the spots on birds eggs, must have some efficient cause; since the uni- formity of their production shews it cannot arise from a fortui- tous concurrence of circumstances: and how is this efficient cause to be detected, or explained, but from its analogy to other animal facts? 2. The nutriment supplied by the female parent in viviparous animals, to their young progeny, may he divided into three kinds, corresponding with the age of the new creature, 1. The nu- triment contained in the ovum, as previously prepared for the embryon in the ovary. 2. The liquor amnii prepared for the fœtus in the uterus, and in which it swims: and, lastly, the milk prepared in the pectoral glands of the new-born child. There is reason to conclude, that variety of changes may be produced, 378 OF GENERATION. SECT. XXXIX. 5. produced, in the new animal, from all these sources of nutri- ment, but particularly from the first of them. The organs of digestion and of sanguification in adults, and afterwards those of secretion, prepare or separate the particles proper for nourishment, from other combinations of matter, or re-combine them into new kinds of matter, proper to excite into action the filaments which absorb or attract them by animal ap- petency. In this process we must attend not only to the action of the living filament which receives a nutritive particle to its bosom, but also to the kind of particle, in respect to form, or size, or colour, or hardness, which is thus previously prepared for it by digestion, sanguification, and secretion. Now, as the first filament of entity cannot be furnished with the preparative organs above mentioned, the nutritive particles, which are at first to be received by it, are prepared by the mother, and de- posited in the ovum ready for its reception. These nurritive particles must be supposed to differ in some respects, when thus prepared by different animals. They may differ in size, solidity colour, and form; and yet may be sufficiently congenial to the living filament to which they are applied, as to excite its activity by their stimulus, and its animal appetency to receive them, and to combine them with itself into organization. By this first nutriment, thus prepared for the embryon, is not meant the liquor amnii, which is produced afterwards, nor the larger exterior parts of the white of the egg; but the fluid pre- pared, I suppose, in the ovary of viviparous animals, and that which immediately surrounds the cicatricula of an impregnated egg, and is visible to the eye in a boiled one. Now, these ultimate particles of animal matter, prepared by the glands of the mother, may be supposed to resemble the simi- lar ultimate particles which were prepared for her own nourish- ment; that is, to the ultimate particles of which her own or- ganization consists. And that hence, when these become com- bined with the new embryon, which, in its early state, is not furnished with stomach or glands to alter them, that new em- bryon will bear some resemblance to the mother. This seems to be the origin of the compound forms of mules, which evidently partake of both parents, but principally of the male parent. In this production of chimeras, the ancients seem to have indulged their fancies; whence the sphinxes, grif- fins, dragons, centaurs, and minotaurs, which are vanished from modern credulity. It would seem, that, in these unnatural conjunctions, when the nutriment deposited by the female was so ill adapted to sti- mulate the living filament, derived from the male, into action, and 379 SECT. XXXIX. 5. OF GENERATION. and to be received or embraced by it, and combined with it into organization, as not to produce the organs necessary to life, as the brain, or heart, or stomach, that no mule was produced. Where all the parts necessary to life, in these compound ani- mals, were formed sufficiently perfect, except the parts of ge- neration, those animals were produced which are now called mules. The formation of the organs of sexual generation, in contra- distinction to that by lateral buds, in vegetables, and in some animals, as the polypus, the tænia, and the volvox, seems the chef d'œuvre, the master-piece of nature; as appears from many flying insects, as in moths and butterflies, who seem to undergo a general change of their forms solely for the purpose of sexual re-production; and in all other animals this organ is not complete till the maturity of the creature. Whence it happens, that, in the copulation of animals of different species, the parts ne- cessary to life are frequently completely formed; but those for the purpose of generation are defective, as requiring a nicer organi- zation, or more exact coincidence of the particles of nutriment to the irritabilities or appetencies of the original living filament. Whereas those mules where all the parts could be perfectly formed, may have been produced in earlier periods of time, and may have added to the numbers of our various species of ani- mals, as before observed. As this production of mules is a constant effect from the con- junction of different species of animals, those between the horse and the female ass always resembling the horse more than the ass; and those, on the contrary, between the male ass and the mare always resembling the ass more than the mare; it cannot be ascribed to the imagination of the male animal, which can- not be supposed to operate so uniformly; but to the form of the first nutritive particles, and to their peculiar stimulus exciting the living filament to select and combine them with itself. There is a similar uniformity of effect in respect to the colour of the progeny produced between a white man and a black woman, which, if I am well informed, is always of the mulatto kind, or a mixture of the two ; which may perhaps be imputed to the peculiar form of the particles of nutriment supplied to the embryon by the mother at the early period of its existence, and their peculiar stimulus; as this effect, like that of the mule progeny above treated of, is uniform and consistent, and cannot therefore be ascribed to the imagination of either of the parents. Dr. Thunberg observes, in his Journey to the Cape of Good Hope, that there are some families, which have descended from blacks in. the female line for three generations. The first D d d generation 380 OF GENERATION. SECT. XXXIX. 5. generation proceeding from an European, who married a tawny slave, remains tawny, but approaches to a white complexion; but the children of the third generation, mixed with Europeans, become quite white, and are often remarkably beautiful, v.i.p. 112. When the embryon has produced a placenta, and furnished itself with vessels for selection of nutritious particles, and for oxygenation of them, no great change in its form or colour is likely to be produced by the particles of sustenance it now takes from the fluid, in which it is immersed; because it has now acquired organs to alter or new combine them. Hence it continues to grow, whether this fluid, in which it swims, be formed by the uterus, or by any other cavity of the body, as in extra-uterine gestation; and which would seem to be produced by the stimulus of the fœtus on the sides of the cavity, where it is found, as mentioned before. And thirdly, there is still less reason to expect any unnatural change to happen to the child, after its birth, from the difference of the milk it now takes; because it has acquired a stomach, and lungs, and glands, of sufficient power to decompose and re-combine the milk; and thus to prepare from it the various kinds of nutritious particles, which the appetencies of the various fibrils or nerves may require. From all this reasoning I would conclude, that though the imagination of the female may be supposed to affect the em- bryon, by producing a difference in its early nutriment; yet that no such power can affect it after it has obtained a placenta and other organs, which may select or change the food which is presented to it either in the liquor amnii or in the milk. Now, as the eggs in pullets, like the seeds in vegetables, are produc- ed gradually, long before they are impregnated, it does not ap- pear how any sudden effect of imagination of the mother, at the time of impregnation, can produce any considerable change in the nutriment already thus laid up for the expected or defined embryon. And that hence any changes of the embryon, ex- cept those uniform ones in the production of mules and mu- lattoes, more probably depend on the imagination of the male parent. At the same time it seems manifest, that those mon- strous births, which consist in some deficiencies only, or some redundancies of parts, originate from the deficiency or redun- dance of the first nutriment prepared in the ovary, or in the part of the egg immediately surrounding the cicatricula, as describ- ed above; and which continues some time to excite the first living filament into action, after the simple animal is complet- ed; or ceases to excite it, before the complete form is accom- plished. 381 SECT. XXXIX. 6. OF GENERATION. plished. The former of these circumstances is evinced by the eggs with double yolks, which frequently happen to our do- masticated poultry, and which, I believe, are so formed before impregnation, but which would be well worth attending to both before and after impregnation, as it is probable something valuable on this subject might be learnt from them. The latter circumstance, or that of deficiency of original nutriment, may be deduced from reverse analogy. There are, however, other kinds of monstrous births, which neither depend on deficiency of parts, nor supernumerary ones; nor are owing to the conjunction of animals of different spe- cies; but which appear to be new conformations, or new dis- positions of parts in respect to each other, and which, like the variation of colours and forms of our domesticated animals, and probably the sexual pares of all animals, may depend on the imagination of the male parent, which we now come to consider. VI. 1. The nice actions of the extremities of our various glands are exhibited in their various productions, which are be- lieved to be made by the gland, and not previously to exist as such in the blood. Thus the glands, which constitute the liver, make bile; those of the stomach make gastric acid; those be neath the jaw, saliva; those of the ears, ear-wax, and the like. Every kind of gland must possess a peculiar irritability, and pro- bably a sensibility, at the early state of its existence; and must be furnished with a nerve of sense, or of motion, to perceive, and to select, and to combine the particles, which compose the fluid it secretes. And this nerve of sense, which perceives the different articles which compose the blood, must at lead be con- ceived to be as fine and subtile an organ as the optic or audi- tory nerve, which perceives light or sound. See Sect. XIV. 9. But in nothing is this nice action of the extremities of the blood-vessels so wonderful as in the production of contagious matter. A small drop of variolous contagion, diffused in the blood, or perhaps only by being inserted beneath the cuticle, after a time, (as about a quarter of a lunation) excites the ex- treme vessels of the skin into certain motions, which produce a similar contagious material, filling it with a thousand pustules. So that by irritation, or by sensation in consequence of irritation, or by association of motions, a material is formed by the extre- mities of certain cutaneous vessels, exactly similar to the stimu- lating material, which caused the irritation, or consequent sen- sation, or association. Many glands of the body have their motions, and in conse- quence their secreted fluid, affected by pleasureable or painful ideas, 382 OF GENERATION. SECT. XXXIX. 6. ideas, since they are, in many instances, influenced by sensitive as- sociations, as well as by the irritations of the particles of the pass- ing blood. Thus the idea of meat, excited in the minds of hun- gry dogs, by their sense of vision, or of smell, increases the dis- charge of saliva, both in quantity and viscidity; as is seen in its hanging down in threads from their mouths, as they stand round a dinner-table. The sensations of pleasure, or of pain, of pe- culiar kinds, excite, in the same manner, a great discharge of tears; which appear also to be more saline at the time of their secretion, from their inflaming the eyes and eye-lids. The paleness from fear, and the blush of shame, and of joy, are other instances of the effects of painful, or pleasureable sensa- tions, on the extremities of the arterial system. It is probable, that the pleasureable sensation excited in the stomach by food, as well as its irritation, contributes to excite into action the gastric glands, and to produce a greater secre- tion of their fluids. The same probably occurs in the secretion of bile; that is, that the pleasureable sensation excited in the stomach, affects this secretion by sensitive association, as well as by irritative association. And, lastly, it would seem that all the glands in the body have their secreted fluids affected, in quantity and quality, by the pleasureable or painful sensations which produce or accom- pany those secretions. And that the pleasureable sensations arising from these secretions may constitute the unnamed plea- sure of existence, which is contrary to what is meant by tædium vitæ, or ennui, and by which we sometimes feel ourselves happy, without being able to ascribe it to any mental cause, as after an agreeable meal, or in the beginning of intoxication. Now, it would appear, that no secretion or excretion of fluid is attended with so much agreeable sensation as that of the semen; and it would thence follow, that the glands, which perform this secretion, are more likely to be much affected by their catenations with pleasureable sensations. This circum- stance is certain, that much more of this fluid is produced in a given time, when the object of its exclusion is agreeable to the mind. 2. A forcible argument, which shews the necessity of pleasureable sensation to copulation, is, that the act cannot be performed without it; it is easily interrupted by the pain of fear or bashfulness; and no efforts of volition or of irritation can effect this process, except such as induce pleasureable ideas or sensations. See Sect. XXXIII. I. 1. A curious analogical circumstance attending hermaphrodite insects, as snails and worms, still further illustrates this theory; if 383 SECT. XXXIX. 6. OF GENERATION. If the snail or worm could have impregnated itself, there might have been a saving of a large male apparatus; but as this is not so ordered by nature, but each snail and worm reciprocally receives and gives impregnation, it appears, that a pleasureable excitation seems also to have been required. This wonderful circumstance of many infects being her- maphrodites, and at the same time not having power to im- pregnate themselves, is attended to by Dr. Lister, in his Ex- ercitationes Anatom. de Limacibus, p. 145: who, amongst many other final causes, which he adduces to account for it, adds, ut tam tristibus et frigidis animalibus majori cum voluptate persiciatur venus. There is, however, another final cause, to which this cir- cumstance may be imputed: it was observed above, that vege- table buds and bulbs, which are produced without a mother, are always exact resemblances of their parent; as appears in grafting fruit-trees, and in the flower-buds of the dioceous plants, which are always of the same sex, on the same tree; hence those hermaphrodite insects, if they could have produced young without a mother, would not have been capable of that change or improvement, which is seen in all other animals, and in those vegetables which are procreated by the male embryon received and nourished by the female. And it is hence probable, that if vegetables could only have been produced by buds and bulbs, and not by sexual generation, that there would not, at this time, have existed one thousandth part of their present number of species, which have probably been original- ly mule productions; nor could any kind of improvement or change have happened to them, except by the difference of soil or climate. 3. I conclude, that the imagination of the male, at the time of copulation, or at the time of the secretion of the semen, may so affect this secretion by irritative or sensitive association, as described in No. 5. 1. of this section, as to cause the pro- duction of similarity of form and of features, with the distinc- tion of sex; as the motions of the chissel of the turner imitate or correspond with those of the ideas of the artist. It is not here to be understood, that the first living fibre, which is to form an animal, is produced with any similarity of form to the future animal; but with propensities, or appetencies, which shall produce, by accretion of parts, the similarity of form, fea- ture, or sex, corresponding to the imagination of the father. Our ideas are movements of the nerves of sense, as of the optic nerve in recollecting visible ideas, suppose of a triangular piece of ivory. The fine moving fibres of the retina act in a manner 384 OF GENERATION. Sect. XXXIX. 6. manner to which I give the name of white; and this action is confined to a defined part of it; to which figure I give the name of triangle. And it is a preceding pleasureable sensation existing in my mind, which occasions me to produce this particular motion of the retina, when no triangle is present. Now, it is probable, that the acting fibres of the ultimate terminations of the secreting apertures of the vessels of the testes, are as fine as those of the retina; and that they are liable to be thrown into that peculiar action, which marks the sex of the secreted em- bryon, by sympathy with the pleasureable motions of the nerves of vision, or of touch; that is, with certain ideas of imagina- tion. From hence it would appear, that the world has long been mistaken in ascribing great power to the imagination of the female; whereas, from this account of it, the real power of imagination, in the act of generation, belongs solely to the male. See Sect. XII. 3. 3. It may be objected to this theory, that a man may be sup- posed to have in his mind the idea of the form and features of the female, rather than his own, and therefore there should be a greater number of female births. On the contrary, the ge- neral idea of our own form occurs to every one almost perpe- tually, and is termed consciousness of our existence; and thus may effect, that the number of males surpasses that of females. See Sect. XV. 3. 4. and XVIII. 13. And what further con- firms this idea is, that the male children most frequently resem- ble the father in form, or feature, as well as in sex; and the female most frequently resemble the mother, in feature, and form, as well as in sex. It may again be objected, if a female child sometimes resem- bles the father, and a male child the mother, the ideas of the father, at the time of procreation, must suddenly change from himself to the mother, at the very instant, when the embryon is secreted or formed. This difficulty ceases when we consider, that it is as easy to form an idea of feminine features with male organs of re-production, or of male features with female ones, as the contrary; as we conceive the idea of a sphinx or mermaid, as easily and as distinctly as of a woman. Add to this, that at the time of procreation, the ideas of the male organs, and of the female features, are often both excited at the same time, by contact or by vision. I ask, in my turn, is the sex of the embryon produced by accident? Certainly, whatever is produced has a cause; but when this cause is too minute for our comprehension, the effect is said, in common language, to happen by chance, as in throw- ing a certain number on dice. Now, what cause can occa- sionally 385 SECT. XXXIX. 6. OF GENERATION. sionally produce the male or female character of the embryon, but the peculiar actions of those glands which form the em- bryon? And what can influence or govern these actions of the gland, but its associations or catenations with other sensitive motions? Nor is this more extraordinary than that the catena- tions of irritative motions, with the apparent vibrations of ob- jects at sea, should produce sickness of the stomach; or that a nauseous dory should occasion vomiting. 4. An argument, which evinces the effect of imagination on the first rudiment of the embryon, may be deduced from the production of some peculiar monsters: such, for instance, as those which have two heads joined to one body, and those which have two bodies joined to one head; of which frequent examples occur amongst our domesticated quadrupeds and poultry. It is absurd to suppose, that such forms could exist in primordeal germs, as explained in No. IV. 4. of this section. Nor is it possible that such deformities could be produced by the growth of two embryons, or living filaments, which should afterwards adhere together; as the head and tail part of differ- ent polypi are said to do (Blumenbach on Generation, Cadel, London); since, in that case, one embryon, or living filament, must have begun to form one part first, and the other another part first. But such monstrous conformations become less difficult to comprehend, when they are considered as an effect of the imagination, as before explained, on the living filament at the time of its secretion; and that such duplicature of limbs were produced by accretion of new parts, in consequence of propensities, or animal appetencies, thus acquired from the male parent. For instance; lean conceive, if a turkey-cock should be- hold a rabbit, or a frog, at the time of procreation, that it might happen, that a forcible or even a pleasureable idea of the form of a quadruped might so occupy his imagination, as to cause a tendency in the nascent filament to resemble such a form by the apposition of a duplicature of limbs. Experiments on the production of mules and monsters would be worthy the attention of a Spallanzani, and might throw much light upon this subject, which at present must be explained by conjectural analogies. The wonderful effect of imagination, both in the male and female parent, is shewn in the production of a kind of milk in the crops both of the male and female pigeons, after the birth of their young, as observed by Mr. Hunter, and mentioned be- fore. To this should be added, that there are some instances of men having had milk secreted in their breads, and who have given 386 OF GENERATION. SECT. XXXIX. 6. given suck to children, as recorded by Mr. Buffon. This effect of imagination, of both the male and female parent, seems to have been attended to in very early times; Jacob is said not only to have placed rods of trees, in part stripped of their bark, so as to appear spotted, but also to have placed spot- ted lambs before the stocks, at the time of their copulation. Genesis, chap. xxx. verse 40. 5. In respect to the imagination of the mother, it is difficult to comprehend, how this can produce any alteration in the fœtus, except by affecting the nutriment laid up for its first re- ception, as described in No. V. 2. of this section, or by affect- ing the nourishment or oxygenation with which she supplies it afterwards. Perpetual anxiety may probably affect the secretion of the liquor amnii into the uterus, as it enfeebles the whole system; and sudden fear is a frequent cause of mis- carriage; for fear, contrary to joy, decreases for a time the action of the extremities of the arterial system; hence sudden paleness succeeds, and a shrinking or contraction of the vessels of the skin, and other membranes. By this circumstance, I imagine, the terminations of the placental vessels are detached from their adhesions, or insertions, into the membrane of the uterus; and the death of the child succeeds, and consequent miscarriage. Of this I recollect a remarkable instance, which could be ascribed to no other cause, and which I shall therefore relate in few words. A healthy young woman, about twenty years of age, had been about five months pregnant, and going down into her cellar to draw some beer, was frighted by a servant- boy starting up from behind the barrel, where he had conceal- ed himself with design to alarm the maid-servant, for whom he mistook his mistress. She came with difficulty up stairs, began to flood immediately, and miscarried in a few hours. She has since borne several children, nor ever had any tendency to mis- carry of any of them. In respect to the power of the imagination of the male over the form, colour, and sex of the progeny, the following in- stances have fallen under my observation, and may perhaps be found not very unfrequent, if they were more attended to. I am acquainted with a gentleman, who has one child with dark hair and eyes, though his lady and himself have light hair and eyes, and their other four children are like their parents. On observing this dissimilarity of one child to the others, he assured me, that he believed it was his own imagination that produced the difference; and related to me the following story. He said, that when his lady lay in of her third child, he became attached 387 SECT. XXXIX. 7. OF GENERATION. attached to a daughter of one of his inferior tenants, and offered her a bribe for her favours in vain; and afterwards a greater bribe, and was equally unsuccessful; that the form of this girl dwelt much in his mind for some weeks, and that the next child, which was the dark-eyed young lady above mentioned, was exceedingly like, in both features and colour, to the young woman who refused his addresses. To this instance I must add, that I have known two families, in which, on account of an intailed estate, in expectation, a male heir was mod eagerly defined by the father; and, on the contrary, girls were produced to the seventh in one, and to the ninth in another; and then they had each of them a son. I conclude that the great desire of a male heir by the father pro- duced rather a disagreeable than an agreeable sensation; and that his ideas dwelt more on the fear of generating a female, than on the pleasureable sensations or ideas of his own male form or organs at the time of copulation, or of the secretion of the semen; and that hence the idea of the female character was more present to his mind than that of the male one; till at length, in despair of generating a male, these ideas ceased, and those of the male character presided at the genial hour. 7. Hence I conclude, that the act of generation cannot exist without being accompanied with ideas, and that a mart must have at that time either a general idea of his own male form, or of the form of his male organs; or an idea of the female form, or of her organs; and that this marks the sex, and the peculiar resemblances of the child to either parent. From whence it would appear, that the phalli, which were hung round the necks of the Roman ladies, of worn in their hair, might have effect in producing a greater proportion of male children; and that the calipædia, or art of begetting beau- tiful children, and of procreating either males or females, may be taught by affecting the imagination of the male-parent; that is, by the fine extremities of the seminal glands imitating the actions of the organs of sense, either of sight or touch. But the manner of accomplishing this cannot be unfolded with sufficient delicacy for the public eye, but may be worth the at- tention of those who are seriously interested in the procrea- tion of a male or female child. Recapitulations VII. 1 . A certain quantity of nutritive particles are produced by the female- parent before impregnation, which require no further digestion, secretion or oxygenation. Such are seen in the unimpregnated eggs of birds, and in the unimpregnated seed-vessels of vegetables. E e e 2. A 388 OF GENERATION. SECT. XXXIX. 7. 2. A living filament is produced by the male, which being inserted amidst these first nutritive particles, is stimulated into action by them; and, in consequence of this action, some of the nutritive particles are embraced, and added to the original living filament; in the same manner as common nutrition is performed in the adult animal. 3. Then this new organization, or additional part, becomes, stimulated by the nutritive particles in its vicinity, and sensa- tion is now superadded to irritation; and other particles are in consequence embraced, and added to the living filament; as is seen in the new granulations of flesh in ulcers. By the power of association, or by irritation, the parts al- ready produced continue their motions, and new ones are ad- ded by sensation, as above mentioned; and lastly, by volition; which last sensorial power is proved to exist in the fœtus in its maturer age, because it has evidently periods of activity and of sleeping; which last is another word for a temporary suspen- sion of volition. The original living filament may be conceived to possess a power of repulsing the particles applied to certain parts of it, as well as of embracing others, which stimulate other parts of it; as these powers exist in different parts of the mature ani- mal: thus the mouth of every gland embraces the particles of fluid which suits its appetency, and its excretory, duct repul- ses those particles which are disagreeable to it. 4. Thus the outline, or miniature of the new animal, is produced gradually, but in no great length of time; because the original nutritive particles require no previous preparation by digestion, secretion, and oxygenation; but require simply the selection and apposition, which is performed by the living fila- ment. Mr. Blumenbach says, that he possesses a human fœ- tus of only five weeks old, which is the size of a common bee, and has all the features of the face, every finger, and every toe, complete; and in which the organs of generation are dis- tinctly seen. P. 76. In another fœtus, whose head was not larger than a pea, the whole of the basis of the skull, with all, its depressions, apertures, and processes, were marked in the most sharp and distinct manner, though without any ossifica- tion. Ibid. 5. In some cases, by the nutriment originally deposited by the mother, the filament acquires parts not exactly similar to those of the father, as in the production of mules and mulat- toes. In other cases the deficiency of this original nutriment, causes deficiencies of the extreme parts of the fœtus, which are last formed, as the fingers, toes, lips. In other cases, a dupli- cature 389 SECT. XXXIX. 7. OF GENERATION. cature of limbs are caused by the superabundance of this origi- nal nutritive fluid, as in the double yolks of eggs, and the thickens from them with four legs and four wings. But the production of other monsters, as those with two heads, or with parts placed in wrong situations, seems to arise from the ima- gination of the father being, in some manner, imitated by the extreme vessels of the seminal glands; as the colours of the spots on eggs, and the change of the colour of the hair and feathers of animals by domestication, may be caused, in the same manner, by the imagination of the mother. 6. The living filament is a part of the father, and has there- fore certain propensities, or appetencies, which belong to him; which, may have been gradually acquired during a million of generations, even from the infancy of the habitable earth; and which now possesses such properties, as would render, by the apposition of nutritious particles, the new fœtus exactly similar to the father; as occurs in the buds and bulbs of vegetables, and in the polypus, and tænia or tape-worm. But as the first, nutri- ment is supplied by the mother, and therefore resembles such nutritive particles as have been used for her own nutriment or growth, the progeny takes, in part, the likeness of the mother. Other similarity of the excitability, or of the form of the male parent, such as the broad or narrow shoulders, or such as constitute certain hereditary diseases, as scrophula, epilepsy, insanity, have their origin, produced in one, or perhaps two ge- nerations; as in the progeny of those who drink much vinous spirits; and those hereditary propensities cease again, as I have observed, if one or two sober generations succeed; otherwise the family becomes extinct. This living filament from the father, is also liable to have its propensities, or appetencies, altered, at the time of its produc- tion, by the imagination of the male parent; the extremities of the seminal glands, imitating the motions of the organs of sense, and thus the sex of the embryon is produced; which may be thus made a male or a female, by affecting the imagination of the father at the time of impregnation. See Sect. XXXIX. 6. 3. and 7. 7. After the fœtus is thus completely formed, together with its umbilical vessels and placenta, it is now supplied with a dif- ferent kind of food, as appears by the difference of consistency of the different parts of the white of the egg, and of the liquor amnii; for it has now acquired organs for digestion or secre- tion, and for oxygenation, though they are as yet feeble; which can, in some degree, change, as well as select, the nutritive par- ticles which are now presented to it; but may yet be affected. by 390 OF GENERATION. SECT. XXXIX. 7. by the deficiency of the quantity of nutrition supplied by the mother, or by the degree of oxygenation supplied to its placenta by the maternal blood. The augmentation of the complete fœtus, by additional par- tides of nutriment, is not accomplished by distention only, but by apposition to every part, both external and internal; each of which acquires, by animal appetencies, the new addition of the particles which it wants. And hence, the enlarged parts are kept similar to their prototypes, and may be said to be ex- tended; but their extension must be conceived only as a neces- . sary consequence of the enlargement of all their parts by appo- sition of new particles. Hence the new apposition of parts is not produced by capil- lary attraction, because the whole is extended; whereas ca- pillary attraction would rather tend to bring the sides of flexible tubes together, and not to distend them. Nor is it produced by chemical affinities; for then a solution of continuity would succeed, as when sugar is dissolved in water: but it is produced by an animal process, which is the consequence of irritation or sensation, and which may be termed animal appetency. This is further evinced from experiments, which have been instituted to shew, that a living muscle of an animal body re- quires greater force to break it, than a similar muscle of a dead body. Which evinces, that besides the attraction of cohesion, which all matter possesses, and besides the chemical attractions of affinities, which hold many bodies together, there is an ani- mal adhesion, which adds vigour to these common laws of the inanimate world. 8. At the nativity of a child, it deposits the placenta or gills, and, by expanding its lungs, acquires more plentiful oxygenation from the currents of air, which it must now continue perpe- tually to respire to the end of its life; as it now quits the liquid element, in which it was produced, and, like the tadpole when it changes into a frog, becomes an aerial animal. 9. As the habitable parts of the earth have been, and conti- nue to be, perpetually increasing by the production of sea-shells and corallines, and by the recrements of other animals and vegetables; so, from the beginning of the existence of this terra- queous globe, the animals which inhabit it have constantly improved, and are still in a state of progressive improvement. This idea of the gradual generation of all things seems to have been as familiar to the ancient philosophers as to the modern ones; and to have given rise to the beautiful hierogly- phie figure of the ----- ---, or first great egg, produced by NIGHT; that is, whose origin is involved in obscurity, and animated 391 SECT. XXXIX. 8. OF GENERATION. animated by ----; that is, by DIVINE LOVE; from whence proceeded all things which exist. Conclusion. VIII. 1. CAUSE AND EFFECT may be considered as the progression, or successive motions, of the parts of the great system of Nature. The state of things, at this moment, is the effect of the state of things which existed in the preceding moment, and the cause of the state of things which shall exist in the next moment. These causes and effects may be more easily comprehended, if motion be considered as a change of the figure of a group of bodies, as proposed in Sect. XIV. 2. 2. inasmuch as our ideas of visible or tangible objects are more distinct than our ab- stracted ideas of their motions. Now, the change of the confi- guration of the system of nature, at this moment, must be an effect of the preceding configuration, for a change of configura- tion cannot exist without a previous configuration; and the proximate cause of every effect must immediately precede that effect. For example; a moving ivory ball could not proceed onwards, unless it had previously began to proceed, or unless an impulse had been previously given it; which previous mo- tion or impulse constitutes a part of the last situation of things. As the effects produced in this moment of time become causes in the next, we may consider the progressive motions of objects as a chain of causes only; whose first link proceeded from the great Creator, and which have existed from the beginning of the created universe, and are perpetually proceeding. 2. These causes may be conveniently divided into two kinds, efficient and inert causes; according with the two kinds of en- tity supposed to exist in the natural world, which may be term- ed matter and spirit, as proposed in Sect. I. and farther treated of in Sect. XIV. The efficient causes of motion, or new configuration, consist either of the principle of general gravita- tion, which actuates the sun and planets; or of the principle of particular gravitation, as in electricity, magnetism, heat; or of the principle of chemical affinity, as in combustion, fer- mentation, combination; or of the principle of organic life, as in the contraction of vegetable and animal fibres. The inert causes of motion, or new configuration, consist of the parts of matter which are introduced within the spheres of activity of the principles above described. Thus, when an apple falls on the ground, the principle of gravitation is the efficient cause, and the matter of the apple the inert cause. If a bar of iron be approximated to a magnet, it may be termed the inert cause of the 392 OF GENERATION. SECT. XXXIX. 8. the motion, which brings these two bodies into contact; while the magnetic principle may be termed the efficient cause. In the same manner, the fibres which constitute the retina may be called the inert cause of the motions of that organ in vision, while the sensorial power may be termed the efficient cause. 3. Another more common distribution of the perpetual chain of causes and effects, which constitute the motions, or changing configurations, of the natural world, is into active and passive. Thus, if a ball in motion impinges against another ball at rest, and communicates its motion to it, the former ball is said to act, and the latter to be acted upon. In this sense of the words, a magnet is said to attract iron, and the prick of a spur to stimulate a horse into exertion; so that, in this view of the works of nature, all things may be said either simply to exist, or to exist as causes, or to exist as effects; that is, to exist either in an active or passive state. This distribution of objects, and their motions, or changes of position, has been found so convenient for the purposes of com- mon life, that on this foundation rests the whole construction or theory of language. The names of the things themselves are termed, by grammarians, Nouns, and their modes of existence are termed Verbs. The nouns are divided into substantives, which denote the principal things spoken of; and into adjectives, which denote some circumstances, or less kinds of things be- longing to the former. The verbs are divided into three kinds, such as denote the existence of things simply, as, to be; or their existence in an active state, as, to eat; or their existence in a passive state, as, to be eaten. Whence it appears, that all lan- guages consist only of nouns and verbs, with their abbreviations, for the greater expedition of communicating our thoughts; as explained in the ingenious work of Mr. Horne Tooke, who has unfolded, by a single flash of light, the whole theory of lan- guage, which had so long lain buried beneath the learned lumber of the schools. Diversions of Purley. Johnson. London. 4. A third division of causes has been into proximate and re- mote: these have been much spoken of by the writers on medical subjects, but without sufficient precision. If, to proximate and remote causes, we add proximate and remote effects, we shall include four links of the perpetual chain of causation; which will be more convenient for the discussion of many philosophical subjects. Thus, if a particle of chyle be applied to the mouth of a lacteal vessel, it may be termed the remote cause of the mo- tions of the fibres, which compose the mouth of that lacteal vessel: the sensorial power is the proximate cause; the con- traction 393 SECT. XXXIX. 8. OF GENERATION. traction of the fibres of the mouth of the vessel is the proximate effect; and their embracing the particle of chyle is the remote effect; and these four links of causation constitute absorption. Thus, when we attend to the rising sun, first the yellow rays of light stimulate the sensorial power residing in the extremities of the optic nerve—this is the remote cause. 2. The sensorial power is excited into a state of activity—this is the proximate cause. 3. The fibrous extremities of the optic nerve are con- tracted—this is the proximate effect. 4. A pleasureable or painful sensation is produced in consequence of the contraction of these fibres of the optic nerve—this is the remote effect; and these four links of the chain of causation constitute the sensitive idea, or what is commonly termed the sensation of the rising sun. 5. Other causes have been announced, by medical writers, under the names of causa procatarctica, and causa proegumina, and causa fine qua non. All which are links more or less dis- tant of the chain of remote causes. To these must be added the final cause, so called by many authors, which means the motive; for the accomplishment of which the preceding chain of causes was put into action. The idea of a final cause, therefore, includes that of a rational mind, which employs means to effect its purposes: thus the desire of preserving himself from the pain of cold, which he has frequent- ly experienced, induces the lavage to construct his hut; the fixing stakes into the ground for walls, branches of trees for rafters, and turf for a cover, are a series of successive voluntary exertions, which are so many means to produce a certain ef- fect. This effect of preserving himself from cold, is termed the final cause; the construction of the hut is the remote effect; the action of the muscular fibres of the man, is the proximate effect; the volition, or activity of desire to preserve himself from cold, is the proximate cause; and the pain of cold, which excited that desire, is the remote cause. 6. This perpetual chain of causes and effects, whose first link is rivetted to the throne of God, divides itself into innu- merable diverging branches, which, like the nerves arising from the brain, permeate the most minute and most remote extremi- ties of the system, diffusing motion and sensation to the whole. As every cause is superior in power to the effect which it has produced, so our idea of the power of the Almighty Creator becomes more elevated and sublime, as we trace the operations of nature from cause to cause, climbing up the links of these chains of being, till we ascend to the Great Source of all things. Hence the modern discoveries in chemistry and in geology, by having 394 OCULAR SPECTRA. SECT. XL. having traced the causes of the combinations of bodies to re- moter origins, as well as those in astronomy, which dignify the present age, contribute to enlarge and amplify our ideas of the power of the Great First Cause. And had those ancient philosophers, who contended that the world was formed from atoms, ascribed their combinations to certain immutable pro- perties received from the hand of the Creator, such as general gravitation, chemical affinity, or animal appetency, instead of ascribing them to a blind chance, the doctrine of atoms, as constituting or composing the material world by the variety of their combinations, so far from leading the mind to atheism would strengthen the demonstration of the existence of a Deity; as the first cause of all things; because the analogy resulting from our perpetual experience of cause and effect would have thus been exemplified through universal nature. The heavens declare the glory of GOD, and the firmament sheweth his handywork! One day telleth another, and one night certifieth another; they have neither speech nor lan- guage, yet their voice is gone forth into all lands, and their words into the ends of the world. Manifold are thy works O LORD! in wisdom hast thou made them all. Psal. xix. civ. SECT. XL. On the OCULAR SPECTRA of Light and Colours, by Dr. R. W. Darwin, of Shrewsbury. Re-printed, by permission, from the Philosophical Transactions, vol. lxxvi. p. 313. Spectra of four kinds. I. Activity of the retina in vision. 2. Spectra from defect of sensibility. 3. Spectra from ex- cess of sensibility. 4. Of direct ocular spectra. 5. Greater stimulus excites the retina into spasmodic action. 6. Of reverse ocular spectra. 7. Greater stimulus excites the retina into various successive spasmodic actions. 8. Into fixed spasmodic action. 9. Into temporary paralysis. 10. Miscellaneous remarks: 1. Direct and reverse spectra at, the same time. A spectral halo. Rule to predetermine the colours of spectra. 2. Variation of spectra from extra- neous light. 3. Variation of spectra in number, figure, and remission. 4. Circulation of the blood in the eye is visible. 5. A new way of magnifying objects. Conclusion. WHEN any one has long and attentively looked at a bright object, as at the letting sun, on closing his eyes, or removing them, an image, which resembles in form the object he was attending 395 SECT. XL. 1. OCULAR SPECTRA. attending to, continues some time to be visible: this appearance in the eye we shall call the ocular spectrum of that object. These ocular spectra are of four kinds: 1st. Such as are owing to a less sensibility of a defined part of the retina; or, spectra from defect of sensibility. 2d. Such as are owing to a greater sensibility of a defined part of the retina, or spectra from excess of sensibility. 3d. Such as resemble their object in its colour, as well as form, which may be termed direct ocular spectra. 4th. Such as are of a colour contrary to that of their object, which may be termed reverse ocular spectra. The laws of light have been most successfully explained by the great Newton, and the perception of visible objects has been ably investigated by the ingenious Dr. Berkeley and M. Malebranche; but these minute phenomena of vision have yet been thought reducible to no theory, though many philosophers have employed a considerable degree of attention upon them: among these are, Dr. Jurin, at the end of Dr. Smith's Optics; M. Æpinus, in the Nov. Com. Petropol. vol. x. M. Beguelin, in the Berlin Memoires, vol. ii. 1771; M. d'Arcy, in the Historie de l'Acad. des Scienc. 1765; M. de la Hire; and, lastly, the ce- lebrated M. de Buffon, in the Memoirs de l'Acad. des Sciene. who has termed them accidental colours, as if subjected to no established laws. Ac. Par. 1743. M. p. 215. I must here apprize the reader, that it is very difficult for dif- ferent people to give the same names to various shades of colours; whence, in the following pages, something must be allowed, if on repeating the experiments, the colours here mentioned should not accurately correspond with his own names of them. I. Activity of the Retina in Vision. FROM the subsequent experiments it appears, that the retina is in an active, not in a passive state, during the existence of these ocular spectra; and it is thence to be concluded, that all vision is owing to the activity of this organ. I. Place a piece of red silk, about an inch in diameter, as in plate 1, at Sect. III. 1. on a sheet of white paper, in a strong light; look strong steadily upon it, from about the distance of half a yard, for a minute; then closing your eye-lids, cover them with your hands, and a green spectrum will be seen in your eyes resembling in form the piece of red silk: after some time this spectrum will disappear, and shortly re-appear; and this alter- nately three or four times, if the experiment is well made, till at length it vanishes entirely. 2. Place on a sheet of white paper, a circular piece of blue silk, about four inches in diameter, in the sunshine; cover the F f f center 396 OCULAR SPECTRA. SECT. XL. 1. center of this with a circular piece of yellow silk, about three inches in diameter; and the center of the yellow silk with a circle of pink silk, about two inches in diameter; and the center of the pink silk with a circle of green silk, about one inch in diameter; and the center of this with a circle of indigo, about half an inch in diameter; make a small speck with ink in the very center of the whole, as in plate 3. at Sect. III. 3. 6. look steadily for a minute on this central spot, and then closing your eyes, and apply your hand at about an inch distance before them, so as to prevent too much or too little light from passing through the eye-lids, you will see the mod beautiful circles of colours that imagination can conceive, which are most re- sembled by the colours occasioned by pouring a drop or two of oil on a still lake in a bright day: but these circular irises of colours are not only different from the colours of the silks above mentioned, but are, at the same time, perpetually chang- ing as long as they exist. 3. When any one in the dark presses either comer of his eye with his finger, and turns his eye away from his finger, he will see a circle of colours like those in a peacock's tail; and a sudden flash of light is excited in the eye by a stroke on it. Newton's Opt. Q. 16. 4. When any one turns round rapidly on one foot, till he becomes dizzy, and falls upon die ground, the spectra of the ambient objects continue to present themselves in rotation, or appear to librate, and he seems to behold them for some time still in motion. From all these experiments it appears, that the spectra in the eye are not owing to the mechanical impulse of light impressed on the retina, nor to its chemical combination with that organ, nor to the absorption and emission of light, as is observed in many bodies; for in all these cases the spectra must either remain uniformly, or gradually diminish; and neither their alternate presence and evanescence, as in the first experiment; nor the perpetual changes of their colours, as in the second; nor the flash of light or colours in the pressed eye, as in the third; nor the ro- tation or libration of the spectra, as in the fourth, could exist. It is not absurd to conceive, that the retina may be stimulat- ed into motion, as well as the red and white muscles which form our limbs and vessels, since it consists of fibres, like those intermixed with its medullary substance. To evince this structure, the retina of an ox's eye was suspended in a glass of warm water, and forcibly torn in a few places; the edges of these parts appeared jagged and hairy, and did not contract, and become smooth like simple mucus, when it is distended till it breaks; 397 SECT. XL. 2. OCULAR SPECTRA. breaks; which shews that it consists of fibres; and this, its fibrous construction, became still more distinct to the light, by adding some caustic alkali to the water, as the adhering mucus was first eroded, and the hair-like fibres remained floating in the vessel. Nor does the degree of transparency of the retina invalidate the evidence of its fibrous structure, since Leeu- wenhoek has shewn that the crystalline humour itself consists of fibres. Arcana Naturæ, vol. i. p. 70. Hence it appears, that as the muscles have larger fibres in- termixed with a smaller quantity of nervous medulla, the organ of vision has a greater quantity of nervous medulla intermixed with smaller fibres; and it is probable that the locomotive mus- cles, as well as the vascular ones, of microscopic animals, have much greater tenuity than these of the retina. And besides the similar laws, which will be shewn in this paper to govern alike the actions of the retina and of the mus- cles, there are many other analogies which exist between them. They are both originally excited into action by irritations, both act nearly in the same quantity, of time, are alike strength- ened or fatigued by exertion, are alike painful if excited into action when they are in an inflamed state, are alike liable to paralysis, and to the torpor of old age. II. Of Spectra from Defect of Sensibility. The retina is not so easily excited into action by less irritation. after having been lately subjected to greater. 1. WHEN any one passes from the bright day-light into a darkened room, the irises of his eyes expand themselves to their utmost extent in a few seconds of time; but it is very long be- fore the optic nerve, after having been stimulated by the greater light of the day, becomes sensible of the less degree of it in the room; and, if the room is not too obscure, the irises will again contract themselves in some degree, as the sensibility of the retina returns. 2. Place about half an inch square of white paper on a black hat, and, looking steadily on the center of it for a minute, remove your eyes to a sheet of white paper; and after a second or two a dark square will be seen on the white paper, which will con- tinue some time. A similar dark square will be seen in the closed eye, if light be admitted through the eye-lids. So after looking at any luminous object of a small size, as at the sun, for a short time, so as not much to fatigue the eyes, this part of the retina becomes less sensible to smaller quantities of light; hence, when the eyes are turned on other less luminous parts of the sky, a dark spot is seen resembling the shape of the sun 398 OCULAR SPECTRA. SECT. XL. 2. sun, or other luminous object which we last beheld. This is the source of one kind of the dark-coloured muscœ volitantes. If this dark spot lies above the center of the eye, we turn our eyes that way, expecting to bring it into the center of the eye, that we may view it more distinctly; and in this case the dark spectrum seems to move upwards. If the dark spectrum is found beneath the center of the eye, we pursue it from the same motive, and it seems to move downwards. This has given rise to various conjectures of something floating in the aqueous humours of the eyes; but whoever, in attending to these spots, keeps his eyes unmoved, by looking steadily at the comer of a cloud, at the same time that he observes the dark spectra, will be thoroughly convinced, that they have no motion but what is given to them by the movement of our eyes in pursuit of them. Sometimes the form of the spectrum, when it has been received from a circular luminous body, will become oblong; and sometimes it will be divided into two circular spectra, which is not owing to our changing the angle made by the two optic axises, according to the distance of the cloud or other bodies to which the spectrum is supposed to be conti- guous, but to other causes, mentioned in No. X. 3. of this section. The apparent size of it will also be variable according to its supposed distance. As these spectra are more easily observable when our eyes are a little weakened by fatigue, it has frequently happened, that people of delicate constitutions have been much alarmed at them, fearing a beginning decay of their sight, and have thence fallen into the hands of ignorant oculists; but I believe they never are a prelude to any other disease of the eye, and that it is from habit alone, and our want of attention to them, that we do not see them on all objects every hour of our lives. But as the nerves of very weak people lose their sensibility, in the same manner as their muscles lose their activity, by a small time of exertion, it frequently happens, that sick people, in the extreme debility of fevers, are perpetually employed in picking something from the bed-clothes, occasioned by their mistaking the appearance of these muscæ volitantes in their eyes. Ben- venuto Celini, an Italian artist, a man of strong abilities, re- lates, that having passed the whole night on a distant mountain with some companions and a conjurer, and performed many ceremonies to raise the devil, on their return in the morning to Rome, and looking up when the sun began to rise, they saw numerous devils run on the tops of the houses, a they passed along; so much were the spectra of their weakened eyes mag- nified by fear, and made subservient to the purposes of fraud or superstition. (Life of Ben. Celini.) 3. Place 399 SECT. XL. 3 OCULAR SPECTRA. 3. Place a square inch of white paper on a large piece of draw-coloured silk; look steadily some time on the white paper, and then move the center of your eyes on the silk, and a spectrum of the form of the paper will appear on the silk, of a deeper yellow than the other part of it: for the central part of the retina having been some time exposed to the stimulus of a greater quantity of white light, is become less sensible to a smaller quantity of it, and therefore sees only the yellow rays in that part of the straw-coloured silk. Facts similar to these are observable in other parts of our system: thus, if one hand be made warm, and the other ex- posed to the cold, and then both of them immersed in subtepid water, the water is perceived warm to one hand, and cold to the other; and we are not able to hear weak sounds for some time after we have been exposed to loud ones; and we feel a chilliness on corning into an atmosphere of temperate warmth, after having been some time confined in a very warm room: and hence the stomach, and other organs of digestion, of those who have been habituated to the greater stimulus of spirituous liquor, are not excited into their due action by the less stimulus of common food alone; of which the immediate consequence is indigestion and hypochondriacism. III. Of Spectra from Excess of Sensibility. The retina is more easily excited into action by greater irri- tation after having been lately subjected to less. 1. If the eyes are closed, and covered perfectly with a hat, for a minute or two, in a bright day, on removing the hat a red or crimson light is seen through the eye-lids. In this experiment the retina, after being some time kept in the dark, becomes so sensible to a small quantity of light, as to perceive distinctly the greater quantity of red rays than of others which pass through the eye- lids. A similar coloured light is seen to pass through the edges of the fingers, when the open hand is opposed to the flame of a candle. 2. If you look for some minutes steadily on a window in the beginning of the evening twilight, or in a dark day, and then move your eyes a little, so that those parts of the retina on which the dark frame-work of the window was delineated, may now fall on the glass part of it, many luminous lines, repre- senting the frame-work, will appear to lie across the glass panes; for those parts of the retina which were before least stimulated by the dark frame-work, are now more sensible to light than the other parts of the retina which were exposed to the more luminous parts of the window. 3. Make 400 OCULAR SPECTRA. SECT. XL. 3. 3. Make with ink, on white paper, a very black spot, about half an inch in diameter, with a tail about an inch in length, so as to represent a tadpole, as in plate 2. at Sect. III. 8. 3. look steadily for a minute on this spot, and, on moving the eye a little, the figure of the tadpole will be seen on the white part of the paper; which figure of the tadpole will appear whiter or more luminous than the other parts of the white paper; for the part of the retina on which the tadpole was delineated, is now more sensible to light than the other parts of it, which were ex- posed to the white paper. This experiment is mentioned by Dr. Irwin, but is not by him ascribed to the true cause, namely, the greater sensibility of that part of the retina which has been exposed to the black spot, than of the other parts which had re- ceived the white field of paper, which is put beyond a doubt by the next experiment. 4. On closing the eyes, after viewing the black spot on the white paper, as in the foregoing experiment, a red spot is seen of the form of the black spot; for that part of the retina on which the black spot was delineated, being now more sensible to light than the other parts of it, which were exposed to the white paper, is capable of perceiving the red rays which pene- trate the eye-lids. If this experiment be made by the light of a tallow candle, the spot will be yellow instead of red; for tallow candles abound much with yellow light, which passes in greater quantity and force through the eye-lids than blue light: hence the difficulty of distinguishing blue and green by this kind of candle-light. The colour of the spectrum may possibly vary in the day-light, according to the different colour of the meri- dian, or the morning or evening light. M. Beguelin, in the Berlin Memoires, vol. ii. 1771, observes, that, when he held a book so that the sun shone upon his half closed eye-lids, the black letters, which he had long inspected, became red, which must have been thus occasioned. Those parts of the retina which had received, for some time, the black letters, were so much more sensible than those parts which had been opposed to the white paper, that to the former the red light which passed through the eye-lids was perceptible. There is a similar story told, I think, in M. de Voltaire's historical works, of a duke of Tuscany, who was playing at dice with the general of a foreign army, and, believing he saw bloody spots upon the dice, portended dreadful events, and retired in confusion. The observer, after looking for a minute on the black spots, of a die, and carelessly closing his eyes, on a bright day, would see the image of a die with red spots upon it, as above explained. 5. On emerging from a dark cavern, where we have long continued, 401 SECT. XL. 3. OCULAR SPECTRA. continued, the light of a bright day becomes intolerable to the eye for a considerable time, owing to the excess of sensibility existing in the eve, after having been long exposed to little or no stimulus. This occasions us immediately to contract the iris to its smallest aperture, which becomes again gradually di- lated, as the retina becomes accustomed to the greater stimulus of the day-light. The twinkling of a bright star, or of a distant candle, in the night, is perhaps owing to the same cause. While we continue to look upon these luminous objects, their central parts gra- dually appear paler, owing to the decreasing sensibility of the part of the retina exposed to their light; whilst, at the same time, by the unsteadiness of the eye, the edges of them are per- petually falling on parts of the retina, that were just before ex- posed to the darkness of the night, and therefore tenfold more sensible to light than the part on which the star or candle had been for some time delineated. This pains the eye in a similar manner as when we come suddenly from a dark room into bright day-light, and gives the appearance of bright scintillations. Hence the stars twinkle most when the night is darkest, and do not twinkle through telescopes, as observed by Musschenbroeck; and it will afterwards be seen why this twinkling is sometimes of different colours, when the object is very bright, as Mr. Mel- vill observed in looking at Sirius. For the opinions of others on this subject, see Dr. Priestley's valuable History of Light and Colours, p. 494. Many facts observable in the animal system are similar to these; as the hot glow occasioned by the usual warmth of the air, or our clothes, on coming out of a cold bath; the pain of the fingers, on approaching the fire after having handled snow; and the inflamed heels from walking in snow. Hence those who have been exposed to much cold, have died on being brought to a fire, or their limbs have become so much inflamed as to mortify. Hence much food or wine, given suddenly to those who have almost perished by hunger, has destroyed them; for all the organs of the famished body are now become so much more irritable to the stimulus of food and wine, which they have long been deprived of, that inflammation is excited, which terminates in gangrene or fever. IV. Of 402 OCULAR SPECTRA. SECT. XL. 4. IV. Of direct Ocular Spectra. A quantity of stimulus somewhat greater than natural excites the retina into spasmodic action, which cause in a few seconds. A CERTAIN duration and energy of the stimulus of light and colours excites the perfect action of the retina in vision; for very quick motions are imperceptible to us, as well as very flow ones, as the whirling of a top, or the shadow on a sun- dial. So perfect darkness does not affect the eye at all; and excess of light produces pain, not vision. 1. When a fire-coal is whirled round in the dark, a lucid circle remains a considerable time in the eye; and that with so much vivacity of light, that it is mistaken for a continuance of the irritation of tire object. In the same manner, when a fiery meteor shoots across the night, it appears to leave a long lucid train behind it, part of which, and perhaps sometimes the whole, is owing to the continuance of the action of the retina after having been thus vividly excited. This is beautifully illustrated by the following experiment: Fix a paper sail, three or four inches in diameter, and made like that of a smoak-jack, in a tube of pasteboard; on looking through the tube at a dis- tant prospect, some disjointed parts of it will be seen through the narrow intervals between the fails; but as the fly begins to revolve, these intervals appear larger; and when it revolves quicker, the whole prospect is seen quite as distinct as if no thing intervened, though less luminous. 2. Look through a dark tube, about half a yard long, at the area of a yellow circle of half an inch diameter, lying upon a blue area of double that diameter, for half a minute; and, on closing your eyes, the colours of the spectrum will appear simi- lar to the two areas, as in fig. 3.; but if the eye is kept too long upon them, the colours of the spectrum will be the reverse of those upon the paper; that is, the internal circle will become blue, and the external area yellow: hence some attention is required in making this experiment. 3. Place the bright flame of a spermaceti candle before a black object in the night; look steadily at it for a short time, till it is observed to become somewhat paler; and, on closing the eyes, and covering them carefully, but not so as to compress them, the image of the blazing candle will continue distinctly to be visible. 4. Look steadily, for a short time, at a window in a dark day, as in Exp. 2. Sect. III. and then closing your eyes, and covering G g g 403 SECT. XL. 5. OCULAR SPECTRA. 403 covering them with your hands, an exact delineation of the window remains for some time visible in the eye. This expe- riment requires a little practice to make it succeed well; since, if the eyes are fatigued by looking too long on the window, or the day be too bright, the luminous parts of the window will appear dark in the spectrum, and the dark parts of the frame work will appear luminous, as in Exp. 2. Sect. III. And it is even difficult for many, who first try this experiment, to perceive the spectrum at all; for any hurry of mind, or even too great attention to the spectrum itself, will disappoint them, till they have had a little experience in attending to such small sensations. The spectra described in this section, termed direct ocular spectra, are produced without much fatigue of the eye; the irritation of the luminous object being soon withdrawn, on its quantity of light being not so great as to produce any degree of uneasiness in the organ of vision; which distinguishes them from the next class of ocular spectra, which are the consequence of fatigue. These direct spectra are best observed in such cir- cumstances, that no light, but what comes from the object, can fall upon the eye; as in looking through a tube, of half a yard long, and an inch wide, at a yellow paper on the side of a room, the direct spectrum was easily produced on closing the eye without taking it from the tube: but if the lateral light is admitted through the eye-lids, or by throwing the spectrum on. white paper, it becomes a reverse spectrum, as will be explain- ed below. The other senses also retain for a time the impressions that have been made upon them, or the actions they have been ex- cited into. So, if a hard body is pressed upon the palm of the hand, as is practised in tricks of legerdemain, it is not easy to distinguish for a few seconds, whether it remains or is remov- ed; and tastes continue long to exist vividly in the mouth, as the smoke of tobacco, or the taste of gentian, after the sapid material is withdrawn. V. A quantity of stimulus somewhat greater than the last mentioned, excites the retina into spasmodic action, which ceases and recurs alternately. VI. On looking for a time on the setting sun, so as not greatly to fatigue the sight, a yellow spectrum is seen when the eyes are closed and covered, which continues for a time, and then disappears, and recurs repeatedly before it entirely vanishes. This yellow spectrum of the sun, when the eye-lids are opened, becomes blue; and if it is made to fall on the green grass, or on 404 OCULAR SPECTRA. SECT. XL. 6. on other coloured objects, it varies its own colour by an inter- mixture of theirs, as will be explained in another place. 2. Place a lighted spermaceti candle, in the night, about one foot from your eye, and look steadily on the center of the flame, till your eye becomes much more fatigued than in Sect. IV. Exp. 3. and on closing your eyes, a reddish spectrum will be perceived, which will cease and return alternately. The action of vomiting in like manner ceases, and is re- newed by intervals, although the emetic drug is thrown up with the first effort: so after-pains continue some time after partu- rition; and the alternate pulsations of the heart of a viper are renewed for some time after it is cleared from its blood. VI. Of reverse Ocular Spectra. The retina, after having been excited into action by a stimu- lus somewhat greater than the last mentioned, falls into opposite spasmodic action. The actions of every part of animal bodies may be advan- tageously compared with each other. This strict analogy con- tributes much to the investigation of truth; while those looser analogies, which compare the phenomena of animal life with those of chemistry or mechanics, only serve to mislead our in- quiries. When any of our larger muscles have been in long, or in- violent action, and their antogonists have been at the same time extended, as soon as the action of the former ceases, the limb is stretched the contrary way for our ease, and a pandiculation or yawning takes place. By the following observations it appears, that a similar cir- cumstance obtains in the organ of vision: after it has been fatigued by one kind of action, it spontaneously falls into the opposite kind. 1 . Place a piece of coloured silk, about an inch in diameter, on a sheet of white paper, about half a yard from your eyes; look steadily upon it for a minute; then remove your eyes upon another part of the white paper, and a spectrum will be seen of the form of the silk thus inspected, but of a colour opposite to it. A spectrum nearly similar will appear if the eyes are closed, and the eye-lids shaded by approaching the hand near them, so as to permit some, but to prevent too much light fall- ing on them. Red silk produced a green spectrum. Green produced a red one. Orange produced blue. Blue produced orange. Yellow 405 SECT. XL. 6. OCULAR SPECTRA. Yellow produced violet. Violet produced yellow. That in these experiments the colours of the spectra are the reverse of the colours which occasioned them, may be seen by examining the third figure in Sir Isaac Newton's Optics, L. II. p. i. where those thin laminæ of air, which reflected yellow, transmitted violet; those which reflected red, transmitted a blue- green; and so of the rest, agreeing with the experiments above related. 2. These reverse spectra are similar to a colour, formed by a combination of all the primary colours, except that with which the eye has been fatigued in making the experiment: thus the reverse spectrum of red must be such a green as would be pro- duced by a combination of all the other prismatic colours. To evince this fact, the following satisfactory experiment was made. The prismatic colours were laid on a circular paste board wheel, about four inches in diameter, in the proportions described in Dr. Priestley's History of Light and Colours, pl. 12. fig. 83. except that the red compartment was entirely left out, and the others proportionably extended so as to complete the circle. Then, as the orange is a mixture of red and yellow, and as the violet is a mixture of red and indigo, it became ne- cessary to put yellow on the wheel instead of orange, and in- digo instead of violet, that the experiment might more exactly quadrate with the theory it was designed to establish or con- fute; because, in gaining a green spectrum from a red object, the eye is supposed to have become insensible to red light. This wheel, by means of an axis, was made to whirl like a top; and on its being put in motion, a green colour was produced, corresponding with great exactness to the reverse spectrum of red. 3. In contemplating any one of these reverse spectra in the closed and covered eye, it disappears and re-appears several times successively, till at length it entirely vanishes, like the direct spectra in Sect. V.; but with this additional circumstance, that when the spectrum becomes faint or evanescent, it is in- stantly revived by removing the hand from before the eye-lids, so as to admit more light: because then not only the fatigued part of the retina is inclined spontaneously to fall into motions of a contrary direction, but being still sensible to all other rays of light, except that with which it was lately fatigued, is, by these rays, at the same time stimulated into those motions which form the reverse spectrum. From these experiments there is reason to conclude, that the fatigued part of the retina throws itself into a contrary mode of action, 406 OCULAR SPECTRA. SECT. XL. 7. action, like oscitation or pandiculation, as soon as the stimulus which has fatigued it is withdrawn; and that it still remains sensible; that is, liable to be excited into action by any other colours at the same time, except the colour with which it has been fatigued. VII. The retina, after having been excited into action by a stimulus somewhat greater than the last mentioned, falls into various successive spasmodic actions. 1. On looking at the meridian sun as long a the eyes can well bear its brightness, the disk first becomes pale, with a lu- minous crescent, which seems to librate from one edge of it to the other, owing to the unsteadiness of the eye; then the whole phasis of the sun becomes blue, surrounded with a white halo; and on closing the eyes, and covering them with the hands, a yellow spectrum is seen, which, in a little time, changes into a blue one. M. de la Hire observed, after looking at the bright sun, that the impression in his eye first assumed a yellow appearance, and then green, and then blue; and wishes to ascribe these ap- pearances to some affection of the nerves. Porterfield on the Eye, vol. i. p. 343. 2. After looking steadily on about an inch square of pink silk, placed on white paper, in a bright sunshine, at the distance of a foot from my eyes, and closing and covering my eye-lids, the spectrum of the silk was at first a dark green, and the spec- trum of the white paper became of a pink. The spectra then both disappeared; and then the internal spectrum was blue; and then, after a second disappearance, became yellow; and, lastly, pink; whilst the spectrum of the field varied into red and green. These successions of different coloured spectra were not ex- actly the same in the different experiments, though observed as near as could be, with the same quantity of light, and other similar circumstances; owing, I suppose, to trying too many experiments at a time, so that the eye was not quite free from the spectra of the colours which were previously attended to. The alternate exertions of the retina in the preceding section, resembled the oscitation or pandiculation of the muscles, as they were performed in directions contrary to each other, and were the consequence of fatigue rather than of pain. And in this they differ from the successive dissimilar exertions of the retina, mentioned in this section, which resemble, in miniature, the most violent agitations of the limbs in convulsive diseases, as epilepsy, chorea S. Viti. and opisthotonos; all which diseases are, 407 SECT. XL. 8, 9. OCULAR SPECTRA. are, perhaps, at first, the consequence of pain, and have their periods afterwards established by habit. VIII. The retina, after having been excited into action by a stimulus somewhat greater than the last mentioned, falls into a fixed spasmodic action, which continues for some days. 1. After, having looked long at the meridian sun, in mak- ing some of the preceding experiments, till the disk faded into a pale blue, I frequently observed a bright blue spectrum of the sun on other objects all the next and the succeeding day, which constantly occurred when I attended to it, and frequently when I did not previously attend to it. When I closed and covered my eyes, this appeared of a dull yellow; and at other times mixed with the colours of other objects on which it was thrown. It may be imagined, that this part of the retina was become insensible to white light, and thence a bluish spectrum became visible on all luminous objects; but as a yellowish spectrum was also seen in the closed and covered eye, there can remain no doubt of this being the spectrum of the sun. A similar appearance was observed by M. Æpinus, which, he ac- knowledges, he could give no account of. Nov. Com. Petrop. Vol. x. p. 2 and 6. The locked-jaw, and some cataleptic spasms, are resembled by this phenomenon; and from hence we may learn the danger to the eye by inspecting very luminous objects too long a time. IX. A quantity of stimulus greater than the preceding, in- duces a temporary paralysis of of the organ of vision. 1. PLACE a circular piece of bright red silk, about half an inch in diameter, on the middle of a sheet of white paper; lay them on the floor in a bright sunshine, and fixing your eyes steadily on the centre of the red circle, for three or four minutes, at the distance of four or six feet from the object, the red silk will gradually become paler, and finally cease to appear red at all. 2. Similar to these are many other animal facts; as purges, opiates, and even poisons, and contagious matter, cease to sti- mulate our system, after we have been habituated to their use. So some people sleep undisturbed by a clock, or even by a forge hammer in their neighbourhood: and not only continued irri- tations, but violent exertions of any kind, are succeeded by temporary paralysis. The arm drops down after violent action, and continues for a time useless; and it is probable, that those who have perished suddenly in swimming, or in scating on the ice, have owed their deaths to the paralysis, or extreme fatigue, which succeed every violent and continued exertion. X. MISCEL- 408 OCULAR SPECTRA. SECT. XL. 10. X. MISCELLANEOUS REMARKS. There were some circumstances occurred in making these experiments, which were liable to alter the results of them, and which I shall here mention for the assistance of others, who may wish to repeat them. 1. Of direct and inverse spectra existing at the same time; of reciprocal direct spectra; of a combination of direct and inverse spectra; of a spectral halo; rules to predeter- mine the colours of spectra. a. When an area, about six inches square, of bright pink Indian paper, had been viewed on an area, about a foot square, of white writing paper, the internal spectrum in the closed eye was green, being the reverse spectrum of the pink paper; and the external spectrum was pink, being the direct spectrum of the pink paper. The same circumstance happened when the internal area was white, and external one pink; that is, the internal spectrum was pink, and the external one green. All the same appearances occurred when the pink paper was laid on a black hat. b. When six inches square of deep violet polished paper was viewed on a foot square of white writing paper, the internal spectrum was yellow, being the reverse spectrum of the violet paper, and the external one was violet, being the direct spec- trum of the violet paper. c . When six inches square of pink paper was viewed on a foot square of blue paper, the internal spectrum was blue, and the external spectrum was pink; that is, the internal one was the direct spectrum of the external object, and the external one was the direct spectrum of the internal object, instead of their being each the reverse spectrum of the objects they belonged to. d. When six inches square of blue paper were viewed on a foot square of yellow paper, the interior spectrum became a brilliant yellow, and the exterior one a brilliant blue. The vivacity of the spectra was owing to their being excited both by the stimulus of the interior and exterior objects; so that the interior yellow spectrum was both the reverse spectrum of the blue paper, and the direct one of the yellow paper; and the exterior blue spectrum was both the reverse spectrum of the yellow paper, and the direct one of the blue paper. e. When the internal area was only a square half-inch of red paper, laid on a square foot of dark violet paper, the inter- nal spectrum was green, with a reddish-blue halo. When the red internal paper was two inches square, the internal spec- trum was a deeper green, and the external one redder. When the 409 SECT. XL. 10. OCULAR SPECTRA. the internal paper was six inches square, the spectrum of it be- came blue, and the spectrum of the external paper was red. ƒ When a square half-inch of blue paper was laid on a six- inch square of yellow paper, the spectrum of the central pa- per in the closed eye was yellow, encircled with a blue halo. On looking long on the meridian sun, the disk fades into a pale blue, surrounded with a whitish halo. These circumstances, though they very much perplexed the experiments till they were investigated, admit of a satisfactory explanation; for while the rays from the bright internal object in exp. a. fall with their full force on the center of the retina, and, by fatiguing that part of it, induce the reverse spectrum, many scattered rays, from the same internal pink paper, fall on the more external parts of the retina, but not in such quan- tity as to occasion much fatigue, and hence induce the direct spectrum of the pink colour in those parts of the eye. The same reverse and direct spectra occur from the violet paper in exp. b. : and in exp. c . the scattered rays from the central pink paper, produce a direct spectrum of this colour on the external parts of the eye; while the scattered rays from the external blue paper produce a direct spectrum of that colour on the central part of the eye, instead of these parts of the retina falling reci- procally into their reverse spectra. In exp. d. the colours be- ing the reverse of each other, the scattered rays from the exte- rior object falling on the central parts of the eye, and there ex- citing their direct spectrum, at the same time that the retina was excited into a reverse spectrum by the central object, and this direct and reverse spectrum being of similar colour, the supe- rior brilliancy of this spectrum was produced. In exp. e. the effect of various quantities of stimulus on the retina, from the different respective sizes of the internal and external areas, in- duced a spectrum of the internal area in the center of the eye, combined of the reverse spectrum of that internal area, and the direct one of the external area, in various shades of colour, from a pale green to a deep blue, with similar changes in the spectrum of the external area. For the same reasons, when an internal bright object was small, as in exp. ƒ. instead of the whole of the spectrum of the external object being reverse to the colour of the internal object, only a kind of halo, or radia- tion of colour, similar to that of the internal object, was spread a little way on the external spectrum. For this internal blue area being so small, the scattered rays from it extended but a little way on the image of the external area of yellow paper, and could therefore produce only a blue halo round the yellow spectrum in the center. H h h If 410 OCULAR SPECTRA. SECT. XL. 10. If any one should suspect that the scattered rays from the exterior coloured object, do not intermix with the rays from the interior coloured object, and thus affect the central part of the eye, let him look through an opake tube, about two feet in length, and an inch in diameter, at a coloured wall of a room with one eye, and with the other eye naked; and he will find, that by shutting out the lateral light, the area of the wall seen through a tube, appears as if illuminated by the sun- shine, compared with the other parts of it; from whence arises the advantage of looking through a dark tube at distant paintings. Hence we may safely deduce the following rules to determine before-hand the colours of all spectra. 1 . The direct spectrum without any lateral light is an evanescent representation of its object in the unfatigued eye. 2. With some lateral light it becomes of a colour combined of the direct spectrum of the central object, and of the circumjacent objects, in proportion to their respective quantity and brilliancy. 3. The reverse spectrum, without lateral light, is a representation, in the fatigued eye, of the form of its objects, with such a colour as would be produced by all the primary colours, except that of the object. 4. With lateral light the colour is compounded of the reverse spectrum of the central object, and the direct spectrum of the circumjacent objects, in proportion to their respective quantity and brilliancy. 2. Variation and vivacity of the spectra occasioned by ex- traneous light. The reverse spectrum, as has been before explained, is simi- lar to a colour, formed by a combination of all rise primary colours, except that with which the eye has been fatigued in making the experiment; so the reverse spectrum of red is such a green as would be produced by a combination of all the other prismatic colours. Now, it must be observed, that this reverse spectrum of red is therefore the direct spectrum of a combina- tion of all the other prismatic colours, except the red; whence, on removing the eye from a piece of red silk to a sheet of white paper, the green spectrum, which is perceived, may either be called the reverse spectrum of the red silk, or the direct spec- trum of all the rays from the white paper, except the red; for in truth it is both. Hence we see the reason why it is not easy to gain a direct spectrum of any coloured object in the day-time, where there is much lateral light, except of very bright objects, as of the setting sun, or by looking through an opake tube; because the lateral external light falling also on the central part of the retina, contributes to induce the reverse spectrum, which is 411 SECT. XL. 10. OCULAR SPECTRA. is at the same time the direct spectrum of that lateral light, de- ducting only the colour of the central object which we have been viewing. And, for the same reason, it is difficult to gain the reverse spectrum, where there is no lateral light to contribute to its formation. Thus, in looking through an opake tube on a yellow wall, and closing my eye, without admitting any lateral light, the spectra were all at first yellow, but at length changed into blue. And on looking, in the same manner, on red paper, I did at length get a green spectrum; but they were all at first red ones: and the same after looking at a candle in the night. The reverse spectrum was formed, with greater facility, when the eye was thrown from the object on a sheet of white paper, or when light was admitted through the closed eye-lids; because not only the fatigued part of the retina was inclined sponta- neously to fall into motions of a contrary direction; but being still sensible to all other rays of light except that with which it was lately fatigued, was, by these rays, stimulated at the same time into those motions which form the reverse spectrum.— Hence, when the reverse spectrum of any colour became faint, it was wonderfully revived by admitting more light through the eye-lids, by removing the hand from before them: and hence, on covering the closed eye-lids, the spectrum would often cease for a time, till the retina became sensible to the stimulus of the smaller quantity of light, and then it recurred. Nor was the spectrum only changed in vivacity, or in degree, by this admis- sion of light through the eye-lids; but it frequently happened, after having viewed bright objects, that the spectrum in the closed and covered eye was changed into a third spectrum, when light was admitted through the eye-lids; which third spectrum was composed of such colours as could pass through the eye-lids, except those of the object. Thus, when an area of half an inch diameter of pink paper was viewed on a sheet of white paper in the sunshine, the spectrum with closed and covered eyes was green; but on removing the hands from before the closed eye-lids, the spectrum became yellow, and returned in- stantly again to green, as often as the bands were applied to cover the eye-lids, or removed from them: for the retina being now insensible to red light, the yellow rays passing through the eye-lids in greater quantity than the other colours, induced a yellow spectrum; whereas, if the spectrum was thrown on white paper, with the eyes open, it became only a lighter green. Though a certain quantity of light facilitates the formation of the reverse spectrum, a greater quantity prevents its forma- tion, as the more powerful stimulus excites even the fatigued parts of the eye into action; otherwise we should see the spec- trum 412 OCULAR SPECTRA. SECT. XL. 10. trum of the last viewed object as often as we turn our eye. Hence the reverse spectra are best seen by gradually approach- ing the hand near the closed eve-lids to a certain distance only, which must be varied with the brightness of the day, or the energy of the spectrum. Add to this, that all dark spectra, as black, blue, or green, if light be admitted through the eye-lids, after they have been some time covered, give reddish spectra, for the reasons given in Sect. III. Exp. 1. From these circumstances of the extraneous light coinciding with the spontaneous efforts of the fatigued retina to produce a reverse spectrum, as was observed before, it is not easy to gain a direct spectrum, except of objects brighter than the am- bient light; such as a candle in the night, the setting sun, or viewing a bright object through an opake tube; and then the reverse spectrum is instantaneously produced by the admission of some external light, and is as instantly converted again to the direct spectrum by the exclusion of it. Thus, on looking at the setting sun, on closing the eves, and covering them, a mellow spectrum is seen, which is the direct spectrum of the setting sun; but on opening the eyes on the sky, the yellow spectrum is immediately changed into a blue one, which is the reverse spectrum of the yellow sun, or the direct spectrum of the blue sky, or a combination of both. And this is again transformed into a yellow one on closing the eyes and so reci- procally, as quick as the motions of the opening and closing eye-lids. Hence, when Mr. Melvill observed the scintillations of the star Sirius to be sometimes coloured, these were proba- bly the direct spectrum of the blue sky on the parts of the re- tina fatigued by the white light of the star. Essays Physical and Literary, p. 81. vol. ii. When a direct spectrum is thrown on colours darker than itself, it mixes with them; as the yellow spectrum of the setting sun, thrown on the green grass, becomes a greener yellow. But when a direct spectrum is thrown on colours brighter than itself, it becomes instantly changed into the reverse spectrum, which mixes with those brighter colours. So the yellow spec- trum of the setting sun, thrown on the luminous sky, becomes blue, and changes with the colour or brightness of the clouds on which it appears. But the reverse spectrum mixes with every kind of colour on which it is thrown, whether brighter than it- self or not: thus the reverse spectrum, obtained by viewing a piece of yellow silk, when thrown on white paper, was a lucid blue green; when thrown on black Turkey leather, becomes a deep violet. And the spectrum of blue silk, thrown on white paper, was a light yellow; on black silk was an obscure orange; and 413 SECT. XL. 10. OCULAR SPECTRA. and the blue spectrum, obtained from orange coloured-silk, thrown on yellow, became a green. In these cases the retina is thrown into activity or sensation by the stimulus of external colours, at the same time that it continues the activity or sensation which forms the spectra; in the same manner as the prismatic colours, painted on a whirling top, are seen to mix together. When these colours of exter- nal objects are brighter than the direct spectrum which is thrown upon them, they change it into the reverse spectrum, like the admission of external light on a direct spectrum, as explained above. When they are darker than the direct spectrum, they mix with it, their weaker stimulus being insufficient to induce the reverse spectrum. 3. Variation of spectra in respect to number, and figure, and remission. When we look long and attentively at any object, the eye cannot always be kept entirely motionless; hence, on inspect- ing a circular area of red silk placed on white paper, a lucid crescent or edge is seen to librate on one side or other of the red circle: for the exterior parts of the retina sometimes falling on the edge of the central silk, and sometimes on the white pa- per, are less fatigued with red light than the central part of the retina, which is constantly exposed to it; and therefore, when they fall on the edge of the red silk, they perceive it more vi- vidly. Afterwards, when the eye becomes fatigued, a green spectrum, in the form of a crescent, is seen to librate on one side or other of the central circle; as by the unsteadiness of the eye a part of the fatigued retina falls on the white paper; and as, by the increasing fatigue of the eye, the central part of the silk ap- pears paler, the edge on which the unfatigued part of the retina occasionally falls will appear of a deeper red than the original silk, because it is compared with the pale internal part of it. M. de Buffon, in making this experiment, observed, that the red edge of the silk was not only deeper coloured than the ori- ginal silk; but, on his retreating a little from it, it became oblong, and at length divided into two, which must have been owing to his observing it either before or behind the point of intersec- tion of the two optic axises. Thus, if a pen is held up before a distant candle, when we look intensely at the pen, two can- dles are seen behind it; when we look intensely at the candle, two pens are seen. If the sight be unsteady at the time of be- holding the sun, even though one eye only be used, many images of the sun will appear, or luminous lines, when the eye is closed. And as some parts of these will be more vivid than others, and some 414 OCULAR SPECTRA. SECT. XL. 10. some parts of them will be produced nearer the center of the eye than others, these will disappear sooner than the others; and hence the number and shape of these spectra of the sun will continually vary, as long as they exist. The cause of some being more vivid than others, is the unsteadiness of the eye of the beholder, so that some parts of the retina have been longer exposed to the sun-beams. That some parts of a complicated spectrum fade and return before other parts of it, the following experiment evinces. Draw three concentric circles; the ex- ternal one an inch and a half in diameter, the middle one an inch, and the internal one half an inch; colour the external and internal areas blue, and the remaining one yellow, as in Fig. 5.; after having looked about a minute on the center of these circles, in a bright light, the spectrum of the external area appears first in the closed eye, then the middle area, and lastly the central one; and then the central one disappears, and the others in inverted order. If concentric circles of more co- lours are added, it produces the beautiful ever changing spec- trum in Sect. I. Exp. 2. From hence it would seem, that the center of the eye pro- duces quicker remissions of spectra, owing, perhaps, to its greater sensibility; that is, to its more energetic exertions. These remissions of spectra bear some analogy to the tremors of the hands, and palpitations of the heart, of weak people; and perhaps a criterion of the strength of any muscle or nerve may be taken from the time it can be continued in exertion. 4. Variation of spectra in respect to brilliancy: the visibility of the circulation of the blood in the eye. 1. The meridian or evening light makes a difference in the colours of some spectra; for as the sun descends, the red rays, which are less refrangible by the convex atmosphere, abound in great quantity. Whence the spectrum of the light parts of a window at this time, or early in the morning, is red; and becomes blue, either a little later or earlier; and white in the meridian day; and is also variable, from the colour of the clouds or sky which are opposed to the window. 2. All these experiments are liable to be confounded, if they are made too soon after each other, as the remaining spectrum will mix with the new ones. This is a very troublesome cir- cumstance to painters, who are obliged to look long upon the same colour; and in particular to those whose eyes, from na- tural debility, cannot long continue the same kind of exertion. For the same reason, in making these experiments, the result. becomes much varied if the eyes, after viewing any object, are removed 415 SECT. XL. 10. OCULAR SPECTRA. removed on other objects for but an instant of time, before we close them to view the spectrum; for the light from the object, of which we had only a transient view, in the very time of closing our eyes, acts as a stimulus on the fatigued retina, and for a time prevents the defined spectrum from appearing, or mixes its own spectrum with it. Whence, after the eye-lids are closed, either a dark field, or some unexpected colours, are beheld for a few seconds, before the defined spectrum becomes distinctly visible. 3. The length of time taken up in viewing an object, of which we are to observe the spectrum, makes a great difference in the appearance of the spectrum, not only in its vivacity, but in its colour; as the direct spectrum of the central object, or of the circumjacent ones, and also the reverse spectra of both, with their various combinations, as well as the time of their duration in the eye, and of their remissions or alterations, de- pend upon the degree of fatigue the retina is subjected to. The Chevalier d' Arcy constructed a machine, by which a coal of fire was whirled round in the dark, and found, that when a lu- minous body made a revolution in eight thirds of time, it pre- sented to the eye a complete circle of fire; from whence he concludes, that the impression continues, on the organ about the seventh part of a second. Mem. de l'Acad. des Sc. 1765. This, however, is only to be considered as the shorted time of the duration of these direct spectra; since, in the fatigued eye, both the direct and reverse spectra, with their intermissions, appear to take up many seconds of time, and seem very variable, in proportion to the circumstances of fatigue or energy. 4. It sometimes happens, if the eye-balls have been rubbed hard with the fingers, that lucid sparks are seen, in quick mo- tion, amidst the spectrum we are attending to. This is similar to the flashes of fire from a stroke on the eye in fighting, and is resembled by the warmth and glow which appears upon the skin after friction, and is probably owing to an acceleration of the arterial blood into the vessels emptied by the previous pres- sure. By being accustomed to observe such small sensations in the eye, it is easy to see the circulation of the blood in this or- gan. I have attended to this frequently, when I have observed my eyes more than commonly sensible to other spectra. The circulation may be seen either in both eyes at a time, or only in one of them; for, as a certain quantity of light is necessary to produce this curious phenomenon, it one hand be brought nearer the closed eye-lids than the other, the circulation in that eye will for a time disappear. For the easier viewing the cir- culation, it is sometimes necessary to rub the eyes with a certain I I i degree 416 OCULAR SPECTRA. SECT. XL. 10. degree of force, after they are closed, and to hold the breath ra- ther longer than is agreeable, which, by accumulating more blood in the eye, facilitates the experiment; but, in general, it may be seen distinctly after having examined other spectra with your back to the light, till the eyes become weary; then hav- ing covered your closed eye-lids for. half a minute, till the spec- trum is faded away which you were examining, turn your face to the light, and removing your hands from the eye-lids, by and by again shade them a little, and the circulation becomes cu- riously distinct. The dreams of blood are, however, generally seen to unite, which shews it to be the venous circulation, ow- ing, I suppose, to the greater opacity of the colour of the blood in these vessels; for this venous circulation is also much more easily seen by the microscope in the tail of a tadpole. 5. Variation of spectra in respect to distinctness and size; with a new way of magnifying objects. 1. It was before observed, that when the two colours viewed together were opposite to each other, as yellow and blue, red and green, &c. according to the table of reflections and trans- missions of light in Sir Isaac Newton's Optics, B. II. fig. 3. the spectra of those colours were of all others the mod brilliant, and bed defined; because they were combined of the reverse spectrum of one colour, and of the direct spectrum of the other. Hence, in books printed with small types, or in the minute gra- duation of thermometers, or of clock-faces, which are to be seen at a distance, if the letters or figures are coloured with orange, and the ground with indigo; or the letters with red, and the ground with green; or any other lucid colour is used for the letters, the spectrum of which is similar to the colour of the ground; such letters will be seen much more distinctly, and with less confusion, than in black or white: for, as the spec- trum of the letter is the same colour with the ground on which they are seen, the unsteadiness of the eye in long attending to them, will not produce coloured lines by the edges of the letters, which is the principal cause of their confusion. The beauty of colours lying in vicinity to each other, whose spectra are thus reciprocally similar to each colour, is owing to this greater ease that the eye experiences in beholding them distinctly; and it is probable, in the organ of hearing, a similar circumstance may constitute the pleasure of melody. Sir Isaac Newton ob- serves, that gold and indigo were agreeable when viewed toge- ther; and thinks there may be some analogy between the sensa- tions of light and sound. Optics, Qu. 14. In viewing the spectra of bright objects, as of an area of red 417 SECT. XL. 10. OCULAR SPECTRA. red silk of half an inch diameter on white paper, it is easy to magnify it to tenfold tits size: for if, when the spectrum is form- ed, you still keep your eye fixed on the silk area, and remove it a few inches further from you, a green circle is seen round the red silk: for the angle now subtended by the silk is less than it was when the spectrum was formed, but that of the spec- trum continues the same, and our imagination places them at the same distance. Thus, when you view a spectrum on a sheet of white paper, if you approach the paper to the eye, you may diminish it to a point; and if the paper is made to recede from the eye, the spectrum will appear magnified in proportion to the distance. I was surprised, and agreeably amused, with the following experiment. I covered a paper about four inches square, with yellow, and with a pen, filled with a blue colour, wrote upon the middle of it, the word BANKS, in capitals, as in Fig. 6. and sitting with my back to the sun, fixed my eyes for a mi- nute exactly on the center of the letter N in the middle of the word; after closing my eyes, and shading them somewhat with my hand, the word was distinctly seen in the spectrum in yel- low letters on a blue field; and then, on opening my eyes on a yellowish wall at twenty feet distance, the magnified name of BANKS appeared written on the wall in golden characters. Conclusion. IT was observed by the learned M. Sauvages, (Nosol. Me- thod. CI. VIII. Ord. 1.) that the pulsations of the optic artery might be perceived by looking attentively on a white wall well illuminated. A kind of net-work, darker than the other parts of the wall, appears and vanishes alternately with every pulsa- tion. This change of the colour of the wall he well ascribes to the compression of the retina, by the diastole of the artery. The various colours produced in the eye by the pressure of the finger, or by a stroke on it, as mentioned by Sir Isaac New- ton, seem likewise to originate from the unequal pressure on various parts of the retina. Now, as Sir Isaac Newton has shewn, that all the different colours are reflected or transmit- ted by the laminæ of soap bubbles, or of air, according to their different thickness or thinness, is it not probable, that the effect of the activity of the retina may be to alter its thickness or thin ness, so as better to adapt it to reflect or transmit the colours which stimulate it into action? May not muscular fibres exist in the retina for this purpose, which may be less minute than the locomotive muscles of microscopic animals? May not these muscular 418 OCULAR SPECTRA. SECT. XL. 10. muscular actions of the retina constitute the sensation of light and colours: and the voluntary repetitions of them, when the object is withdrewn, constitute our memory of them? And lastly, may not the laws of the sensations of light, here inves- tigated, be applicable to all our other senses, and much con- tribute to elucidate many phenomena of animal bodies, both in their healthy and diseased state; and thus render this investiga- tion well worthy the attention of the physician, the metaphy- sician, and the natural philospher? November 1, 1785. Dum, Liber! astra petis volitans trepidantibus alis, Irruis immemori, parvula gutta, mari. Me qupque, me currente rota, revolubilis ætas Volverit in tenebras, -i, Liber, ipse sequor. END OF THE FIRST VOLUME. INDEX. TO THE SECTIONS OF PART FIRST. A ABSORPTION of solids, xxxiii. 3. 1. xxxvii. - of fluids in anasarca, xxxv. 1.3. Absorbent vessels, xxii. 2. xxix. 1. - regurgitate their fluids, xxix. 2. - their valves, xxix. a. - communicate with vena portarum, xxvii. 2. Accumulation of sensorial power, iv. a. xii. 5. 2. Activity of system too great, cure of, xii. 6. - too small, cure of, xx. 7. Age, old, xii. 3. 1. xxxvii. 4. Ague-fit, xii. 7. 1. xxxii. 3. 4. xxxii. 9. - how cured by bark, xii. 3. 4. - periods, how occasioned, xii. 2. 3. xxxii. 3. 4. xvii. 3. 6. Ague cakes, xxxii. 7. xxxii. 9. Air, sense of fresh, xiv. 8. - - - injures ulcers, xxviii. 2. - - - injected into veins, xxxii. 5. Alcohol deleterious, xxx. 3. Alliterations, why agreeable, xxii. a Aloes in lessened doses, xii. 3. 1. American natives indolent, xxxi. 2. - narrow shouldered, xxxi. 1. Analogy intuitive, xvii. 3. 7. Animals less liable to madness, xxxiii. 1. - less liable to contagion, xxxiii. 1. - how to teach, xxii. 3. 2. - their similarity to each other, xxxix. 4. 8. - their changes after nativity, xxxix. 4. 8. - their changes before nativity, xxxix. 4. 8. - less liable to contagious diseases, why xxxiii. 1. 5. - less liable to delirium and insanity, why, xxxiii. 1. 5. - easier to preserve than to reproduce xxxvii - food, distaste of, xxxviii. 1. - appetency, xxxix. 4. 7. Antipathy, x. 2. 2. Appetites, xi. 2. a. xiv. 8. Aphthæ. 420 INDEX. Aphthæ, xxviii. Apoplexy, xxxiv. i. 7. - not from deficient irritation, xxxii. 2. 1 Architecture, xii. 3. 3. xvi. 10. Arts, fine, xxii. a. Asparagus, its smell in urine, xxix. Association defined, ii. 11. iv. 7. v. a. - associate motions, x. - stronger than irritative ones, xxiv. 2. 8. - formed before nativity, xi. 3. - with irritative ones, xxiv. 8. - with retrograde ones, xxv. 7. xxv. 10. xxv. 15. - diseases from, xxxv. Asthma, xviii. 15. Attention, language of, xvi. 8. 6. Atrophy, xxviii. Aversion, origin of, xi. 2. 3. B Balance ourselves by vision, xx. 1. Bandage increases absorption, xxxiii. 2. 11. Barrenness, xxxvi. 2. 3. Battement of sounds, xx. 7. Bath, cold. See Cold Bath. Beauty, sense of, xvi. 6. xxii. 2. Bile-ducts, xxx. - stones, xxx. 3. - regurgitates into the blood, xxiv. 2. 7. - vomiting of, xxx. 3. Birds of passage, xvi. 12. - nests of, xvi. 13. - colour of their eggs, xxxix. 5. Biting in pain, xxxiv. 1. 3. - of mad animals, xxxiv. 1. 3. Black spots on dice appear red, xi. 3. Bladder, communication of with the intestines, xxix. 3. - of fish, xxiv. 1. 4. Blood, transfusion of in nervous fevers, xxxii. 4. - deficiency of, xxxii. 2. and 4. - from the vena portarum into the intestines, xxvii. 2. - its momentum, xxxii. 5. 2. - momentum increased by venesection, xxxii. 5. 4. - drawn in nervous pains, xxxii. 5. 4. - its oxygenation, xxxviii. Breathing, how learnt, xv. 4. Breasts of men, xiv. 8. Brutes differ from men, xi. 2. 3. xvi. 17. Brutes. See Animals. Buxton bath, why it feels warm, xii. 2. 1. xxxii. 3. 3. Capillary 421 INDEX. C Capillary vessels are glands, xxvi. 1. Catalepsy, xxxiv. 1. 5. Catarrh from cold skin, xxxv. 1. 3. xxxv. 2. 3. - from thin caps in sleep, xviii. 15. Catenation of motions defined, ii. 11. iv. 7. - cause of them, xvii. 1. 3. - described, xvii. - continue sometime after their production, xvii. 1. 3. - voluntary ones dissevered in sleep, xvii. 1. 12. xvii. 3. 13. Cathartics external, their operation, xxix. 7. 6. Causation, animal, defined, ii. 11. iv. 7. Cause of causes, xxxix. 4. 8. Causes inert and efficient, xxxix. 8. 2. - active and passive, xxxix. 8. 3. - proximate and remote, xxxix. 8. 4. Chick in the egg, oxygenation of, xxxviii. 2. Child riding on a stick, xxxiv. 2. 6. Chilness after meals, xxi. 3. xxxv. 1. 1. Cholera, case of, xxv. 13. Circulation in the eye visible, xi. 10. 4. Cold in the head, xii. 7. 5. - perceived by the teeth, xxxii. 3. 1. xiv. 6. - air, uses of in fevers, xxxii. 3. 2. - feet, produces coryza, xxxv. 2. 3. xxxv. 1. 3. - bath, why it strengthens, xxxii. 3.3. - short and cold breathing in it, xxxii. 3. 2. - produces a fever-fit, xxxii. 3. 2. - fit of fever the consequence of hot fit, xxxii. 9. 3. - bathing in pulmonary hæmorrhage, xxvii. 1. - fits of fever, xxxii. 4. xxxii. 9. xvii. 3. 3. Comparing ideas, xv. 3. Consciousness, xv. 3. 4. Consciousness in dreams, xviii. 13. Consumption, its temparament, xxxi. 1. and 2. - of dark eyed patients, xxvii. 2. - of light-eyed patients, xxviii. 2. - is contagious, xxxiii. 2. 7. Consent of parts. See Sympathy. Contagion, xii. 3. 6. xix. 9. xxxiii. 2. 6. and 8. xxxii. 3. 3, - does not enter the blood, xxxiii. 2. 10. xxii. 3. 3. Contraction and attraction, iv. 1. - of fibres produces sensation, iv. 5. xii. 1. 6. - continues some time, xii. 1. 5. - alternates with relaxation, xii. 1. 3. Convulsion, xvii. 1. 8. xxxiv. 1. 1. and 4. iii. 5. 8. - of particular muscles, xvii. 1. 8. - periods of, xxxvi. 3. 9. K k k Colours 422 INDEX. Colours of animals, efficient cause of, xxxix. 5. - of eggs from female imagination, xxxix. 5. - of the choroid coat of the eye, xxxix. 5. - of birds nests, xvi. 1 3. Coryza. See Catarrh. Cough, nervous, periods of, xxxvi. 3. 9. Cramp, xviii. 15. xxiv. 1. 7. Critical days from lunations, xxxvi. 4. D Darkish room, why we see well in it, xii. 2. 1. Debility sensorial and stimulatory, xii. 2. 1. - direct and indirect of Dr. Brown, xii. 2. 1. xxxii. 3. 2. - See Weakness. - from drinking spirits, cure of, xii, 7. 8. - in fevers, cure of, xii. 7. 8. Deliberation, what, xxxiv. 1. Desire, origin of, xi. 2. 3. Diabetes explained, xxix. 4. - with bloody urine, xxvii. 2. Diarrhœa, xxix. 4. Digestion, xxxiii. 1. xxxvii. - strengthened by emetics, xxxv. 1. 3. - strengthened by regular hours, why, xxxvi. 2. 1. Digitalis, use of in dropsy, xxix. 5. 2. Dilirium, two kinds of, xxxiii. 1.4. xxxiv. 2. 2. - cases of, iii. 5. 8. -prevented by dreams, xviii. 2. Distention acts as a stimulus, xxxii. 4. - See Extension. Distinguishing, xv. 3. Diurnal circle of actions, xxv. 4. Doubting, xv. 3. Dreams, viii. 1. 2. xiv. 2. 5. - their inconsistency, xviii. 16. - no surprise in them, xviii. 17. - much novelty of combination, xviii. 9 Dropsies explained, xxix. 5. 1. Dropsy cured by insanity, xxxiv. 2. 7. - cure of, xxix. 5. 2. Drunkenness. See Intoxication, xxi. - diminished by attention, xxi. 8. Drunkards weak till next day, xvii. 1. 7. - stammer, and stagger, and weep, xii. 4. 1. xxi. 4. - see objects double, why, xxi. 7. - become delirious, sleepy, stupid, xxi. 5. Dyspnœa in cold both, xxxii. 3. 2. Ear, 423 INDEX. E Ear, a good one, xvi. 10. - noise in, xx. 7. Eggs of frogs, fish, fowl, xxxix. 2. - of birds, why spotted, xxxix. 5. - with double yolk, xxxix. 4. 4. Electricity, xii. 1. xiv. 9. - jaundice cured by it, xxx. 2. Embryon produced by the male, xxxix. 2. consists of a living fibre, xxxix. 4. - absorbs nutriment, receives oxygen, xxxix. 1. - its actions and sensations, xvi. 2. Emetic. See Vomiting. Emotions, xi. 2. 2. Ennui, or tædium vitæ, xxxiv. 2. 3. xxxiii. 1. 1. xxxix. 6. Class ii. 1. 1. Epileptic fits explained, xxxiv. 1.4. xxvii. 2. - in sleep, why, xviii. 14. and 15. Equinoxial lunations, xxxii. 6. Excitability perpetually varies, xii. 1. 7. - synonymous to quantity of sensorial power, xii. 1. 7. Exercise, its use, xxxii. 5. 3. Exertion of sensorial power defined, xii. 2. 1. Existence in space, xiv. 2. 5. Extension, sense of, xiv. 7. Eyes become black in some epilepsies, xxvii. 2. F Face, flushing of after dinner, xxxv. 1. 1. - why first affected in small-pox, xxxv. 1. 1. - red from inflamed liver, xxxv. 2. 2. Fainting fits, xii. 5. 1. xiv. 7. Fear, language of, xvi. 8. 1. - a cause of fever, xxxii. 8. - cause of, xvii. 3. 7. Fetus. See Embryon, xvi. 2. xxxix. 1. Fevers, irritative, xxxii. 1. - intermittent, xxxii. 1. xxxii. 3. - sensitive, xxxiii. 1. - not an effort of nature for relief, xxxii. 10. - paroxysms of, xii. 7. 1. xii. 2. 3. xii. 3. 5. - why some intermit and not others, xxxvi. 1. - cold fits of, xxxii. 4. xxxii. 9. xvii. 3. 3. - period. 1. of, xxxvi. 3. - have solar or lunar periods, xxxii. 6. - source of the symptoms of, xxxii. 1. - prostration of strength in, xii. 4.1. xxxii. 3. 2. - cure of, xii. 6. 1. Fevers, 424 INDEX. Fevers, how cured by the bark, xii. 3. 4. - cured by increased volition, xii. 2. 4. xxxiv. 2. 8. - best quantity of stimulus in, xii. 7. 8. Fibres. See Muscles. - their mobility, xii. 1. 7. xii. 1.1. - contractions of, vi. xii. 1. 1. - four classes of their motions, vi. - their motions distinguished from sensorial one’s, v. 3. Figure, xiv. 2. 2. iii. 1. Fish, their knowledge, xvi. 14. Foxglove, its use in dropsies, xxix. 5. 2. - overdose of, xxv. 1 7. Free-will, xv. 3. 7. G Gall-stone, xxv. 17. See Bile-stones. Generation, xxxiii. 1. xxxix. Gills of fish, xxxviii. 2. Glands, xxii. 1. conglobate glands, xxii. 2. - have their peculiar stimulus, xi. 1. - their senses, xiv. 9. xxxix. 6. - invert their motions, xxv. 7. - increase their motions, xxv. 7. Golden rule for exhibiting wine, xii. 7. 8. - for leaving off wine, xii. 7. 8. Gout from inflamed liver, xxxv. 2. 2. xviii. 15. xxiv. 2. 8. - in the stomach, xxi. 2. 8. xxv. 17. - why it returns after evacuations, xxxii. 4. - owing to vinous spirit only, xxi. 10. - periods of, xxxvi. 3. 6. Grinning in pain, xxxiv. 1. 3. Gyration on one foot, xx. 5. and 6. H Habit defined, ii. 11. iv. 7. Hæmorrhages, periods of, xxxvi. 3. 10. - from paralysis of veins, xxvii. 1. and 2. Harmony, xxii. 2. Head-achs, xxxv. 2. 1. Hearing, xiv. 4. Heat, sense of, xiv. 6. xxxii. 3. 1. - produced by the glands, xxii. 3. - external and internal, xxxii. 3. 1. - atmosphere of heat, xxxii. 3. 1. - increases during sleep, xviii. 15. Hemicrania, xxxv. 2. 1. Hemicrania from decaying teeth, xxxv. 2. 1. Hepatitis, cause of, xxxv. 2. 3. Hereditary diseases, xxxix. 7. 6. Hermaphrodite 425 INDEX. Hermaphrodite insects, xxxix. 5. Herpes, xxviii. 2. - from inflamed kidney, xxxv. 2. 2. Hunger, sense of, xiv. 8. Hydrophobia, xxii. 3. 3. Hypochondriacism, xxxiii. 1. 1. xxxiv. 2. 3. I Ideas defined, ii. 7. - are motions of the organs of sense, iii. 4. xviii. 5. xviii. 10. xviii. 6. - analogous to muscular motions, iii. 5. - continue some time, xx. 6. - new ones cannot be invented, iii. 6. 1. - abstracted ones, iii. 7. 4. - inconsistent trains of, xviii. 16. - perish with the organ of sense, iii. 4. 4. - painful from inflammation of the organ, iii. 5. 5. - irritative ones, vii. 1. 4. vii. 3. 2. xv. 2. xx. 7. - of resemblance, contiguity, causation, viii. 3. 2. x. 3. 3. - resemble the figure and other properties of bodies, xiv. 2. 2. - received in tribes, xv. 1. - of the same sense easier combined, xv. 1. 1. - of reflection, xv. 1. 6. ii. 12. Ideal presence, xv. 1. 7. Identity, xv. 3. 5. xviii. 13. Iliac passion, xxv. 15. Imagination, viii. 1. 2. xv. 1. 7. xv. 2. 2. - of the male forms the sex, xxxix. 6. Immaterial beings, xiv. 1. xiv. 2. 4. Imitation, origin of, xii. 3. 3. xxxix. 5. xxii. 3. xvi. 7. Impediment of speech, xvii. 1. 10. xvii. 2. 10. Infection. See Contagion. Inflammation, xii. 2. 3. xxxiii. 2. 2. - great vascular exertion in, xii. 2. 1. - not from pains from defect of stimulus, xxxiii. 2. 3. - of parts previously insensible, xii. 3. 7. - often distant from its cause, xxiv. 8. - observes solar days, xxxii. 6. - of the eye, xxxiii. 3. 1. - of the bowels prevented by their continual action in sleep, xviii. 2. Inoculation with blood, xxxiii. 2. 10. Insane people, their great strength, xii. 1. Insanity (see Madness) pleasureable one, xxxiv. 2. 6. Insects, their knowledge, xvi. 15. and 16. - in the heads of calves, xxxix. 1. - class of, xxxix. 4. 8. Instinctive actions defined, xvi. 1. Intestines 426 INDEX. Intestines, xxv. 3. Intoxication relieves pain, why, xxi. 3. - from food after fatigue, xxi. 2. - diseases from it, xxi. 10. - See Drunkenness. Intuitive analogy, xvii. 3. 7. Invention, xv. 3. 3. Irritability increases during sleep, xviii. 15. Itching, xiv. 9. J Jaw-locked, xxxiv. 1. 5. Jaundice from paralysis of the liver, xxx. 2. - cured by electricity, xxx. 2. Judgment, xv. 3. K Knowledge of various animals, xvi. 11 . L Lacrymal sack, xvi. 8. xxiv. 2. and 7. Lacteals, paralysis of, xxviii. See Absorbents. Lady playing on the harpsichord, xvii. 2. - distressed for her dying bird, xvii. 2. 10. Language, natural, its origin, xvi. 7. and 8. - of various passions described, xvi. 8. - artificial, of various animals, xvi. 9. - theory of, xxxix. 8. 3. Lapping of puppies, xvi. 4. Laughter explained, xxxiv. 1. 4. from tickling, xvii 3.5. xxxiv. 1. 4. - from frivolous ideas, xxxiv. 1.4. xviii. 12. Life, long, art of producing, xxxvii. Light has no momentum, iii. 3. 1. Liquor amnii, xvi. xxxviii. 2. - is nutritious, xxxviii. 3. - frozen, xxxviii. 3. Liver, paralysis of, xxx. r.4. - large of geese, xxx. 1.6. Love, sentimental, its origin, xvi. 6. - animal, xiv. 8. xvi. 5. Lunar periods affect diseases, xxxii. 6. Lust, xiv. 8. xvi. 5. Lymphatics, paralysis of, xxviii. See Absorbents. M Mad-dog, bite of, xxii. 3. 3. Madness, xxxiv. 2. 1. xii. 2. 1. Magnetism, xii. 1. 1. Magnifying 427 INDEX. Magnifying objects, new way of, xl. 10. 5. Male animals have teats, xxxix. 4. 8. - - - pigeons give milk, xxxix. 4. 8,, Man distinguished from brutes, xi. 2. 3. xvi. 17. Material world, xiv. 1. xiv. 2. 5. xviii. 7. Matter, penetrability of, xiv. 2. 3. - - - - purulent, xxxiii. 2. 4. Measles, xxxiii. 2. 9. Membranes, xxvi. 2. Memory defined, ii. 10. xv. 1. 7. xv. 3. Menstruation by lunar periods, xxxii. 6. Miscarriage from fear, xxxix. 5. Mobility of fibres, xii. 1. 7. Momentum of the blood, xxxii. 5. 2 - sometimes increased by venesection, xxxii. 5. 4. Monsters, xxxix. 4. 4. and 5. 2. - without heads, xxxviii. 3. Moon and sun, their influence, xxxii. 6. Mortification, xxxiii. 3. 3. Motion is either cause or effect, i. xiv. 2. 2. - primary and secondary, i. - animal, i. iii. 1. - propensity to, xxii. 1. - animal, continue some time after their production, xvii. 1.3. - defined a variation of figure, iii. 1. xiv. 2. 2. xxxix. 7. Mucus, experiment on, xxvi. 1. - secretion of, xxvi. 2. Mules, xxxix. 4, 5. and 6. xxxix. 5. 2. Mule plants, xxxix. 2. Muscæ volitantes, xi. 2. Muscles constitute an organ of sense, xiv. 7. ii. 3. - stimulated by extension, xi 1. xiv. 7. - contract by spirit of animation, xii. 1. 1. and 3. Music, xvi. 10. xxii. 2. Musical time, why agreeable, xii. 3. 3. N Nausea, xxv. 6. Nerves and brains, ii. 2. 3. - extremities of form the whole system, xxxvii. 3. - are not changed with age, xxxvii. 4. Nervous pains defined, xxxiv. 1. 1. Number defined, xiv. 2. 2. Nutriment for the embryon, xxxix. 5. 2. Nutrition owing to stimulus, xxxvii. 3. - by animal selection, xxxvii. 3. when the fibres are elongated, xxxvii. 3. - like inflammation, xxxvii. 3. Objects 428 INDEX. O Objects long viewed become faint, iii. 3. 2. Ocular spectra, xl. Oil externally in diabetes, xxix. 4. Old age from inirritability, xxxvii. Opium is stimulant, xxxii. 2. 2. - promotes absorption after evacuation, xxxiii. 2. 10. - in increasing doses, xii. 3. 1. Organs of sense, ii. 5. and 6. Organs when destroyed cease to produce ideas, iii. 4. 4. Organic particles of Buffon, xxxvii. 3. xxxix. 3. 3. Organ-pipes, xx. 7. Oxygenation of the blood, xxxviii. P Pain from excess and defect of motion, iv. 5. xii. 5. 3. xxxiv. 1. xxxv. 2. 1. - not felt during exertion, xxxiv. 1. 2. - from greater contraction of fibres, xii. 1. 6. - from accumulation of sensorial power, xii. 5. 3. xxiii. 3. 1; - from light, pressure, heat, caustics, xiv. 9. - in epilepsy, xxxv. 2. 1. - distant from its cause, xxiv. 8. - from stone in the bladder, xxxv. 2. 1. - of head and back from defect, xxxii. 3. - from a gall-stone, xxxv. 2. 1. xxv. 17. - of the stomach in gout, xxv. 17. - of shoulder in hepatites, xxxv. 2. 4. - produces volition, iv. 6. Paleness in cold fit, xxxii. 3.2. Palsies explained, xxxiv. 1. 7. Paralytic limbs stretch from irritation, vii. 1. 3. - patients move their sound limb much, xii. 5. 17 Paralysis from great exertion, xii. 4. 6. - from less exertion, xii. 5. 6. - of the lacteals, xxviii. - of the liver, xxx. 4. - of the right arm, why, xxxiv. 1. 7. - of the veins, xxvii. 2. Particles of matter will not approach, xii. 1. 1. Potions, xi. 2. 2. - connate, xvi. 1. Pecking of chickens, xvi. 4. Perception defined, ii. 8. xv. 3. 1. Periods of agues, how formed, xxxii. 3. 4. - of diseases, xxxvi. - of natural actions and of diseased actions, xxxvi. Perspiration in fever-fits, xxxii. 9. See Sweat. Petechiæ, 429 INDEX. Petechiæ, xxvii. 2. Pigeons secrete milk in their stomachs, xxxix. 4. 8. Piles, xxvii. 2. Placenta a pulmonary organ, xxxviii. 2. Pleasure of life xxxiii. 1. xxxix. 5._ - from greater fibrous contractions, xii. 1. 6. - what kind causes laughter, xxxiv. 1. 4. - what kind causes sleep, xxxiv. 1. 4. Pleurisy, periods of, xxxvi. 3. 7. - cause of, xxxv. 2. 3. Prometheus, story of, xxx. 3. Prostration of strength in fevers, xii. 4. 1. Pupils of the eyes large, xxxi. 1. Pulse quick in fevers with debility, xii. 1. 4. xii. 5. 4. xxii. 2. 1. - in fevers with strength, xxxii. 2. - from defect of blood, xxxii. 2. 3. xii. 1. 4. - weak from emetics, xxv. 17. Q Quack advertisements injurious. Apology. Quadrupeds have no sanguiferous lochia, xxxviii. 2. - have nothing similar to the yolk of eggs, xxxix. 1. R Rhaphania, periods of, xxxvi. 3. 9. Reason, ix. 1. 2. xv. 3. Reasoning, xv. 3. Recollection, ii. 10. ix. 1.2. xv. 2. 3. Relaxation and bracing, xxxii. 3. 2. Repetition, why agreeable, xii. 3. 3. xii. 2. Respiration affected by attention, xxxvi. 2. 1. Restlessness in fevers, xxxiv. 1. 2. Retrograde motions, xii. 5. 5. xxv. 6. xxix. 11. - of the stomach, xxv. 6. - of the skin, xxv. 3. - of fluids, how distinguished, xxix. 8. - how caused, xxix. 11. 5. - diseases, synopsis of, xxix. 9. Retina is fibrous, iii. 2. xl. 1. - is active in vision, iii. 3. xl. 1. - excited into spasmodic motions, xl. 7. - is sensible during sleep, xviii. 5. xix. 8. Reverie, xix. 1. xxxiv, 3. - case of a sleep-walker, xix. 2. - is an epileptic disease, xix. 2. Rocking young children, xxi. 4. Rot in sheep, xxxii. 7. Ruminating animals, xxv. 1. Rhymes in poetry, why agreeable, xxii. 2, L l l Saliva 430 INDEX. S Saliva produced by mercury, xxiii. - by food, xxiii. i. - by ideas, xxiii. 2. and 5. - by disordered volition, xxiii. 7. Schirrous tumours revive, xii. 2. 2. Screaming in pain, xxxiv. 1. 2. Scrophula, its temperament, xxxi. 1. - xxviii. 2. xxxix. 4. 5. Scurvy of the lungs, xxvii. 2. Sea-sickness, xx. 4. - stopped by attention, xx. 5. Secretion, xxxiii. 1. xxxvii. - increased during sleep, xviii. 16. Seeds require oxygenation, xxxviii. 2. Sensation defined, ii. 9. v. 2. xxxix. 8. 4. - diseases of, xxxiii. - from fibrous contractions, iv. 5. xii. 1. 6. - in an amputated limb, iii 7. 3. - affects the whole sensorium, xi. 2. - produces volition, iv. 6. Sensibility increases during sleep, xviii. 15. Sensitive motions, viii. xxxiii. 2. xxxiv 1. - fever of two kinds, xxxiii. 1. 2. - ideas, xv. 2. 2. Sensorium defined, ii. 1. Senses correct one another, xviii. 7. - distinguished from appetites, xxxiv. 1. 1. Sensorial power. See Spirit of Animation. - great expence in the vital motions, xxxii. 3. 2. - two kinds of exerted in sensitive fevers, xxxiii. 1. 3. - powers defined, v. 1. - motions distinguished from fibrous motions, v. 3. - not much accumulated in sleep, xviii. 2. - powers, accumulation of, xii. 5. 1. - exhaustion of, xii. 4. 1. - wasted below natural in hot fits, xxxii. 9. 3. - less exertion of produces pain, xii. 5. 3. - less quantity of it, xii. 5. 4. Sensual motions distinguished from muscular, ii. 7. Sex owing to the imagination of the rather, xxxiv. 5. - xxxix. 7. 6. xxxix. 6. 2. xxxix. 6. 7. Shingles from inflamed kidney, xxxv. 2. 2. Shoulders broad, xxxi. 1. xxxix. 7. 6. Shuddering from cold, xxxiv. i. 1. and 2. Sight, its accuracy in men, xvi. 6. Skin, skurf on it, xxvi. 1. Sleep suspends volition, xvii. 1. Sleep 431 INDEX. Sleep defined, xviii. 21. - remote causes, xviii. 20. - sensation continues in it, xvii. 2. - from food, xxi. 1. - from rocking, uniform sounds, xxi. 1. - from wine and opium, xxi. 3. - why it invigorates, xii. 5. 1. - pulse slower and fuller, xxxii. 2. 2. - interrupted, xxvii. 2. - from breathing less oxygene, xviii. 20. - from being whirled on a millstone, xviii. 20. - from application of cold, xviii. 20. Sleeping animals, xii. 2. 2. Sleep-walkers. See Reverie, xix. 1. Small-pox, xxxiii. 2. 6. xxxix. 6. 1. - eruption first on the face, why, xxxv. 1. 1. xxxiii, 2. 10. - the blood will not infect, xxxiii. 2. 10. - obeys lunations, xxxvi. 4. Smell, xiv. 5. xvi. 5. Smiling, origin of, xvi. 8. 4. Solidity, xiv. 2. 1. Somnambulation. See Reverie, xix. 1. Space, xiv. 2. 2. Spasm, doctrine of, xxxii. 10. Spectra, ocular, xi. - mistaken for spectres, xi. 2. - vary from long inspection, iii. 3. 5. Spirit of animation. See Sensorial power. - of animation causes fibrous contraction, iv. 2. ii. 1. xiv. 2. 4. - possesses solidity, figure, and other properties of matter, xiv. 2. 3. Spirits and angels, xiv. 2. 4. Stammering explained, xvii. 1. 16. xvii. 2. 10. Stimulus defined, ii. 13. iv. 4. xii. 2. 1. - of various kinds, xi. 1. - with lessened effect, xii. 3. 1. - with greater effect, xii. 3. 3. - ceases to produce sensation, xii. 3. 3. Stomach and intestines, xxv. - inverted by great stimulus, xxv. 6. - its actions decreased in vomiting, xxxv. 1. 3. - a blow on it occasions death, xxv. 17. Stools black, xxvii. 2. Strangury, xxxv. 2. 1. Sucking before nativity, xvi. 4. Suckling children, sense of, xiv. 8. Suggestion, defined, ii. 10. xv. 2. 4. Sun 432 INDEX Sun and moon, their influence, xxxii. 6. Surprise, xvii. 3. 7. xviii. 17. Suspicion attends madness, xxxiv. 2. Swallowing, act of, xxv. 1. xvi. 4. Sweat, cold, xxv. 9. xxix. 6. - in hot fit of fever, xxxii. 9. - in a morning, why, xviii. 15. Sweaty hands cured by lime, xxix. 4. 9. Swinging and rocking, why agreeable, xxi. 3. Sympathy, xxxv. 1. Syncope, xii. 7. 1. xxiv. 1. 6. T Tape-worm, xxxix. 2. Taste, sense of, xiv. 5. Tears, secretion of, xxiv. - from grief, xvi. 8. 2. - from tender pleasure, xvi. 8. 3. - from stimulus of nasal duct, xvi. 8. xxiv. 4. - by volition, xxiv. 6. Teeth decaying cause headachs, xxxv. 2. 1. Temperaments, xxxi. Theory of medicine, wanted. Apology. Thirst, sense of, xiv. 8. - why in dropsies, xxix. 5. Tickle themselves, children cannot, xvii. 3. 5. Tickling, xiv. 9. Time, xiv. 2. 2. xvii. 12. - lapse of, xv. 3. 6. - poetic and musical, why agreeable, xxii. 2. - dramatic, xviii. 12. Tædium vitæ. See Ennui. Tooth-edge, xvi. 10. iii. 4. 3. xii. 3. 3. Touch, sense of, xiv. 2. 1. - liable to vertigo, xxi. 9. - of various animals, xvi. 6. Trains of motions inverted, xii. 5. 5. Transfusion of blood in nervous fever, xxxii. 4. Translations of matter, xxix. 7. Typhus, best quantity of stimulus in, xii 7. 8. - periods of observe lunar days, xxxii. 6. U Ulcers, art of healing, xxxiii. 3. 2. - of the lungs, why difficult to heal, xxviii. 2. Uniformity in the fine arts, why agreeable, xxii. 2. Urine pale in intoxication, xxi. 6. - paucity of in anasarca, why, xxix. 5. - its passage from intestines to bladder, xxix. 3. - copious during sleep, xviii. 15. Variation, 433 INDEX. V Variation, perpetual, of irritability, xii. 2. 1. Vegetable buds are inferior animals, xiii. i. - exactly resemble their parents, xxxix. - possess sensation and volition, xiii. 2. - have associate and retrograde motion; xii; 4. xxix. 9. - their anthers and stigmas are alive, xiii. 5. - have organs of sense and ideas, xiii. 5. - contend for light and air, xxxix. 4. 8. - duplicature of their flowers, xxxix. 4. 4. Veins are absorbents, xxvii. 1. - paralysis of, xxvii. 1. Venereal orgasm of brutes, xxxii. 6. Venesection in nervous pains, xxxii. 5. 4. Verbs of three kinds, xv. 3. 4. Verses, their measure, xxii. 2. Vertigo, xx. defined, xx. 11. - in looking from a tower, xx. 1. - in a ship at sea, xx. 4. - of all the senses, xxi. 9. - by intoxication, xxxv. 1. 2. Vibratory motions perceived after sailing, xx. 5. xx. 10. Vis medicatrix of nature, xxxix. 4. 7. Vision, sense of, xiv. 3. Volition defined, v. 2. xxxiv. 1. - affects the whole sensorium, xi. 2. - diseases of, xxxiv. Voluntarily, x. 2. 4. Voluntary motions, ix. xxxiv. 1. - ideas, xv. 2. 3. - criterion of, xi. 2. 3. xxxiv. 1. Vomiting from vertigo, xx. 8. - from drunkenness, xx. 8. xxi. 6. - by intervals, xxv. 8. - by voluntary efforts, xxv. 6. - of two kinds, xxxv. 1. 3. - in cold fit of fever, xxxii. 9. 1. - stopped by quicksilver, xxv. 16. - weakens the pulse, xxv. 17. W Waking, how, xviii. 14. Walking, how learnt, xvi. 3. Warmth in sleep, why, xviii. 13. Weakness defined, xii. 1. 3. xii. 2. 1. xxxii. 3. 2. - cure of, xii. 7. 8. See Debility. Wit producing laughter, xxxiv. 1. 4. World generated, xxxix. 4. 8. Worm-fluke, xxxii. 7. PLATES. I. The Plate consisting of one red spot, at Sect. III. 1. 2.- Consisting of one black spot, at Sect. III. 3. 3. 3.- Consisting of five concentric coloured circles, at Sect. III. 3. 6. 4.- Consisting of one yellow circle surrounded by one blue one, at Sect. XL. 4. 2. 5.- Consisting of one yellow circle and two blue ones, at Sect. XL. 10. 3. 6.- Consisting of the word BANKS in blue on a yellow ground, at Sect, XL. 10. 5. ADVERTISEMENT. WHEN Proposals were first offered for printing Doctor DARWIN'S ZOONOMIA, it was the intention of the Pub- lishers to have entered upon the work immediately—But, from a deficiency of subscriptions, and some other causes, it could not then be commenced; and the publication of it has been necessarily delayed until this time.—As the second volume of the ZOONOMIA has recently been published in England, and as those who have subscribed for this would unquestionably wish to possess that also, the Publishers beg leave to inform the Public that they have determined to put the second volume to press immediately upon its arrival in this country, and that they will receive subscriptions for it—to be printed in uni- formity with the first, and to correspond in binding. A list of the names of those gentlemen who may favour the Pub- lishers with their subscriptions shall be inserted at the end of the work.— Subscribers will receive their books 20 per cent, cheaper than non-subscribers. 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