Mi:!ii£IW!i:; M\&$ VM.1H,ED(,C. ''H.al.h*- NATIONAL LIBRARY MEDICINE Washington.D.C. HUMAN PHYSIOLOGY; ILLUSTRATED BY ENGRAVINGS. BY ROBLEY DUNGLISON, M.D. PROFESSOR OF THE INSTITUTES OF MEDICINE AND MEDICAL JURISPRUDENCE IN JEFFERSON MEDICAL COLLEGE, PHILADELPHIA ; ONE OF THE SECRETARIES TO THE AMERICAN PHILOSOPHICAL SOCIETY, ETC. ETC. " Vastissimi studii primas quasi lineas circumscripsi."—Haller. iFourt!) Efcftfon, WITH NUMEROUS ADDITIONS AND MODIFICATIONS. IN TWO VOLUMES. VOL.1. JSUZgISm^U* PHILADELPHIA: LEA AND BLANCHARD !7ilil 1841. D9lt>h v. l Entered, according to the Act of Congress, in the year 1841, by Robley Dunglison, in the Clerk's Office of the District Court for the Eastern District of Pennsylvania. C. Sherman & Co. Printers, 19 St. James Street. DEDICATION TO THE FIRST AND SECOND EDITIONS. TO JAMES MADISON, EX-PRESIDENT OF THE UNITED STATES, ETC. ETC. ALIKE DISTINGUISHED AS AN ILLUSTRIOUS BENEFACTOR OF HIS COUNTRY ; A ZEALOUS PROMOTER OF SCIENCE AND LITERATURE, AND THE FRIEND OF MANKIND— BTJlfe OTotft, INTENDED TO ILLUSTRATE THE FUNCTIONS EXECUTED BY THAT BEING, WHOSE MORAL AND POLITICAL CONDITION HAS BEEN WITH HIM AN OBJECT OF ARDENT AND SUCCESSFUL STUDY, IS, WITH HIS PERMISSION, INSCRIBED, IN TESTIMONY OF UNFEIGNED RESPECT FOR HIS TALENTS AND PHILANTHROPY, AND OF GRATITUDE FOR NUMEROUS EVIDENCES OF FRIENDSHIP, BY HIS OBEDIENT AND OBLIGED SERVANT, THE AUTHOR. DIRECTIONS TO THE BINDER. 1. The plates of the System of Respiratory Nerves, and of the Regular or Symmetrical Nerves, between pages 66 and 67. 2. Plate of the Craniological Division of Gall, at page 308. 3. The plates of the Bones, at page 336. ^2< PREFACE TO THE FOURTH EDITION. The great advances, daily making in the knowledge of the various subjects that appertain to Physiology, render the prepara- tion of a new edition of any work, which has received the general favour of the profession, a. task by no means easy. In the short period, that has elapsed since the appearance of the third edition, the investigations of the physiologist have been so numerous and diversified as to render it necessary to make many modifications and additions. The extent of these cannot be appreciated by a cursory examination. They have imposed upon the author the necessity for considerable labour. The mere reference, indeed, to the various contributions—scattered through the journals of different countries, and languages, as well as contained in ex prqfesso treatises—requires no little time and industry. The author has found it requisite to make the most numerous modifications and additions in the second volume. The subject of Histogeny or the developement of the tissues, although much cultivated by recent physiologists, belongs perhaps more properly to general anatomy, and on this account has not been treated of in extenso in the present work. It was impossible, however, to pass over the recent labours of Valentin, Bischoff, Warner, Martin Barry, T. W. Jones and others, without notice. The first part of the " Elements of Physiology" of Dr. Rudolph Wagner, translated by Dr. Robert Willis, with notes by that X PREFACE. gentleman, and others, has furnished the author much valuable matter. He has likewise added several engravings, to elucidate either topics, already touched upon in the work, or such as are new in the present edition, and has endeavoured to place it in all respects on a level with the existing state of the science. Philadelphia, August, 1841. CONTENTS OF VOL. I. Preliminary Observations. Chap. I. Of Natural Bodies - - - - - 13 1. Difference between Inorganic and Organized Bodies - 14 2. Difference between Animals and Vegetables - 19 General Physiology of Man. Chap. I. On the Material Composition of Man • - - 24 a. Organic Elements that contain Azote . - 27 6. Organic Elements that do not contain Azote - - 30 c. Of the Solid parts of the Human Body . - 33 d. Of the Fluids of the Human Body - - - 38 e. Of the Elementary Structure of Animal Substances 40 /. Physical Properties of the Tissues - - - 44 Chap. II. Of the Functions of Man . . - - 49 BOOK I. Animal Functions, or Functions of Relation. Chap. I. Of Sensibility or the Function of the Sensations - - 53 1. Of the Nervous System - - - - 53 2. Physiology of Sensibility ... - 82 a. Of the Sensations - - - - - 82 b. External Sensations ----- "0 Sense of Tact or Touch—Palpation - - - - 93 1. Anatomy of the Skin, Hair, Nails, &c. - - 93 2. Physiology of Tact and Touch - - - 79 Sense of Taste or Gustation ... - 109 1. Anatomy of the Organs of Taste . - - 109 2. Of Savours.....1U 3. Physiology of Taste - - - - 114 Of the Sense of Smell or Olfaction - - - 121 1. Anatomy of the Organ of Smell - 121 2. Of Odours.....121 3. Physiology of Olfaction - - - - 130 Of the Sense of Hearing or Audition - 137 1. Anatomy of the Organ of Hearing - - - 137 2. Of Sound ----- 146 3. Physiology of Audition - 151 Of the Sense of Sight or Vision - - - - 168 1. Of Light......169 2. Anatomy of the Organ of Vision - - 178 3. Accessory Organs . - - - 189 4. Physiology of Vision - 194 5. Phenomena of Vision .... 214 Additional Senses ----- 259 b. Internal Sensations .... 261 Xll CONTENTS. Of the Mental Faculties, &c. . - - - 264 1. Physiology of the Intellectual and Moral Faculties 284 Chap. II. Of Muscular Motion, especially of Locomotility or Voluntary Motion. ------ 321 1. Anatomy of the Motory Apparatus - - 322 2. Of the Muscles.....322 3. Of the Bones.....330 4. Physiology of Muscular Motion - 337 5. Of the Attitudes .... 389 6. Of the Movements - - - - - 395 7. Locomotive Movements ... 397 a. Walking ------ 397 b. Leaping - - - - - 399 c. Running - - 401 d. Swimming ----- 402 e. Flying......405 f. Other Varieties of Muscular Action - - 406 8. Of the Function of Expression or of Language - 408 a. Of the Voice - 408 1. Anatomy of the Vocal Apparatus - 408 2. Physiology of the Voice ... 412 1. Intensity or Strength of the Voice - - 416 2. Tone of the Voice ... - 410 3. Timbre or Quality of the Voice ... 425 4. Of Natural or Inarticulate Language - 432 5. Of Artificial or Articulate Language - - 434 6. Of Singing ----- 446 b. Of the Gestures ----- 449 Ciliary Motion .... 4Q5 BOOK II. Nutritive Functions. Chap. I. Of Digestion - 1. Anatomy of the Digestive Organs - 2. OftheFoodofMan - 3. Physiology of Digestion 4. Digestion of Solid Food a. Hunger - b. Prehension of Food - c. Oral or Buccal Digestion d. Deglutition - e. Chymification - / Action of the Small Intestines g. Action of the Large Intestines 5. Digestion of Liquids - 6. Of Eructation, Regurgitation, and Rumination a. Eructation .... b. Regurgitation - c. Rumination ... d. Vomiting .... - 467 467 - 491 502 - 502 502 - 509 512 - 515 519 - 550 559 - 566 570 - 570 570 - 571 571 HUMAN PHYSIOLOGY. PROLEGOMENA. I. ON NATURAL BODIES. The extensive domain of Nature is divisible into three great classes:—Minerals, Vegetables, and Animals. This division was universally adopted by the ancients, and still prevails, especially amongst the unscientific. When, however, we carefully examine their characteristics, we discover that the animal and the vegetable resemble each other in many essential particulars. This resem- blance has given occasion to the partition of all bodies into two classes;—the Inorganic, or those not possessing organs, or instru- ments adapted for the performance of particular actions or func- tions, and the Organized, or such as possess this arrangement. In all ages, philosophers have attempted to point out a " Vast chain of being, which from God began, Natures ethereal, human, angel, man, Beast, bird, fish, insect, what no eye can see, No glass can reach—" the links of which chain they have considered to be constituted of all natural bodies; passing by insensible gradations through the in- organic and the organized, and forming a rigid and unbroken series, and in which, they have conceived, "------each moss, Each shell, each crawling insect, holds a rank Important in the plan of Him who framed This scale of beings—holds a rank which, lost, Would break the chain, and leave behind a gap Which Nature's self would rue." Crystallization has been esteemed by them as the highest link of the inorganic kingdom; the lichen, which encrusts the stone, as but one link higher than the stone itself; the mushroom and the coral, as the connecting links between the vegetable and the animal; and the immense space, which separates man—the highest of the mam- malia—from his Maker, they have conceived to be occupied, in succession, by beings of gradually increasing intelligence. If, however, we investigate the matter minutely, we discover that many links of the chain appear widely separated from each other; vol. i. 2 14 NATURAL BODIES. and that, in the existing state of our knowledge, the catenation can- not be esteemed rigidly maintained." Let us inquire into the great characteristics of the different king- doms, and endeavour to describe the chief points in which living bodies differ from those that have never possessed vitality, and into the distinctions between organized bodies themselves. 1. DIFFERENCE BETWEEN INORGANIC AND ORGANIZED BODIES. Inorganic bodies possess the common properties of matter. Their elements are fixed, under ordinary circumstances. Their study con- stitutes Physics, in its enlarged sense, or Natural Science. Organized bodies have properties in common with the inorganic, but they have likewise others superadded, which control the first in a singular manner. They are beings, whose elements are undergoing constant mutation, and the sciences treating of their structure and functions are Anatomy and Physiology. They differ from each other in— 1. Origin.—Inorganic bodies are not born; they do not arise from a parent; they spring from the general forces of matter—-the par- ticles being merely in a state of aggregation, and their motions are regulated by certain fixed and invariable laws. The animal and the vegetable, on the other hand, are the products of generation; they must spring from beings similar to themselves, and they possess the principle of life, which controls the ordinary forces of matter. Yet it has been supposed that they are capable of creating life; in other words, that a particular organization presupposes life. This is not the place for entering into the question of generation. It will be sufficient at present to remark, that in the upper classes of animals, the necessity of a parent cannot be contested; the only difficulty that can possibly arise regards the very lowest classes, and analogy has appeared, in their case, to warrant the conclusion, that every living being must spring from an egg or a seed. 2. Shape.—The shape of inorganic bodies is not fixed in a deter- minate manner. It is true, that by proper management every mineral can be reduced to a primitive nucleus, which is the same in all minerals of like composition; still the shape of the mineral, as it presents itself to us, differs. Carbonate of lime, for example, although it may always be reduced to the same primitive nucleus, assumes various appearances; being sometimes rhomboidal; at others, in regular hexae'dral prisms; in solids, terminated by twelve scalene triangles, or in dodecaedrons, whose surfaces are pentagons. In organized bodies, on the contrary, the shape is constant. Each animal and vegetable has the one that characterizes its species, so that no possible mistake can be indulged; and this applies not only to the whole body, but to every one of its parts, numerous as they are. 3. Size.—The size of an inorganic body is by no means fixed. It * Fleming's Philosophy of Zoology, i. 4. Edinburgh, 1822. INORGANIC AND ORGANIZED. 15 may be great, or small, according to the quantity present of the par- ticles that have to form it. A crystal, for example, may be minute or the contrary, according to the number of saline particles in the solution. On the other hand, organized bodies attain a certain size, —at times by a slow, at others by a more rapid growth,—but in all cases the due proportion is preserved between the various parts,— between the stem and the root, the limb and the trunk. Each vege- table and each animal has its own size, by which it is known; and although we occasionally meet with dwarf or gigantic varieties, these are infrequent, and mere exceptions proving the position. 4. Chemical character.—Great difference exists between inor- ganic and organized bodies in this respect. In the mineral kingdom are found all the elementary substances, or those which chemistry, at present, considers simple, amounting to at least fifty-four, and comprising oxygen, hydrogen, boron, carbon, phosphorus, sulphur, selenium, iodine, fluorine, chlorine, bromine, azote, silicon, zirconium, thorinum, aluminum, yttrium, glucinum, magnesium, calcium, stron- tium, barium, sodium, potassium, lithium, manganese, zinc, iron, tin, arsenic, molybdenum, vanadium, tungsten, columbium, chromium, antimony, uranium, cerium, cobalt, titanium, bismuth, cadmium, copper, tellurium, lead, mercury, nickel, osmium, rhodium, silver, gold, platinum, palladium, and iridium.51 In the organized, a few only of these elements of matter are met with, viz. oxygen, hydro- gen, azote, carbon, sulphur, phosphorus, &c. In inorganic bodies, the composition is more simple; several consist of but one element; and, when composed of more, the com- bination is rarely higher than ternary. The organized body, on the other hand, is never simple, nor even binary. It is always at least ternary or quaternary.11 The simplest vegetable consists of a union of oxygen, carbon, and hydrogen; the simplest animal, of oxygen, hydrogen, carbon, and azote. The composition of the mineral, again, is constant. Its elements have entirely satisfied their affinities, and all remains at rest. In the organized kingdom, however, the affinities are not satisfied; com- pounds are formed to be again decomposed, and this happens from the earliest period of foetal formation till the cessation of life : all is in commotion, and the chemical character of the corporeal fabric is incessantly undergoing modification. In chemical nomenclature, the term element has a different accep- tation, according as it is applied to inorganic or organic chemistry. In the former, it means a substance, which, in the present state of the science, does not admit of decomposition. We say, " in the present state of the science," for several bodies, now esteemed a Chemistry, Meteorology, &c. By Wm. Prout, M. D., F. R. S. (Bridgewater Treatise.) Amer. edit. p. 73. Philad. 1834. b Allgemeine Anatomie des Menschlichen Korpers, von H. E. Weber, s. 66. Braun- schweig, 1830:—-being the first volume of the fourth edition of Weber's Hildebrandt's Handbuch der Anatomie des Menschen. 16 NATURAL BODIES. compound, were, not many years ago, classed amongst the simple, or elementary. It is not more than twenty-eight years since the alka- lies were found to be composed of two elements. Previously uiey were considered simple. In the animal and the vegetable, we nnd substances, also called elements, but with the epithet organic, because only found in organized bodies, and therefore the exclusive products of organization and life. For example, in both animals and vege- tables we meet with oxygen, hydrogen, carbon, azote, and different metallic substances: these are chemical or inorganic elements, and we further meet with albumen, gelatine, fibrine, ozmazome, &c. sub- stances, which constitute the various organs, and which, therefore, have been termed organic elements or compounds of organization; yet they are capable of decomposition, and in one sense, therefore, not elementary. In the inorganic body, all the elements, that constitute it, are formed by the agency of general chemical affinities; but, in the or- ganized, the formation is produced by the force, that presides oyer the formation of the organic elements themselves—the force of life. Hence, the chemist is able to recompose many of the inorganic bodies, whilst the products of organization and of life set his art at defiance. The different parts of an inorganic body enjoy an existence inde- pendent of each other; whilst those of the organized are materially dependent. No part can, indeed, be injured without the mass and the separated portion being more or less affected. If we take a piece of marble, which is composed of carbonic acid and of lime, and break it into a thousand fragments, each portion will be found to consist of carbonic acid and of lime. The mass will be destroyed, but the pieces will not suffer from the disjunction. They will continue as fixed and unmodified as at first. Not so with an organized body. If we tear the branch from a tree, the stem itself participates more or less in the injury; the detached branch speedily undergoes striking changes; it withers; becomes shrivelled, and, in the case of the succulent vegetable, undergoes decomposition; certain of its constituents, no longer held in control by the vital agency, enter into new combinations, are given off in the form of gas, and the remain- der sinks to earth. Changes, no less impressive, occur in the animal when a limb is separated from the body. The parent trunk suffers; the system re- coils at the first infliction of the injury, but subsequently arouses itself to a reparatory effort,—at times with such energy as to destroy its own vitality. The separated limb, like the branch, is given up, un- controlled, to new affinities; and putrefaction soon reduces the mass to a state in which its previously admirable organization is no lono-er perceptible. Some of the lower classes of animals may indeed be divided with impunity, and with no other effect than that of multiply- ing the animal in proportion to the number of sections, but these cases are exceptions; and we may regard the destructive process,__ set up when parts of organized bodies are separated,—as one of INORGANIC AND ORGANIZED. 17 the best modes of distinction between the inorganic and organized classes. 5. Texture.—In this respect the inorganic and organized differ considerably,—a difference which has given rise to their respective appellations. To the structure of the latter class only can the term texture be with propriety applied. If we examine a vegetable or animal substance with attention, we find, that it has a regular and determinate arrangement or structure; and we readily discover, that it consists of various parts;—in the vegetable, of wood, bark, leaves, roots, flowers, &c.; and in the animal, of muscles, nerves, vessels, &c.; all of which appear to be instruments or organs for specific purposes in the economy of the being. Hence the body is said to be organized, and the result, as well as the process, is often called organization. Properly, organiza- tion means the process by which an organized being is formed; organism, the result of such process, or the organic structure.* The particles of matter in an organized body, so far as we can detect them, constitute fibres, which interlace and intersect each other in all directions, and form a spongy areolar texture or tissue. (Fig. 1.) Of these tissues the various organs of the body are composed. In the inorganic substance the mass is homogeneous; the smallest parti- cle of marble consists of carbonic acid and lime; and all the particles concur alike in the formation and preservation of the body. Lastly, whilst an inorganic body, of a de- terminate species, has always a fixed compo- sition, the living being, although constituting a particular species, may present individual differences, giving rise, in the animal, to various temperaments, con- stitutions, &c. 6. Mode of preservation.—Preservation of the species is, in the or- ganized, the effect of reproduction. As regards individual preserva- tion, that of the mineral is dependent upon the same actions that effected its formation, on the persistence of the affinities of cohesion and combination, which united its various particles. The animal and the vegetable, on the other hand, are maintained by a mechanism peculiar to themselves. From the bodies surrounding them, they lay hold of nutritious matter, which, by a process of elaboration, they assimilate to their own composition; at the same time, they are constantly absorbing or taking up particles of their own struc- ture, and throwing them off. The actions of composition and de- composition are constant whilst life exists, although subject to par- ticular modifications at different periods of existence, and under different circumstances. » Rudiments of Physiology, by John Fletcher, M. D., F. R. C. S. E. Part I. p. 2. Edinburgh, 1835. 2* 18 NATURAL BODIES. Again:—the inorganic and organized are alike subject to changes during their existence; but the character of these changes, in tne two classes, differs essentially. The mineral retains its form, unless acted upon by some mechanical or chemical force. Within, all tne particles are at rest, and no internal force exists which can subJec£ them to modification. There is no succession of conditions which can be termed ages. How different is the case with organized bodies! Internally, there is no rest; from birth to death all is in a state of activity. The plant and the animal are subject to incessant changes. Each runs through a succession of conditions or ages. We see it successively develope its structure and functions, attain maturity, and finally decay. Characteristic differences likewise exist in the external conforma- tion of the beings of the two divisions, as well as in their mode of increase. Inorganic bodies have no covering to defend them, no exterior envelope to preserve their form: a stone, for example, is the same at its centre as at its circumference;—whilst organized bodies are protected by an elastic and extensible covering, differing from the parts beneath, and inservient to valuable purposes in the economy. Every change, to which an inorganic body is liable, must occur at its surface. It is there that the particles are added or abstracted when it experiences increase or diminution of size. This increase— for growth it can scarcely be termed—takes place by accretion or juxtaposition, that is, by the successive application of fresh particles upon those that form the primitive nucleus; and diminution in bulk is produced by the removal of the external layers or particles; but in organized substances, increase or growth is caused by particles deposited internally, and diminution by particles substracted from within. We see them, likewise, under two conditions, to which there is nothing similar in the mineral kingdom—health, and disease. In the former, the functions are executed with freedom and energy; in the latter, with oppression and restraint. 7. Termination.—Every body, inorganic or organized, may cease to exist, but the mode of cessation varies greatly in the two classes. The mineral is broken down by mechanical violence, or it ceases to exist, in consequence of modifications in the affinities, which held it concrete. It has no fixed duration, and its existence may be ter- minated at any moment, when the circumstances, that retained it in aggregation, are destroyed. The vegetable and the animal, on the other hand, can carry on their functions for a period only, which is fixed and determinate for each species. For a time, new particles are deposited internally. The bulk is augmented, and the external envelope distended, until maturity or full developement is attained; but, after this, decay commences; the functions are exerted with gradually diminishing energy; the fluids decrease in quantity; and the solids become more rigid,—circumstances premonitory of the total cessation of vitality. This term of duration is very different in different species. Whilst many of the lower classes of animals ANIMALS AND VEGETABLES. 19 and vegetables have but an ephemeral existence, some of the more elevated individuals of the two kingdoms outlive a century. 8. Motive forces.—Lastly, observation has satisfactorily proved, that there are certain forces which affect matter in general, the in- organic as well as the organized, but that, in addition to these, the organized possess a peculiar force or forces, which modify them in the most remarkable manner, Hence, we have general forces, and special or vital; the first acting upon all matter, the dead and the living, and including the forces of gravitation, cohesion, chemical affinity, &c.; the latter being exclusive to living beings. Such are the chief distinctions to be drawn between the two great divisions of natural bodies, the inorganic and the organized. By the comparison which has been instituted, the objects of physio- logy, the phenomena of life, have been indicated. To inquire into the mode in which a living being is born, nourished, reproduced, and dies, is the legitimate object of this science. We have, however, entered only into a comparison between the inorganic and the organized. The two divisions constituting this latter class differ also materially from each other. Into these differ- ences we shall now inquire. 2. DIFFERENCE BETWEEN ANIMALS AND VEGETABLES. The distinctions between these divisions of organized bodies are not so rigidly fixed, or so readily appreciated, as those we have just considered. There are certain functions possessed by each, and hence called vegetative, plastic, or organic—nutrition and reproduction for exam- ple ; but vegetables are endowed with these only. All organized bodies must have the power of assimilating foreign matters to their own substance, and of producing a living being similar to them- selves, otherwise the species, having a limited duration, would perish. In addition to these common functions, animals have two others, sensation and voluntary motion, by the possession of which they are said to be animated. Hence they are termed animals, and the con- dition is called animality. This division of the functions into animal and organic has been adopted, with more or less modification, by the generality of physiologists. Between animals and vegetables, that are situate high in their respective classes, no error can possibly be indulged. The charac- ters are obvious at sight. No one can confound the horse with the oak, the butterfly with the potato. It is on the lower confines of the two kingdoms that we are liable to be deceived. Many of the zoophytes have alternately been considered vegetable and animal; and it is not until of modern date that the sponge has been almost uni- versally elevated to that kingdom to which it is entitled. Nor is this to be wondered at. In its attachment to the rock, it is as immova- ble as the lichen is to the slate, and almost equally deficient in the usual characteristics of animality. In general, however, we are 20 NATURAL BODIES. able to classify any doubtful substance with accuracy, and the fol- lowing are the principal points of difference. 1. Composition.—The essential elements of organized matter are, carbon, oxygen, hydrogen, and azote, with alkaline and earthy salts, variously combined. Vegetables consist of the three first of these elements, carbon, oxygen, and hydrogen. Azote is possessed in addition by the animal; yet there are many animal substances that contain no azote. Plants have scarcely any; and generally, when it is ""met with in them, it is found in some part,—scarcely ever dis- tributed through the whole. In the fungi, traces of a vegeto-animal matter have been detected by the chemist, but they have only been traces. In consequence of this difference of composition, animal substances are easily known from vegetable by burning;—a fact, which, as Dr. Fleming3 has remarked, is interesting to the young naturalist, if uncertain to which kingdom to refer any substance met with in his researches. The smell of a burnt sponge, of coral, or other zoophytic animal, is so peculiar, that it can scarcely be mis- taken for that of a vegetable body in combustion. 2. Texture.—In this respect, important differences are observable. Both animals and vegetables consist of solid and fluid parts. In the former, however, the fluids bear a large proportion: in the latter, the solids. This is the cause why decomposition occurs so much more rapidly in the animal than in the vegetable, and in the succulent than in the dry vegetable. If we analyze the structure of the vege- table, we cannot succeed in detecting more than one elementary tissue, which is vesicular, or arranged in areolae or vesicles, and ap- pears to form every organ of the body, whilst, in the animal, we discover at least three of these anatomical elements, the cellular— analogous to that of the vegetable—the muscular, and the nervous. The vegetable again has no great splanchnic cavities containing the chief organs of the body. It has a smaller number of organs, and none that are destined for sensation or volition; in other words, no brain, no nerves, no muscular system; and the organs of which it consists, are simple, and readily convertible into each other. This is not the case with the animal. But these differences in organization, striking as they may appear, are not sufficient for rigid discrimination, as they are applicable only to the upper classes of each kingdom. In many vegetables, the fluids appear to preponderate over the solids; numerous animals are de- void of muscular and nervous tissues, and apparently of vessels, and distinct organs; whilst MM. Dutrochet,b Brachet,c and others/1 admit the existence of a rudimental nervous system even in vegetables. * Philosophy of Zoology, i. 41, Edinburgh, 1822, and Sir J. E. Smith's Introduction to Botany, 7th edit, by Sir W. J. Hooker, p. 3. Lond. 1833. b Recherches Anatomiques et Physiologiques sur la Structure Intime des Animaux et des Veg6taux, et sur leur Motilite. Paris, 1824. ' <= Recherches Experimentales sur les Fonctions du Systeme Nerveux Ganalionaire &c. Paris, 1830. " ' <* Sir J. E. Smith, Op. citat. p. 40. ANIMALS AND VEGETABLES. 21 3. Sensation and voluntary motion.—One manifest distinction exists between animals and vegetables. Whilst the latter receive their nutrition from the objects situate around them—irresistibly and without volition, or the participation of mind—and whilst the func- tion of reproduction is effected without the union of the sexes; voli- tion and sensation are both necessary for the nutrition of the former, and for the acts requisite for the reproduction of the species. Hence, the necessity of two faculties or functions in the animal, which are wanting in the vegetable, viz. sensibility, or the faculty of conscious- ness and feeling; and motility, or the power of moving the whole body or any of its parts at the will of the being. Vegetables are possessed of spontaneous, but not of voluntary motion. Of the former we have numerous examples in the direction of the branches and upper surfaces of the leaves, although repeatedly disturbed, to the light; and in the unfolding and closing of flowers, at stated periods of the day. This, however, is quite distinct from the sensibility and motility that characterize the animal. By sensibility man feels his own existence,—becomes acquainted with the universe,—appre- ciates the bodies that compose it, and experiences all the desires and inward feelings that solicit him to the performance of those external actions, which are requisite for his preservation, as an individual, and as a species; and by motility he executes those external actions which his sensibility may suggest to him. By some naturalists it has been maintained, that those plants, which are borne about on the waves, and fructify in that situation, exhibit to us examples of the locomotility, which is described as characteristic of the animal. One of the most interesting novelties, in the monotonous occurrences of a voyage across the Atlantic to- wards the Gulf of Florida, is the almost interminable quantity of the Fucus natans, Florida weed or Gulf weed, with which the surface of the ocean is covered. But how different is this motion from the locomotility of animals! It is a subtlety to conceive them identical. The weed is passively and unconsciously borne whithersoever the winds and the waves may urge it, whilst locomotion requires the direct agency of volition, of a nervous system that can excite, and of muscles that can act under such excitement. The spontaneity and perceptivity of plants, as they have been termed, must also be explained in a different manner from the ele- vated function of sensibility on which we shall have to dwell. These properties must be referred to the fact of certain vegetables being possessed of the faculty of contracting on the- application of a stimulus, independently of sensation or consciousness. If we touch the leaf of the sensitive plant, Mimosa pudica? the various leaflets collapse in rapid succession. In the barberry bush, Berberis vulga- ris, we have another example of the possession of this faculty. In the flower, the six stamens, spreading moderately, are sheltered under the concave tips of the petals, till some extraneous body, as a Mayo's Outlines of Human Physiology, 4th edition, p. 11. London, 1837. 22 NATURAL BODIES. the feet or trunk of an insect in search of honey, touches thesinner part of each filament, near the bottom. The susceptibility oi this part is such, that the filament immediately contracts, and stipes us anther, full of pollen, against the stigma. Any other part ot tne nia- ment may be touched without this result, provided no concussion be given to the whole. After a while, the filament retires gradually and may be again stimulated, and when each petal, with its annexed filament, has fallen to the ground, the latter, on being touched, shows as much sensibility as ever.a These singular effects are produced by the power of contractility or irritability, the nature of which will fall under consideration here- after. It is possessed equally by animals and vegetables, and is essentially organic and vital. This power, we shall see, needs not the intervention of volition: it is constantly exerted in the animal without consciousness, and therefore necessarily without volition. Its existence in vegetables does not, consequently, demonstrate that they are possessed of consciousness. 4. Nutrition.—A great difference exists between plants and ani- mals in this respect. The plant, being fixed to the soil, cannot search after food. It must be entirely passive, and obtain its supplies from the materials around, and in contact with it; and the absorbing vessels of nutrition must necessarily open on its exterior. In the ani- mal, on the other hand, the aliment is scarcely ever found in a state fit for absorption: it is crude, and in general—Ehrenbergb thinks always—requires to be received into a central organ, or stomach, for the purpose of undergoing changes, by a process termed digestion, which adapts it for the nutrition of the individual. The absorbing vessels of nutrition arise, in this case, from the internal or lining membrane of the alimentary tube. The analogy, however, that exists between these two kinds of absorption is great, and had not escaped the attention of the ancients :—" Quemadmodum terra arboribus, ita animalibus ventriculus sicut humus," was an aphoristic expression of universal reception. With similar feelings, Boerhaave asserts, that animals have their roots of nutrition in their intestines; and Dr. Alston0 has fancifully termed a plant an inverted animal.A Again, in both plants and animals the residue of the matters ab- sorbed is ejected from the body; but the form and character of the rejected portion vary in the two kingdoms. In the plant, the super- fluous quantity is thrown off in gaseous, hydrogenated, or aqueous exhalations: in the animal, the useless portion is excreted, or rejected as excrement, of which azote is a constituent. After all, the most essential difference consists in the steps that a Sir J. E. Smith's Introduction to Botany, p. 325. b See Dr. Gairdner's account of Ehrenberg's Researches, in Edinb. New Philosophi- cal Journal for Sept. 1831; and ibid, for Jan. 1838, p. 232; also Dr. Southwood Smith's Philosophy of Health, vol. i. p. 35, London, 1835; and M. Meyen on the Digestive Or- gans of Infusoria, abridged in Lond. Lancet, May 16, 1840, p. 287. c Tirocinium Botanicum Edinburgense, 8vo. Edinb. 1753. d Fletcher's Rudiments of Physiology, Part II. a. p. 9. Edinb. 1836; and Rullier art. Accroissement, Diet, de Med.; torn, i, Paris, 1821. ANIMALS AND VEGETABLES. 23 are preliminary to the reception of food. These, in the animal, are voluntary,—requiring prehension, often locomotion, and always con- sciousness. 5. Reproduction.—In this function we find a striking analogy be- tween animals and vegetables; but differences exist, which must be referred to the same cause, that produced many of the distinctions already pointed out—the possession, by the animal, of sensibility and locomotility. For example, every part of the generative act is, in the vegetable, without the perception or volition of the being:— the union of the sexes, fecundation, and the birth of the new indivi- dual are alike automatic. In the animal, on the other hand, the approximation of the sexes is always voluntary, and effected con- sciously—the birth of the new individual being not only perceived, but somewhat aided by volition. Fecundation alone is involuntary and irresistible. Again, in the vegetable the sexual organs do not exist at an early period, and are not developed until reproduction is practicable. They are capable of acting for once only, and perish after fecun- dation ; and if the plant be vivacious, they fall off after each repro- duction, and are annually renewed. In the animal, on the contrary, they exist from the earliest period of foetal developement, survive repeated fecundations, and continue during the life of the individual. Lastly, the possession of sensibility and locomotility leads to other characteristics of animated beings. These functions are incapable of constant, unremitting exertion. Sleep, therefore, becomes neces- sary. The animal is also capable of expression or of language, in a degree proportionate to the extent of his sensibility, and of his power over the beings that surround him. But these differences in function are not so discriminative as they may at first appear. There are many animals, which are as irre- sistibly attached to the soil as the vegetables themselves. Like the latter, they must, of necessity, be compelled to absorb their food in the state in which it is presented to them. Sensibility and locomo- tility appear, in the zoophyte, to be no more necessary than in the vegetable. No nervous, no muscular system is required ; and, ac- cordingly, none can be traced in them; whilst many of those spon- taneous motions of the vegetable, which have been described, have been considered by some to indicate the first rudiments of sensibility and locomotility: and Linnaeus1 has regarded the closure of the flowers towards night as the sleep, and the movements of vegeta- bles, for the approximation of the sexual organs, as the marriage of plants.b a Amoenit. Academ.; torn. iv. b See, also, on the differences between Animals and Vegetables, Lepelletier, Physio- logie Medicale, &c. i. 34, Paris, 1831; Tiedemann, Traite Complet de Physiologie de l'Homme, traduit par A. J. L. Jourdan, i. 166, Paris, 1831; Willis, in art. Animal, of Cyclopasdia of Anatomy and Physiology, Part II. Lond. 1835; Southwood Smith's Philosophy of Health, Part I. chap. i. Lond. 1835 ; Virey, Philosophic de l'Histoire Naturelle, &c. p. 253, Paris, 1835; Weber, loc. citat.; Midler's Handbuch der Phy- siologie des Menschen, Coblenz, 1835, 1837, or Baly's translation, Part I. p. 40, Lond. 1837; and Dr. W. B. Carpenter's Principles of General and Comparative Physiology, Introduction, Lond. 1839. , 24 MATERIAL COMPOSITION OF MAN. II. GENERAL PHYSIOLOGY OF MAN. The observations made on the difference between animals and vegetables have anticipated many topics, which would require con- sideration under this head. Those general properties, which man possesses along with other animals, have been referred to in a cur- sory manner. They will now demand a more special investigation. 1.--ON THE MATERIAL COMPOSITION OF MAN. The detailed study of human organization is the province of the anatomist,—of its intimate composition, that of the chemist. In ex- plaining the functions executed by the various organs, the physio- logist will frequently have occasion to trench upon both of these departments. The bones, in the aggregate, form the skeleton. The base of this skeleton is a series of vertebrae, with the skull as a capital—itself regarded as a vertebra by De Blainville. This base is situate on the median line through the whole trunk, and contains a cavity, in which are lodged the brain and spinal marrow. On each side of this, other bones are arranged in pairs, which by some have been called appendices. Upon the skeleton are placed muscles, for moving the different parts of the body, and for changing its situation with regard to the soil. The body is again divided into trunk and limbs. The trunk, which is the principal portion, is composed of three splanchnic cavities, situate one above the other—the abdomen, thorax, and head. These contain the most important organs of the body—those that effect the functions of sensibility, digestion, respi- ration, circulation, &c. The head comprises the face, which con- tains the organs of four of the senses—those of sight, hearing, smell, and taste,—and the cranium, which lodges the brain—the organ of the mental manifestations, and the most elevated part of the nervous system. The thorax or chest contains the lungs—organs of respira- tion—and the heart, the great organ of the circulation. The abdomen contains the principal organs of digestion, and (if we include in it the pelvis,) those of the urinary secretion and of generation. Of the limbs, the upper, suspended on each side of the thorax, are instruments of prehension, and are terminated by the hand, the great organ of touch. The lower are situate beneath the trunk, and are agents for supporting the body, and for locomotion. Vessels, emanating from the heart, are distributed to every part; conveying to them the5blood necessary for their vitality and nutrition: these are the arteries. Other vessels communicate with them, and convey the blood back to the heart—the veins; whilst a third set communicate also with the arteries, and convey into the circulation, by a particular channel a fluid called lymph—whence they derive the name of lymphatics Nerves, communicating with the great central masses of the nervous system, are distributed to every part to complete their vitality • and lastly, a membrane or layer, possessed of acute sensibility—the skin —serves as an outer envelope to the whole body. MATERIAL COMPOSITION OF MAN. 25 It has been already remarked, that the animal body consists essentially of four ultimate elements—oxygen, hydrogen, carbon, and azote. This is correct as a general principle; but organic chemistry has shown us, that some of the constituents afford little or no traces of azote. It was likewise observed, that two kinds of elements enter into the composition of the body—the chemical or inorganic, and the organic, which are compound, and formed only under the principle of life. The chemical or inorganic elements, met with, are—oxygen, hy- drogen, carbon, azote, phosphorus, calcium; and, in smaller quantity, sulphur, iron, manganese, silicium, chlorine; also, sodium, magne- sium, &c. 1. Oxygen.—This is widely distributed in the solids and fluids, and a constant supply of it from the atmosphere is indispensable to animal life. It is almost always found combined with other bodies, often in the form of carbonic acid—that is, united with carbon. In a separate state it is met with in the air-bag of fishes, in which it is found varying in quantity, according to the species, and the depth at which the fish has been caught. 2. Hydrogen.—This gas occurs universally in the animal kingdom. It is a constituent of all the fluids, and of many of the solids; and is generally in a state of combination with carbon. In the human in- testines it has been found pure, as well as combined with carbon and sulphur. 3. Carbon.—This substance is met with under various forms, in both fluids and solids. It is most frequently found under that of car- bonic acid. Carbonic acid has been detected in an uncombined state in urine, by Proust, and by Vogel1 in the blood. It likewise exists in the intestines of animals; but it is chiefly met with in ani- mal bodies, in combination with the alkalies or earths; and is emitted by all animals in the act of respiration. 4. Azote.—This gas is likewise widely distributed as a component part of animal substances. Indeed, so generally does it prevail, that it often affords a distinctive mark by which they may be known from vegetables. It likewise occurs, in an uncombined state, in the swimming bladder of certain fishes. 5. Phosphorus is found united with oxygen—in the state of phos- phoric acid—in many of the solids and fluids. This is the acid, that is combined with the earthy matter of bones, and with potassa, soda, ammonia, and magnesia, in other parts. It is supposed to give rise to the luminousness of certain animals—as of the firefly, the Pyro- soma atlanticum, &c.—but nothing precise is known on this subject. 6. Calcium.—This metal is found only in the state of oxide or lime in the animal economy; and it is generally united with the phosphoric or carbonic acid. It is the earth, of which the hard parts of animals are constituted. 7. Sulphur is not met with extensively in the animal solids or * Annals of Philosophy, vii. 56. VOL. I. 3 26 MATERIAL COMPOSITION OF MAN. fluids; nor is it ever found free, but always in combination with oxygen, united to soda, potassa, or lime. It seems to be an invaria- ble concomitant of albumen, and is found in the lower part of the intestines, in the form of sulphuretted hydrogen gas; and as an emanation from fetid ulcers. 8. Iron.—This metal has been detected in the colouring matter of the blood; in bile, and in milk. For a long time it was considered to be, in the first of these fluids, in the state of phosphate or sub- phosphate. Berzelius,* however, showed, that this was not the case; that the ashes of the colouring matter always yielded oxide of iron in the proportion of l-200th of the original mass. That distinguished chemist was, however, unable to detect the condition in which the metal exists in the blood, and could not discover its presence by any of the liquid tests. More recently, Engelhart,b a German chemist, has shown that the fibrine and albumen of the blood, when carefully separated from colouring particles, do not contain a trace of iron; whilst he could procure it from the red globules by incineration. He also succeeded in proving its existence in the red globules by liquid tests, and his experiments have been repeated, with the same results, by Rose of Berlin.0 In milk, iron seems to be in the state of phosphate. 9. Manganese has been found in the state of oxide, along with iron, in the ashes of the hair. 10. Copper and lead.—It was conceived by Devergie, that copper i and lead may exist naturally in the tissues; but a commission of the Academie Royale de Medecine of Paris was unable to confirm the opinion in regard to the existence of copper ; and the results of the investigations of Professor F. de Cattanei di Momo,d of Pa via, seem to prove the non-existence of lead also. 11. Silicium.—Silica is found in the hair, urine, and in urinary calculi. 12. Chlorine.—In combination with hydrogen, and forming mu- riatic acid, chlorine is met with in most of the animal fluids. It is generally united with soda. Free muriatic acid has also been found by Proute in the stomach of the rabbit, hare, horse, calf, and dog; and he has discovered the same acid in the sour matter ejected from the stomachs of those labouring under indigestion. Mr. Children has made similar observations, and Messrs. Tiedemann and Gmelin/ Professor Emmet, and the authors found it in considerable quantity, in the healthy gastric secretions of man. a Medico-Chirurgical Transact, vol. iii. b Commentatio de Vera Materia? Sanguini Purpureum Colorem Impertientis Natura. Gotting. 1825. c Turner's Chemistry, fifth ed. p. 963, Lond. 1834. a Annali Universali di Medicina, Aprile, 1840; and British and Foreign Medical Review, Jan. 1841, p. 226. e Philosoph. Transact, for 1824, p. 45. f Recherches Experimentales, &c. sur la Digestion, trad, par A.G. L. Jourdan Art 4, p. 94, Paris, 1827. s See under the head of " Digestion," and the author's Elements of Hygiene p 222 Philadelphia, 1835. J& ' *' ' ORGANIC ELEMENTS. 27 13. Sodium.—The oxide of sodium, soda, forms a part of all the fluids. It has never been discovered in a free state, but is united, (without an acid,) to albumen. Most frequently, it is combined with the muriatic and phosphoric acids; less so, with the lactic, carbonic, and sulphuric acids. 14. Potassium.—The oxide, potassa, is found in many animal fluids, but always united with acids—the sulphuric, muriatic, phos- phoric, &c. It is much more common in the vegetable kingdom, and hence one of its names—vegetable alkali. 15. Magnesium.—The oxide, magnesia, exists sparingly in bones, and in some other parts, but always in combination with the phos- phoric acid. The Organic Elements, proximate principles or compounds of organization are the primary combination of two or more of the elementary substances, in definite proportions. Formerly, four only were admitted—gelatine, fibrine, albumen, and oil. Of late, how- ever, organic chemistry has pointed out numerous others, which are divided into two classes—first, those that contain azote, as albumen, gelatine, fibrine, ozmazome, mucus, caseine, urea, uric acid, the red colouring principle of the blood, the yellow colouring principle of the bile, &c; and secondly, those that do not contain azote, as oleine, stearine, the fatty matter of the brain and nerves, the acetic, oxalic, benzoic, and lactic acids, the sugar of milk, sugar of diabetes, picromel, the colouring principle of the bile, and that of other solids and liquids. a. Organic Elements that contain Azote, 1. Albumen.—This is one of the most common organic constitu- ents, and appears under two forms—liquid and concrete. In its purest state, the former is met with in the white of egg—whence its name;—in the serum of the blood, the lymph of the absorbents, the serous fluid of the great splanchnic cavities and of the cellular mem- brane, and in the synovial secretion. It is colourless and transparent, without smell or taste, and is coagulated by acids, alcohol, ether, metallic solutions, infusion of galls, and by a temperature of 165° Fahrenheit. It is excreted by the kidneys in large quantities, in the disease, which, owing to its presence in the urine, has been called Albuminuria. Concrete, coagulated or solid albumen is white, tasteless, and elas- tic; insoluble in water, alcohol, or oil, but readily soluble in alkalies. Albumen is always combined with soda. It exists, in abundance —both liquid and concrete—in different parts of the animal body. Hair, nails, and horn consist of it; and it is, in some form or other, the great constituent of many tumours. 2. Gelatine.—This is the chief constituent of the cellular tissue, skin, tendons, ligaments, and cartilages. The membranes and bones also contain a large quantity of it. It is obtained by boiling 2S MATERIAL COMPOSITION OF MAN. these substances for some time in water; clarifying the concen- trated solution; allowing it to cool, and drying the substance, thus obtained, in the air. In this state it is called glue; in a more liquid form, jelly. Gelatine dissolves readily in hot water: it is soluble in acids and alkalies; insoluble in alcohol, ether, and in the fixed and volatile oils. Alcohol precipitates it from its solution in water. Gelatine, nearly in a pure state, forms the air-bag of different kinds of fishes, and is well known under the name of isinglass. It is used also extensively in the arts, under the forms of glue and she, on account of its adhesive quality. What is called portable soup is dried jelly, seasoned with various spices. 3. Fibrine.—This proximate principle exists in the chyle; enters into the composition of the blood; forms the chief part of muscular flesh, and may be looked upon as one of the most abundant animal substances. It is obtained by beating the blood, as it issues from a vein, with a rod. The fibrine attaches itself to each twig in the form of red filaments, which may be deprived of their colour by repeated washing with cold water. Fibrine is solid, white, flexible, slightly elastic, insipid, inodorous, and heavier than water. It is neither soluble in water, alcohol, nor acids; it dissolves in liquid potassa or soda, in the cold, without much change, but, when warm, becomes decomposed. Fibrine constitutes the buffy coat of blood; alone, or associated with albumen, it is thrown out from the blood-vessels, as a secretion, in many cases of inflammation, becoming subsequently organized, or penetrated by blood-vessels and nerves. 4. Osmazome.—This is the matiere extinctive du bouillon, extrac- tive, and saponaceous extract of meat.—When flesh, cut into small fragments, is macerated in successive portions of cold water, the albumen, osmazome, and salts are dissolved; and, on boiling the so- lution, the albumen is coagulated. From the liquid remaining, the osmazome may be procured in a separate state, by evaporating to the consistence of an extract, and treating it with cold alcohol. This substance is of a reddish brown colour, and is distinguished from the other animal principles by solubility in water and alcohol—whether cold or at the boiling point—and by not forming a jelly when its solution is concentrated by evaporation. Osmazome exists in the muscles of animals, in the blood, and in the brain. It gives the peculiar flavour of meat to soups; and, ac- cording to Fourcroy,a the brown crust of roast meat consists of it. 5. Mucus.—This term has been applied to various substances; and hence the discordant characters ascribed to it. Applying it to the fluid secreted by mucous surfaces, it varies somewhat according to the source whence it is derived. Its leading characters may be exemplified in that derived from the nostrils, which has the follow- ing properties: it is insoluble in alcohol and water, but imbibes a » System of Chemical Knowledge, &c. by W. Nicholson, vol. ix. Lond. 1804, ORGANIC ELEMENTS. 29 little of the latter, and becomes transparent; it is neither coagulated by heat, nor rendered horny; but is coagulated by tannin. Mucus, in a liquid state, serves as a protecting covering to dif- ferent parts. Hence it differs somewhat in its characters, according to the office it has to fulfil. When inspissated, it forms, according to some, the minute scales that are detached from the surface of the body by friction, corns, and the thick layers of the soles of the feet, the nails, and horny parts; and it is contained in considerable quantity in hair, wool, feathers, scales of fishes, &c. 6. Caseum or Caseine or Caseous matter.—This substance exists only in milk, and is the basis of cheese. To obtain it, milk must be left at rest, at the ordinary temperature, until it is coagulated; the cream that collects on the surface must be taken off; the clot well washed with water, drained upon a filter, and dried. The residuum is pure caseum. It is a white, insipid, inodorous substance, insoluble in water, but readily soluble in the alkalies, especially in ammonia. It possesses considerable analogy with albumen. Proust ascribes the characteristic flavour of cheese to the presence of the caseate of ammonia. 7. Urea.—This proximate principle exists in the urine of the mammalia when they are in a state of health. In human urine it is less abundant after a meal, and it nearly disappears in diabetes, and in affections of the liver. It is obtained by evaporating urine to the consistence of syrup. The syrup is then treated with four parts of alcohol, which are afterwards volatilized by heating the alcoholic extract. The mass, that remains, is dissolved in water, or rather in alcohol, and crystallized. The purest urea that has been obtained assumes the shape of acicular prisms, similar to those of the muriate of strontian. It is colourless, devoid of smell, or of action on blue vegetable colours, transparent, and somewhat hard. Its taste is cool, slightly sharp, and its specific gravity greater than that of water. 8. Uric or lithic acid.—This acid is found in the urine of man, birds, serpents, tortoises, crocodiles, lizards, in the excrements of the silk-worm, and very frequently in urinary calculi. It is obtained by dissolving any urinary calculus which contains it, or the sedi- ment of human urine, in warm liquid potassa, and precipitating the uric acid by the muriatic. Pure uric acid is white, tasteless, and inodorous. It is insoluble in alcohol, and is dissolved very sparingly by cold or hot water, requiring about 10,000 times its weight of that fluid, at 60° of Fahrenheit, for solution. The xanthic acid, found by Marcet in urinary calculi, seems to have been this acid. 9. Red colouring principle of the blood.—It has been already ob- served that Engelhart and Rose, German chemists, had detected iron in the red globules of the blood, and had not found it in the other principles of that fluid. It has been considered probable, there- fore, that it has something to do with the colour. Engelhart's ex- periments have not, however, determined the manner in which it 3* 30 MATERIAL COMPOSITION OF MAN. acts, nor in what state it exists in the blood. The sulphocyanic acid which is found in the saliva, forms, with the peroxide of iron, a colour exactly like that of venous blood; and it is possible that the colouring matter may be a sulpho-cyanate of iron. To obtain the red colouring matter, allow the crassamentum or clot, cut into thin pieces, to drain as much as possible on bibulous paper, triturating it with water and then evaporating the solution, at a temperature not exceeding 122° of Fahrenheit. When thus prepared the colouring particles are no longer of a bright red colour, and their nature is somewhat modified, in consequence of which they are insoluble in water. When half dried, they form a brownish-red, granular, friable mass; and, when completely dried, at a temperature between 167° and 190°, the mass is tough, hard, and brilliant. 10. Yellow colouring principle of the bile.—This substance is pre- sent in the bile of nearly all animals. It enters into the composition of almost all gall-stones, and is deposited in that organ under the form of magma. It is solid, pulverulent when dry, insipid, inodorous, and heavier than water. When decomposed by heat it yields car- bonate of ammonia, charcoal, &c. It is insoluble in water, in alcohol, and the oils, but is soluble in the alkalies. b. Organic Elements that do not contain Azote.3, 1. Oleine and Stearine.—Fixed oils and fats are not pure proxi- mate principles, as was at one time supposed. They consist of two substances, one of which is solid at the ordinary temperature of the atmosphere, and the other fluid: the former of these is called Stearine, from tfrsap, suet, the latter Elaine, or Oleine from sXaiov, oil. Stearine is the chief ingredient of vegetable and animal suet, of fat and butter, and is found, although in small quantity, in the fixed oils. In the suety bodies, it is the cause of their solidity. Elaine and stearine may be separated from each other by exposing fixed oil to a low temperature, and pressing it, when congealed, between folds of bibulous paper. The stearine is thus obtamed in a separate form, and by pressing the bibulous paper under water, an oily matter is procured, which is elaine in a state of purity. 2. Fatly matter of the Brain and Nerves.—Vauquelinb found two varieties of fatty matter in the brain,—the one white, the other red, the properties of which have not been fully investigated. Both pos- sess the property of giving rise to phosphoric acid by calcination, without there being any evidence of an acid, or a phosphate in their composition. They may be obtained by repeatedly boiling the cere- bral substance in alcohol, filtering each time, mixing the various liquors, and suffering them to cool:—a lamellated substance is de- posited, which is the white fatty matter. By then evaporating the alcohol, which still contains the red fatty matter and osmazome, to a Thenard, Traite de Chimie, torn. v. Paris, 1824. t> Annales de Chim. lxxxi. 37 ORGANIC ELEMENTS. 31 the consistence of bouillie, and exposing this, when cold, to the action of alcohol, the osmazome is entirely dissolved, whilst the alcohol takes up scarcely any of the red fatty matter. 3. Jlcelic acid.—This acid exists in a very sensible manner in the sweat, urine, and in milk—even when entirely sweet. It, or the lactic acid, is formed in the stomach in indigestion; has been found by Professor Emmet and the author3 to be contained in the gastric se- cretions in health, and is one of the constant products of the putrid fermentation of animal or vegetable substances. It is the most preva- lent of the vegetable acids, and the most easily formed artificially. 4. Oxalic acid.—This acid,—which exists extensively in the vege- table kingdom, but always united with lime, potassa, soda, or oxide of iron,—is only found as an animal constituent in certain urinary calculi, combined with lime. 5. Benzoic acid.—This acid, found in many individuals of the vegetable kingdom, is likewise met with in the urine of the horse, cow, camel, rhinoceros; and sometimes in that of man, especially of children. 6. Lactic acid.—The acid of milk is met with in the blood, gastric juice, urine, milk, marrow, and also in muscular flesh. Sometimes it is in a free state, but usually united with the alkalies. However much it may be concentrated, it does not crystallize, but remains under the form of syrup or extract. When cold it is tasteless, but when heated has a sharp acid taste. 7. Sugar of milk.—This substance, which is so called because it has a saccharine taste, and exists only in milk, differs from ordinary sugar in not fermenting. It is obtained by evaporating whey, formed during the making of cheese, to the consistence of honey; allowing the mass to cool, dissolving it, clarifying, and crystallizing. It com- monly crystallizes in regular parallelopipedons, terminated by pyra- mids with four faces. It is white, semitransparent, hard, and of a slightly saccharine taste. 8. Sugar of diabetes.—In the disease, called diabetes mellitus, the urine, which is passed in enormous quantity, contains, at the expense of the economy, a large amount of peculiar saccharine matter, which, when properly purified, appears identical, both in properties and composition, with vegetable sugar, approaching nearer to the sugar of grapes than to that of the cane. It is obtained in an irre- gularly crystalline mass, by evaporating diabetic urine to the con- sistence of syrup, and keeping it in a warm place for several days. It is purified, by washing in cold, or, at the most, gently heated alcohol, till the liquor comes off colourless, and then dissolving it in hot alcohol. By repeated crystallization it is thus rendered pure.b In the notes of two cases of diabetes mellitus now before us, we find that sixteen ounces of the urine of one of the patients, of the specific gravity 1.034, afforded a straw-coloured extract, which, when cold and consolidated, weighed one ounce and five drachms. The same 1 Elements of Hygiene, p. 222. b Prout, Medico-Chirurg* Transact, viii. 538. 32 MATERIAL COMPOSITION OF MAN. quantity of the urine of the other patient, specific gravity 1.040, yielded one ounce and seven drachms. Neither extract appeared to contain urea when nitric acid was added, but when a portion was dissolved in water, and subjected to a temperature of 212 , traces of ammonia were manifested on the vapour being presented to the fumes of muriatic acid. From this a conclusion was drawn that urea was present, as it is the only known animal matter, which is decomposed by the heat of boiling water. During a little more than one month, the subject of the latter case passed about four hundred and eighty pints of urine, or about seventy-five pounds troy of dia- betic sugar! 9. Picromel.—Thenard* discovered this principle in the bile of the ox, sheep, dog, cat, and of several birds; Chevallier, in that of man. To obtain it, the acetate of lead of commerce must be added to bile until there is no longer any precipitate. By this means, the yellow matter of the bile and the whole of the fatty matter are thrown down, united with the oxide of lead; the phosphoric acid of the phosphate of soda, and the sulphuric acid of the sulphate of soda, are likewise precipitated. The picromel may then be thrown down from the filtered liquor by the subacetate of lead. The precipitate, which is a combination of picromel with oxide of lead, must now be washed and dissolved in acetic acid. Through this solution, sul- phuretted hydrogen is passed to separate the lead; the solution is then filtered, and the acetic acid driven off by evaporation. Pure picromel is devoid of colour, and has the same appearance and consistence as thick turpentine. Its taste is at first acrid and bitter, but afterwards sweet. Its smell is nauseous, and its specific gravity greater than that of water. When digested with the resin of the bile, a portion of the latter is dissolved, and a solution is ob- tained, which has both a bitter and a sweet taste, and yields a pre- cipitate with the subacetate of lead and the stronger acids. This is the compound that causes the peculiar taste of the bile. 10. Colouring principle of the fo7e.—Of the nature of this principle, which exists in the bile of different animals, we have no definite ideas. It is generally precipitated along with the fatty matter; and, by means of ether which dissolves it, may be obtained pure. The colouring principles of other parts of animals are not suffi- ciently known to admit of classification. These inorganic and organic elements, variously combined and modified by the vital principle, constitute the different parts of the animal fabric. Chemistry, in its present improved condition, enables us to separate them, and to investigate their properties; but all the information we derive from this source relates to bodies, which have been influenced by the vital principle, but are no longer so; and in the constant mutations that are occurring in the system whilst life exists, and under its controlling agency, the same textures mio-ht exhibit very different chemical characteristics, could our researches ■ Memoir. d'Arcueil, i. 23, and Traite de Chimie, torn, iii SOLID PARTS. 33 be directed to them under those circumstances. Wrhenever, there- fore, the physiologist has to apply chemical elucidations to opera- tions of the living machine, he must recollect, that all his analogies are drawn from dead matter—a state so widely differing from the living as to suggest to him the necessity of a wise and discriminating caution.* The components of the animal body are invariably found under two forms—solids and fluids. Both of these are met with in every animal, the former being derived from the latter; for, from the blood every part of the body is separated; yet they are mutually dependent, for every liquid is contained in a solid. The blood itself circulates in a solid vessel: both, too, possess an analogous composition, are in constant motion, and are incessantly converted from one into the other. Every animal consists of a union of the two, and this union is indispensable to life. Yet certain vague notions, with regard to their relative preponderance in the economy, and to their agency in the production of disease, have lead to very discordant doctrines of pathology,—the solidisls believing, that the cause of most affections is resident in the solids; the humorists, that we are to look for it in the fluids. In this, as in similar cases, the mean will lead to the most rational result. The causes of disease ought not to be sought in the one or the other exclusively. c. Of the Solid Farts of the Human Body. A solid is a body, whose particles adhere to each other, so that they will not separate by their own weight, but require the agency of some extraneous force to effect the disjunction. Anatomists re- duce all the solids of the human body to twelve varieties: bone, car- tilage, muscle, ligament, vessel, nerve, ganglion, follicle, gland, mem- brane, cellular membrane, and viscus. J. Bone is the hardest of the solids. It forms the skeleton—the levers for the various muscles to act upon, and serves for the pro- tection of important organs. 2. Cartilage is of a white colour, formed of very elastic tissue, covering the articular extremities of bones to facilitate their move- ments ; sometimes added to bones to prolong them, as in the case of the ribs; at others, placed within the articulations, to act as elastic cushions; and, in the foetus, forming a substitute for bone; hence, cartilages are divided into articular or incrusting, cartilages of pro- longation, inter articular cartilages, and cartilages of ossification. 3. The muscles constitute the flesh of animals. They consist of fasciculi of red and contractile fibres, extending from one bone to another, and are the agents of all movements. 1 See Rudolphi, Grundriss der Physiologie, Berlin, 1821; Berzelius, Traite de Chimie, par Jourdan, torn. v. Paris, 1829; and Adelon, Physiologie de I'Homme, seconde edition, Paris, 1829. 34 MATERIAL COMPOSITION OF MAN. 4. The ligaments are very tough, difficult to tear, and under the form of cords or membranes serve to connect different parts with each other, particularly the bones and muscles; hence their division, by some anatomists, into ligaments of the bones—as the ligaments of the joints ; and into ligaments of muscles—as the tendons and apo- neuroses. . , i'ii 5. The vessels are solids, having the form of canals, in which the fluids circulate. They are called—according to the fluid they con- vey—sanguineous (arterial and venous,) chyliferous, lymphatic, &c. 6. The nerves are solid cords, consisting of numerous fasciculi. These are connected with the brain, spinal marrow, or great sym- pathetic ; and they are the organs by which impressions are con- veyed to the nervous centres, and by which each part is endowed with vitality. There are two great divisions of the nerves,—the encephalo-spinal and the organic. 7. A ganglion is a solid knot, situate in the course of a nerve, and seeming to be formed by an inextricable interlacing of the ner- vous filaments. The term is likewise applied, by many modern anatomists, to a similar interlacing of the ramifications of a lym- phatic vessel. Ganglions, may, consequently, either be nervous or vascular; and the latter, again, may be divided into chyliferous, or lymphatic, according to the kind of vessel in which they appear. Chaussier, a distinguished anatomist and physiologist, has given the name glandiform ganglions to certain organs, whose nature and functions are unknown to us, but which he considers to be organs for the admixture and elaboration of fluids,—as the thymus gland, the thyroid gland, &c. 8. Follicles or crypts are secretory organs, shaped like mem- branous ampulke or vesicles, always seated in the substance of one of the outer membranes of the body—the skin or the mucous sur- faces—and secreting a fluid intended to lubricate them. They are often divided into the simple or isolated, the conglomerate, and the compound, according to their size, or the number in which they are grouped and united together. 9. The gland is also a secretory organ, but differing from the last. The fluid secreted by it, is of greater or less importance. Its organization is more complex than that of the follicle ; and the fluid, after secretion, is poured out by means of one or more excre- tory ducts. 10. Membrane.—This is one of the most extensive and important of the substances formed by the cellular tissue. It is spread out in the shape of a web, and, in man, serves to line the cavities and reser- voirs, and to form, support, and envelope all the organs. Bichat divides membranes into two kinds, the simple and the com- pound, according as they are formed of one or more layers fib ou°s Simple membranes are of three kinds'the serous> mucous, and 1st. The serous membranes are those that constitute all the sacs SOLID PARTS. 35 or shut cavities of the body,—those of the chest and abdomen, for example. Idly. The mucous, or those that line all the outlets of the body,— the air passages, alimentary canal, urinary and genital organs, &c. 3dly. Fibrous membranes, or those which form tendon, aponeu- rosis, ligament, &c. The compound membranes are formed by the union of the simple, and are divided into fibro-serous, as the pericardium ; sero-mucous, as the gall-bladder, at its lower part; and fibro-mucous, as the ureter. In the view of Rapsail,* the truly simple animal membrane is the paries of a vesicle. In this state of simplicity it is so transparent, that it is only perceptible by the plaits or folds it forms on being moved, but if it were a compound membrane, the rays of light would be reflected. On this ground he disputes the accuracy of the observations of Sir Everard Home,b Edwards,0 and others, main- taining that the pretended globules, seen and figured by them, were optical illusions produced by the play of light on the different folds of the membrane. 11. The cellular or laminated tissue—to be described presently— is a sort of spongy or areolar structure, which forms the frame- work of all the solids, fills up the spaces between them, and serves, at the same time, as a bond of union and of separation. 12. The viscus is the most complex solid of the body, not only as regards intimate organization but use. This name is given to organs contained in the splanchnic cavities,—brain, thorax, and abdomen, —and hence called cerebral, thoracic, or abdominal. Every animal solid is either amorphous or fibrous; that is, it is either without apparent arrangement, like jelly, or is disposed in minute threads, which are called fibres. The disposition of these threads, in different structures, is various. Sometimes, they retain the form of threads; at others, they have that of laminae, lamella?, or plates. Accordingly, when we examine any animal solid, where the organization is perceptible, it is found to be either amorphous, or fibrous and laminated. This circumstance led the ancients to endeavour to discover an elementary fibre or filament, from which all the various organs might be formed. Hallerd embraced the idea, and endeavoured to unravel every texture to this ultimate element,—asserting that it is to the physiologist what the line is to the geometer; and that, as all figures can be constructed from the line, so every tissue and organ a Nouveau Systeme de Chimie Organique, p. 76, Paris, 1833. b Pliilos. Trans, for 1821, and Lectures on Comparative Anatomy, vol. iii. London, 1823. c Sur la Structure Etementaire des Principaux Tissus Organiques des Animaux; in Archives Generates de Medecine, 1823, torn. iii. and Recherches Microscopiques, etc. in Annales des Sciences Naturelles, 1824, torn. ix. p. 362. d Elementa Physiologiae, vol. i. lib. i. sect i. 36 MATERIAL COMPOSITION OF MAN. of the body may be built up from the filament. Haller, however, admits that this elementary fibre is not capable of demonstration, and that it is visible only to the " mind's eye,"—" invisibilis est ea fibra, sola mentis acie distinguimus.,, It must be regarded, indeed, as a pure abstraction; for, as different animal substances have different proportions of carbon, hydrogen, oxygen and azote, it is fair to con- clude, that the elementary fibre must differ also in the different structures. The ancients believed, that the first product of the elementary fibre was cellular tissue, and that this tissue formed every organ of the body;—the difference in the appearance of these organs arising from the different degrees of condensation of its laminae. Anatomists, however, have been unable to reduce all the animal solids to cellular tissue solely. In the upper classes of animals, three primary fibres or tissues or anatomical elements are usually admitted,—the cellular or laminated, the muscular, and the nervous, pulpy or medullary. 1. The cellular or laminated fibre or tissue.—This is the most simple and abundant of the animal solids. It exists in every organized being, and is an element of every solid. In the enamel of the teeth only it has not been detected. It is formed of an assemblage of thin lamina?, of delicate whitish, extensible filaments, interlacing and leaving between each other areolae or cells. (See Fig. 1.) These plates or filaments—although possessed like every living tissue of contractility or the power of feeling an appropriate irritant and of moving responsive to such irritant—do not move perceptibly under the influence of mechanical or chemical stimuli. They are composed of concrete gelatine. The great bulk of animal solids consists of cellu- lar tissue, arranged in the form of membrane. 2. Muscular fibre or tissue.—This is a substance of a peculiar nature, arranged in fibres of extreme delicacy. The Fig. 2. fibres are linear, soft, grayish or reddish, (See Fig. 2.) and manifestly possessed of contractility or irritability; that is, they move very perceptibly under the influence of mechanical or chemical stimuli. They are compos- ed, essentially, of fibrine. Prochaska,* a distinguished anatomist of Vienna, maintains, that the ultimate fibre or filament of muscular tissue is discernible; that it is, in every part, of the same magnitude—about -^\\\ part of the diameter of the red globule of the blood, or about TinrWth part of an inch in diameter. It is probable, however, that were our means of examining minute objects still further improved, we should be able to de- tect a filament even more delicate than this. The muscular fibres, which are arranged in the form of membranous expansions or muscular coats, differ from proper 1 De Came Musculari, &c. p. 25, Vienna, 1778; and Oper. Minor, part i. 198. PRIMARY AND COMPOUND TISSUES. 37 muscles chiefly in the mechanical ar- Fig. 3. rangement of their fibres. (Fig. 3, a and b.) But the physical and chemical characters of both are identical. The cij fibres, instead of being collected into fasciculi, are in layers, and, instead of being parallel, interlace. This tissue does not exist in the zoophytes. 3. Nervous, pulpy, or medullaryI fibre or tissue.—This tissue is much less distributed than the preceding. It is of a pulpy consistence, is composed essentially of albumen united to a fatty matter, and is the organ of sensibility, or for receiving and transmitting impressions to the mind. Of it, the brain, cerebellum, medulla spinalis, nerves and their ganglia are composed. The ultimate nervous filament is considered by Fon- tana,a Reil,b and others, to be about twelve times larger than the ultimate muscular filament. The sa me remarks, however, may be made here concerning our limited means of observation, as were made on the elementary muscular fibre. Professor Chaussierc has added another primary fibre or tissue,— the albugineous. It is white, satiny, very resisting, of a gelatinous nature, and constitutes the tendons and tendinous structure. Chaus- sier is, perhaps, the only anatomist that admits this tissue. Others properly regard it as a very condensed variety of the cellular. These various fibres or tissues, by uniting differently, constitute the first order of solids; and these, again, by union, give rise to com- pound solids, from which the different organs, bones, glands, &c. are- formed. A bone, for example, is a compound of various tissues, osseous in its body, medullary in its interior, fibrous externally, and cartilaginous at its extremities. Bichatd was the first anatomist who possessed any clear views regarding the constituent tissues of the animal frame; and whatever merit may accrue to after anatomists and physiologists, he is entitled to the credit of having pointed out the path, and facilitated the labours of the anatomical analyst/5 In combining to form the different structures, the solids are ar- ranged in a variety of ways. Of these, the chief are in filaments or elementary fibres, tissues, organs, apparatuses, and systems. The filament, we have seen, is the elementary solid. A fibre con- sists of a number of filaments united together. Occasionally, this is called a tissue:—the term tissue usually, however, means a particu- * Sur les Poisons; t. ii. t> De Structure Nervorum, c. 1-4. c Table Synoptique des Solides Organiques. d Anatomie Generate, Paris, 1801, torn. i. e For various arrangements of the tissues, see Lepelletier, Physiologie Medicale; torn. i. Paris, 1831-1832; Meckel's Handbuch, Doane's translation, vol. i., Phila- delphia, 1822; Grainger's Elements of General Anatomy, Lond. 1829. VOL. I. 4 38 MATERIAL COMPOSITION OF MAN. lar arrangement of fibres. An organ is a compound of several tissues. An apparatus is an assemblage of organs, concurring to the same end:—the digestive apparatus consists of the organs of mastication, insalivation, and deglutition, of the stomach, duo- denum, pancreas, liver, &c. These organs may be, and are of very dissimilar character, both as regards their structure and func- tions ; but, if they concur in the same object, they form an appa- ratus. A system, on the other hand, is an assemblage of organs, all of which possess the same or an analogous structure. Thus, all the muscles of the body have a common structure and function, and they constitute, in the aggregate, the muscular system. All the vessels of the body, and all the nerves, for like reasons, constitute respectively the vascular, and nervous systems. d. Of the Fluids of the Human Body. The positive quantity or proportion of the fluids in the human body does not admit of easy appreciation, as it must obviously vary at different periods and under different circumstances. The younger the animal, the greater is the preponderance. When we first see the embryo, it appears to be almost fluid. As it becomes gradually developed, the solid parts increase in their relative proportion, until the adult age; after which the proportion becomes less and less as the individual advances in life. During the whole of existence, too, the quantity of fluids in the body fluctuates. At times, there is ple- thora or unusual fulness of vessels; at others, the blood is less in quantity. Experiments have been made for the purpose of ascer- taining the relative proportion of the fluids to the solids. Richerand says that they are in the ratio of six to one; Chaussier," of nine to one. The latter professor put a dead body, weighing one hundred and twenty pounds, into a heated oven, and dried it. After desicca- tion, it was found to be reduced to twelve pounds. It is probable, however, that some of the more solid portions were driven off by the heat employed, and hence, that the evaluation of the proportion of the fluids was too high. In the Egyptian mummies, which are com- pletely deprived of fluid, the solids are extremely light, not weigh- ing more than seven pounds; but as we are ignorant of the original weight of the body, we cannot arrive at any approximation. The dead bodies found in the arid sands of Arabia, as well as the dried preparations of the anatomical theatre, afford additional instances of this reduction by desiccation. To a less extent, we have the same thing exhibited in the excessive diminution in weight which occurs in disease, and occasionally in those who are apparently in health. Not many years ago, an Anatomie vivante was exhibited, in London^ to the gaze of the curious and scientific, whose weight was not more than eighty pounds. Yet the ordinary functions were carried on apparently unmodified. In the year 1830, a still more wonderful a Traite d'Anatomie Descriptive, par H. Cloquet, i. 5, Paris 1821 anH T?;koo ;„ Mem. de la Societe Med. d'Emdation, viii. Parish 1817. ' ' d RlbeS> m FLUIDS. 39 phenomenon was exhibited in New York, who was called the " living skeleton." This extraordinary being was forty-two years old, five feet two inches high, and weighed but sixty pounds. His weight had formerly been one hundred and thirty-five pounds. For sixteen years previously, he had been gradually losing flesh, wilhout any apparent disease, having enjoyed perfect health and appetite, and eating, drinking, and sleeping as well as any one. We have it also on the authority of Captain Riley ,a that after protracted suffer- ings in Africa, he was reduced from two hundred and forty pounds to below ninety.[?] The fluids are variously contained ; sometimes in vessels—as the blood and lymph; at others, in cavities—as the fluids secreted by the pleura, peritoneum, arachnoid coat of the brain, &c.; others are in minute areolae—as the fluid of the cellular membrane ; whilst others again are intimately combined with the solids. They differ likewise in density, some existing in the state of halitus or vapour; others being very thin and aqueous—as the fluid of the serous mem- branes ; others of more consistence—as the secretion of the mucous membranes, the animal oils, &c. The physical and chemical properties of the fluids will engage our attention when they fall individually under consideration, and we shall find that one of them at least—the blood—exhibits certain phenomena analogous to those of the living solid. The fluids have been differently classed, according to the particu- lar views that have from time to time prevailed in the schools. The ancients referred them all to four—blood, bile, phlegm or pituita, and atrabilis; and each of these was conceived to abound in one of the four ages, seasons, climates, or temperaments. The blood pre- dominated in youth, in the spring, in cold mountainous regions, and in the sanguine or inflammatory temperament. The pituita or phlegm had the mastery in old age, in winter, in low and moist coun- tries, and in the lymphatic temperament. The bile predominated in mature age, in summer, in hot climates, and in the bilious tempera- ment ; and lastly, the atrabilis was the characteristic of middle age, of autumn, of equatorial climes, and of the melancholic tempera- ment. This was their grand humoral system, which has vanished before a better observation of facts, and more improved methods of physical and metaphysical investigation. The atrabilis was a crea- ture of the imagination; the pituitous condition is unintelligible to us; and the doctrine of the influence of the humours on the ages, tem- peraments, &c. is irrational. Subsequently, the humours were classed according to their phy- sical and chemical properties; for instance, they were divided into liquids, vapours, and gases; into acid, alkaline, and neutral; into thick and thin; into aqueous, mucilaginous, gelatinous, and oily; into saline, oily, saponaceous, mucous, albuminous, and fibrinous, &c. In more modern times, endeavours have been made to arrange them a Narrative of the loss of the American Brig Commerce, &c, p. 302. New York, 1817. 40 MATERIAL COMPOSITION OF MAN. according to their uses in the economy into 1. recrementdial fluids, or those intended to be again absorbed; 2, excrementitial, or those that have to be expelled from the body; and 3, those which partici- pate in both uses, and are hence termed excremento-recrementitial. Blumenbach* divided them into crude humours, blood, and secreted humours, a division which has been partly adopted by Adelon ;b and lastly by Professor Chaussier, whose anatomical arrangements and nomenclature have rendered him justly celebrated, reckons five classes:—1, those produced by the act of digestion,—the chyme, and the chyle; 2, the circulating fluids,—the lymph and the blood; 3, the perspired fluids; 4, the follicular; and 5, the glandular. This ar- rangement has been adopted by Magendie,c and is as satisfactory as any that has been proposed. The following is an enumeration of the different fluids or humours of the body, all of which will have to engage attention hereafter. 1. The chyme and the chyle. 2. The blood and the lymph. 3. The perspired or exhaled fluids, including the serous fluids, the synovia, the fat, the medulla, the colouring matter of the skin, the colouring matters of the uvea and choroid of the eye, the three humours of the eye, the liquor of Cotugno, the cephalo-spinal fluid, the fluid of the lymphatic and glandiform ganglions, the humour exhaled from the interior of vessels, the liquor amnii, the water of the chorion and that of the umbilical vesicle, the cutaneous transpiration, the pulmo- nary transpiration, the perspired humours of the digestive apparatus, those of the urinary and genital organs, and in the female, during the time she is capable of fecundation, the monthly exhalation called the catamenia or menses; and, after delivery, a similar secretion, called the lochia. 4. The follicular fluids are—the sebaceous hu- mour of the skin, the cerumen, the humour of Meibomius, that of the caruncula lachrymalis, the humour secreted at the base of the glans in the male, and within the vulva of the female, the humour of the mucous follicles of the respiratory, digestive, urinary, and genital apparatuses, including that of the tonsils, cardiac glands, prostate, Cowper's glands, &c. 5. The glandular fluids are—the tears, saliva, pancreatic juice, bile, urine, sperm, and milk. e. Of the Elementary Structure of Animal Substances. Anatomists have not been content with endeavouring to reduce the different organized textures to primary fibres and filaments, but, by the aid of the microscope, they have attempted to discover the particular arrangement of the constituent corpuscles. The discovery of that valuable instrument gave the impulse, and very soon the scientific world was presented with the results obtained by numerous observers. These observations have been, from time to time, con- tinued until the present day. It is, however, to be regretted, that a Elements of Physiology, by Elliotson, 4th edit. Lond. 1828. b Physiologie de I'Homme, 2de 6dit. i. 124, Paris, 1829. c Precis Elementaire de Physiol. 2de edit. i. 20, Paris, 1825. ELEMENTARY STRUCTURE. 41 our information, derived from this source, has not been as accurate as it might be. From different quarters we have the most dis- cordant statements, exhibiting clearly, either that the narrators employed instruments of very different powers, or that they were blinded, or had the vision depraved, by preconceived theories or hypotheses. One of the very first effects of the discovery of the microscope was the detection of a globular structure of the primi- tive tissues of the body, by Leeuenhoek,1 an announcement that gave rise to much controversy, which has continued, indeed, till the pre- sent time, and has engaged the attention particularly of Prochaska,b Fontana,c Sir Everard Home, Mr. Bauer, the brothers Wenzel,d Dr. Milne Edwards, MM. Prevost and Dumas,e Dutrochet, Hodgkin/ Raspail, and others. The observations and experiments of Dr. Edwards especially have occasioned much inferesting speculation and inquiry. They may perhaps be taken as the foundation on which the believers in the globular structure rest their opinions. His views were first pub- lished in 1823, in a communication, entitled " Memoire sur la Struc- ture elementaire des principaux Tissues Organiques des Animaux;" and in a second article in the Annales des Sciences Naturelles, for December, 1826, entitled " Recherches microscopiques sur la Struc- ture intime des Tissues Organiques des Animaux." He examined all the principal textures of the body, the cellular tissue, the mem- branes, tendons, muscular fibre, nervous tissue, the skin, the coats of the blood-vessels, &c. When the cellular tissue was viewed through a powerful lens, it seemed to consist of cylinders; but, by using still higher magnify- ing powers, these cylinders were found to be formed of rows of globules, all of the same size, that is, about the rrooth or ^oWtn of an inch in diameter (Fig. 4.); separated from each other, and lying in various directions; crossing and in- p\„ 4_ terlacing; some of the rows straight, others bent, and some twisted, forming irregular lay- ers, united by a kind of network. The membranes, which consist of cellular tissue, were found to present exactly the same kind of arrangement. The muscular fibre, when examined in the like manner, was found to be formed of glo- bules also ao'-oo^h part of an inch in diameter. Here, however, the rows of globules are al- ways parallel. The fibres never intersect each other like those of cellular tissue, and this is the only discerni- a Opera Omnia, &c. Lugdun. Batav. 1722. b De Structura Nervorum, Vind. 1779. c Sur les Poisons, ii. 18. d De Structura Cerebri, Tubing. 1812. e Bibliotheque Universelle des Sciences et Arts, t. xvii. f In Drs. Hodgkin and Fisher's translation of W. Edwards, Sur les Agens Physiques, Lond. 1832; and Hodgkin's Lectures on the Morbid Anatomy of the Serous and Mu- cous Membranes, p. 26, Lond. 1836; or Dunglison's Amer. Med. Lib. Edit. Phil. 1838. 4# i 42 MATERIAL COMPOSITION OF MAN. ble difference, the form and size of the globules being alike. The size of the globules, and the linear ar- rangement they assume, seem to be the same in all animals that possess a muscular structure, {t ig. ^.) The nervous structure has, by almost all observers, been esteemed globular—and one of the recent ob- servers1 has satisfied himself that this is certainly the most uniform appearance. The examination of Dr. Edwards yielded similar results. It seemed to be composed of lines of globules of the same size with those that form the cellular membrane and the muscles; but holding an intermediate place as to the regularity of their arrangement, and having a fatty matter interposed between the rows. In regard to the size of the globules, Dr. Edwards differs mate- „. rially from an accurate and experienced mi- croscopic observer, Mr. Bauer,b who asserts that the cerebral globules are of various sizes. (Fig. 6.) From the results of his own diversified ob- servations, Dr. Edwards concludes, that " sphe- rical corpuscles, of the diameter of ^th of a millimeter, constitute, by their aggregation, all the organic textures, whatever may be the pro- perties, in other respects, of those parts, and the functions for which they are destined." The harmony and simplicity, which would thus seem to reign through the structures of the animal body, have attracted great attention to the labours of Dr. Edwards. The vege- table kingdom was subjected to equal scrutiny; and, what seemed still more astounding, it was affirmed, that the microscope proved it also to be constituted of globules exactly like those of the animal, and of the same magnitude, -gVootn of an inch in diameter; hence, it was assumed, that all organized bodies possess the same elemen- tary structure, and of necessity, that the animal and the vegetable are readily convertible into each other under favourable circum- stances, and that they differ only in the greater or less complexity of their organization. Independently of all other objections, how- ever, the animal differs, as we have seen, from the vegetable, in composition; and this difference must exist not only in the whole, but in its parts; so that, even were it demonstrated, that the globules of the beings of the two kingdoms are alike in size, it would by no means follow, that they should be identical in intimate composition.0 a Dr. Luigi Calori, in Bulletino delle Scienze Medich. di Bologna, Sett. 1836, p. 152. b Philosoph. Transact, for 1818 ; and Sir E. Home's Lectures on Comparative Ana- tomy, vol. iii. lect. 3, Lond. 1823. c See an interesting article on the accordance in the structure and mode of growth of Animals and Plants, from the Cytoblast or " germinal cell,"—being a review of the Researches of Schwann and Schleiden,—in British and Foreign Medical Review for April, 1840, p. 495. ELEMENTARY STRUCTURE. 43 The discordance which we have deplored, is strikingly applicable to the case before us. The appearance of the memoir of Dr. Ed- wards excited the attention of Dutrochet, and in the following year his " Researches" on the same subject were published, in which he asserts, that the globules, which compose the different structures of the invertebrated animals, are considerably larger than those of the vertebrated; that the former appear to consist of cells, containing other globules still smaller; and hence he infers, that the globules of vertebrated animals are likewise cellular, and contain series of still smaller globules. Dr. Edwards, in his experiments, found that the globules of the nervous tissue, whether examined in the brain, in the spinal cord, in the ganglia, or in the nerves, have the same shape and diameter, and that no difference can be distinguished in them, from whatever animal the tissue is taken. Dutrochet, on the other hand, considers, with Sir Everard Home and the brothers Wenzel, that the globules of the brain are cellules of extreme minuteness, containing a medul- lary or nervous substance, which is capable of becoming concrete by the action of heat and of acids. This structure, he remarks, is strikingly evidenced in certain molluscous animals; and he instances the small pulpy nucleus, forming the cere- Fig. 7. bral hemisphere of the Umax rufus, and the helix po- matia, composed of globular, agglomerated cellules, on the parietes of which a considerable number of globular or ovoid corpuscles are perceptible. (Fig. 7.) M. Dutrochet, again, has not found the structure of the nerves to correspond with that of the brain. He asserts, that the elementary fibres, which enter into their composi- tion, do not consist simply of rows of globules, according to the opinion of Edwards and others, but that they are cylinders of a diaphanous substance, the surface of which is studded with globular corpuscles, and that, as these cover the whole surface of the cylin- der, we are led to believe that they are situated internally. After de- tailing this difference of structure between the brain and the nerves, the former consisting chiefly of nervous corpuscles, the latter chiefly of cylinders or fibres, Dutrochet announces the hypothesis, which exhibits too many indications of having been formed prior to his microscopic investigations,—that these cerebral corpuscles are destined for the production of the nervous power, and that the ner- vous fibres are tubes, filled with a peculiar fluid, by the agency of which nervimotion is effected. For further developements of the analysis of Dutrochet, the reader is referred to the work itself, which exhibits all the author's ingenuity and enthusiasm, but can scarcely be considered historical. The beautiful superstructure of Dr. Edwards, and the ingenuity of Dutrochet have, however, been most fatally assailed by subse- quent experiments, with a microscope of unusual power, by Dr. Hodgkin. The globular structure of the animal tissues, so often developed, and apparently so clearly and satisfactorily established by 44 MATERIAL COMPOSITION OF MAN. Dr. M. Edwards, is, we are told by Dr. Hodgkin,a a mere deception; and we have again to refer the most minute parts of the cellular membrane, muscles, and nerves to the striated or fibrous arrange- ment. A part of the discrepancy between Messrs. Edwards and Dutrochet may be explained by the fact of the former using an in- strument of greater magnifying power than the latter, who employed the simple microscope only. It has been observed, that when Dr. Edwards used an ordinary lens, the arrangement of a tissue appear- ed cylindrical, which, with the compound microscope, was distinctly globular. The discordance between Messrs. Edwards and Hodgkin is reconcilable with more difficulty. On the whole subject, indeed, our minds must be kept in a state of doubt, and we must wait until the point is fully ascertained, if ever destined to be so. In our uncertainty regarding the existence of the globules themselves, it is hardly necessary to inquire into the opinion, professed by Messrs. Prevost and Dumas, and by Dr. Edwards, that all the proximate principles—albumen, fibrine, gelatine, &c.—assume a globular form, whenever they pass from the fluid to the solid state, whatever may be the cause producing such conversion. M. Raspailb has ranged himself among those who consider, that the ultimate structure of all organic textures is vesicular, and that the organic molecule, in its simplest form, is an imperforate vesicle, endowed with the faculty of inspiring gaseous and liquid substances, and of expiring again such of their decomposed elements, as it can- not assimilate;—properties, which he conceives it to possess under the influence of vitality. Lastly, J. F. Meckel,0 from his observations, infers, that all the solids and fluids of the human body are formed of two elementary substances: first, of an amorphous matter, which is concrete in the former and fluid in the latter; and secondly, of globules. Of these two substances, the former may exist alone, and constitute some of the textures ;—for instance, the cellular tissue, the bones, cartilages, &c. The globules, on the contrary, are always united with the amorphous substance, which, in the solids, serves as a bond of union, and in which -the globules are immersed in the fluids. This anato- mist believes that the globules differ in shape, size, and number, in different animals, and in different parts of the same animal, and even in the same part, according to age.d f. Physical Properties of the Tissues. The tissues of the body possess the physical properties of matter in general. They are found to vary in consistence,—some being hard, and others soft, as well as in colour, transparency, &c. We find, also, certain physical properties, analogous, indeed, to what are » Op. citat. p. 466. See, also, Grainger's Elements of General Anatomv Lond 1829 b Op. citat. § 126. J «•■«.<-'«'*'■ c Handbuch, u. s. w. and A. S. Doane's translation, vol. i. Philad. 1832 d Weber's Allgemeine Anatomie, u. s. w., s. 131, Braunschweig, 1830. PHYSICAL PROPERTIES OF TISSUES. 45 met with in several inorganic substances, but generally superior in degree. These axe flexibility, extensibility, and elasticity, which are variously combined and modified in the different forms of animal matter, but exist to a greater or less extent in every organ. Elas- ticity is only exerted under particular circumstances: when the part, for example, in which it is seated, is put upon the stretch or is com- pressed, the force of elasticity restores it to its primitive state, as soon as the distending or compressing cause is removed. The tis- sues, in which elasticity is inherent, are so disposed through the body, as to be kept in a state of distension by the mechanical cir- cumstances of situation; but, as soon as these circumstances are de- ranged, elasticity comes into play, and produces shrinking of the substance. It is easy to see, that these circumstances, owing to the constant alteration in the relative situation of parts, must be ever varying. Elasticity is, therefore, constantly called into action, and in many cases acts upon the tissues as a new power. The carti- lages of the ribs, joints, &c. are in this manner valuable agents in particular functions. We have other examples of the mode in which elasticity exhibits itself, under similar circumstances, when the con- tents of hollow parts are withdrawn, and whenever muscles are divided transversely. The gaping wound, produced by a cut across a shoulder of mutton, is familiar to all. Previous to the division, the force of elasticity is kept neutralized by the mechanical circum- stances of situation,—or by the continuity of the parts; but as soon as this continuity is disturbed, or, in other words, as soon as the me- chanical circumstances are altered, the force of elasticity is exerted and produces recession of the edges. This property has been de- scribed under various names. It has been called tone or tonicity, contractilite de tissu, contractilite par defiant ^extension, &c. The other properties—-flexibility and extensibility—vary greatly according to the structure of the parts. The tendons, which are composed of the cellular tissue, exhibit very little extensibility, and this for wise purposes. They are the conductors of the force deve- loped by the muscle, and were they to yield, it would be at the ex- pense of the muscular effort; but they possess great flexibility. The articular ligaments are very flexible, and somewhat more extensible. On the other hand, the fibrous or ligamentous structures, which are employed to support weights, or which are antagonists to muscular action,—such as the ligamenium nuchce or the strong ligament, which passes from the spine to the head of the quadruped,—are very extensible and elastic. Another physical property, possessed by animal substances, is a kind of contractility, accompanied with sudden corrugation and curling. This effect, which Bichat terms racornissement, is pro- duced by heat, and by chemical agents, especially by the strong mineral acids. The property is exhibited by leather when thrown into the fire. An effect, in some measure resembling this, is caused by the eva- poration of the water which is united to animal substances. This 46 MATERIAL COMPOSITION OF MAN. constitutes what Dr. Rogeta calls the hygrometric properly of animal membranes. It is characteristic of dry, membranous structures, an of which are found to contract, more or less, by the evaporation 01 moisture, and to expand again by its re-absorption; hence the em- ployment of such substances as hygrometers. According to unev- reul,b many of the tissues are indebted for their physical ProPJ^ies to the water they contain, or with which they are imbibed, wnen deprived of this fluid, they become unfit for the purposes for wlncn they are destined in life, and resume them as soon as they have re- covered it. . , A most important property possessed by the tissues of organized bodies, is that of imbibition ; a property to which attention has been chiefly directed of late years. If a liquid be put in contact with any organ or tissue, in process of time the liquid will be found to have passed into the areolae of the organ or tissue, as it would enter the cells of a sponge. The length of time, occupied in this imbibition, will depend upon the nature of the liquid and the kind of tissue. Some parts of the body, as the serous membranes and small vessels, act as true sponges, absorbing with great promptitude: others resist imbibi- tion for a considerable time,—as the epidermis. Liquids penetrate equally from within to without: the process is then called transudation, but it does not differ from imbibition. Within the last few years some singular facts have been observed regarding the imbibition of fluids and gases. On filling membra- nous expansions, as the intestine of a chicken, with milk or some dense fluid, and immersing it in water, Dutrochet0 observed, that the milk left the intestine, while the water entered it; and hence he con- cluded, that whenever an organized cavity, containing a fluid, is im- mersed in another fluid, less dense than that which is in the cavity, there is a tendency in the cavity to expel the denser and absorb the rarer fluid. This Dutrochet terms endosmose or " inward impul- sion;" and he conceives it to be a new power,—a "physico-organic or vital action." Subsequent experiments snowed, that a reverse operation could likewise take place. If the internal fluid was rarer than the external, the transmission occurred in the opposite direc- tion. To this reverse process, Dutrochet gives the name exosmose, or " outward impulsion." Soon after the appearance of Dutrochet's essay, similar experi- ments were repeated, with some modifications, by Dr. Faust,d and by Dr. Togno,e of Philadelphia, and with like results. The fact of this imbibition and transudation was singular and impressive; and, 1 Art. Physiology, in Supplement to Encyclopaedia Britannica; and Roget's Outlines of Physiology, with an appendix on Phrenology. First American edition, with notes by the author of this work, p. 73, Philad. 1839. b Precis Elementaire de Physiologie, par Magendie, 2de edit. 1825, i. 13. 0 L'Agent Immediate du Mouvoment Vital Devoile, &c. Paris, 1826; and Nouvelles Recherches sur PEndosmose, &c. Paris, 1828; art. Endosmosis, by Dutrochet, in Cyclopaedia of Anatomy and Physiology, part x. p. 98, June, 1837; and H. Milne Ed- wards, Outlines of Anatomy and Physiology, translated by J. F. W. Lane M D. p. 56, Boston, 1841. 1829. I. Animal or of Relation. Functions. / , ) II. Nutritive. III. Reproductive. 52 FUNCTIONS OF MAN. prevail amongst observers, such differences will be attempted to be reconciled, where practicable. The functions, executed by different organs of the body, can be deduced by direct observation, although the minute and molecular action, by which they are accomplished in the very tissue of the organ, may not admit of detection. We see, for example, blood proceeding to the liver, and the vessels that convey it ramifying in the texture of the viscus, and becoming so minute as to escape vision, even when aided by a powerful microscope. We find, again, other canals in the organ, becoming perceptible, gradually augment- ing in size, and ultimately terminating in akrger duct, that opens into the small intestine. If we examine each of these orders of vessels in their most minute appreciable ramifications, we discover, in the one, always blood, and, in the other, always a very different fluid,— bile. We are hence led to the conclusion, that in the intimate tissue of the liver, and in some part communicating directly or indirectly with both these orders of vessels, bile is separated from the blood; in other words, that the liver is the organ of the biliary secretion. On the other hand, functions exist, which cannot be so demonstra- tively referred to an organ. We have every reason for believing, that the brain is the exclusive organ of the mental and moral mani- festations ; but, as few opportunities occur for seeing it in action, and as the operation is too molecular to admit of direct observation when we do see it, we are compelled to connect the organ and func- tion by a process of reasoning only; yet we shall find, that the re- sults, at which we arrive in this manner, are often by no means the least satisfactory. The forces that preside over the various functions are either gene- ral,—that is, physical or chemical; or special—that is, organic or vital. Some of the organs afford us examples of purely physical instruments. We have, for instance, in the eye, an eye-glass,'if we may so call it, of admirable construction; in the organ of voice, an instrument of music ; in the ear, one of acoustics; the circulation is carried on through an ingenious hydraulic apparatus, and station and progression involve various laws of mechanics. In many of the functions, again, we have examples of chemical agency, whilst all those, in which innervation is concerned, we are incapable of explain- ing on any physical or chemical principle, and are constrained to esteem vital. ANIMAL FUNCTIONS. 53 BOOK I. ANIMAL FUNCTIONS OR FUNCTIONS OF RELATION. The functions of relation consist, first, of sensibility, and secondly, of muscular motion, including expression or language. All these actions are subject to intermission, constituting sleep ; a condition which has, consequently, by many physiologists, been investigated under this head; but as the functions of reproduction are also in- fluenced by the same condition, the consideration of sleep will be deferred until the third class of functions has engaged attention. CHAPTER I. OF SENSIBILITY OR THE FUNCTION OF THE SENSATIONS. Sensibility is the function by which an animal experiences feeling, or has the perception of an impression. In its general acceptation, it means the property possessed by living parts of receiving impres- sions, whether the being, exercising the property, has consciousness of it or not. To the first of these cases—in which there is con- sciousness—Bichat gave the epithet animal; to the second, organic; the latter being common to animals and vegetables, and presiding over the organic functions of nutrition, absorption, exhalation, secre- tion, &c.; the former existing only in animals, and presiding over the sensations, internal as well as external. Animal sensibility, will engage us here. Pursuing the plan, already laid down, we shall commence the study of this interesting and elevated function, by pointing out, as far as may be necessary, the apparatus that effects it, which com- prises the whole nervous system. 1. OF THE NERVOUS SYSTEM. Under the name nervous system anatomists include all those or- gans, that are composed of the nervous or pulpy tissue. In man, it is constituted of three portions; first, of what has been called the cerebro-spinal axis, a central part having the form of a long cord, expanded at its superior extremity, and contained within the cavities of the cranium and spine ; secondly, of cords, called nerves, in num- ber thirty-nine pairs, according to some,—forty-two according to others,—passing laterally between the cerebro-spinal axis and every part of the body; and, lastly, of a nervous cord, situate on each side of the spine, from the head to the pelvis, forming ganglia oppo- site each vertebral foramen, and called the great sympathetic nerve. i. Of the Encephalon.—Under this term are included the contents of the cranium, namely, the cerebrum or brain proper; the cerebel- 5* 54 NERVOUS SYSTEM. lum or little brain, and the medulla oblongata. These various parts have been included by some under the name of brain. When we look at a section of the encephalon, and at the three organs in their natural position, we find many distinct parts, and appearances of numerous and separate organs. So various, indeed, are the prominences and depressions observable on the dissection of the brain, that it is generally esteemed one of the most difficult sub- jects of anatomy; yet, owing to the attention paid to it in all ages, it is now one of the structures best understood by the anatomist. This complicated organ affords us a striking illustration of the truth, that the most accurate anatomical knowledge will not neces- sarily teach the function. The elevated actions, which the encepha- lon has to execute, have, indeed, attracted a large share of the attention of the physiologist,—too often, however, without any satis- factory result; yet it may, we think, be safely asserted, that we have become better instructed regarding the uses of particular parts of the brain, within the last few years, than during the whole of the century preceding. The encephalon being of extremely delicate organization, and its functions easiiy deranged, it was necessary that it should be securely lodged and protected from injuries. Accordingly, it is placed in a round, bony case; and, by an admirable mechanism, is defended against damage from surrounding bodies. Amongst these guardian agents or tutamina cerebri must be reckoned;—the hair of the head, the skin, muscles, pericranium, bones of the skull, the diploe sepa- rating the two tables of which the bones are composed, and the dura mater. It is not an easy matter to assign probable uses to the hair on va- rious parts of the body. On the head its function seems more readily appropriable. It deadens the concussion, which the brain would ex- perience from the infliction of heavy blows, and prevents the skin of the scalp from being injured by the attrition of bodies. In military service, the former of these uses has been taken advantage of, and an arrangement, somewhat similar to that which exists naturally on the head, has been adopted with regard to the helmet. The metallic substance, of which the ancient and modern helmets are formed, is readily thrown into vibration; which vibration, being communicated to the brain, might, after heavy blows, derange its functions more even than a wound inflicted by a sharp instrument. To obviate this, in some measure, the helmet has been covered with horse-hair; an arrangement which prevailed in the helmet worn by-the Roman soldier. There can be no doubt, likewise, that being bad conductors of caloric, and forming a kind of felt which intercepts the air, the hairs may tend to preserve the head of a more uniform temperature. They are, moreover, covered with an oily matter, which prevents them from imbibing moisture, and causes them to dry speedily. An- other use, ascribed to them by Magendie/ is somewhat more hypo- * Precis Elementaire, edit. cit. i. 177. SKULL. 55 thetical;—that, being bad conductors of electricity, they may put the head in a state of insulation, so that the brain may be less affected by the electric fluid! It is unnecessary to explain in what manner the different layers of which the scalp is composed, the cellular membrane beneath, the panniculus carnosus or occipito-frontalis muscle, and the pericra- nium covering the bone, act the parts of tutamina. The most im- portant of these protectors is the bony case itself. In an essay written by one of the most distinguished physiologists of the present day,1 we have some beautiful illustrations of the wisdom of God as displayed in the mechanism of man, and of his skull in particular, and although some of his remarks may be liable to the censures which have been passed upon them by Dr. Arnott,b the greater part are admirably adapted to the contemplated object. It is impossible, indeed, for the uninitiated to rise from the perusal of his interesting essay, without being ready to exclaim with the poet, " how won- derful, how complicate is man! how passing wonder He that made him such!" Sir Charles attempts to prove, that the best illustration of the form of the head is the dome; whilst Dr. Arnott considers it to be " the arch of a cask or barrel, egg-shell, or cocoa-nut, &c. in which the tenacity of the material is many times greater than necessary to resist the influence of gravity, and comes in aid, therefore, of the curve, to resist forces of other kinds approaching in all directions, as in falls, blows, unequal pressures," &c. The remarks of Dr. Arnott on this subject are just; and it is owing to this form of the cranium, that any blow received upon one part of the skull is rapidly distributed to every other; and that a heavy blow, inflicted on the forehead or vertex, may cause a fracture, not in the parts struck, but in the occipital or sphenoidal bones. The skull does not consist of one bone, but of many. These are joined together by sutures,—so called from the bones seeming as if they were stitched together. Each bone consists likewise of two ta- Fig. 8. bles; an external, fibrous and tough, and an internal, of a harder cha- racter and more brittle, hence called tabula vitrea. These two tables are separated from each other by a cel- lular or cancellated structure, call- ed diplo'e. On examining the mode in which the tables form a junction with each other at the sutures, we find additional evidences of design skuii. PTrhihifpfl Thf> pdfrps of the OUter A' The parietal bone. B. The frontal bone. exniDltea. ±UC euges 01 me uuiei c Tneoccjpita, bone. D. The temporal bone. table are serrated, and so arranged e. The sphenoid bone. a Sir Charles Bell, in Animal Mechanics—Library of Useful Knowledge, London, 1829. b Elements of Physics, or Natural Philosophy, General and Medical, London, 1827 —reprinted in this country, with notes by Dr. Hays. 56 NERVOUS SYSTEM, as to be accurately dovetailed into each other; the tough fibrous texture of the external plate being well adapted for such a junction. On the other hand, the tabula vitrea, which, on account of its greater hardness, would be liable ^ 9" to fracture, to chip off, is merely united with its fel- low at the suture, by what is called harmony: the ta- bulae are, in other words, merely placed in contact. The precise object of these sutures is not appa- rent. In the mode in which ossification takes place in the bones of the skull, the radii from different ossi- fic points must necessari- ly meet by the " law of conjugation," in the pro- gress of ossification. This has, by many, been es- teemed the cause of the su- tures, but the explanation is insufficient. Howsoever it may be, the kind of junction affords an exam- ple of beautiful adapta- tion. During the foetal state, the sutures do not exist. They are fully form- ed in youth, are distinct in the adult age, but, in Disarticulated Bones of the Skull. - . . n vr U 1. The frontal bone. (The central division between the two alter periods Of lite, be- bones does not exist in the »dult.)-8. Parietal bone.-3. Oc- come entirely obliterated, cipitalbone.—4. Temporal bone.—5. Ethmoid bone.—6. Sphe- . J . ' noid bone.—7. Superior maxillary bone.—8. Cheek bone.—9. the DOne then forming a solid spheroid. Itdoesnot seem, however, that after the sutures are established, any displacement of the bones can take place; and observation has shown, that they do not possess much, if any, effect in putting a limit to fractures. In all cases of severe blows, the skull appears to resist as if it were constituted of but one piece. But the separation of the skull into distinct bones, which have a membranous union, is of striking advantage to the foetus in parturi- tion. It enables the bones to overlap each other; and, in this way, to occupy a much smaller space than if ossification had united them, as in after life. It has, indeed, been imagined by some, that there is this advantage in the pressure made on the brain by the investing bones, —that the foetus does not suffer from the violent efforts made to ex- trude the child; but that, during the passage through the pelvis, it is in a state of fortunate insensibility; and that pressure suddenly ex- -8. Cheek bone Palate bone.—10. Lachrymal bone.—11. Nasal bone.—12. In ferior maxillary bone. ENCEPHALON. 57 erted upon the brain is attended with these effects is well known to the pathologist. It is, indeed, the great principle to be borne in mind in the management of apoplexy, fracture of the skull, &c. The uses of the diplo'e, which separates the two tables of the skull, are not equivocal. Composed of a cancellated structure, it is well adapted to deaden the force of blows, and as it forms, at the same time, a bond of union and of separation, a fracture might be in- flicted upon the outer table of the skull, and yet be prevented from extending to the tabula vitrea. Such cases have occurred, but they are rare. It will generally happen, that a blow, intended to cause serious bodily injury, will be sufficient to break through both tables or neither. Lastly, the dura mater, which has been reckoned as one of the tutamina cerebri, lines the skull, and constitutes a kind of internal periosteum to it. It may also be inservient to useful purposes, by deadening the vibrations, into which the head may be thrown by sudden concussions; as the vibrations of a bell are arrested by lining it with some soft material. It is chiefly, however, to protect the brain against itself, that we have the arrangement, which prevails. The cerebrum, as well as the cerebellum, consists of two hemi- spheres ; and its posterior part is situate immediately above the cerebellum. It is obvious, then, that without some protection, the hemisphere of one side would press upon its fellow, when the head is inclined to the opposite side; and that the posterior lobes of the brain would weigh upon the cerebellum in the erect attitude* Fig. 10. Posterior view of the Encephalon, the Cranium and Dura Mater being removed. The hemispheres (A A, Fig. 10,) are separated from each other by the falx cerebri, in the upper margin of which is the superior Ion- 58 NERVOUS SYSTEM. gitudinal sinus (d d). The falx passes between the hemispheres (a a, Fig. 11). The tentorium cerebello super externum--^ prolonga- tion of the dura mater-passes horizontally forwards (at c c,) so as to support the posterior lobes of the brain, and prevent them irom pressing injuriously on the cerebellum (B B). A process of the dura mater passes also between the hemispheres of the cerebellum (B B). Independently of the protection afforded to the encephalon, the dura mater lodges the great sinuses into which the veins discharge their blood. These different sinuses empty themselves into the torcular Herophili or confluence of the sinuses, (at d, Fig. 10 and 11,) and ultimately proceed in the direction c c, constituting the lateral sinuses, which pass through the temporal bone, and form the inter- nal jugular veins, one of which is represented at e, Fig. 11. Fig. 11. a a. The falx cerebri. d. The torcular Herophili. c c. The lateral sinuses. jugular vein. e. The internal The tutamina are not confined to the contents of the cranium. The spine appears to be, if possible, still better protected. In the skull, we see a firm, bony case; in the spine, a structure admitting considerable motion of the parts, without risk of pressure to the spinal marrow. Accordingly, the spine consists of numerous dis- tinct bones or vertebrae, with fibro-cartilaginous—technically called intervertebral—substances placed between each, so that, although the extent of motion between any two of these bones may be small, the amount, when all are concerned, is considerable. The great use of this intervertebral substance is to prevent the jar, that would necessarily be communicated to the delicate parts within the cavities of the spine and cranium, were the spine composed entirely of one bone. In falls from a height, upon the feet or breech, these elastic ENCEPHALON. 59 cushions are forcibly compressed, but they immediately return to their former condition, and deaden the force of the shock. In this they are aided by the curvatures of the spine, which give it the shape of the Italic s, and enable it to resist—in the same manner as a steel spring—any force acting upon it in a longitudinal direction. So well is the medulla spinalis protected by the strong bony pro- cesses, jutting out in various directions from the spine, that it is ex- tremely rare to meet with lesions of the part; and it is compara- tively of late years that any ex professo treatises have appeared on the subject. Besides the protection afforded by the bony structure to the deli- cate medulla, Magendie1 has pointed out another, which he was the first to detect. The canal, formed by the dura mater around the spinal cord, is much larger than is necessary to contain that organ; but, during life, the whole of the intermediate space is filled with a serous fluid, which strongly distends the membrane, so that it will frequently spirt out to a distance of several inches, when a puncture is made in the membrane. To this fluid he has given the epithet cephalo-spinal; and he conceives, that it may act as one of the tuta- mina of the marrow, (which is, as it were, suspended in the fluid,) and exert upon it the pressure necessary for the healthy performance of its functions. Beneath the dura mater is situate a very delicate membrane, the arachnoid, belonging to the class of serous membranes. It sur- rounds the encephalon in every part, but is best seen at the base of the brain. Its chief use is to secrete a thin fluid, to lubricate the brain. This membrane enters into all the cavities of the organ, and in them fulfils a like function. When the fluid accumulates to a great extent, we have the disease called hydrocephalus chronicus. Anatomists usually describe a third tunic of the brain—the pia mater. As a distinct membrane this is not demonstrable. It is ge- nerally conceived to consist of the minute terminations of the cere- bral arteries, and those of the corresponding veins, forming, at the surface of the brain, a vascular network, which passes into the cavities; and, in the ventricles, forms the plexus choroidcs, and tela choroidea. The dura and pia mater were so called, by the older anatomists, because they were conceived to be the origin of all the other membranes of the body. The cerebrum or brain proper has the form of an oval, larger be- hind. On its outer surface are various undulating eminences, called convolutions, because they have been thought to resemble the folds of the intestines—separated from each other by depressions, called anfractuosities. (See Fig. 13.) They form the hemispherical gan- glion of Mr. Solly. In the brain of man, these convolutions are larger than in animals, and the anfractuosities deeper. In different brains, the number, size, and arrangement of these vary. They a Precis, &c. ^dit. cit. i. 181. 60 NERVOUS SYSTEM. are not the same, indeed, in the same individual; those of the right hemisphere being disposed differently from those of the left. The hemispheres, we have seen, are separated above by the talx cerebri: below, they are united by a white medullary commissure, the corpus callosum, mesolobe or great commissure, the great transverse commissure of Mr. Solly. If we examine the brain at its base, we find that each hemisphere is divided into three lobes,—an anterior, which rests on the vault or roof of the orbit,—a middle or temporal, filling the middle and lateral parts of the base of the cranium, and separated from the former by a considerable depression, called the fissure of Sylvius,—and a posterior, which rests on the tentorium cerebelli. This part of the cerebrum is divided into two very dis- tinct portions by the medulla oblongata. Anterior to it are the crura cerebri or cerebral peduncles,—by most anatomists considered to be a continuation of the anterior fasciculi which form the spinal mar- row and medulla oblongata, and proceeding to form the hemispheres of the brain. Between the anterior extremities of the peduncles are two hemispherical projections, called eminentice mammillares, which are possessed by man exclusively, have the shape of a pea, and are formed of the white nervous tissue externally, of the gray within. Anterior to these again is the infundibulum, and, a little farther for- wards, the chiasma of the optic nerves or the part at which these nerves come in contact. Laterally, and at the inferior surface of the anterior lobes, is a groove or furrow, running from behind to before, and from without to within, in which the olfactory nerve is lodged. At the extremity of this furrow is a tubercle, which is trifling in man, but in certain animals is equal to the rest of the brain in bulk. From this the olfactory nerve has been conceived to arise. It is called the olfac- tory tubercle or lobe. When we examine the interior of the brain, we find a number of parts to which the anatomist assigns distinct names. Of these, the following chiefly concern the physiologist. It has been already re- marked, that the corpus callosum forms at once the bond of union and of separation between the two hemispheres. It is distinctly per- ceived, on separating these parts from each other, in the form of a long and broad white band. Beneath the corpus callosum is the septum lucidum or median septum, which passes perpendicularly downwards and separates from each other the two largest cavities of the brain—the lateral ventricles. It is formed of two laminae, which leave a cavity between them, called the fifth ventricle. The fornix or inferior longitudinal commissure of Mr. Solly, whose office is to connect the anterior and posterior parts of the same hemi- sphere, as the transverse commissures do those of the opposite hemi- spheres, is placed horizontally below the last. The band of fibres, which runs, in each hemisphere, above the eorpus callosum, on the edge of the longitudinal fissure, is the superior longitudinal commis- sure of Mr. Solly. Its use is supposed to resemble that ascribed to ENCEPHALON. 61 the inferior longitudinal commissure. The fornix is of a triangular shape, and constitutes the upper paries of another cavity—the third ventricle. Beneath the fornix, and behind it, is the pineal gland, and its peduncles, forming the pineal commissure of Mr. Solly, respect- ing which so much has been said, by Descartes,1 and others, as the seat of the soul. Within it, is a small cavity; and, after six or seven years of age, it always contains some concretions. Again, anterior to the pineal gland, and immediately below the fornix, is another cavity—the third ventricle. Its bottom is very near the base of the brain, and is formed by the nervous layer, which unites the peduncles of the brain with the eminentias mammillares. (Fig. 12.) At the sides it has the thalami nervorum opticorum. Fig. 12. Base of the Brain. A A. Anterior lobes of the.Brain. B B. Middle lobes. C C Posterior lobes. D D. Cerebellum. a. Medulla oblongata, b. Pons Varolii, c. Chiasm of the optic nerves, d. Olfactory nerves, e. Crus cerebri. /. Crus cerebelli. In the lateral ventricles, situated on each side of the corpus cal- losum, some parts exist which demand attention. In the upper or anterior half, commonly called the anterior cornu, and in the ante- rior part of this, two pyriform eminences are seen, of a brownish gray colour, and which, owing to their being formed of an assem- blage of alternate layers of white and gray substance, are called the corpora striata, the anterior cerebral ganglions of Mr. Solly. Be- hind these, are two whitish medullary bodies, called thalami nervorum * Tractatus de Homine, p. 5. > VOL. I. 6 62 NERVOUS SYSTEM. opticorum, which are situate before the corpora quadrigemina, and envelope the anterior extremities of the crura cerebri. The cerebellum occupies the lower occipital fossa?, or the whole of the cavity of the cranium, which is beneath the tentorium cerebelli. The size and weight of the cerebellum, like those of the brain, differ according to the individual, and the age of the subject under examination. We do not observe convolutions in it. It appears rather to consist of laminae in superposition, separated from each other by furrows. We shall see hereafter that the number of cere- bral convolutions has been esteemed, in some respects, to accord with the intellect of the individual; and Malacarnea asserts, that he has observed a similar correspondence, as regards the number of the laminae composing the cerebellum; that he found only three hundred and twenty-four in the cerebellum of an insane individual, whilst in others he had counted upwards of eight hundred. From the medullary part of the cerebellum, two large white cords Fig. 13. 1 1. Section of the corpus callosum. 2 2. Lateral ventricle, the septum beine removpd 1 ? Th„ lormi. 4. Third ventricle. 5. Pineal gland. C. Tubercula quadrigemina 7 FW?h\J ,' • , A Iter a tertio ad quartum ventriculum 9 9. Internal carotid artery 10 w Art™,!?.* nt"Cle- callosuqj, 11 11 H h. superior longitudinal sinus. 12 12. Fourth sinus A A (V*K,™ th?,C?,rpllS bellum. C Pons Varolii. E E. Medulla spinalis. F. Medulla oblongata Cerebrum. B. Cere- * Nuova Esposizione delta Vera Struttura del Cerveletto Humane, Torino, 1776. ENCEPHALON. 63 pass to the pons varolii, having the same disposition as the crura cerebri. They are the crura cerebelli. Owing to the peculiar arrangement of the white and gray cerebral substances, when one of the hemispheres of the cerebellum is divided vertically, an arborescent appearance is presented,—the trunks of the arborization being white, the surrounding substance gray. This appearance is called arbor vitce. The part where all these arborizations meet, near the centre of the cerebellum, is called cor- pus denticulatum vel rhomboidale. Gall is of opinion, that this body has great agency in the production of the cerebellum. Lastly, the cerebellum covers the posterior part of the medulla oblongata, and forms with it a cavity, called the fourth ventricle. The medulla oblongata is so called, because it is the continuation of the medulla spinalis in the cavity of the cranium. It is likewise termed mesocephale, from its being continuous with the spinal mar- row in one direction, and sending towards the brain strong pro- longations—the crura cerebri; and to the cerebellum similar pro- longations—the crura cerebelli; so that it appears to be the bond of union between these various parts. In its lower portion, (Fig. 12, a,) it appears to be merely a continuation of the medulla spinalis, except that it is more expanded superiorly where it joins the pons varolii, b. This portion of the medulla oblongata is called, by some, the tail of the medulla oblongata; by others, the rachidian bulb; and by others again it is regarded as the whole medulla oblongata. Its lower surface, seen in the figure, rests on the basilary gutter of the occipital bone, and exhibits a groove which divides the spinal cord into two portions. On each side of this furrow are two oblong eminences, the innermost of which is called corpus pyramidale, the outermost, corpus olivare, (Fig. 14,) which arise from the anterior column of the medulla spinalis, or are a continuation and subdivision of this column. On the posterior surface of the medulla oblongata, the posterior fasciculi separate to form the fourth ventricle (Fig. 13, 7,); at the sides of this ventricle are the corpora restiformia, or inferior peduncles of the cerebellum, so called, because they seem to aid in the formation of that part of the encephalon; and on the inner side of each corpus restiforme, is the small body—the posterior pyra- mid. Again, in addition to the corpora pyramidalia and olivaria— which derive their origin from, or are continuous with, the anterior fasciculi of the spinal cord, and are destined, according to some, to form the brain—and the corpora restiformia, which are continuations of the posterior fasciculi, and are destined to form the cerebellum, there exists, according to some anatomists, other fasciculi in the rachidian bulb. All these are interesting points of anatomy, but are not yet of much importance physiologically; if we except, perhaps, the views promulgated by Sir Charles Bell.a He considers, that a column exists between the corpora olivaria and corpora restiformia, a The Nervous System of the Human Body : from Transactions of the Royal Society from 1821 to 1829, London, 1830. Reprinted in this country, Washington, 1833. 64 NERVOUS SYSTEM. which extends below through the whole spine, but above does not proceed farther than the point where the rachidian bulb joins the tuber annulare, and that this column gives origin to a particular order of nerves—those inservient to respiration. The corpora olivaria, and the posterior corpora pyramidalia, are regarded by Mr. Sollya as ganglia—the former of the function of respiration— the latter of the sense of hearing. The anterior and upper half of the medulla oblongata bears the names pons varolii, tuber annulare, and nodus cerebri; and to this are attached, superiorly, the corpora or tubercula qudrigemina. In the very centre of the pons, the crura cerebri bury themselves; and are, by many, considered to decussate; and by others, to be pro- longations of the anterior column of the spinal marrow. Sir C. Bell thinks, that the pons varolii stands in the same relation to the lateral portions of the cerebellum that the corpus callosum does to the cerebrum; that it is the great commissure of the cerebellum, uniting its lateral parts and associating the two organs. 2. The spinal marrow extends, in the vertebral canal, from the foramen magnum of the occipital bone, above, to the cauda equina, below.' It is chiefly composed of medullary matter, but not entirely so. Within, the cineritious substance is ranged irregularly, but has a crucial form when a section of it is made. From the calamus scriptorius in the fourth ventricle, and the rima—formed by the cor- pora pyramidalia, before—two fissures extend downwards, which divide the spinal marrow into lateral portions. The two lateral por- tions are divided into an anterior and posterior, so that the cord has four distinct portions. By some, indeed, it is conceived to consist of three columns—an anterior, posterior, and middle. The vertebral canal is connected by a strong ligamentous sheath, running down its whole length. The dura mater likewise envelopes the medulla at the occipital foramen, being firmly united to the liga- ments, but farther down it constitutes a separate tube. The tunica arachnoidea from the brain adheres loosely to the cord, having the cephalo-spinal fluid within it; and the pia mater closely embraces it.b 3. Nerves.—The nerves are cords of the same nervous substance as that which composes the encephalon and spinal marrow, extending from these parts, and being distributed to the various organs of the body, many of them interlacing in their course, and forming plexuses; others having knots or ganglions upon them; and almost all vanish- ing in the parts to which they are distributed. The generality of English anatomists reckon thirty-nine pairs of nerves ; the French, with more propriety, forty-two. Of these, nine, according to the English—twelve, according to the French—draw their origin from, or are connected with, the encephalon, and are hence called encephalic \ TJleTHuman Brain, its Configuration, Structure, Developement, and Physiology &c ft fit n°I!,d0n' !83?- x,See' on this subJect> Dr- John Reid' on the Anatomyof the Medulla Oblongata, in Edinb. Med. and Surg. Journ. Jan. 1841, p. 12. J b See, on the General and Special Anatomy of the Spinal Marrow Prof. W E Horner, Treatise on General and Special Anatomy, 5th edit. ii. 328 ; Philad 1839 NERVES. 65 Fig nerves ; thirty from the medulla spinalis, and hence termed spinal. The encephalic nerves emerge from the cranium by means of fora- mina at its base. They are—proceeding from before to behind—the first pair or olfactory, distributed to the organ of smell; the second pair or optic, the expansion of which forms the retina; the third pair, motores oculi or common oculo-muscular, which send filaments to most of the muscles of the eye; the fourth pair, trochleares, pathetici, or internal oculo-muscular, distributed to the greater oblique muscle of the eye; the fifth pair, trifacial, trigemini, or symmetrical nerve of the head, (Bell,) which send their branches to the eye, nose, and tongue ; the sixth pair, abdu- centes, or external oculo-mus- cular, which are distributed to ,the abductor or rectus exter- nus oculi; the facial nerve, portio dura of the seventh pair, nervus communicansfaciei, or respiratory nerve of the face, distributed to the muscles of the face; the acoustic nerve, auditory nerve, or portio mol- lis of the seventh pair, which passes to the organ of hearing; the eighth pair,pneumogastric, par vagum, or middle sympa- thetic, which is dispersed par- ticularly to the larynx, lungs, heart, and stomach; the glosso- pharyngeal, often considered as Dart of the last and whose ^ase°f ^e Brain and origin of the Encephalic Nerves. name indicates its distribution to the tongue and pharynx; A. Anterior lobes of the brain. B. Middle lobes. C Posterior lobes. D. Cerebellum. E. Pons varolii. F. Medulla oblongata. G. Crura cerebri. H. Crura ,, cerebelli. I. Fissure of Sylvius. K. Eminentiae mam- the great hypOglOSSUS, ninth millares. L. Infundibulum. M. Corpora Pyramidalia. !,' i 600 Loml 51838 ElementS of Physioloff7» bv J- Muller> translated'^ W. Baly, b De Structura Nervorum, Hal., 1796. SYSTKM OF ItKSriUATOKY NE.KVKS ^'*Wm^!*t /'>/ m the latter, T^ths. He found the different parts of the brain to be composed as follows: The whole Brain. White portion. / Gray portion. Water, 77.0 73.0 85.0 Albumen, 9.6 9.9 7.5 White fatty matter, 7.2 13.9 1.0 Red fatty matter, 3.1 0.9 3.7 Osmazome, lactic acid and salts, 2.0 1.0 1.4 Earthy phosphate, 1.1 1.3 1.2 100.0 100.0 100.0d Raspail6 has pointed out two other differences. First, when a nerve is left upon a plate of glass in a dry air, it becomes dry, with- out putrefying, whilst the cerebral substance putrefies in twenty-four hours; and secondly; this dried nerve has all the physical charac- ters of the corneous substances,—nails, hair, and other analogous bodies; and in their chemical relations, he says, these bodies do not differ sufficiently to repel the analogy. Neither the chemical analysis of the nervous system, nor inquiry into its minute struc- ture by the aid of the microscope, has, however, thrown light upon the wonderful functions executed by this elevated part of the economy. To the naked eye, the nervous substance appears under two forms, the one gray, and of a softer consistence; the other white, * Annales de Chim. Ixxxi. 37 ; Annals of Philosophy, i. 332. b Annales de Chimie et de Physique, lvi. 160. c See John's Analysis of the white and gray cerebral matter, in Journal de Chimie Medicale, Aout, 1835. d Journal de Chim. Medic.; and Pharmaceutisches Central Blatt,Nov. 19,1836, s. 765. • Chimie Organique, p. 217, Paris, 1833. 7* 78 NERVOUS SYSTEM. and more compact. The former is called the cortical, cineritious, or pulpy substance; the latter, the white, medullary, or fibrous. The gray substance is not always, however, at the exterior, nor the medullary in the interior. In the medulla spinalis, their situation is the reverse of what it is in the brain. Ruysch considered, that the cineritious portion owes its colour to the blood-vessels which enter it;a and, in this opinion, Haller and Adelonb concur; but this is not probable, and it has been by no means demonstrated. The medul- lary portion has the appearance of being fibrous, and it has been so regarded by Leeuenhoek,c Vieussens, Steno, and by Gall and Spurzheim.a Malpighie believed the gray cortical substance to be an assemblage of small follicles, intended to secrete the nervous fluid, and the white medullary substance to be composed of the excretory vessels of these follicles. Gall and Spurzheim, on the other hand, conjecture, that the use of the cineritious is, to be the source or nou- risher of the white fibres. The facts, on which they support their view, are, that the nerves appear to be enlarged when they pass through a mass of cineritious matter, and that masses of this sub- stance are deposited in all parts of the spinal cord where it sends out nerves; but Tiedemannf has remarked, that in the foetus the medullary is developed before the cortical portion, and he conceives the use of the latter to be—to convey arterial blood, which may be needed by the medullary portion for the due execution of its functions. Sir Charles Bells affirms, that he has found, at different times, all the internal parts of the brain diseased, without loss of sense, but that he has never seen disease general on the surface of the hemi- spheres, without derangement or oppression of mind during the pa- tient's life; and hence he concludes, that the cineritious matter of the brain is the seat of the intellect, and the medullary of the sub- servient parts. A similar use has been ascribed to the cineritious portion, from pathological observations, by MM. Foville and Pinel Grandchamp.h This view would afford considerable support to the opinions of Gall, Spurzheim, and others, who consider the organs of the cerebral faculties to be constituted of expansions of the columns of the spinal marrow and medulla oblongata, and to terminate by radiating fibres on the periphery of the brain; as well as of Desmoulins,1 and those, who regard the convolutions as the seat of mind. We have how- ever, cases on record, which signally conflict with this view of the c SS^iSV p.^010^ de 1,H°mme'2de 6dit" «*• - Paris' ™*- cl^X^JjS: NerVGUX en G^raI' et sur celui de c— - P-ti" « In Oper. Malpighii, and in Mangeti Bibl. Anat. i. 321 Anatomie und Bildungsgeschichte des Gehirns, mit Tafeln. Nurnbem 1816 1827 7 Physiolo?y» 5tl* American edit, by J. D. Godman, p. 29, New York, h Sur le Systeme Nerveux, Paris, 1820. 1 Anatomie des Systemes Nerveux des Animaux it Vertebres, p. 599, paris 1925 CIRCULATION OF THE ENCEPHALON. 79 subject; cases in which the cortical substance has been destroyed, and yet the moral and intellectual manifestations have been little, if at all, injured. Many years ago the author dissected the brain of an individual of rank in the British army of India, the anterior lobes of which were in such a state, that neither medullary nor cortical por- tion could be distinguished, both one and the other appearing to be broken down into a semi-purulent, amorphous fluid; yet the intel- lectual faculties had been nearly unimpaired, although the morbid process must have been of considerable duration. The encephalon affords us many striking instances of the differ- ent effects produced by sudden and by gradual interference with its functions. Whilst a depressed portion of bone or an extravasation of blood may suddenly give rise to the abolition of the faculties, the gradual compression, produced by a tumour, may scarcely interfere with any of its manifestations. The circulation of blood in the encephalon requires mention. The arteries are four in number,—two internal carotids, and two vertebrals; to these may be added the spinal artery or middle artery of the dura mater or arteria meningcea media. The carotid arteries enter the head through the carotid canals, which open on each side of the sella turcica, or of the chiasma of the optic nerves. The ver- tebral arteries enter the head through the foramen magnum of the occipital bone; unite on the medulla oblongata to form the basilary artery, which passes forward along the middle of the pons varolii, and, at the anterior part of the pons, gives off lateral branches, which inosculate with corresponding branches of the carotids, and form a kind of circle at the base of the brain, which has been called the circulus arteriosus of Willis. The passage of the blood-vessels is extremely tortuous, so that the blood does not enter the brain with great impetus; and the ves- sels become capillary before they penetrate the organ,—an arrange- ment of essential importance, when we regard the large amount of blood sent to the encephalon. This has been estimated as high as one-eighth of the whole fluid transmitted from the heart. The amount does not admit of accurate appreciation, but it is consider- able. It must of course vary according to circumstances. In hyper- trophy of the heart," the quantity sent is sometimes increased; as well as in ordinary cases of what are called determinations of blood to the head. Here, too large an amount is sent by the arterial ves- sels ; but an equal accumulation may occur, if the return of the blood from the head, by means of the veins, be in any manner im- peded,—as when we stoop, or compress the veins of the neck by a tight cravat, or by keeping the head turned for a length of time. Congestion or accumulation of blood may therefore arise from very different causes. Sir Astley Cooperb found by experiment, that the vertebral arteries * Bricheteau, Clinique Medicale, p. 133, Paris, 1835; or the author's translation in his American Medical Library, Philad. 1837. b Guy's Hospital Reports, i. 472, London, 1836. 80 NERVOUS SYSTEM. are much more important vessels as regards the brain and its func- tions in certain animals, as the rabbit, than the carotid arteries. The nervous power is much lessened by tying them ; and, in his experi- ments, the animal did not, in any case, survive the operation more than a fortnight. In the dog also he tied the carotids with little effect, but the ligature of the vertebrals had a great influence. The effect of the operation was to render the breathing immediately difficult and laborious, owing, in Sir Astley's opinion, to the supply of blood to the phrenic nerves and the whole tractus respiratorius of Sir Charles Bell being cut off. The animal became dull, and indisposed to make use of exertion or to take food. Compression of the carotids and the vertebrals at the same moment in the rabbit destroyed the nervous functions immediately. This was effected by the application of the thumbs to both sides of the neck, the trachea remaining quite free from pressure. Respiration entirely ceased, with the exception of a few convulsive gasps. The same fact was evinced in a clearer and more satisfactory manner by the application of ligatures on the four vessels, all of which were tightened at the same instant. Stoppage of respiration and death immediately ensued. The cerebral, like other arteries, are accompanied by branches of the great sympathetic. The encephalic veins are disposed as already mentioned, terminating in sinuses formed by the dura mater, and conveying their blood to the heart by means of the lateral sinuses and internal jugulars. (See Fig. 11.) No lymphatic vessels have been detected in the encephalon; yet, that absorbents exist there is proved by the dissection of apoplectic and paralytic individuals. In these cases, blood is sometimes effused within the brain, the red par- ticles are gradually taken up, with a portion of the fibrinous part of the blood, leaving a cavity called an apoplectic cell, which is at the same time the evidence of previous extravasation and of subsequent absorption. When the skull of the new-born infant, which, at the fontanelles, consists of membrane only—or the head of one who has received an injury, that exposes the brain—is examined, two distinct move- ments are perceptible. The one, which is generally obscure, is synchronous with the pulsation of the heart and arteries ; the other, much more apparent, is connected with respiration, the organ seem- ing to sink down at the time of inspiration, and to rise during expi- ration. This phenomenon is not confined to the brain, but exists likewise in the cerebellum and spinal marrow. The motion of the encephalon, synchronous with that of the heart, admits of easy explanation. It is owing to the pulsation of the circle of arteries at the base of the brain elevating the organ at each sys- tole of the heart. The other movement is not so readily intelligible. It has been attributed to the resistance, experienced by the blood iii its passage through the lungs during expiration, owing to which an accumulation of blood takes place in the right side of the heart; this extends to the veins and to the cerebral sinuses, and an augmenta- PROPERTIES OF THE CEREBRAL SUBSTANCE. 81 tion of bulk is thus occasioned. We shall see hereafter, that one of the forces conceived to propel the blood along the vessels, is at- mospheric pressure. According to that view, the sinking down of the brain, during inspiration, is explicable:—the blood is rapidly drawn to the heart; the quantity in the veins is consequently dimi- nished, and sinking down of the brain succeeds. On dissection, we find that the encephalon fills the cavity of the cranium; during life, therefore, it must be pressed upon, more or less, by the blood in the vessels, and by the serous fluid exhaled by the arachnoid. The spinal marrow, as we have seen, does not fill the vertebral canal, but the cephalo-spinal fluid exerts upon it the necessary pressure; added to which, the pia mater seems to press more upon this organ than upon the rest of the cerebro-spinal system. A certain degree of pressure appears, indeed, necessary for the due performance of its functions, and if this be either suddenly and con- siderably augmented, or diminished, derangement of function is the result. Magendie,1 however, asserts, that he has known animals, from which the fluid had been removed, survive without any sen- sible derangement of the nervous functions. It is this fluid, which is drawn off by the surgeon when he punctures in a case of spina bifida. When the brain is examined in the living body, it exhibits pro- perties, which, some years ago, it would have been esteemed the height of hardihood and of ignorance to ascribe to it. The opinion has universally prevailed, that all nerves are exquisitely sensible. We shall have many opportunities for remarking how far this sen- timent is founded on fact; but we are now prepared' to assert, that even the encephalon itself,—the organ in which perception takes place,—is insensible, in the common acceptation of the term; that is, we may prick, lacerate, cut, and even cauterize it, yet no painful impression will be produced. Experiment leaves no doubt regarding the truth of this, and we find the fact frequently confirmed by pathological cases. Portions of brain may be discharged from a wound in the skull, and yet no pain be evidenced. In his " Anatomy and Physiology," Sir C. Bellb remarks, that he cannot resist stating, that on the morn- ing ort which he was writing, he had had his finger deep in the an- terior lobes of the brain, when the patient, being at the time acutely sensible, and capable of expressing himself, complained only of the integument. A pistol-ball had passed through the head, and Sir Charles having ascertained that it had penetrated the dura mater by forcing his finger into the wound, trepanned on the opposite side of the head, and extracted it. a Precis Elementaire, seconde edit. i. 192. See, also, Dr. Skinner, in Amer. Journal of Medical Sciences for Nov. 1836, p. 109. b 5th Amer. edit, by J. D. Godman, ii. 6, 1827. See, also, Sir E. Home's Lectures on Compar. Anat. ii. 93, Lond, 1823. 82 SENSATIONS By the experiments, instituted by Magendie1 and others, it has been shown, that an animal may live several days, and even weeks, after the whole of the hemispheres has been removed; nay, that in certain animals, as reptiles, no change is produced in their habitudes by such abstraction. They move about as if unhurt. Injuries of the surface of the cerebellum exhibit, that it also is not sensible to that kind of irritation; but deeper wounds, and especially those that interest the peduncles, have singular results, to be explained here- after. The spinal cord is not exactly circumstanced in the same manner. Its sensibility is very exquisite on the posterior surface; much less on the anterior, and almost null at the centre. These columns, as we have seen, have been esteemed the origins of the nerves of sensibility, motion, and respiration. Considerable sensi- bility is also found within, and at the sides of, the fourth ventricle; but this diminishes as we proceed towards the anterior part of the medulla oblongata, and is very feeble in the tubercula quadrigemina of the mammalia. It has been shown, that the spinal nerves, by means of their pos- terior roots, convey general sensibility to the parts to which they are distributed. But there are other nerves, which, like the brain, are themselves entirely devoid of general sensibility. This has given occasion to a distinction of nerves into those of general and of spe- cial sensibility. As nerves which must be considered insensible or devoid of general sensibility, may be instanced the optic, olfactory, and auditory. Each of these has, however, a special sensibility, and although they may exhibit no pain when irritated, they are capable of being impressed by appropriate stimuli, as by light, in the case of the optic nerve; by odours, in that of the olfactory; and by sound, in that of the auditory. Yet we shall find, that every nerve of special sensibility requires the influence of a nerve of general sensibility, the fifth pair. Many other nerves appear devoid of sensibility, as the third, fourth, and fifth pairs; the portio dura of the seventh ; the ninth pair of encephalic nerves; and, as has been shown, all the anterior roots of the spinal nerves. The parts of the encephalon, concerned in muscular motion, will fall under consideration hereafter. 2. PHYSIOLOGY OF SENSIBILITY. Sensibility we have defined to be—the function by which an ani- mal experiences feeling, or has the perception of an impression. It includes two great sets of phenomena, the sensations, properly so called, and the intellectual and moral manifestations. These we shall consider in succession. a. Of the Sensations. A sensation is the perception of an impression made on some organ; or, in the language of Gall, it is the perception of any irrita- * Precis Elementaire, i. 335. SENSATIONS. 83 tion whatever. By the sensations we receive a knowledge of what is passing within or without the body; and, in this way, our notions or ideas of them are obtained. When these ideas are reflected upon, and compared with each other, we exert thought and judgment; and they can be recalled, with more or less vividness and accuracy, by the exercise of memory. The sensations are numerous, but they may all be comprised in two divisions,—the external and the internal. Vision and audition afford us examples of the former, in which the impression, made upon the organ, is external to the part impressed. Hunger and thirst are instances of the latter, the cause here being internal, necessary, and depending upon influences seated in the economy itself. Let us endeavour to discover in what they resemble each other. In the first place, every sensation, whatever may be its nature,— external, or internal,—requires the intervention of the encephalon. The distant organ,—as the eye or ear,—may receive the impression, but it is not until this impression has been communicated to the encephalon, that sensation is effected. The proofs of this are easy and satisfactory. If we cut the nerve proceeding to any sensible part, if we put a ligature around it, or compress it in any manner; it matters not that the object, which ordinarily excites a sensible impression, be applied to the part, no sensation is experienced. Again, if the brain, the organ of perception, be prevented in any way from acting, it matters not that the part impressed, and the nerve communicating with it, be in a condition necessary for the due performance of the function, sensation is not effected. We see this in numerous instances. In pressure on the brain, occasioned by fracture of the skull, or in apoplexy, a disease generally depen- dent upon pressure, we find all sensation, all mental manifestation, lost; and they are not regained until the compressing cause has been removed. The same thing occurs if the brain be stupified by opium, or any other narcotic; and, to a less degree, in sleep, or when the brain is engaged in intellectual meditations. Who has not found, that in a state of reverie or brown study, he has succeeded in threading his way through a crowded street, carefully avoiding every obstacle, yet so little impressed by the objects around him as not to retain the slightest recollection of them? On the other hand, how vivid are the sensations when the attention is directed to them? Again, we have numerous cases in which the brain itself engen- ders the sensation, as in dreams, and in insanity. In the former we see, hear, speak, make use of every one of our senses apparently, yet there has been no impression from without. Although we may behold in our dreams the figure of a friend long since deceased, there can obviously be no impression made on the retina from without.* The whole history of spectral illusions, of morbid hallucinations, and maniacal phantasies, is to be accounted for in this manner. a Adelon, Art. Encephale (Physiologie) in Diet, de M6d. vii. 514, Paris, 1823, and Physiol, de I'Homme, torn. i. p. 239, 2de edit. Paris, 1829. 84 SENSATIONS. Whether, in such cases, the brain reacts upon the nerves of sense and produces an impression upon them from within, similar to what they experience from without during the production of a sensation, will form the subject of future inquiry. Pathology also affords several instances where the brain engenders the sensation, most of which are precursory signs of cerebral derangement. The appear- ance of spots flying before the eyes, of spangles, depravations of vision, of hearing, &c. and a sense of numbness in the extremities, are referable to this cause, as well as the singular fact well known to the operative surgeon, that pain is often felt in a particular part of a limb, years after the limb has been removed from the body.a These facts prove, that every sensation, although referred to some organ, must be perfected in the brain. The impression is made upon the nerve of the part, but the appreciation takes place in the common sensorium.b There are but few organs of the body, which could be regarded insensible, provided we were aware of the precise circumstances under which their sensibility is elicited.6 The old doctrine—as old indeed as Hippocrates'1—was, that the tendons and other membra- nous parts are among the most sensible organs of the body. This opinion was implicitly credited by Boerhaave, and his follower Van Swieten,e and in many cases had a decided influence, on surgical practice especially. As the bladder consists principally of mem- brane, it was agreed for ages by lithotomists, that it would be im- proper to cut or divide any part of it; and therefore, in order to extract the stone, dilating instruments were used, which caused the most painful lacerations of the parts implicated in the operation/ Hallere considered the tendons, ligaments, periosteum, bones, me- ninges of the brain, different serous membranes, arteries, and veins, entirely insensible; yet we know, that these parts are exquisitely sensible when attacked with inflammation. One of the most painful affections to which man is liable is the variety of whitlow that im- plicates the periosteum; and in all affections of the bone, which in- flame or press forcibly upon that membrane, we have excessive sensibility exhibited. Many parts, too, are affected by special irritants; and, after they have appeared insensible to a multitude of agents, will show great sensibility when a particular irritant is applied. Bichat endeavoured to elicit the sensibility of ligaments in a thousand ways, and without success; but when he subjected them to distension or twisting, they immediately gave evidence of it. It is obvious, then, that before we determine that a part is insensible, we must have submitted it to a Porterfield on the Eye, i. 364. b Elliotson's Blumenbach, 4th edit. p. 215, Lond. 1828. c Mojon's Leggi Fisiologiche, &c. translated by Skene, p. 11, Lond. 1827 d loesn (Econom. Hippocr. " Nevgov." e Aphorism. 164, and Comment. f Bostock's Elementary System of Physiology, 3d edit. p. 23, Lond. 1836 6 Oper. Minor, torn. i. SENSATIONS. 85 every kind of irritation. Adelon affirms, that there is no part but what may become painful by disease. From this assertion the cuticle might safely be excepted. It is, so far as we know, totally devoid of blood-vessels and nerves,—the elements of sensibility,—and ap- pears to be extra-organic. If we are right, indeed, in our view of its origin and uses, as described hereafter, sensibility would be of no advantage to it, but the contrary. In the present state, then, of our knowledge, we are justified in asserting, that bones, cartilages, and membranes are not sensible to ordinary external irritation, when in a state of health, or in other words, that we are not aware of the irritants, which are adapted to exhibit their sensibility. That sensibility is due to the nerves distributed to a part is so generally admitted as not to require comment. It is true, however, that such sensibility is by no means in proportion to the number of nerves it may receive. Nay, some parts are acutely sensible in dis- ease into which nerves cannot be traced. To explain these cases, Reil* supposed, that each nerve is surrounded at its termination by a nervous atmosphere, by which its action is extended beyond the part in which it is seated. This opinion is a mere creation of the imagination. We have no evidence of any such atmosphere, and it is more philosophical in us to presume, that the reason we do not discover nerves in these parts may be owing to the imperfection of our vision. We may conclude, then, that the action of impression occurs in the nerves of the part to which the sensation is referred. The facts, already mentioned, show, that the action of perception takes place in the brain, and that the nerve is merely the conductor of the impression between the part impressed and that organ. If a ligature be put round a nerve, sensation is lost below the ligature, but it is uninjured above it. If two ligatures be placed, sensibility is lost in the portion included between the ligatures, but it is restored if the upper ligature be removed. The spinal marrow is sensible along the whole of its posterior column, but it also acts only as a conductor of the impression. Flourens destroyed the spinal cord from below, by slicing it away, and he found that sensibility wras gradually extinguished in the parts corresponding to the destroyed medulla, but that the parts situate above evidently continued to feel. Perception therefore occurs in the encephalon; and not in the whole, but in some of its parts. Many physiologists, amongst whom may be mentioned Haller, Lorry, Rolando, and Flourens,b have sliced away the brain, and found that the sensations continued until the knife reached the level of the corpora quadrigemina; and again it has been found, that if the spinal cord be sliced away from below upwards, the sensations persist until we reach the medulla oblongata. It is, then, in the medulla oblongata that we must place the cerebral * Exercitat. Anatom. Fascic. i. p. 28, and Archiv. filr die Physiologie, B. iii. b Rolando, Saggio sopra la vera Struttura del Cervello, Sassari, 1809; and Flourens, op. cit. p. 273. VOL. I. 8 86 SENSATIONS. organs of the senses, and it is with this part of the cephalo-spinal axis, that the nerves of the senses are found to communicate. Mr. Lawrence1 saw a child with no more encephalon than a bulb, which was a continuation for about an inch above the foramen magnum of the medulla spinalis, and with which all the nerves from the fifth to the ninth pair were connected. The child's breathing and temperature were natural; it discharged urine and faeces; took food, and at first moved very briskly. It lived four days. If we divide the posterior roots of the spinal nerves and the fifth pair, all general sensibility is lost; but if we divide the nerves of the senses, we destroy only their functions. We can thus under- stand why, after decapitation, sensibility may still remain for a time in the head. It is instantly destroyed in the trunk, owing to the removal of all communication with the encephalon, but the fifth pair remains entire in the head, as well as the nerves of the organs of the senses. Death must of course follow almost instantaneously from loss of blood, but there is doubtless an appreciable space, during which the head may continue to feel, or in other words, during which the external senses may act.b M. Julia Fontanelle0 has indeed concluded, from a review of all the observations made on this matter, that, contrary to the common opinion, death by the guillotine is one of the most painful, that could be invented; that the pains of decollation are horrible, and endure even until there is an entire extinction of animal heat! It need scarcely be said, that all these inferences are imaginative, and perhaps equally fabulous with the oft told story of Charlotte Corday scowling at the executioner after her head was removed from the body by the guillotine; and this opinion is strongly con- firmed by the results of experiments,—on a robber who was be- headed with the sword,—made by Drs. Bischoff, Heerman, and Jolly, who concluded, that consciousness must have ceased instan- taneously.d It has been remarked, that the cerebral hemispheres may be sliced away without abolishing the senses. The experiments of Rolando and Flourens, which have been repeated by Magendie, show, however, that the sight is an exception;—that it is lost by the removal of the hemispheres. If the right hemisphere be sliced away, the sight of the left eye is lost, and conversely;—one of the facts proving the decussation of the optic nerves. The experiments of these gentlemen show, that vision, more than the other senses, requires a connexion with the organ of the intellectual faculties— the cerebral hemispheres; and this, as Magendie has ingeniously remarked, because vision rarely consists in a simple impression a Medico-Chirurg. Transact, v. 166. b Berard, Rapports du Physique et du Moral, p. 93, Paris, 1823. c Phoebus, Art. Enthauptung, in Encyclopad. Worterb. der Medicin. Wissenschaft. xi. 204, Berlin, 1835; and Art.Gehirn, in Pierer's Anat. Physiol. Realworterb. iii. 387, Leipz. 1819. A See a condensed account of Dr. Bischoff's Remarks, in Miiller's Archiv. by S. L. L. Bigger, in the Dublin Journal of Medical Science, Sept. 1839, p. 1. NERVOUS FLUID. 87 made by the light, but is connected with an intellectual process, by which we judge of the distance, size, shape, &c. of bodies. Having arrived at a knowledge of the part of the encephalon in which perception occurs, our acquaintance with this mysterious process is suddenly arrested. We know not, and we probably never shall know, the action of the brain in accomplishing it. It is certainly not allied to any physical phenomenon, and if we were ever justified in referring functions to the class of organic and vital, it would be those, that belong to the elevated phenomena, which have to be considered under the head of the animal functions. We know them only by their results; yet we are but little better ac- quainted with many topics of physical inquiry;—with the pheno- mena of the electrical or magnetic fluid, for example. The organs, then, that form the media of communication be- tween the parts impressed and the brain, are the nerves and spinal marrow. Broussais,a indeed, affirms, that every stimulation, capa- ble of causing perception in the brain, runs through the whole of the nervous system of relation; that it is repeated in the mucous membranes, whence it is again returned to the centre of perception, w7hich judges of it according to the view of the viscus to which the mucous membrane belongs, and adapts its action according as it perceives pleasure or pain. We are totally unacquainted with the material character of the fluid, which passes with the rapidity of lightning along these cords, and it is as impossible for us to describe its mode of transmission, as it is to depict that of the electric fluid along a conducting wire. As in this last case, we are aware of such transmission only by the result. Still, hypotheses, as in every obscure matter of inquiry, have not been wanting.b Of these, three are chiefly deserving of notice. The first, of greatest antiquity, is, that the brain secretes a subtile fluid, which circulates through the nerves, called animal spirits, and which is the medium of communication between the different parts of the nervous system; the second regards the nerves as cords, and the transmission as effected by means of the vibra- tions or oscillations of these cords; whilst the third ascribes it to the operation of electricity. The hypothesis of animal spirits has prevailed most extensively. It was the doctrine of Hippocrates, of Galen,0 of the Arabians, and of most of the physicians of the last centuries. Descartesd adopted it energetically, and was the cause of its more extensive diffusion. The great grounds, assigned for the belief, were, first, that as the brain receives so much more blood than is necessary for its own nutrition, it must be an organ of seci*etion; secondly, that the nerves seem to be a continuation of the medullary matter of the brain; and 1 Traite de Physiologie, &c., Paris, 1822; and Drs. Bell and La Roche's transla- tion, 3d Amer. Edit. p. 63, Philad. 1832. b See Fletcher's Rudiments of Physiology, P. ii. b. p. 68, Edinb. 1836. c Good's Study of Medicine, Physiological Proem to Class iv. 2. d Tractatus de Homine, §. 14. 88 SENSATIONS. it has already been remarked, that Malpighi considered the cortical part of the brain to be follicular, and the medullary to consist of secretory tubes. It was not unnatural, therefore, to regard the nerves as vessels for the transmission of these spirits. As, however, the animal spirits had never been met with in a tangible shape, in- genuity was largely invoked in surmises regarding their nature; and, generally, opinions settled down into the belief, that the fluid was of an ethereal character. For the various opinions, that have been held upon the subject, the reader is refered to Haller,a who was himself an ardent believer in the existence of the animal spirits, and has wasted much time and space in an unprofitable inquiry into their nature. The truth is, that we have not sufficient evidence, direct or in- direct, of the existence of any nervous fluid of the kind described. The observations of Ehrenbergb led him to infer, that the nerves consist of tubes, and Mr. Pritchard0 is in favour of the tubular struc- ture of the cerebral substance also. He states the diameter of the constricted parts of the tubes, in the brain of a sheep, to vary from the TjVo-tn to the -r^th of an inch; whilst Berresd affirms, that the forms, in which the nervous substance presents itself under the magnifying glass, can only be compared to those of canals and vesicles, but whether they be hollow he does not attempt to decide. Raspaile has concluded, that the opinion of their being hollow, and containing a fluid, is unsupported by facts, for although he admits, that Bogrosf succeeded in injecting the nerves with mercury, he thinks, that the passage of the metal along the nerves was owing to its having forced its way by gravity. Raspail found the nerve, under the microscope, presenting a homogeneous structure, without the slightest trace of solution of continuity. We have, in truth, no reason for considering the brain the organ of any ponderable secre- tion. Yet the term " animal spirits," although their existence is not now believed in, adheres to us in popular language. We speak of a man who has a great flow of animal spirits, but without regard- ing the hypothesis whence the expression originated. The term nervous fluid is still constantly used by physiologists. By this, however, they simply mean the medium of communication or of conveyance, by which the nervous influence is carried, with the rapidity of lightning, from one part of the system to another, a Elementa Physiologic, x. 8. b See a Translation of his Observations by Dr. Craigie, in Edinb. Med. and Surgical Journal, Oct. 1837, p. 257. ' 8 c Lond. Med. Gazette, for Dec. 1836. d (Esterreich. Med. Jahrbuch, vol. ix., and Brit, and Foreign Med. Review, January, 1838, p. 219. e Chimie Organique, p. 218. Paris, 1833. f Note sur des Canaux Decouverts dans les Nerfs,—Memoire lu a l'Acad. des Sciences Mai 2, 1825 ; Repert. General. d'Anat. &,c, iv. 115, 1827. See, also, J. Mailer, Pro- gress of the Anatomy and Physiology of the Nervous System, during the year 1836 in Archiv. fur Anatomie, Jahrg. 1837, Heft 3: and Brit, and For. Med Rev Jan 1838 p. 293; Oct. 1838 p. 394, and April 1839, p. 500; and Elements of Physiology, by J. Midler, translated by W. Baly, M. D., i. 633, Lond. 1838. J \ NERVOUS FLUID. 89 but without committing themselves as to its character; so that, after all, the idea is in part retained, although the term, as applied to the nervous fluid, is exploded. Gooda directly admits them under the more modern title; Earleb firmly believes in the existence of a circulation in the nervous system,—and it is not easy to conceive, that the brain does not pos- sess the function of elaborating some fluid,—galvanoid or other,— which is the great agent in the nervous function. The hypothesis of vibrations is ancient, but has been by no means as generally admitted as the last. Among the moderns it has re- ceived the support of Condillac,c Hartley,*1 Blumenbach,e and others; some supposing, that the nervous matter itself is thrown into vibra- tions ; others, that an invisible and subtile ether is diffused through it, which acts the sole or chief part. As the latter is conceived, by- many, to be the mode in which electricity is transmitted along con- ducting wires, it is not liable to the same objections as the former. Simple inspection, however, of a nerve at once exhibits that it is incapable of being thrown into vibrations. It is soft, never tense, always pressed upon in its course; and, as it consists of filaments destined for very different functions,—sensation, voluntary and in- voluntary motion, &c.—we cannot conceive how one of these fila- ments can be thrown into vibration without the effect being extended laterally to others, and great confusion being thus induced. The last hypothesis is of later date—subsequent to the discoveries made in animal electricity. The rapidity, with which sensation and volition are communicated along the nerves, could not fail to suggest a resemblance to the mode in which the electric and galvanic fluids fly along conducting wires. Yet the great support of the opinion was in the experiments instituted by Dr. Wilson Philipf and others, from which it appeared, that if the nerve proceeding to a part be destroyed, and the secretion, which ordinarily takes place in the part, be thus arrested, the secretion may be restored by causing the galvanic fluid to pass from one divided extremity of the nerve to the other. The experiments, connected with secretion, will be noticed more at length hereafter. It will likewise be shown, that in the effect of galvanism upon the muscles, there is the same analogy;—that the muscles may be made to contract for a length of time after the death of the animal, even when a limb has been removed from the body, on the application of the galvanic stimulus; and comparative anatomy exhibits to us great developement of nervous structure in a Study of Medicine, with Notes by S. Cooper, Doane's Amer. edit. vol. ii. in Proem to Class iv. Neurotica, New York, 1835. b New Exposition of the Functions of the Nerves, by James William Earle, Part I. London, 1833. c GEuvres, Paris, 1822. d Observations on Man, &c. chap. i. sect. 1. e Physiology, by Elliotson, § 226. f Philosoph. Trans, for 1815, and Lond. Med. Gazette for March 18, p. 929, and March 25, 1837. 8* 90 SENSATIONS. those electrical animals, which surprise us by the intensity of the electric shocks they are capable of communicating. Physiologists of the present day generally, we think, accord with the electrical hypothesis. The late Dr. Young,a so celebrated for his knowledge in numerous departments of science, adopted it prior to the interesting experiments of Dr. Philip; and Mr. Abernethy,b whilst he is strongly opposing the doctrines of materialism, goes so far as to consider some subtile fluid not merely as the agent of nervous transmission, but as forming the essence of life itself. Dr. Bostock,c however, has remarked, that before the electric hypo- thesis can be considered proved, two points must be demonstrated; first, that every function of the nervous system may be performed by the substitution of electricity for the action of the nerves; and secondly, that all the nerves admit of this substitution. This is true, as concerns the belief in the identity of the nervous and electrical fluids; but we have, even now, evidence sufficient to show their similarity, and that we are justified in considering the nervous fluid to be electroid or galvanoid in its nature, emanating from the brain by some action unknown to us, and distributed to the different parts of the system to supply the expenditure, which must be constantly going on. Reil,'1 Senac,e Prochaska, Scarpa/ and others are of opinion, that the nervous agency is generated through all the nervous system, and that every part derives sensation and motion from its own nerves. We have satisfactorily shown, however, that a communication with the brain is absolutely necessary in all cases, and that we can im- mediately cut off sensation in the portion of a nerve included be- tween two ligatures, and as instantly restore it by removing the upper ligature and renewing the communication with the brain. a. External Sensations. The externa] sensations are those perceptions that are occasioned by the impressions of bodies external to the part impressed. They are not confined to impressions made by objects external to us. The hand applied to any part of the body, any two of its parts brought into contact, the presence of its own secretions or excretions, may equally excite them. Adelon^ has divided the external sensations into two orders—first, the senses, properly so called, by the aid of which the mind acquires its notion of external bodies and of their different qualities; and secondly, those sensations which are still caused by the contact of some body, and yet afford no information to the mind. a Med. Literature, p. 93, Lond. 1813, and Lectures on Natural Philosophy i. 740. b Physiological Lectures, exhibiting a view of Mr. Hunter's Physioloffv &c Lond 1817. SJ' ' c An Elementary System of Physiology, 3d edit. p. 148, Lond. 1836. See also J. Muller, in art. Electricitat. (Thierische) in Encyclopad. Wtaterb. der Medicin. Wisi sensch. x. 522, Berlin, 1834. a De Structura Nervorum, Hal. 1796. e Trait6 de la Structure du Coeur, &c. Liv. iv. chap. 8, Paris 1749 * Tabulae Neurologic. Ticin. 1794, §22. b Physiologie de I'Homme, torn. i. p. 259, 2de 6dit. Paris, 1829. EXTERNAL SENSATIONS. 91 It is by the agency of the organs of the external senses, that we become acquainted with the bodies that surround us. They are the instruments by which the brain receives its knowledge of the universe; but they are only instruments, and cannot be considered as the sole regulators of the intellectual sphere of the individual. This we shall see is dependent upon another and still higher nervous organ,—the brain. The external senses are generally considered to be five in num- ber ; for, although others have been proposed, they may perhaps be reduced to some modification of these five,—tact or touch, taste, smell, hearing, and vision. All these have some properties in com- mon. They are all situate at the surface of the body, so as to be capable of acting with due facility on external bodies. They all con- sist of two parts:—the one, physical, which modifies the action of the body, that causes the impression ; the other nervous or vital, which receives the impression, and conveys it to the brain. In the eye and the ear, we have better exemplifications of this distinction than in the other senses. The physical portion of the eye is a true optical instrument, which modifies the light, before it impinges upon the retina. A similar modification is produced by the physical portion of the ear on the sonorous vibrations, before they reach the auditory nerve; whilst in the other senses, the physical portion forms part of the common integument in which the nervous portion is situate, and cannot therefore be easily distinguished. Some of them, again, are symmetrical; that is, composed of two separate and similar halves, united by a median line,—as the skin, tongue, and nose. Others, as the eye and the ear, are in pairs; and this, partly perhaps, to enable us to judge of the distances of external objects. We shall find, at least, that there are certain cases, in which both the organs are necessary for accurate appreciation. Two of the senses—vision and audition—have, respectively, a nerve of special sensibility; and, until of late years, the smell has been believed to be similarly situate. In the present state of our knowledge, we cannot decide upon the precise nerve of taste, although it will be seen that a plausible opinion may be indulged on the subject. The general sense of touch is seated in the nerves of general sensibility. All, however, seem intimately connected with one of the nerves of general sensibility,—the fifth encephalic pair,— and, in the case of those senses more particularly, which possess nerves of special sensibility, it is found, that they are under the presidency of this nerve of general sensibility; for, if it be cut, the function is abolished, although the nerve of special sensibility may remain entire. Being instruments by which the mind becomes acquainted with ex- ternal bodies, it was manifestly of importance, that the senses should be influenced by volition. Most of them are so. The touch has the pliable upper extremity, admirably adapted for the purpose. The tongue is movable in almost every direction. The eye can be turned towards objects in almost all positions, by its own immediate 92 EXTERNAL SENSATIONS. muscles. The ear and the nose possess the least individual motion; but the last four, being seated in the head, are capable of being assisted by the muscles adapted for its movement. All the senses may be exercised passively, or actively. By direct- ing the attention, we can render the impression much more vivid; and hence the difference between simply seeing or passive vision, and looking attentively; between hearing and listening; smelling and snuffing; touching and feeling attentively. It is to this active exercise of the senses, that we are indebted for many of the plea- sures and comforts of social existence. Yet, to preserve the senses in the vigour and delicacy, which they are capable of acquiring by attention, the impressions must not be too constantly or too strongly made. The occasional use of the sense of smell, under the guidance of volition, may be the test on which the chemist, or the perfumer, or the wine-merchant, may rely in the discrimination of the nume- rous odorous characteristics of bodies ;. but, if the olfactory nerves be constantly or too frequently stimulated by excitants of this or any other kind, dependence can no longer be placed upon this means of discrimination. The maxim, that " habit blunts feeling," is true only in such cases as the last. Education can indeed render it extremely acute.a Volition, on the other hand, enables us to deaden the force of sen- sations. By corrugating the eyebrows and approximating the eye- lids, we can diminish the quantity of light when too powerful. We can breathe through the mouth, when a disagreeable odour is ex- haled around us; or we can completely shut off'the passage by the nostrils, with the aid of the upper extremity. Over the hearing we have less command, as regards its individual action: the upper ex- tremity is here always called into service, when we desire to dimi- nish the intensity of any sonorous impression. Lastly. It is a common observation, that the loss of one sense occasions greater vividness in the others. This is only true as re- gards the senses which administer chiefly to the intellect,—those of touch, audition, and vision, for example. Those of smell and taste may be destroyed, and yet the more intellectual senses may be un- influenced in their action. The cause of the superiority of the remaining intellectual senses, when one or more has been lost, is not owing to any superior organization in these senses, but is another example of the influence of education. The remaining senses are exerted attentively to com- pensate for the privation, and they become surprisingly delicate. We proceed to the consideration of the separate senses, beginning with that of tact or touch, because it is the most generally distributed, and may be regarded as that from which all the others are derived. They are all, indeed, modifications of the sense of touch. In the taste, the sapid body; in the smell, the odorous particle; in the hear- 1 Berard, Rapport du Physique et^du Moral, p. 245; Paris, 1823. SENSE OF TACT OR TOUCH. 93 ing, the sonorous vibration ; and in the sight, the particle of light, must impinge upon or touch the nervous part of the organ, before sensation can, in any of the cases, be effected. SENSE OF TACT OR TOUCH.—PALPATION. The sense of tact or touch is the general feeling or sensibility, possessed by the skin especially, and which instructs us regarding the temperature and the general qualities of bodies. By some, touch is confined to the sense of resistance alone; and hence they have conceived it necessary to raise into a distinct sense one of the attri- butes of tact or touch. The sense of heat, for example, has been separated from tact,a but we think on insufficient grounds. It pro- perly belongs to the sense we are considering, in the acceptation here given to it, and adopted by all the French physiologists. Ac- cording to them, tact is spread generally in the organs, and espe- cially in the cutaneous and mucous surfaces. It exists in all animals; whilst touch is exercised only by parts evidently destined for that purpose. Touch does not exist in every animal. It is nothing more than tact, joined to muscular contraction and directed by volition. So that, in the exercise of tact, we may be esteemed passive; in that of touch, active. The organs, concerned in touch, execute other functions besides; and in this respect touch differs from the other senses. Its chief organ, however, is the skin; and hence it is necessary to inquire into its structure, so far as is requisite for our purpose. 1. ANATOMY OP THE SKIN, HAIR, NAILS, &C. The upper classes of animals agree in possessing an outer enve- lope or skin, through, which the insensible perspiration passes, a slight degree of absorption takes place, the parts beneath are pro- tected, and the sense of touch is accomplished. In man, the skin consists of four parts,—the cuticle, rete muco- sum, corpus papillare, and corium. 1. The epidermis or cuticle is the outermost layer It is a dry, membranous structure, devoid of vessels and nerves, yet it is described by recent investigators as a tissue of a somewhat com- plex organization, connected with the functions of exhalation and absorption; but its vitality is regarded by them to be on a par with that of vegetables. The absence of nerves proper to it renders it insensible; it is coloured, exhales and absorbs in the manner of vegetables.b It is, so far as we know, entirely insensible. It resists putrefaction for a long time, and may be easily obtained in a separate state from the other layers, by maceration in water. It is the thin pellicle raised by a blister. The cuticle is probably a secretion from the true skin, which concretes on the surface, becomes dried, and affords an efficient pro- a Fleming's Philosophy of Zoology, i. 171, Edin. 1822; and Bostock's Physiology, 3d edit. p. 734, Lond. 1836. " Brit, and For. Med. Review, No. IV. p. 253, Oct. 1836. 94 SENSE OF TOUCH. tection to the corpus papillare beneath. It is composed, according to some, of concrete albumen; according to others, of mucus; and is said to be pierced by oblique pores for the passage of hairs, and for the orifices of exhalent and absorbent vessels. Breschet and Roussel de Vauzeme* affirm, that there is a special " blennogenous or mucific apparatus" for the secretion of this mucous matter, composed of a glandular parenchyma or organ of secretion situate in the substance of the derma, and of excretory ducts, which issue from the organ, and deposite the mucous matter between the papillae. It is probable, that this substance is placed at the surface of the body, not simply to protect the corpus papillare, but to prevent the constant imbibition and transudation that might take place did no such en- velope exist. The cuticle exfoliates, in the form of scales, from our heads; and, in large pieces, from every part of the body, after certain cutaneous diseases. According to Raspail,b it is formed of a collection of vesicles deprived of their contents, closely applied together, dried, and thrown off in the form of branny scales. He regards it as the outer layer of the corium. M. Flourens0 considers the derma to be covered by two layers of epidermis; the innermost of which is the seat of colour in the European. The colour of the areola around the mamma is owing to the same; whilst in the black or coloured races, there is, beneath the two membranes an organ for the secretion of the colouring matter. 2. The corpus or rete mucosum, rete Malpighii or mucous web, is the next layer. It was considered by Malpighi to be mucus, secreted by the papillae, and spread on the surface of the corpus papillare, to preserve it in the state of suppleness necessary for the performance of its functions. In this rete mucosum, the colouring matter of the dark races seems to exist. It is black in the African, or rather in the Ethiopian; and copper-coloured in the mulatto.11 Gaultiei*. considers the rete mucosum to be composed of four layers, but this notion is not universally admitted, and scarcely concerns the present inquiry. Breschet affirms, that there is a particular " chromato- genous or colorific apparatus," for producing the colouring matter, composed of a glandular or secreting parenchyma, situate a little below the papillae, and presenting particular excreting canals, which pour out the colouring matter on the surface of the derma. 3. The corpus papillare, or what Breschet calls the " neurothelic or mammillary nervous apparatus," is seated next below the rete mucosum. It consists of a collection of small papillae, formed by the extremities of nerves and vessels, which, after having passed through the corium beneath, are grouped in small pencils or villi in * Nouvelles Recherches sur la Structure de la Peau, par M. Breschet, Paris, 1835. See, also, Clinical Lectures on the Skin, by Dr. Wm. Wallace, in London Lancet Nov and Dec. 1837 ; Meckel's Handbuch, B. ii. and Weber's Hildebrandt i 189 b Chimie Organique, p. 245, Paris, 1833. c Gazette Medicale de Paris, Mars, 1838. t Sir E. Home, Lect. on Comp. Anat. v. 278. • Recherches Anatomiques sur le Systeme Cutane de I'Homme, Paris, 1811. ORGANS OF TOUCH. 95 a spongy, erectile tissue. These pencils are disposed in pairs, and, when not in action, are relaxed, but become erect when employed in the sense of touch. They are very readily seen, when the cutis vera is exposed by the action of a blister, and are always evident at the palmar surface of the hand, and especially at the tips of the fingers, where they have a concentric arrangement. These villi are sometimes called the papillae of the skin. 4. The corium, cutis vera, derma, or true skin, is the innermost of the layers of the skin. It consists of a collection of dense fibres, intersecting each other in various directions, and leaving between them holes for the passage of vessels and nerves. It forms a firm stratum, giving the whole skin the necessary solidity for accom- plishing its various ends. The true skin consists chiefly of gelatine. Hence it is used in the manufacture of glue. Gelatine, when united with tannin, forms a substance which is insoluble in water; and it is to this combina- tion, that leather owes the properties it possesses. The hide is first macerated in lime-water to remove the cuticle and hairs, and leave the corium or gelatine. This is then placed in an infusion of oak bark, which contains the tannin. The tannin and the skin unite, and leather is the product. These four strata con- Fig. 16. stitute the shin, as it is commonly called ; yet all are comprised in the thickness of two or three lines. The cutis vera is united to the struc- tures below by Cellular Common Integument. I A 4-W -+U 1. Cuticle. 2. Rete mucosum. 3. Corpus papillare. 4. Cutis memorane; and tniS Wltn vera. 5. Cellular membrane. 6. Panniculus carnosus. the layers external to it, forms the common integument. In certain parts of the body, and in animals more particularly, the cutis vera is adherent to muscular fibres; inserted more or less obliquely, as at 6, Fig. 16. These form the muscular web, mantle or panniculus carnosus. The layer is well seen in the hedge-hog and porcupine, in which it rolls up the body, and erects the spines; and in birds, it raises the feathers. In man, it can hardly be said to exist. Some muscles, however, exe- cute a similar function. By the occipito-frontalis, for instance, many persons can move the hairy scalp: and by the dartos, the skin of the scrotum can be corrugated. These two parts, therefore, act as panniculi carnosi. In the skin are situate numerous sebaceous follicles or crypts, which separate an oily fluid from the blood, and pour it over the surface to lubricate and defend it from the action of moisture. They are most abundant, where there are folds of the skin, or hairs, or where the surface is exposed to friction. We can generally see them on the pavilion of the ear, and their situation is often indicated by small dark spots on the surface, which, when pressed between 96 SENSE OF TOUCH. the fingers, may be forced out along with the sebaceous secretion, in the form of small worms. By the vulgar, indeed, these are considered to be worms. The follicular secretions will engage us hereafter. At present, it is sufficient to remark, that they differ materially according to the part of the body where they exist ;— the characters of the fluids secreted in the axillae, groins, feet, &c. varying considerably. The consideration of the hair belongs naturally to that of the skin. The roots of the hair are in the form of bulbs, taking their origin in the cellular membrane. Around each bulb there are two capsules, the innermost of which is vascular. The hair itself con- sists of a horny, external covering, and a central part, called the medulla or pith. When we take hold of a hair by the base, with the thumb and forefinger, and draw it through them from the root towards the point, it feels smooth to the touch; but if we draw it through, from the point to the root, we feel the surface rough, and it offers considerable resistance. It is, therefore, concluded, that the hair is bristled, or consists of eminences pointing towards its outer extremity, and it is upon this structure, that the operation of felting is dependent—the hairs being mechanically entangled to- gether, and retained in that state by the inequalities of their surface. Observers have, however, frequently failed in detecting this striated appearance, by the aid of the microscope; and Dr. Bostocka affirms, that he had an opportunity of viewing the human hair, and the hair of various kinds of animals, in the excellent microscope of Mr. Bauer, but without being able to detect it. Still, Bichat,b and more recently, Dr. Goring,0 have assigned this as their structure;—the fact having been exhibited by the microscope, and, in their minds, admitting of no doubt. The colour of the hair is singularly different in different races and individuals. By some, this is considered to depend upon the fluids contained in the pith. Vauquelind analyzed the hair most atten- tively, and found that it consists chiefly of an animal matter, united to a portion of oil, which appears to contribute to its flexibility and cohesion. Besides this, there is another substance, of an oily nature, from which he considers the colour of the hair to be derived. The animal matter, according to that chemist, is a species of mucus, but other chemists believe it to be chiefly albumen. Vauquelin found that the colouring matter of the hair is destroyed by acids; and he suggests, that when it has suddenly changed colour and become gray, in consequence of any great mental agitation, this may be owing to the production of an acid in the system, which acts upon the colouring matter. The explanation is purely hypothetical, and is considered, and characterized as such by Dr. Bostock; but the same objection must be admitted to apply to the view he has substi- tuted for it. He conceives it " more probable that the effect depends * Physiology, p. 52, 3d edit., Lond. 1836. " b Anat. General, torn. iv. Journal of Science, New Series, vol. i. 433. d Annales de Chimie, torn. Iviii. 41, Paris, 1806. ORGANS OF TOUCH. 97 upon the sudden stagnation of the vessels, which secrete the colour- ing matter, while the absorbents continue to act and remove that which already exists." There is, however, no more real evidence of " stagnation of vessels" than there is of the formation of an acid. Our knowledge is limited to the fact, that a sudden and decided change in the whole pileous system occurs after great or prolonged mental agitation." But a similar, though more gradual change, is produced by age. We find some persons entirely gray at a very early period of life; and, in old age, the change happens universally. It is not then difficult to suppose, that some alteration in the nutrition of the hair may be induced, resembling that which occurs under these circumstances. Dr. Bostock doubts the fact of such sudden conversions; but the instances are too numerous for us to consider them entirely fabulous. Besides, as we have seen, the cases are not so preternatural as they might at first sight appear. The change induced is identical with that which occurs naturally to every indi- vidual, sooner or later. Lepelletierb ascribes the change of colour to two very different causes. First, to defective secretion of the colouring fluid, without any privation of nutrition. In this case, the hairs may live and retain their hold, as we observe in young individuals:—and secondly, to the canals, which convey the fluid into the hair, being obliterated, as in old age. The same cause, acting on the nutritious vessels of the bulb, produces, successively, privation of colour, death, and loss of these epidermoid productions. According to other physiologists, the seat of colour is in the horny covering of the hair; and, in the largest hairs or spines of the por- cupine, this seems to be the case, the pith being manifestly white, and the horny covering coloured. The exact relations between the cuticle, the rete mucosum and the hair are not known. It is not determined, whether the layers are simply perforated by the hair in its passage outwards, or whether they furnish it coats as it proceeds along. There is often, however, an intimate relationship observed between the colour of the hair and that of the rete mucosum. The fair complexion is accompanied a " My hair is gray, but not with years, Nor grew it white in a single night, As men's have grown from sudden fears." Byron's " Prisoner of Chillon.'" " Danger, long travail, want and wo, Soon change the form that best we know: For deadly fear can time outgo, And blanch at once the hair. Hard toil can roughen form and face, And want can quench the eye's bright grace, Nor does old age a wrinkle trace More deeply than despair." Scott's "Marmion." b Traite de Physiologie Medicale et Philosophique, torn. iii. p. 42, Paris, 1832. VOL. I. 9 98 SENSE OF TOUCH. with light hair;—the swarthy with dark;—and we see the connexion still more signally displayed in those animals that are spotted—the colour of the hair being variegated like that of the skin. Hairs differ very materially, according to the part of the body on which they appear. In some parts they are short, as in the armpits, whilst on the head it is not easy to say what would be the precise limit to the growth, were they left entirely to nature. In the Malay, it is by no means uncommon to see them touch the ground. The hair has various names assigned to it, according to the part on which it appears,—as beard, ivhiskers, mustachios, eyebrows, eye- lashes, &c. In many animals it is long and straight; in others crisped, when it is called wool. If stiff, it is termed a bristle ; if in- flexible, a spine. The hairs are entirely insensible, and, excepting in their bulbous portion, are not liable to disease. Dr. Bostock affirms, that under certain circumstances they are subject to a species of inflammation, when vessels may be detected, at least in some of them, and they become acutely sensitive. The sensibility of the hair, under any known circumstance, may, however, be doubted. It appears to be almost anorganic, except at its root; and, like the cuticle, resists putrefaction for a great length of time. Bichat and Gaultier were of the opinion of Dr. Bostock;—misled, apparently, by erroneous reports concerning the plica polonica; but Baron Larreya has satis- factorily shown, that the affection is confined to the bulbs, and that the hairs themselves continue totally devoid of sensibility. It is difficult to assign a plausible use for the hair. That of the head has already engaged our attention; but the hair, which appears on certain parts at the age of puberty and not till then, and that on the chin and upper lip of the male sex only, set our ingenuity at defiance. In this respect, however, the hair is not unique. Many physiologists regard certain parts, which exist in one animal, appa- rently without function, but which answer useful purposes in ano- ther, to be vestiges, indicating the harmony which reigns through nature's works. The useless nipple on the breast of one sex might be looked upon in this light; but the tufts of hair on various parts cannot, in any way be assimilated to the hairy coating, that en- velopes the bodies of animals, and is, in them, manifestly intended as a protection against cold. There is another class of bodies connected with the skin, and analagous in nature to the last described,—the nails. These serve a useful purpose in touch, and consequently require notice here. In the system of De Blainville, they constitute a subdivision of the hairs, which he distinguishes into simple and compound—simple, when each bulb is separated, and has a distinct hair— compound, when several pileous bulbs are agglomerated, so that the different hairs, as they are secreted, are cemented together to form one solid a Memoires de Chirurgie Militaire, t. iii. 108, Paris, 1812. PHYSIOLOGY OF TOUCH. 99 body of greater or less size,—a nail, scale, horn, See. In man, the nail alone exists, the chief and obvious use of which is to support • the pulp of the finger, whilst it is exercising touch. Animals are provided with horns, beaks, hoofs, nails, spurs, scales, &c. All these, like the hair, grow from roots, and are considered to be analogous in their physical and vital properties. Meckel, and De Blainville, Bonn, Walther, Lavagna,a and others, are, indeed, of opinion, that the teeth are of the same class, and that they belong, originally, to the skin of the mouth. For physiological purposes the above description is enough, and r more than enough. A few words will be necessary regarding the mucous membranes, which resemble the skin so much in their proper- ties, as to be, with propriety, termed dermoid. If we trace the skin into the various outlets, we find, that a continuous, soft, velvety membrane exists through their whole extent; and, if the channel have two outlets, as in the case of the alimentary canal, this mem- brane, at each outlet, commingles with the skin, and appears to differ but slightly from it. So much indeed, do they seem to form part of the same organ, that physiologists have described the absorption, which takes place from the intestinal mucous membrane, as external. They cannot, however, in the higher order of animals, be con- sidered completely identical; nor is the same membrane alike in its whole extent. They have all been referred to two great surfaces; —the gastro-pulmonary—comprising the membranes of the outer surface of the eye, of the ductus ad nasum, of the nose, of the mouth, and of the respiratory and digestive passages; and the genito-urinary—which line the whole of the genital and urinary apparatuses. In addition to these, a membrane of similar character lines the meatus auditorius externus, and the excretory ducts of the mammae. The analogy between the skin and mucous membranes is farther shown by the fact, that if we invert the polypus, the mucous mem- brane gradually assumes the characters of the skin, and the same circumstance is observed in habitual descents of the rectum and uterus. In the mucous membranes—especially at their extremities, which appear to be alone concerned in the sense of touch—the same super- position of strata exists as in the skin—viz. epidermis, rete mucosum, corpus papillare, and cutis vera. They have likewise similar folli- cles, called mucous, but nothing analogous to the hairs, unless we regard the teeth to be so, in correspondence with the views of Meckel, De Blainville, and others. 2. PHYSIOLOGY OP TACT AND TOUCH. In describing the physiology of the sense of touch it will be con- venient to revert to the distinction, already made, between the sense 1 Art. Schleimhaute, in Pierer's Anat. Phys. Real. Worterb. vii. 272, Altenb. 1827. 100 SENSE OF TOUCH. when passively and when actively exerted, or between tact, and touch. The mode, however, in which the impression is made on each is alike, and equally simple. It is merely necessary, that the substance, which has to cause it, should be brought in contact with the physical part of the organ—the cuticle; the nervous part is seated in the corpus papillare, for if the nerves proceeding to this layer of the skin be cut, the sense is destroyed. In the exercise of touch, each of the layers seems to have its appropriate office: the corium, which forms the innermost layer—the base on which the others rest—offers the necessary resistance, when bodies are applied to the surface; the rete mucosum is either unconcerned in the func- tion, or keeps the corpus papillare in the necessary state of supple- ness: the erectile tissue, on which the papillae are grouped, probably aids them in their appreciation of bodies; and the epidermis modifies the tactile impression, which might become too intense, or be pain- ful, did this envelope not exist. The degree of perfection of the sense is, indeed, greatly influenced by the state of the cuticle. Where it is thin,—as upon the lips, glans penis, clitoris, &c.—the sense is very acute; but, where thick and hard, it is very obtuse; and where removed,—as by blistering,—the contact of bodies gives pain, but does not occasion the appropriate impressions of touch. Professor Webera has shown, that the tactile power of the skin is not proportionate to its sensibility. The mammae, for example, are easily tickled, and susceptible of great pain when irritated, yet they are moderately endowed with the sense of touch. The dif- ferent parts of the skin, too, vary considerably in their tactile power. The left hand, in most persons, is more sensible to temperature than the right, probably owing to the epidermis being thinner from less use. It has been supposed, that some of the recorded instances of great resistance to heat have been caused by unusual thickness, and com- pactness of cuticle, together with a certain degree of insensibility of the skin. The latter may be an important element in the explana- tion, but some of the feats, executed by persons of the character alluded to, could hardly have been influenced by the former, as the resistance seemed almost equally great in the delicately organized mucous membranes. A Madame Girandelli,—who exhibited in Great Britain, many years ago,—was not only in the habit of draw- ing a box with a dozen lighted candles along her arm, and of putting her naked foot upon melted lead, but of dropping melted sealing- wax upon her tongue, and impressing it with a seal, without ap- pearing to experience the slightest uneasiness; and, some years ago, (1832,) a man of the name of Chabert excited in this country, the surprise, which followed his exhibitions in London a year or two previously, and which gained him the appellation of the " Fire * See, on the sensibility, &c. of various parts of the skin, Prof. Weber's experiments detailed by Dr. Allen Thomson, in Edinb. Med. and Surg. Journal, for July, 1833, or the analysis of Weber's work, De Pulsu, Resorptione, Auditu et Tactil, &c, Lips. 1834; in Dublin Journal of Medical Science, March, 1836. PHYSIOLOGY OF TOUCH. 101 King." In addition to the experiments performed by Madame Girandelli, Chabert swallowed forty grains of phosphorus, washed his fingers in melted lead, and drank boiling Florence oil with per- fect impunity. In the case of the phosphorus he professed to take an antidote, and doubtless did so. It is probable, also, that agents were used by him to deaden the painful impressions ordinarily pro- duced by hot bodies, when applied to the surface. A solution of borax or alum, spread upon the skin is said to exert a powerful effect of this kind; but, in addition to the use of such agents, there must be a degree of insensibility about the corpus papillare, otherwise it is difficult to understand why these hot substances did not injure the coats of the stomach. We see, daily, striking differences in the sensibility of the mucous membrane of the mouth and gullet, and are frequently surprised at the facility with which certain persons swallow fluids, at a temperature, which would excite the most uneasy sensations in others. In this, habit has«unquestionably much to do.a In the mucous membranes, tact is effected precisely in the same way as in the skin. The layers, of which it is constituted, partici- pate in like manner; but the sense is more exercised at the extremi- ties of the membrane than internally. The food, received into the mouth, is felt there, but after it has passed into the gullet it excites hardly any tactile impression, and it is not until it reaches the lower part of the membrane, in the shape of excrement, that its presence is again indicated by this sense. Pathologically, we have some striking instances of this difference in the different parts of a mucous membrane. If an irritation exists within the intestinal canal, the only notice we may have of it is by itching of the nose,—in other words, at one of the extremities of the membrane. In like manner, a calculus in the bladder is indicated by itching of the glans penis. A similar exemplification is offered during the passage of a gall-stone through the ductus communis choledochus: calculi occasionally form in the biliary passages, and, after a time, enter the common duct in their way to the intestine: on their first entrance, the pain experienced is of the most violent character; this, after a time, subsides,—as soon, indeed, as the cal- culus has got fairly into the canal; but violent irritation is again ex- perienced when it is about to clear the duct and enter the intestine. One of the great purposes of the sense of tact is to enable us to judge of the temperature of bodies. This office it executes alone. No other sense participates in it. It requires no previous exercise; is felt equally by the infant and the adult, and requires only the proper developement of its organs. The relative temperature of bodies is accurately designated by the instrument called the thermometer; very inaccurately by our own sensations, and the reason of this inaccuracy is sufficiently a Beckmann's History of Inventions and Discoveries, translated by Johnson, vol. iii. p. 276, Lond. 1817; and Sir D. Brewster's Letters on Natural Magic, Amer. edit, p 274, New York, 1832. 9* 102 SENSE OF TOUCH. intelligible. In both cases, the effect is produced by the disengage- ment of a subtile fluid, called caloric or the matter of heat, which pervades all bodies, and is contained in them to a greater or less extent. This caloric is constantly passing, and repassing, between bodies, either by radiation or by positive contact, until they attain the like temperature, or until there is an equilibrium of caloric, and all have the same temperature as indicated by the thermometer. Hence, objects in the same apartment will exhibit, ceteris paribus, the like temperature by this test. From this law, however, the animal body must be excepted. The power which it possesses of generating its own heat, and of counteracting the external influences of temperature, preserves it constantly at the same point. This will fall under consideration in another place. Although, however, all objects may exhibit the same temperature, in the same apartment, when the thermometer is applied to them, the sensations experienced may be very different. Hence the diffi- culty, which the uninstructed have in believing that they are actually of identical temperature;—that a hearth-stone, for instance, is of the same degree of heat as the carpet in a chamber. The cause of the different sensations, experienced in the two cases, is, that the hearth- stone is a much better conductor of the matter of heat than the carpet. The consequence is, that caloric is more rapidly abstracted by it from the part of the body which comes in contact with it, than it is by the carpet; and the stone appears to be the colder of the two. For the same reason, when these two substances are raised in tem- perature above that of the human body, the hearth-stone will appear the hotter of the two; because, it conducts caloric and communi- cates it more rapidly to the body than the carpet.a When the temperature of the surrounding air is higher than 98°, we receive caloric from the atmosphere, and experience the sensa- tion of heat. The human body is capable of being penetrated by the caloric of substances exterior to it, precisely like those substances themselves; but, within certain limits, it possesses the faculty of consuming the heat and retaining the same temperature. When the temperature of the atmosphere is only as high as our own—an elevation which it not unfrequently attains in many parts of the United States—we still experience the sensation of unusual warmth: yet no caloric is communicated to us. The cause of this feeling is, that we are accustomed to live in a medium of a less elevated temperature, and consequently to give off caloric habitually to the atmosphere. Lastly, in an atmosphere of a temperature much lower than that of the body, heat is incessantly abstracted from us; and, if rapidly abstracted, we have the sensation of great cold. From registers, kept by the illustrious founder of the University of Virginia, Mr. Jefferson, at his residence at Monticello,b lat. 37° * Turner's Elements of Chemistry, 6th Amer. edit, by Dr. F. Bache, Philad 1835 b Virginia Literary Museum, p. 36, Charlottesville, 1830. PHYSIOLOGY OF TOUCH. 103 58', long. 78° 40', it appears that the mean temperature of this part of Virginia is about 55^° or 56°; that the thermometer varies from 5^° in the coldest month, to 94° in the warmest. Now, the tem- perature of the human body being 98°, it follows, that heat must be incessantly taken from us, and that we ought therefore to expe- rience constantly the sensation of cold; and this we should unques- tionably do, were we not protected by clothing, and aided by the artificial temperature of our fires during the colder seasons. Yet, accustomed as the body is to give off caloric, there is a tem- perature, in which, clothed as we are, we do not feel cold, although we may be disengaging heat to some extent. This temperature may perhaps be fixed somewhere between 70° and 80°, in the climate of the middle portions of the United States. So much, however, are our sensations in this respect dependent upon the temperature which has previously existed, that the comfortable point will be found to vary at different seasons. If the thermometer, for instance, has ranged as high as 98°, and if, for a few days, it has maintained this elevation, a depression of 15° or 20° will be accompanied by feelings of discomfort; whilst a sudden elevation from 30° to 75° may occa- sion an oppressive feeling of heat. In northern Siberia, M. von Wrangel* found, that only a few degrees of frost was currently denominated " warm weather;" and that after having been accus- tomed to the winter temperature of that climate, it seemed to him, that 10° of cold, 22° below the freezing point of Fahrenheit, was quite a mild temperature. During the voyages, made by Captain Parry and others, to discover a northwest passage, it was found, that after having lived for some days in a temperature of 15° or 20° below 0, it felt quite mild and comfortable when the thermometer rose to zero. This is the great source of the deceptive nature of our sensations of warmth and cold. They enable us merely to judge of the com- parative conditions of the present and the past; hence it is, that a deep cellar appears warm to us in winter and cold in summer. At a certain distance below the surface, the temperature of the earth indicates the medium heat of the climate; yet, although this may be stationary, our sensations on descending to it in winter and in sum- mer would be by no means the same. If two men were to meet each other on the middle of the South American Andes,—the one having descended, and the other ascended,—their sensations would be very different. The one, who had descended, coming from a colder to a warmer atmosphere, would feel warm; whilst the tra- veller, who had ascended, would feel correspondency cool. An experiment, often performed in the chemical lecture-room, although strictly physiological, exhibits the same fact. If, after having held one hand in iced water, and the other in warm water, we plunge both into water of a medium heat, it will seem warm to the one hand and cold to the other. But our sensations are not guided solely by bodies surrounding a Reise des Kaiserlich Russischen Fotten Lieutenants F. v. Wrangel, langs der Nordkilste von Siberien, u. s. w. Berlin, 1839. 104 SENSE OF TOUCH. us. They are often greatly dependent, especially in disease, on the state of the animal economy itself. If the power, which the system possesses of forming heat, be morbidly depressed—or if, in consequence of old age, or of previous sickness, calorification does not go on regularly and energetically, a temperature of the air, which to the vigorous is agreeable, may produce an unpleasant impression of cold. Under opposite circumstances, a feeling of heat may exist. By tact we are likewise capable of forming a judgment of many of the qualities of bodies,—such as their size, consistence, weight, distance, and motion. This faculty, however, is not possessed ex- clusively by the sense in question. We can judge of the size of bodies by the sight; of distances, to a certain extent, by the ear, &c. To appreciate these characteristics, it is necessary, that the sense should be used actively, and that we should call into exercise the admirable instrument with which we are provided for that purpose. In treating of the external senses generally, it was remarked, that we are capable of judging, by their aid, of impressions made on us by portions of our own body. By the sense of touch we can de- rive information regarding its temperature, shape, consistence, &c. An opinion has, indeed, been advanced, that this sense is best adapted for proving our own existence, as every time that two por- tions of the body come into contact, two impressions are conveyed to the brain, whilst if we touch an extraneous body we have but one. The tact of the mucous membranes is extremely delicate. The great sensibility of the lips, tongue, conjunctiva, Schneiderian mem- brane, lining membrane of the trachea and urethra is familiar to all. Excessive pain is produced in them by the contact of extraneous bodies; yet, in many cases, we see the effect of habit in blunting sensation singularly exemplified. The first introduction of a bougie into the urethra will produce intense irritation; but after a few repetitions the sensation may become scarcely disagreeable. To appreciate accurately the shape and size of objects, it is neces- sary, that they should be embraced by a part of the body, which can examine their various surfaces and be applied to them in every direction. In man, the organ well fitted for this purpose is the hand. This is situate at the free extremity of a long and flexible member, which admits of its being moved in every direction, and renders it not only well adapted for the organ of touch but for that of pre- hension, as will be seen in another place. Man alone possesses a true hand; for although other animals have organs of prehension very similar to his, they are much less complete. Aristotle, indeed, and Galen term it the instrument of instruments. The chief supe- riority of the hand consists in the size and strength of the thumb, which stands out from the fingers, and can be brought in opposition to them, so as to enable us to grasp bodies, and to execute various mechanical processes under the guidance of the intellect. So im- portant an organ was the thumb esteemed by Albinus,a that he a De Sceleto, p. 465. PHYSIOLOGY OF TOUCH. 105 called it a lesser hand assisting the larger—" manus parva majori adjulrix^ and the construction of the hand has been considered worthy of forming the subject of one of the " Bridgewater Trea- tises"—"On the Power, Wisdom, and Goodness of God, as mani- fested in the Creation,"—a task assigned to Sir Charles Bell.b In addition to the advantages referred to, the hand is furnished with a highly sensible integument. The papillae are largely deve- loped, especially at the extremities of the fingers, where they are ranged in concentric circles, and rest upon a spongy tissue, by many physiologists considered to be erectile, and serving as a cushion. At the posterior extremity of the fingers, the nails are situate, which support the pulps of the fingers behind, and render the contact with bodies more immediate. This happy organization of the soft parts of the hand alone concerns the sense of touch directly. The other advantages, which it possesses, relate to the power of applying it under the guidance of volition. Of the mode in which touch is effected it is not necessary to treat:—being nothing more than tact, exerted by an appropriate instrument, the physiology of the two must be identical. Metaphysicians have differed widely regarding the services that ought to be attributed to the touch. Some have greatly exaggerated them, considering it the sense par excellence or the first of the senses. It is an ancient notion to ascribe the superiority of man over ani- mals and his pre-eminence in the universe—his intelligence, in short —to the hand. Anaxagoras asserted, and Helvetiusc revived the idea, "that man is the wisest of animals because he possesses hands." The notion has been embraced, and expanded by Condillac,d Buffon,e and many modern physiologists and metaphysicians. Buffon, in particular, assigned so much importance to the touch, that he be- lieved the cause why one person has more intellect than another is, his having made a more prompt and repeated use of his hands from early infancy. Hence he recommended, that infants should be allowed to use them freely from the moment of birth. Other metaphysicians have considered the hand the source of our mechanical capabilities; but the same answer applies to all these views. The hand can only be regarded as an instrument by which information of particular kinds is conveyed to the brain, and by which other functions are executed, under the direction of the will. The idiot has the sense frequently more delicate than the man of genius or than the best mechanician, whilst the most ingenious artists have by no means the most delicate touch. We have, indeed, some striking cases to show, that the hand is not entitled to this » Lawrence's Lectures on Physiology and Zoology, &c, Lond. 1819. b The Hand, its Mechanism, and Vital Endowments, as evincing Design. Amer. Edit. Philad. 1833 ; see also, Kidd on the Adaptation of External Nature to the Physi. cal Condition of Man (Bridgewater Treatise), Amer. Edit. Philad. 1833, p. 33. e De I'Homme, &c. torn. i. d Traite des Sensations, P. i. e Histoire Naturelle, torn. vi. 106 SENSE OF TOUCH. extravagant commendation. Not many years ago, a Miss Biffin was exhibited in London, who was totally devoid of both upper and lower extremities; yet she was unusually intelligent and ingenious. It was surprising to observe the facility with which she hem-stitched, turning the needle with the greatest rapidity in her mouth, and in- serting it by means of the teeth. She also painted miniatures faith- fully, and beautifully;—holding the pencil between her head and neck. All her motions were, in fact, confined to the tongue and lips, and to the muscles of the neck. Magendie3 alludes to a similar case. He says, that there was, at that time, in Paris, a young artist, who had no signs of arm, forearm, or hand, and whose feet had one toe less than usual—the second; yet his intelligence was, in no respect, inferior to that of boys of his own age; and he even gave indications of distinguished ability. He sketched and painted with his feet. Within the last few years, a Miss Honeywell, born without arms, has travelled about this country. She has acquired so much dexterity in the use of the scissors, as to be able, by holding them in her mouth, to cut like- nesses, watch-papers, flowers, &c. She also writes, draws, and executes all kinds of needlework with the utmost ease and despatch. How fatal are these authentic examples to the views of Helvetius, and others! But, it has been said, the touch is the least subject to error of all the senses, and that it is the regulating—the geometrical sense. In part only is this accurate. It certainly possesses an advantage in allowing the organ to be brought into contact with the body that excites the impression, whilst, in the cases of vision and olfaction, the organ receives only the impression of an emanation from the body; and, in that of audition, only a vibration of an intervening medium. Yet some of the errors into which it falls are as grievous as those that happen to the other senses. How inaccurate is its appreciation of the temperature of bodies! We have attempted to show, that it affords merely relative knowledge,—the same substance appearing hot or cold to us, according to the temperature of the substance previously touched. Nay, this infallibility so little exists, that we have the same sensation communicated to us by a body that rapidly abstracts caloric from us, as by one that supplies it rapidly. By touching frozen mercury, which requires a temperature of—40° of Fahrenheit to congeal, we experience the sensation of a burn! Again, if we cross the fingers and touch a rounded body—a marble, for instance—with two of the pulps at the same time; instead of experiencing the sensation of one body, we feel as if there were two,—an illusion produced by the lateral portions of fingers being brought in opposition, which are naturally in a dif- ferent situation, and at a distance from each other ; and, as these twro parts habitually receive distinct impressions when apart, they continue to do so when applied to opposite sides of the rounded bodv. a Precis Elementaire, 2de 6dit. i. 154, Paris, 1825, PHYSIOLOGY OF TOUCH. 107 It has been asserted, again, that the touch is the great corrector of the errors into which the other senses fall. But let us inquire, whether, in this respect, it possesses any decided superiority over the other senses. For this purpose, it is well to adopt the distinction of the functions of the senses into immediate and mediate. Each sense has its immediate function, which it possesses exclusively; for which, in other words, no other can be substituted. The touch instructs us regarding temperature; the taste appreciates savours; the smell, odours; audition, sound ; and vision, colours. These are the immediate functions of the senses, each of which can be accom- plished by its own organs, but by no other.1 As concerns the im- mediate functions of the senses, therefore, the touch can afford no correction. Its predominance, as regards the mediate functions of the senses, is likewise exaggerated. The mediate functions are those that are auxiliary to the senses, consisting in the impressions they furnish to the mind, and by aid of which it acquires its notions of bodies. The essential difference between these two sets of functions is, that the mediate can be effected by several senses at once. Vision, olfaction, and audition participate in judging of distances, as well as touch; the sight instructs us regarding shape, &c. It has, indeed, been affirmed by metaphysicians, that the touch is necessary to several of the senses to give them their full power, and that we could form no notion of the size, shape, and distance of bodies, unless instructed by this sense. The remarks already made have proved the inaccuracy of this opinion. The farther examination of it will be resumed under the subject of vision. The senses are, in truth, of mutual assistance. If the touch falls into error, as in the case of inaccurate appreciation of temperature, the sight, aided by appropriate instruments, dispels it. If the crossed fingers convey to the brain the sensation of two rounded bodies, when one only exists, the sight apprises us of the error; and if the sight and touch united impress us with a belief in the identity of two liquids, the smell or the taste will often detect the erroneous inference. But it has been said by some, touch is the only sense that gives us any notion of the existence of bodies. Destutt-Tracyb has satis- factorily opposed this, by showing that our notion of the existence of bodies is a work of the mind, in acquiring which the touch does not assist more immediately than any other sense. " The tactile sensations," he observes, " have not of themselves any prerogative essential to their nature, which distinguishes them from every other. If a body affect the nerves beneath the skin of my hand, or if it produce certain vibrations in those distributed on the membranes of my palate, nose, eye, or ear, it is a pure impression which I receive; a simple affection which I experience; and there seems to be no reason for believing that one is more instinctive than another; that one is a Mullcr's Elements of Physiology, by Baly, Part v. p. 1069, London, 1839. b Elemens d'Ideologic, Partie i. 114,2de edit. Paris, 1804. 108 SENSE OF TOUCH. more adapted than another for enabling me to judge that it proceeds from a body exterior to me. Why should the simple sensation of a puncture, burn, titillation, or pressure, give me more knowledge of the cause, than that of a colour, sound, or internal pain ? There is no reason for believing it." There are, indeed, numerous classes of bodies, regarding whose existence the touch affords us not the slightest information, but which are detected by the other senses. On the whole, then, we must conclude, that the senses mutually aid each other in the execution of certain of their functions ; but. that each has its province, which cannot be invaded by any of the others; and that too much preponderance has been ascribed to the touch by metaphysicians and physiologists. Ministering, however, so largely to the mind, it has been properly ranked with vision and audition as an intellectual sense.* By education, the sense of touch is capable of acquiring extraor- dinary acuteness. To this circumstance we must ascribe the sur- prising feats we occasionally meet with in the blind. Saunderson, —who lost his eyesight in the second year of his life, and was Pro- fessor of Mathematics at Cambridge, England,—could discern false from genuine medals, and had a most extensive aquaintance with numismatics.b Baczko, referred to by Rudolphi,0 and who describes his own case, could discriminate between samples of woollen cloth of equal quality but of different colours. The black appeared to him among the roughest and hardest; to this succeeded dark blue and dark brown, which he could not, however, distinguish from each other. The colours of cotton and silk stuff he was unable to discriminate, and he properly enough doubts the case of a Count Lynar, who was blind, and said to be capable of judging of the colour of a horse by the feel. The only means the blind can possess of discriminating colours must be through the inequalities of surface produced by them; and if these were insufficient to enable Baczko to detect the differences between cotton and silk fabrics, it is not probable that the sleek surface of the horse would admit of such discrimination. In animals the organ of touch varies. The monkey's resembles that of man. In other quadrupeds it is seated in the lips, snout, or proboscis. In molluscous animals the tentacula, and in insects, the antennas or feelers, are organs of touch, possessing, in some, very great sensibility. Bats appear to have this sensibility to an unusual degree. Spallanzani observed these animals, even after their eyes had been destroyed and ears and nostrils shut up, flying through intricate passages, without striking against the walls, and dexterously avoiding cords and lines placed in their way. The membrane of the wings is, in the opinion of many, the organ that receives the impres- sion produced by a change in the resistance of the air. M. Jurine, a Gall, sur les Fonctions du Cerveau, i. 99, Paris, 1825. b Abercrombie's Inquiries concerning the Intellectual Powers; Amer. Edit p 55 New York, 1832. ' ' c Grundriss der Physiologie, Berlin, 1821, &c. ORGANS OF TASTE. 109 indeed, concludes that neither the sense of touch, hearing, nor smell is the medium through which bats obtain perceptions of the pre- sence and situation of surrounding bodies. He ascribes this extra- ordinary faculty to ihe great sensibility of the skin of the upper jaw, mouth, and external ear, which are furnished with very large nerves; whilst Sir Anthony Carlisle attributes it to the extreme delicacy of hearing possessed by the animal;a but certain experiments, made by Mr. Broughton,b sanction the idea, that it'may be dependent upon their whiskers. These whiskers, which are found on the upper lip of feline and other animals, are plentifully supplied with nerves, which seem to proceed from the second branch of the fifth pair, and are lost in the substance of the bristles. In an experiment, which Mr. Broughton made on a kitten, he found that whilst the whiskers were entire, it was capable of threading its way, blindfold, out of a labyrinth, in which it was designedly placed; but that it was totally unable to do so when the whiskers were cut off. It struck its head repeatedly against the sides; ran against all the corners; and tum- bled over steps placed in its way, instead of avoiding them as it did prior to the removal of the whiskers. From facts like these Mr. Broughton drew the conclusion, that certain animals are supplied with whiskers for the purpose of ena- bling them to steer clear of opposing bodies in the dark. SENSE OF TASTE OR GUSTATION. The sense of taste teaches us the quality of bodies called sapidity It is more nearly allied to touch in its mechanism than any other of the senses, as it requires the immediate contact of the body with the organ of taste; and as that organ is, at the same time, capable of receiving tactile impressions distinct from those of taste. Of this w7e have a striking example. If we touch various parts of the tongue with the point of a needle, we find two distinct perceptions occasioned. In some parts we experience the sensation of a pointed body without savour; and in others a metallic taste is manifested. Pathological cases, too, exhibit, that the sense of taste may be lost, whilst the general sensibility remains,—and conversely. The organ of gustation is not, therefore, restricted to the production of that sense, but participates in the sense of touch. Yet so distinct are those functions, that the touch can, in no wise, supply the place of its fellow, in detecting the sapidity of bodies. This last is the imme- diate instruction afforded by gustation. 1. ANATOMY OF THE ORGANS OF TASTE. The chief organ of taste is the tongue, or rather the mucous membrane covering the upper surface, and sides of that organ. The lips, inner surface of the cheeks, the palate, and fauces, participate in the function, especially when particular savours are concerned. Magendie0 includes the oesophagus and stomach, but we know not a Roget's Animal and Vegetable Physiology, ii. 399, Amer. Edit. Phila. 1836. b London Medical and Physical Journal, for 1823. c Precis de Physiol., i. 139. VOL. I. 10 110 SENSE OF TASTE. Fig. 17. on what grounds. His subsequent remarks, indeed, controvert the idea. The lingual branch of the fifth pair is, according to him, in- contestably the nerve of taste; and, as this nerve is distributed to the mouth, we can understand, why gustation should be effected there, but not how it can be accomplished in the oesophagus and stomach. The tongue consists almost entirely of muscles, which give it great mobility, and enable it to fulfil the various functions assigned to it; for it is not only an organ of taste, but of mastica- tion, deglutition, and articulation. These muscles, being under the influence of volition, enable the sense to be executed passively or actively. As regards gustation, the mucous membrane is the portion that immediately concerns us. This is formed, like the mucous mem- branes in general, of the different layers already described. The corpus papillare, however, requires additional notice. If the surface of the tongue be examined, it will be found to consist of myriads of fine papillae or villi, giving the organ a velvety appearance. These papilla? are, doubtless, formed like those of the skin, of the final ramifications of nerves, and of the radicles of exhalent and absorbent ves- sels, united by means of a spongy erectile tissue. Great confusion exists among ana- tomists in their descriptions of the papillae of the tongue. Those concerned in the sense of taste may, however, all be included in two divisions:— 1 st, the conical or pyramidal, —the finest sort being by some called filiform; and 2dly, the fungiform. The former are broader at the base than at the top, and are seen over the whole surface of the tongue, from the tip to the root. The latter, which are larger at the top than at the base, and resemble the mushroom,—whence their name,—are spread about, here and there, upon the sur- face of the organ. These pa- pillae of taste must be distinguished from a third set, the papillce capi- tate, which are mucous follicles, and of course accomplish a very different function. a. Foramen of Morpagni. b. Fungiform papillae. Conical papillae, d. Papilla; capitatae. e. Epiglottis. SAVOURS. Ill All the nerves that pass to the parts whose office it is to ap- preciate savours must be considered to belong to the gustatory apparatus. These are the inferior maxillary, several branches of the superior, filaments from the spheno-palatine and naso-palatine ganglions, the lingual branch of the fifth pair, the whole of the ninth pair or hypoglossal, and the glossopharyngeal. To which of these must be assigned the function of gustation we shall inquire presently. Like the skin and mucous membranes in general, that of the tongue and mouth contains, in its substance, numerous mucous follicles, which secrete a fluid that lubricates the organ, and keeps it in a condition best adapted for the accomplishment of its functions. Some of these are placed very conspicuously in the mucous membrane of the tougue. They are the papilla capilatce of many anatomists,—erroneously named, as they are not formed like the papillas, and, as we have said, execute a very different office. They are mucous follicles, and ought to be so called. They are situate near the base of the tongue, and the last perceptible rows unite anteriorly at an angle close to the foramen ccecum of Mor- gagni. (Fig. 17.) The fluids, exhaled from the mucous membrane of the mouth, and the secretion of the different salivary glands likewise aid in gustation; but they are more concerned in mas- tication and in salivation, and will require notice under another head. 2. OF SAVOURS. Before proceeding to explain the physiology of gustation, it will be necessary to inquire briefly into the nature of bodies, connected with their sapidity, or, in other words, into savours, which are the cause of sapidity. The ancients were of opinion, that the cause of sapidity is a pe- culiar principle, which, according to its combination with the con- stituents of bodies, gives rise to the various savours that are found to exist. This notion has been long abandoned; and chiefly, be- cause we observe no general or common characters amongst sapid bodies, which ought to be expected if they were pervaded by the same principle; and because it is found that bodies may be deprived of their sapidity by subjecting them to appropriate agents. Many of our culinary processes have been instituted for this purpose: the infusion of tea is indebted for all its attractions to the power we possess of separating, by boiling water, its savoury from its insipid portions. A savour must, therefore, be esteemed an integrant mole- cule of a body; not identical in all cases, but as heterogeneous in its nature as the impressions that are made upon the organ of taste. When the notion was once entertained, that savour is an inte- grant molecule, sapidity was attempted to be explained by the shape of the molecule. It was said, for instance, that if the savour be sweet, the molecule must be round; if sharp, angular; and so forth. Sugar was said to possess a spherical,—acids, a pointed, or angular molecule. We know, however, that substances, which resemble 112 SENSE OF TASTE. each other in the primitive shape of their crystal, impress the organ of taste very differently; and that solution, which must destroy most —if not all—of the influence from shape, induces no change in the savour. Others have referred sapidity to a kind of chemical action be- tween the molecules and the nervous fluid. This view has been suggested by the fact, that, as a general principle, sapid bodies, like chemical agents, act only when in a state of solution; that the same savours usually belong to bodies possessed of similar chemical pro- perties as is exemplified by the sulphates and nitrates; and that, in the action of acids on the tongue and mouth, we witness a state of whiteness and constriction, indicative of a first degree of combina- tion. All these circumstances, however, admit of another explana- tion. There are unquestionably many substances, which do combine chemically,—not with a nervous fluid, of whose existence we know nothing,—but with the mucus of the mouth, and the sapidity re- sulting from such combination is appreciated by the nerves of taste; but there are many bodies, which are eminently sapid, and yet afford us instances of very feeble powers of chemical combination; nay, in numerous cases, we have not the least evidence that such powers are existent. Vegetable infusions or solutions afford us strong examples of this kind,—of which syrup may be taken as the most familiar. The effect of solution is easily intelligible; the particles of the sapid body are in this way separated and come suc- cessively into contact with the gustatory organ; but there is some reason to believe, that solution is not always requisite to give sapidity. Metals have generally a peculiar taste, which has been denominated metallic; and this, even if the surface be carefully rubbed, so as to free it from oxide, which is more or less soluble. Birds, too, whose organs of taste are as dry as the corn they select from a mass of equally arid substances, are probably able to ap- preciate savours. The taste produced by touching the wires of a galvanic pile with the tongue has been offered as another instance of sapidity exhibited by dry bodies. This is, more probably, the effect of that chemical action on the fluids covering the mucous membrane of the tongue, which always follows such contact/ Such chemical change must, however, be confined to these fluids, and when once produced, the nerve of taste is compelled to appreciate the savour developed in the same manner as it does in cases of mor- bid alterations of the secretion of the mucous membrane, when, it is well known, that a body possessing considerable and peculiar sapidity, may fail to impress the nerves altogether, or may do so inaccurately. The notion of any chemical combination with the nervous fluid must of course be discarded. There is not the slightest shadow of evidence in favour of the hypothesis. Yet the epithet chemical was once applied to this sense on the strength of it, in opposition to the senses of touch, vision, and audition, which were * Wilbrand, Physiologie des Menschen, s. 279, Giessen, 1815. OF SAVOURS. 113 called mechanical, and supposed to be produced by vibration of their nerves. The savours, met with in the three kingdoms of nature, are innu- merable. Each body has its own, by which it is distinguished: but few instances occur in which any two can be said to be identical. This is the great source of difficulty, when we attempt to throw them into classes, as has been done by many physiologists. Of these classifications, the one by Linnasus3 is the best known. It will elu- cidate the unsatisfactory character of the whole: he divides sapid bodies into sicca, aquosa, viscosa, salsa, acida, styptica, dulcia, pin- guia, amara, acria, el nauseosa. He gives also examples of mixed savours—the acido-acria, acido-amara, amaro-acria, amaro-acerba, amaro-dulcia, dulci-styptica, dulci-acida, dulci-acria and acri-vis- cida; and he remarks, that the majority are antitheses to each other, two and two, as the dulcia and acria; the pinguia and styptica; the viscosa and salsa; and the aquosa and sicca. Boerhaaveb again divides them into primary and compound; the former including the sour, sweet, bitter, saline, acrid, alkaline, vinous, spirituous, aromatic, and acerb;—the latter resulting from the union of some of the pri- mary savours.0 There is, however, no accordance amongst physio- logists regarding those that should be esteemed primary, and those that are secondary and compound; although the division appears to be fairly admissible. The acerb, for example—which is con- sidered primary by Boerhaave—is by others, with more propriety, classed among the secondary or compound, and believed to consist of a combination of the acrid and acid. Still we understand suffi- ciently well the character of the acid, acrid, bitter, acerb, sweet, &c; but when, in common language, we have to depict other savours, we are frequently compelled to take some well known substance as the standard of comparison. According to Adelon,d the only distinction, which we can make amongst them, is,—into the agreeable and the disagreeable. Yet of the unsatisfactory nature of this classification he himself adduces numerous and obvious proofs. It can only, of course, be applicable to one animal species, often even to an individual only; and often again only to this individual, when in a given condition. Animals are known to feed upon substances, which are not only disagreeable but noxious to other species. The most poisonous plants in our soil have an insect which devours them greedily and with impunity: the southern planter is well aware, that this is the case with his tobacco, unless the operation of worming be performed in due season. The old adage, that " one man's meat is another man's poison," is meta- phorically accurate. Each individual has, by organization or asso- ciation, dislikes to particular articles of food, or shades of difference in his appreciation of tastes, which may be regarded peculiar; and in certain cases these peculiarities are signal and surprising. a Amcenit. Academ. ii. 335. b Pralect. Academ. torn. iv. c Lepelletier, Physiologie Medicale, p. 66, Paris, 1832. d Physiologie de I'Homme, seconde edit. i. 301, Paris, 1829. 10* 114 SENSE OF TASTE. Of the strange differences, in this respect, that occur in the same individual under different circumstances, we have a common and forcible instance in the pregnant female, who often has the most ardent desire for substances, which were previously perhaps repug- nant to her, or at all events not relished. The sense, too, in certain diseases—especially of a sexual character, or which are connected with the state of the sexual functions—becomes remarkably de- praved, so that substances, which can, in no way, be ranked as eatables, are greedily sought after. A young lady was under the care of the author, whose greatest bonne bouche was slate pencils. At other times, we find chalk, brick-dust, ashes, dirt, &c. obtaining the preference. Habit, too, has considerable effect in our decisions regarding the agreeable. The Roman liquamen or garum, the most celebrated sauce of antiquity, was prepared from the half putrid intestines of fish; and one of the varieties of the Ofog 2iX Bostock's Physiology, 3d edit. p. 732, Lond. 1836; and Mayo, Outlines of Physio- logy, 4th edit. p. 314, Lond. 1837. « Edinburgh Medical and Surgical Journal, for Jan, 1838, p. 129, also, on this dis- puted topic, Alcock, in Dublin Journal, for Nov. 1836. and J. Guyot, Archives Gone. rales de Medecine, Janvier, 1837. Elements of Physiology, byBaly, P. v. p. 1321. Lond. 1839. USES OF TASTE. 119 proceed from numerous pairs, are equally inservient to touch or tact.a The immediate function of the sense of taste, as has been re- marked, is to give the sensation of savours. This function, like the touch, is instinctive, requires no education, cannot be supplied by any of the other senses, and is accomplished as soon as the tongue has acquired the necessary degree of developement. To this it may be replied that the very young infant is not readily affected by savours. In all cases, however, certain sapid bodies excite their usual impression: and, in the course of a few months, when the organ becomes completely developed, the sense acquires a high, and often an inconvenient degree of acuteness. The mediate or auxiliary offices of gustation are few in number, and limited in extent. It does not afford much instruction to the mind. The chemist and mineralogist occasionally gain information regarding bodies by its agency; but it is never considered by the physiologist as worthy of the rank of an intellectual sense; on the contrary, it is classed with olfaction as corporeal. To appreciate a savour accurately, the sapid substance must remain for some time in the mouth: when rapidly swallowed, the impression is extremely feeble, and almost null. Of this fact we take advantage when compelled to swallow any nauseous substance: whilst we retain a savoury article long in the mouth, in order that we may extract all its sweets. How different, too, is the consent of the auxiliary organs under these two circumstances. Whilst a luscious body augments the secretion of the salivary glands—or causes the mouth "to water," as it has been called—projecting the saliva, at times, to a distance of some feet from the mouth, and dis- posing every part to approach or mingle with it; a nauseous sub- stance produces constriction of every secretory organ, and this effect extends even to the stomach itself, so that it will often reject the offending article, as soon as it reaches the cavity. We can thus understand how, cceteris paribus, an article, which is pleasing to the palate, may be more digestible than one which excites disgust, and conversely. Of the " consent of parts," exerted by the stomach on the organ of taste, we have a familiar illustration in the fact,—that whatever may be the gout, with which we commence a meal on a favourite article of diet, we find that the relish is blunted as the stomach becomes filled; and hence the Romans were in the habit of leaving the table once or twice during a meal, and, after having unloaded the stomach, of returning again to the charge—" vomunt ut edant, edunt ut vomant." If we place a sapid substance in the mouth, and then close the nostrils, the taste is diminished,—a fact, which has given rise to the generally prevalent opinion, that a very intimate relation exists between the smell and the taste. They are, however, entirely * Adelon, op. cit. i. 309. 120 PHYSIOLOGY OF TASTE. separate. Most sapid substances have a distinct odour or flavour, and this is not appreciated when we prevent the air from passing through the nasal fossae." This causes the impression on the gus- tatory nerves to be less marked, but it exists. Gustation is likewise diminished by the new sensation produced in the nostrils by their closure, so that the same degree of attention is not directed to the sense of taste.b Among animals we see great diversities in this sense. Whilst none possess the refined taste of man, there are many, which are capable, by taste or smell, of knowing those plants that are nutritive from those that are noxious to them ; and it is very unusual for us to find that an animal has died from eating those which are unques- tionably poisonous to it. Yet, as we have remarked, a substance, which is noxious to one, may be eaten with impunity by another: and, if we select animals, and place them in a field, containing plants, all of which are ranked by us as poisons, and which are poisonous to a majority of those animals, we find that not only has a selection been made by each animal of that which is innocuous to it, but that the substance has furnished nourishment to it, whilst to others it would have proved fatal. All this must be dependent upon peculiar, and inappreciable organization. The sense of taste is more than any other under the influence of volition. It is provided with a muscular apparatus, by which it can be closed or opened at pleasure; and, in addition, it ordinarily requires the assistance of the upper extremity, to convey the sapid substance to the mouth. The sense can, therefore, be exercised either passively or actively; and, by cultivation, it is capable of being largely developed. The spirit taster to extensive commercial esta- blishments exhibits the truth of this in a striking manner. He has, of course, in his vocation, not only to taste numerous samples, but to appreciate the age, strength, flavour, and other qualities of each: yet the practised individual is rarely wrong in his discrimination. With almost all, if not all these " tasters," the custom is to take a small quantity of the liquor into the mouth; throw it rapidly around that cavity, and then eject it. A portion in this way comes in con- tact with every part of the membrane, and of course impresses not only the lingual branch, but the other ramifications of the fifth pair. The gourmet of the French—somewhat more elevated in the scale than our ordinary epicure—prides himself upon his discrimi- nation of the nicest shades of difference and of excellence in the materials set before him. Many gourmets profess to be able to pro- nounce, by sipping a few drops of wine, the country whence it comes, and its age; and, according to Stelluti, can tell by the taste, whether birds put upon the table, are domesticated or wild—male or female.0 Dr. Kitchener/ indeed, asserts, that many epicures are , ,a Pf.out1^oLond- Med' and Physical Journal, for 1812, and Elliotson's Blumenbach, 4th edit. 1828, p. 239. ' *> Mojon's Leggi Fisiologiche, &c. translated by Skene, p. 18. Lond 1829 See also, Dr. Wing, in Boston Med. Magazine, June 15, 1835. « American Quart, ii. 427. a Cook's Oracle, 3d edit., Lond 1821 p 229 SENSE OF SMELL. 121 capable of saying in what precise reach or stretch of the Thames the salmon on the table has been caught. Such acuteness of sense is by no means desirable. Doomed to meet, in his progress through life, with such a preponderance of what demands obtuseness rather than acuteness of feeling, the epicure must be liable to continual annoyances and discomforts, which the less favoured can never experience. OF THE SENSE OF SMELL OR OLFACTION. The object of this sense is to appreciate the odorous properties of bodies. It differs from the last in the circumstance of the body not coming into immediate contact. It is only necessary that an odorous emanation from it shall impinge upon the organ of sense. Still, it does not essentially vary in its physiology from the sense of taste. 1. -ANATOMY OF THE ORGAN OF SMELL. The organ of smell is a mucous membrane, which lines the nasal cavities, and is called the Schneiderian or pituitary. It resembles that which covers the organ of taste, except that the nervous papillae are still more delicate, to correspond with the greater tenuity of the body, which has to make the impression. The membrane lines the whole of the bony cavities called the nasal fossce, which are con- stantly open anteriorly and posteriorly, to permit the air which traverses them, to proceed to the lungs. The anterior aperture is covered by a kind of pent-house or capital, for the purpose of col- lecting the odorous particles. The capital is called the nose. The essential part of the organ of smell is the pituitary or olfactory membrane—the other parts being superadded in animals to perfect the sense. The bony portions of the nose are separated from each other by a bone called the vomer. This septum* is extended, by means of cartilage, to the anterior extremity of the nose, so that the nasal fossae are divided into like parts, which have no communication with each other, but open together posteriorly into the top of the pharynx. Within each of the nares, are two convoluted or turbinated bones —generally called ossa spongiosa vel turbinata; and by the French, cornets. These are situate one above the other; the superior being formed of a plate of the ethmoid bone—the inferior being a distinct bone. They divide the general cavity of each nostril into three passages or meatus, as exhibited in Fig. 18, where figures 7 and 10 represent the superior and inferior spongy bones respectively, and 11 the vomer;—the three meatus being chiefly comprised between these bones. The inferior meatus is broad and long, the least ob- lique and the least tortuous ; the middle is narrow, almost as long, but more extensive from above to below; and the superior is much shorter, more oblique and still narrower. The narrowness of these passages, in the living subject, is so great, that the slightest tume- VOL. I. 11 122 ORGANS OF SMELL. faction of the pituitary membrane renders the passage of air through the nasal fossae extremely difficult. This is the cause of the difficulty of breathing through the nose, that attends a " cold in the head." Into the two upper passages cavities in certain bones open, which enlarge considerably the extent of the nasal fossae. These are called sinuses, and are the maxillary, palatine, frontal, sphenoidal, ethmoidal,—the last being sometimes termed ethmoidal cells. Fig. 18. Transverse vertical section near the middle of the Nasal Fossa, seen from behind. ft Os frontis deprived of dura mater. 2. Os frontis covered by the dura mater. 5 5. Anterior part of the cribriform plate of the ethmoid bone. 6. Vertical plate of the ethmoid. 7. Os spongio- sum superius. 8 8 8. Ethmoid cells. 9. Orbitar plate of the ethmoid bone. 10 10. Os spongiosum inferius. 11. Vomer. 12. Upper maxillary bone. 14 14. Anterior part of the maxillary sinus. 15 & 16. The fibrous and the mucous linings of the sinus. 18. Palatine arch. 20. Teeth. 26. Probe passed through the ductus ad nasum. 28. Orifice of the maxillary sinus. All the cavities are lined by the delicate membrane—the Schnei- derian or pituitary—or by a prolongation of it. In the nasal fossae, it augments the thickness of the turbinated bones. It resembles the mucous membranes in general in its composition, and adheres firmly to the bones and cartilages, which it covers. Its aspect is velvety, owing to a multitude of minute papillae, and it receives a great num- ber of vessels and nerves. The sinuses are lined by a prolongation, apparently of the same membrane; differing, however, in some respects from the other. The whole of this membrane is the seat SENSE OF SMELL. 123 of the secretion of the nasal mucus, which, doubtless, performs a part in olfaction as important as the secretion from the mucous membrane of the mouth does in gustation. The same nerve is not distributed over the whole of this mem- brane. In some parts, the olfactory or first pair can be traced; in others, we see only filaments of the fifth pair. Fig. 10. Lateral vertical section of the Face. a. Frontal sinus, b. Ethmoidal cells, c. Sphenoidal sinus, d. Nasal fossie. e. Maxillary sinus. The first of these—the olfactory or ethmoidal nerves—have not always been regarded as the nerves of smell. Anciently, they were presumed to be canals for the passage of the pituita or phlegm, which was supposed to be secreted by the brain.a At the present day, anatomists are doubtful only regarding their origin; some de- riving them from the anterior lobes of the brain, others from the corpora striata, which have, in consequence, been called thalami nervorum ethmoidalium; and others, again, with Gall,b and with probability, referring them, like every other nerve of sense, to the medulla oblongata. Beclard affirms, that in a hydrocephalic patient, where a part of the brain had been destroyed by disease, he actually detected this origin.0 * Haller, op. cit. torn. v. p. 181. b Recherches sur le Systeme Nerveux en general et sur celui du Cerveau en parti- culier, Par F. J. Gall &. G. Spurzheim, Paris, 1809. c Adelon, Physiologie de I'Homme, edit. cit. i. 330. 124 SENSE OF SMELL The nerve proceeds directly forwards, (see Fig. 12,) until it reaches the upper surface of the cribriform plate of the ethmoid bone, when it divides into a number of filaments, which pass through the foramina in the plate, and attain the nasal fossae, where they are dispersed on the upper and middle part of the Schneiderian mem- brane, but cannot be traced on the lower. Most anatomists are of opinion, that here they constitute, with vessels of exhalation and absorption, the papillae ; whilst others, as Scarpa, not having been able to trace them thither, have been of opinion that the filaments interlace to constitute a kind of proper membrane. Our means of observation cannot be considered sufficient to enable us to decide this question positively. In the case of the mouth, we have seen, that anatomy has not succeeded in following the nerve to its minute termination; nor has it in the case of the olfactory or of any other nerve, if we except those of vision and audition, and in these we see the terminations but imperfectly. The olfactory nerve has not been traced on the os spongiosum inferius, on the inner surface of the middle spongy bone, or in any of the sinuses. Besides the first pair of nerves, the pituitary membrane receives several branches from the fifth encephalic pair; for example, the nasal twig of the ophthalmic branch of the fifth, and filaments from the frontal branch of the same, from the spheno-palatine ganglion, the palatine nerve, the vidian nerve, and from tne anterior dental branch of the superior maxillary. One of these twigs enters the anterior naso-palatine canal, and, in its course to the roof of the mouth, passes through a small ganglion, which has been described by H. Cloquet* under the name naso-palatine, and which he con- ceives to be the organ of sympathy between the senses of smell and taste. The pituitary membrane is kept moist by the nasal mucus, as well as by the exhalation constantly taking place from it. It receives, likewise, the superfluous tears by means of the ductus ad nasum,—a duct passing from the inner canthus of the eye, and opening into the nasal fossae below the lower spongy bone. The constant evaporation which must take place from the membrane, owing to the passage of the air during respiration, requires that the secretion should be continuous and copious, otherwise the membrane would become dry. The nasal fossae communicate externally by means of the nostrils, the shape, size, and direction of which vary considerably, so as to give rise to the aquiline, Roman, pug, and other varieties of nose. At the extremity of the nostrils long hairs are situate—technically called vibrissce—whose function, it is conceived, may be to sift, as it were, the air passing through, during respiration, and thus to prevent extraneous bodies from entering the fossae. The nostrils are also capable of being expanded or contracted by appropriate muscles. * A System of Human Anatomy; translated by Robert Knox, M.D. Edinb. 1828. ODOURS. 125 In this sense, we have a more clear separation between the phy- sical and nervous part of the apparatus than in either of those we have considered;—the nose proper forming the essential physical portion ; and the nerves of smell the organic or nervous. 2. OF ODOURS. The comprehension of the physiology of olfaction will not be complete without an inquiry into odours, or those emanations from odorous bodies, which give character to them, and impress the organ of smell. It was long maintained, as in the case of savours, that odours are dependent upon a peculiar principle, which, according to its particular combination with the constituents of bodies, gives rise to the various odours. To this principle the terms aroma and spiritus rector have often been assigned; but the notion has been long aban- doned, because no general or common characters were observable amongst odorous bodies, which ought to be expected, were they indebted for their odour to the same principle ; and because, again, bodies can be deprived of their odour by exposing them to appro- priate agents, as when we subject them to infusion and distillation. Walther, a German physiologist, is of opinion that an odorous body is only such by virtue of a vibratory motion, analogous to that made by a sonorous body. We have, however, the most satis- factory evidence, that there are special odorous, as there are special savoury molecules. We can, for example, prevent an odorous body from impressing our olfactory nerves, by covering it with a glass receiver. Odours can likewise be separated by infusion and distil- lation. The fact, however, has been directly proved by an experi- ment of Berthollet. On nearly filling a tube with mercury, and placing a piece of camphor at the top of the tube, he found that, after a time, the mercury descended, the camphor had diminished in size, and the space above the metal was occupied by an odorous gas.a But what is the cause of the disengagement of these odorous molecules 1 By most writers on this subject it has been considered to be dependent upon the solvent action of caloric on the body. The opinion, that all bodies are odorous, is as old as Theophrastus, and it is one which it is very difficult not to embrace, if we add— provided they are subjected to the appropriate agents for disengaging the odorous particles; and the probability is, that the reason we esteem particular bodies inodorous is, that our olfactory nerves are not organized with sufficient delicacy to enable us to distinguish their odorous properties. Heat assists the escape of odorous par- ticles from a variety of bodies, and hence it has been maintained that every body which is volatile must be odorous. Adelonb asserts that this is not the case, but it is difficult to accord with him. The a Cloquet, Art. Odeurs, Diet, des Sciences M6dicales, p. 89, torn, xxxvii. Paris, 1819. >> Op. cit. i. 322. 11* 126 SENSE OF SMELL. fact of our not appreciating the odour is no proof of its non-exis- tence. In truth, bodies that are inodorous to one animal or indivi- dual may be the contrary to another. In cases, too, in which the smell is morbidly acute, a substance may appear overwhelmingly odorous, which may hot even impress the sense in healthy indivi- duals. H. Cloquef refers to the case of a celebrated Parisian phy- sician, who was subject to violent attacks of hemicrania or megrim, and who was dreadfully tormented, during one of the paroxyms, by the smell of copper, exhaled from a pin that had been dropped in the bed! Calorie seems to be only one of the causes of the disengagement of odours. Some are retained by so feeble a degree of affinity, that they appear to be exhaled equally at all temperatures. Light influ- ences their escape materially, in particular cases; some plants giving off their fragrance during the day, others perfuming the air only at night. Dampness, too, in many cases, assists their escape—hence the fragrance of a garden after a summer's shower and the smell afforded by all argillaceous substances, when breathed upon—a fact, the knowledge of which is of considerable importance to the chemist. Lastly, substances, which appear to us entirely devoid of odour, may exhale a strong one, when rubbed together. All these circum- stances tend greatly to prove, that every substance is possessed of odorous qualities, provided we are aware of the precise mode for causing their emanation, although our olfactory nerves may not be sufficiently delicate to appreciate them. Around the odorous bodies, the molecules, as they escape, must form an atmosphere, which, of course, will be denser, the nearer it is to the body. These particles are diffused around,—not, probably, in the same manner as light or sound, but as one fluid mixes with another; and, when the air is still, it is conceived, that their strength will be inversely as the square of the distance from the substance exhaling them. There is a great difference, however, in odours with regard to their diffusibility in the atmosphere. Some extend to a great distance, whilst others are confined to a small compass. The odours of many flowers are so delicate as not to be appreciated, un- less they are brought near the olfactory organs; whilst that of cin- namon is said to be experienced at sea, at the distance of twenty- five miles from Ceylon. Lord Valentiab affirms, that he himself distinctly smelt the aromatic gale at nine leagues' distance—but Dr. Ruschenbergerc was not equally fortunate. The author was in- formed by Commodore Stewart, of the navy, that he had distinctly discovered the spicy emanations when two hundred miles from Ceylon, and the terebinthinite odours of the pines of Virginia, when one hundred miles from the coast. a Osphr6siologie ou Trait6 des Odeurs, Paris, 1821. b Voyages and Travels in India, London, 1809. c Embassy to the courts of Muscat and Siam, &c. p. 154, Philad. 1838. ODOURS. 127 Facts of the above kind are employed by the natural philosopher to exhibit the excessive divisibility of matter. Scales, in which a few grains of musk have been weighed, have retained the smell for twenty years afterwards, although they must have been constantly exhaling odorous molecules during the whole of this period. Hallera kept some papers, for more than forty years, which had been per- fumed by a single grain of amber; and, at the end of that time, they did not appear to have lost any of their odour. That distinguished physiologist and mathematician calculated, that every inch of their surface had been impregnated by s^Tse 4T7o-t>m °f a grain of amber, and yet they had scented for 14,600 days a stratum of air at least a foot in thickness. But how much larger must these molecules be than those of light—provided we regard it as consisting of mole- cules—seeing that glass is capable of retaining the former, but suffers the other to penetrate it in every direction without obstacle! The air is not the only vehicle for odours. It has been seen, that they adhere to solid bodies; and that, in many cases, they can be separated by aqueous or spirituous distillation. The art of the per- fumer consists in fixing and preserving them in the most agreeable and convenient vehicles. Yet, it was at one time strenuously denied, that they could be conducted through water; and, as a natural con- sequence of this view, that fishes could smell. Dumeril, for example, maintained, that odours, being essentially of a volatile or gaseous nature, cannot exist in fluids;—and, moreover, that fishes have no proper olfactory organ;—that the part which is commonly consi- dered as such, is their organ of taste. The opinion is now enter- tained by few. We have seen, that odours can be retained in fluids, and not many naturalists of the present day will be hardy enough to deny that fishes have an organ or sense of smell. At all events, few anglers, who have used their oil of rhodium, or other attractive bait, will be disposed to give up the results of their experience with- out stronger grounds than any that have been assigned by the advo- cates of that view of the subject. Besides air is contained in con- siderable quantity in water, so that odorous substances might reach the olfactory organs through it. When it was determined, that odours consist in special molecules, given off from bodies, it was attempted to explain their action on the pituitary membrane in the same manner as that of savours on the membrane of the tongue. It was conceived, for example, that the shape of the molecules of a pungent odour is pointed, that of an agreeable one, round. Others, again, were of opinion, that olfaction is owing to some chemical union between the odorous molecule and the nervous fluid, or between it and the nasal mucus. None, how- ever, have attempted to specify the precise chemical composition, that renders a body odorous. The sensations do not present the most favourable occasions for exhibiting chemical agency; and, in this particular sense, it is probably no farther concerned than in the * Element. Physiol, torn. v. lib. 14, sect. 2, p. 157, Lausann. 1773. 128 SENSE OF SMELL. sense of touch, and not so much as in that of taste. It is sufficient for the odorous particle—animal, vegetable, or mineral—to come in contact with the olfactory nerves, in order that the odour may be appreciated; and we may, in vain, look for chemical action in many of those animal and vegetable perfumes,—as musk, amber, camphor, vanilla, &c—which astonish us by their intensity and diffusibihty. The same remarks, that were made on the classification of savours, are applicable to that of odours. They are not less numerous and varied; and each substance, as a general principle, has its own, by which it is distinguished. Numerous attempts have been made to group them, but all are unsatisfactory. The classification, proposed by Linnaeus/ was—into Odores aro- matici, as those of the flowers of the pink, bay leaves, &c.; 0. fra- grantes, as those of the lily, jessamine, &c.; 0. ambrosiaci, as those of amber, musk, &c; 0. alliacei, as those of garlic, assafcetida, &c.; 0. hircini, (like that of the goat,) as those of the Orchis hircina, Chenopodium vulvaria, &c.; 0. tetri, or repulsive or virous, as those of the greater part of the family solanece; and lastly, 0. nauseosi, as that of the flowers of the veratrum, &c. A simple glance at this division will exhibit its glaring imperfections. No two individuals could, in fact, agree to which of any two of the cognate classes a particular odour should be referred. None of the other classifications, which have been proposed, are more satisfactory. Fourcroy divided them into the extractive or mucous, the fugaceous oily, the volatile oily, the aromatic and acid, and the hydrosulphureous;—and Lorry into the camphorated, nar- cotic, ethereal, volatile acid, and alkaline.^ The distinction into animal, vegetable, and mineral, is not more commendable. Musk is the product of an animal of the ruminant family, but the odour is not confined to this animal. It is contained in the civet, in the flesh of the crocodile, and in the musk-rat. Haller asserts, that his own perspiration smelled of it. It is met with, likewise, in the vegetable kingdom—in the Erodium moscha- turn, in the seeds of the Abelmoschus, the flowers of the Rosa mos- chata, and of the Adoxa moschatellina, and in some of the varieties of the melon and the pear; and, what is perhaps more surprising, in mineral substances;—as in certain preparations of gold, and in some earths of which tea-pots are formed in China and Japan. The odour of garlic, again, is found not only in that vegetable, but in assafcetida; in arsenic, when thrown upon hot coals; and in the Bufo pluvialis, a species of toad. In by far the majority of cases, we can only designate an odour by comparing it with that of some well known substance,—hence the epithets musky, alliaceous, spermatic, &c. Adelon asserts, that the sole classification, which can be adopted, is into the agreeable and disagreeable. But even the miserably imperfect division pro- a Amrjenitat. Academic. Erlang. 1787,1790. b Richerand's Elemens de Physiologie, 6dit. 13, par Berard, p. 201, Bruxelles,1837. ODOURS. 129 posed by Haller1 is better than this: he made three classes—Odores suaveolentes, 0. medii, and 0. foetores. The truth is that all the objections, made to the division of savours into the agreeable and disagreeable, are equally applicable to odours. Assafoetida, we have seen, was employed by the ancients as a condiment; and although with us it has the name devil's dung, it is by many of the Asiatics called the food of the gods. We find, too, certain animals that are almost enravished by particular odours. The cat, for example, if the catmint—Nepeta cataria—or the root of the valerian—Valeriana officinalis—be placed in its way. These differences, like those in the appreciation of savours by animals, must be referred to minute and inappreciable organization. Odours have been considered to be possessed of medicinal and even of poisonous properties. Some individuals, whose peculiarity, of constitution renders them very liable to the action of ipecacuanha or jalap, will experience the emetic effects of the former, or the cathartic qualities of the latter, by merely smelling them for a short time, and the majority of individuals, by pounding jalap or rhubarb for a long period, will find themselves more or less affected. By smelling strong alcohol for a considerable time, intoxication may be induced, as not unfrequently happens to the spirit taster, who is young in his vocation. It has also been asserted, that the cdnstant application of this sense to the discrimination of teas, in the English East India Company's warehouses, has laid the foundation for nu- merous head affections; but the report originated in prejudice or in accidental coincidences, and has not been found to be accurate. In all these cases, in which we see medicinal or poisonous effects actually produced by substances inhaled through the nostrils, we cannot attempt to explain them, by the simple impression, made by the odorous particle on the olfactory nerve. They must be accounted for by the circumstance of the minute particles of the medicinal or poisonous substance being diffused in the atmosphere and coming into contact with the mucous membranes, from which they are absorbed, and in this manner enter the circulation. Odours have, likewise, been considered to possess nutritive pro- perties ; and this chiefly, perhaps, from the effect known to be pro- duced by savoury smells upon the appetite. It is not probable, that absorption can, in this case, occur to a sufficient extent to account for the apparent satiation. The fact can only be explained by the effect upon the nervous system, which influences the appetite mate- rially, as we see in the operation of various mental emotions. The first impact of a nauseous odour, or even the view of a disgusting object, will frequently convert the keenest appetite, on the instant, into loathing. Yet, anciently, it was believed that life might be sustained for some time, by simply smelling nutritious substances. Democritus is said to have lived three days on the vapour of hot bread, and Bacon refers to a man, who supported an abstinence of 1 Elementa Physiolog., torn. v. lib. xiv. p. 162, Lausann. 1763. 130 SENSE OF SMELL. several days by inhaling the odour of a mixture of aromatic and alliaceous herbs. Two hundred years ago, these notions were entertained to a great extent; and they afford the basis for the viaticum, suggested for travellers proceeding to the moon, accord- ing to the plan proposed by Dr. John Wilkins, Bishop of Chester.1 " If we must needs feed upon something," he remarks, " why may not smells nourish us? Plutarch and Pliny, and divers other ancients, tell us of a nation in India, that lived only upon pleasing odours; and it is the common opinion of physicians, that these do strangely both strengthen and repair the spirits." Fuller,b a learned contemporary of the Bishop, affords an amusing instance of litigation, arising from this supposed nourishing character of odours. A poor man being very hungry, stayed so long in a cook's shop who was dishing up the meat, that his stomach was satisfied with only the smell thereof. The choleric cook demanded of him to pay for his breakfast; the poor man denied having had any; and the controversy was referred to the decision of the next man that should pass by, who chanced to be the most notorious idiot in the whole city; he, on the relation of the matter, determined that the poor man's money should be put betwixt two empty dishes, and that the cook should be recompensed with the jingling of the money, as he was satisfied with the smell of the cook's meat. It need scarcely be said, that if the vapour from alimentary sub- stances be capable, in any manner, of serving the purposes of nutri- tion, it can only be through the agency of the absorbents. 3. PHYSIOLOGY OF OLFACTION. In order that the sense of smell may be duly exercised, it is neces- sary that the emanation from an odorous body shall not only impinge upon the pituitary membrane, but that it shall impinge with some degree of force. It must, in other words, be drawn in with the inspired air. Perraultc and Lower*1 found, that by making an open- ing into the trachea of animals, and thus preventing the inspired air from passing through the nasal fossae, smell was not effected; and that dogs, which were the subjects of the experiment, readily ate food they had previously refused. These experiments were repeated by Professor Chaussier, and with like results.6 They explain, why we use considerable effort to draw in air loaded with an odour that is agreeable to us; and why, on the contrary, we arrest the respira- tion, or make it pass entirely through the mouth, when disagreeable. Still odours are occasionally so diffusible and expansible, that they a The Discovery of a New World, or a Discourse tending to prove, that 'tis possible there may be another Habitable World in the Moon, with a Discourse concerning the possibility of a passage thither, Lond. 1638. •> Holy State, London, 1640. c Ess. de Phys. iii. 29. d Needham, de Format. Foetus, p. 165; and Haller, edit. cit. v. 173. e Richerand, edit. cit. p. 203; and Adelon, op. cit. i. 335. PHYSIOLOGY OF OLFACTION. 131 will reach the olfactory membrane, and we are compelled to shut them off" by calling in the aid of the upper extremity. The air being the ordinary medium for the conveyance of odorous mole- cules, we can understand why the organ of smell should form a part of the air passages. The use of the nose itself is to direct the air, charged with odours, towards the upper part of the nasal fossae. Its situation is well adapted for the reception of emanations from bodies beneath it, and its appropriate muscles allow the nostrils to be more or less ex- panded or contracted. The uses we have assigned to the nose are demonstrated by the fact, that they, whose noses are deformed— especially the flat-nosed—or whose nostrils are directed forwards, instead of downwards, have commonly the sense very feebly deve- loped. The loss of the nose, too, either by accident or disease, has been found to completely destroy the sense; and, by no means the least advantage of the Rhinoplastic operation is the enjoyment afforded by the restoration of this corporeal sense. M. Beclard affirms, that an artificial nose, formed of paper or other appropriate material, is sufficient to restore it, so long as the substitute is attached.* It is proper to remark, however, that in a case at this time under the author's observation, although the nose has been lost by syphilis, the smell persists. The mode, in which olfaction is effected, appears to be as fol- lows:—The inspired air, loaded with odorous particles, traverses the nasal fossae; and, in this passage, comes in contact with the pituitary membrane, through the medium of the nasal mucus. The use of this mucus appears to be, not only to keep the organ pro- perly lubricated, but to arrest the particles as they pass,—not by any chemical attraction, but in a purely mechanical manner. The olfactory nerves being distributed on the membrane, receive the im- pression of the molecules as they impinge, and, in this manner, the sensation is accomplished. The use of the different spongy or turbinated bones would seem to be to enlarge the olfactory surface. According to some, how- ever, their office is, to form channels to direct the air towards the openings of the sinuses. The sinuses, themselves, afford subjects for physiological discussion. By many they are considered, also, to add to the extent of olfactory surface: by others, to furnish the nasal mucus. No hesitation would be felt in pronouncing both the spongy bones and sinuses to be highly useful in olfaction, were it not that the olfactory nerves, or first pair, have not been traced on the pituitary membrane covering the middle and inferior spongy bones, or on that which lines the different sinuses;—that the sinuses are wanting in the infant, which, notwithstanding, can appreciate odours;—that they exist only in the mammalia;—and that experi- ments would seem to show, that the upper part of the olfactory 5 Magendie, Precis Elementaire, 2de edit. i. 136, Paris, 1825; and Hesse, in Pierer's Anat. Phys. RealwOrterb. s. 578, Altenb. 1825. 132 SENSE OF SMELL. organ is more particularly destined for the function, and that the sinuses, which, as well as the membrane covering the middle and lower spongy bones, are supplied by filaments from the fifth pair of nerves, are not sensible to odours. That the upper part of the nasal fossae is the great seat of smell, is proved by the facts referred to regarding the uses of the nose. Dessault, too, mentions the case of a young female, who had a fistula in the frontal sinuses, and who could not perceive an odorous sub- stance, when presented at the orifice of the fistula, because there was no communication with the proper portion of the nasal fossae, even although she was capable of breathing through the, opening. Des- champs, the younger, also relates a case of a man, who had a fistula of the frontal sinus, through which ether might be injected without being appreciated, provided all communication had been previously cut off between the sinus and the upper part of the nasal fossae ; but if this precaution had not been taken, the sense was more vivid, when the odours passed through the fistulous opening, than when they reached the organ by the ordinary channel. Professor Richerand,a again, found that highly odoriferous injec- tions, thrown through a fistulous opening in the maxillary sinus or antrum of Highmore, produced no olfactory sensation whatever. All these facts would seem to lead to the belief, that the upper part of the nasal fossae, on which the first pair or olfactory nerves are distributed, is the chief seat of olfaction, and that the inferior portions of these fossae, as well as the different sinuses communi- cating with them, are not primarily concerned in the function; but, doubtless, offer secondary advantages of no little importance. This conclusion wrould, however, seem to admit, what is not by any means universally admitted, that the olfactory nerve is the sole or chief nerve of smell. Especially difficult is it to embrace^ this view, and not to believe that the spongy bones and sinuses, on which the fifth pair are distributed, are agents in perfecting the sense, when we find them largely developed in animals that possess unusual deli- cacy of smell, as in the dog and elephant. It has already been re- marked, that the ancients believed the olfactory nerves to be canals for conveying away the pituita or phlegm from the brain. Diemer- broeck maintained this opinion.b At the early part of the last cen- tury, however, the olfactory was supposed to be the proper nerve of smell, and this opinion prevailed, with scarcely a dissentient voice, until within the last few years. Inspection of the origin and dis- tribution of this nerve seems to indicate it as admirably adapted for a nerve of special sensibility connected with smell. It is largely developed in animals in proportion to their acuteness of smell, and is distributed on the very part of the pituitary membrane to which it is necessary to direct air, loaded with odorous emanations, in order that they may be fully appreciated. Magendiec has, however, en- 1 Edit. cit. 202. b Anatome Corporis Humani, lib. iii. cap. 8, Ultraiect. 1672. c Precis Elementaire, 2de 6dit. i. 132. PHYSIOLOGY OF OLFACTION. 133 deavoured to show by experiment, that the sense of smell is in no wise, or but little, dependent upon the olfactory nerves, but upon the branches of the fifth pair. Prior to the institution of his experi- ments, he had observed with astonishment, that after he had removed the cerebral hemispheres with the olfactory nerves of animals, they still preserved this faculty. He had noticed, too, that the sense had continued in some lunatics, who had fallen into a state of stupor, and in whom the substance of the brain appeared, on dissection, greatly disorganized. These facts induced him to expose the olfactory nerves on living animals, and to experiment upon them. In the course of his experiments he found, in the first place, that the nerves were insensible to puncture, pressure, and to the contact of the most odorous substances. He afterwards satisfied himself, that after their division the pituitary membrane not only preserved its general sensibility, appreciated the contact of bodies, but that it continued to feel strong odours, those of ammonia, acetic acid, oil of lavender, Dippel's oil, &c. On the other hand, having divided the fifth pair of nerves within the cranium, and left the olfactory nerves untouched, he remarked that the pituitary membrane had lost its general sensi- bility ; was no longer sensible to contact of any kind; and that it had lost the power of appreciating odours. From these experiments, he considered himself justified in infer- ring, that the olfactory nerve does not preside over the general sensi- bility of the nose; that it has, at the most, but a special sensibility as concerns odours; and that if the olfactory nerve be the nerve of smell, it at least requires the influence of the fifth pair, in order that it may act: lastly; he asks, may not the general and special sensibility be comprised in the same nerve in the sense of smell, as they are in that of taste;—in the fifth pair ? These experiments are highly interesting; but they do not entirely establish, that the fifth pair is the olfactory nerve. The numerous facts, already mentioned, attract us irresistibly to the first pair, or olfactory, as they have been exclusively called. It has been already remarked, that the fifth is concerned in all the facial senses; that it conveys to them general sensibility, or feeling; and that some of them are unquestionably supplied with nerves of special sensibility; —the eye, for example, with the optic nerve; and the ear with the auditory ; but that neither one nor the other can exert its special function, without the integrity—the presidency—of the fifth pair. The olfactory-nerve is probably in this category,—is the nerve of special sensibility. It is true, that in the experiments of Magendie the animal appeared to be affected by odorous substances, after the division of the first pair; but a source of fallacy might exist here, in discriminating accurately between the general and special sensi- bility. Some of the substances employed were better adapted for eliciting the former than the latter;—ammonia and acetic acid, for example. The immediate function of the sense of smell is to appreciate vol. i. 12 134 SENSE OF SxMELL. odours. In this it cannot be supplied by any other sense. The func- tion is instinctive; requires no education; and is exerted as soon as the parts have attained the necessary degree of deyelopement. In many respects this sense is intimately connected with that of taste, and the impressions made upon each are frequently confounded. In the nutritive function, the smell serves as a kind of advanced guard or sentinel to the taste, and warns us of the disagreeable or agreeable nature of the aliment; but if a substance, that is repugnant to the smell, be agreeable to the taste, the smell soon loses its aversion, or at least becomes less disagreeably impressed. The smell is not, however, so useful to man as a sentinel to the taste, as it is to ani- mals: there are many bodies,—those containing prussic acid for example,—which are extremely pleasing by the odours they exhale, and yet are most noxious to the human frame. In the animal king- dom, this sense is greatly depended upon, and is rarely a fallacious guide. It enables animals to make the proper selection of the noxious from the innocent—the alimentary from that which is devoid of nutriment—the agreeable from the disagreeable; and this power appears to be instinctive or dependent upon inappreciable varieties of structure in the olfactory organs. As an intellectual sense, the smell is not entitled to a higher rank than the taste. Its mediate functions are very limited. It enables the chemist, the mineralogist, and the perfumer to discriminate bodies from each other. We can, likewise, form a slight—but only a slight—idea by it, regarding the distance and direction of bodies, owing to the greater intensity of odours near an odorous body, than at a distance from it. Under ordinary circumstances, the informa- tion of this kind, which we derive by olfaction, is inconsiderable; but in the blind, and in the savage, who are accustomed to exercise all their external senses more than the civilized individual, the sphere of utility and accuracy of this sense is largely augmented. Of this we shall have to speak presently. We find it, too, surprisingly developed in some animals; in which it is considered,by the eloquent Buffon, as an eye that sees objects not only where they are, but where they have been,—as an organ of gustation, by which the animal tastes not only what it can touch and seize, but even what is remote, and cannot be attained; and he esteems it a universal organ of sensation, by which animals are soonest and most frequently impressed, and by which they act and determine, and recognise whatever is in accordance with, or in opposition to their nature. The hound, amongst quadrupeds, affords us a familiar example of the extreme delicacy of this sense. For hours after the passage of game, it is capable of detecting the traces; and the bloodhound can be trained to indicate the human footsteps with unerring certainty. Until of late it was almost universally believed, that many of the birds of prey possess an astonishingly acute sense of smell. Hum- boldt relates, that in Peru, Quito, and in the province of Popayan, when they are desirous of taking the gigantic condor—the Vultur gryphus of Linnaeus—they kill a cow, or horse, and in a short time, ACUTENESS OF SMELL IN ANIMALS. 135 the odour of the dead animal attracts those birds in numbers, and in places where they were scarcely known to exist. It is asserted, too, that vultures went from Asia to the field of battle at Pharsalia, a dis- tance of several hundred miles, attracted thither by the smell of the killed !a Pliny,b however, exceeds almost all his contemporaries in his assertions on this matter. He affirms, that the vulture and the raven have the sense of svrfell so delicate, that they can foretell the death of a man three days beforehand, and, in order not to lose their prey, they arrive upon the spot the night before his dissolu- tion ! The turkey-buzzard of the United States is a bird of this class, and it is surprising to see how soon they collect from immense dis- tances after an animal has died in the forests. The observations and experiments of the ornithologist Audubon0 would seem to show, that this bird possesses the sense of smell in a less degree than the carnivorous quadruped. Audubon stuffed the skin of a deer with hay, and after the whole had become perfectly dry and hard, he placed it in an open field on its back, and in the attitude of a dead animal. In the course of a few minutes a vulture was observed flying towards it. It alighted near, and began to attack it, tearing open the seams, and pulling out the hay; but finding that it could obtain nothing congenial to its taste, it took to flight. It was found, too, that when animals in an advanced state of putridity, were lightly covered over so as to prevent the vultures from seeing them, they remained undisturbed, and undiscovered, although the birds repeatedly flew over them. In some other experiments it was found, that birds of prey were even attracted by well executed representations of dead animals, painted on canvass and exposed in the fields,—and in other experiments, that young vultures, en- closed in a cage, exhibited no tokens of their perceiving food, when it could not be seen by them, however near to them it was brought. These results are strange, inasmuch as the olfactory apparatus of the turkey-buzzard, when examined by the comparative anatomist, exhibits great developement, and admirable adaptation for acuteness of smell. As the organ of smell, in all animals that respire air, is situate at the entrance of the organs of respiration, it is probable that its seat, in insects, is in the mouth of the air tubes. This sense appears to guide them to the proper kinds of food, and to the execution of most of the few offices they have to perform during their transient existence. Occasionally, however, they are deceived by the resem- blance between the odours of substances very different in other qualities. Some plants, for example, emit a cadaverous odour, similar to putrid flesh, by which the flesh-fly is attracted, and led to deposit its ova in parts that can furnish no food to the future progeny. a Haller, edit. cit. torn. v. p. 158. b Nat. Hist., lib. x. cap. 6, p. 230, Edit. Lugd. 1587. c Ornithological Biography, p. 33, Boston, 1835 ; Roget's Animal and Vegetable Physiology, ii. 288, Amer. Edit. Phila. 1836; and Dr. Bachman, in Loudon's Mag. of Nat. Hist. vii. 167. 136 SENSE OF SMELL. As regards the extent of the organ of smell, man is undoubtedly worse situate than most animals, and all things being, in other respects, equal, it may be fair to presume, that those, in which the olfactory membrane is most extensive, possess the sense of smell most exquisitely. It is curious, however, that certain animals, which have the sense of smell in the highest degree, feed on the most fetid substances. The dog, for instance, riofis in putridity; and the birds of prey, to which reference has been made, but whose acuteness of smell, we have seen, has been contested, have similar enjoyment. The turkey-buzzard is so fetid and loathsome, that his captors are generally glad to loosen him from bondage; and it is affirmed, that if his ordinary fetor is insufficient to produce his release, he affords an irresistible incentive, by ejecting the putrid contents of his stomach upon his possessor !a One inference may, perhaps, be drawn from this penchant of animals with the most exquisite olfactories for putrid substances;— that the taste of the epicure for game, kept until it has attained the requisite fumet, is not so unnatural as it might at first sight appear. Like the senses already described, that of smell is to a certain extent under the influence of volition; in other words, it can be exerted actively, and passively. Its active exercise—as when we smell any substance to enjoy its sweets, or to test its odorous quali- ties—generally requires prehension; the proper direction of the head towards the object, and more or less contraction of certain muscles of the alae nasi. Doubtless, here again, the papillae are capable of being erected under the attention, as in the senses of taste and touch. On the other hand, we can throw obstacles in the way of the reception of disagreeable odours; and, if necessary, can prevent their ingress altogether, by compressing the nostrils with the upper extremity. Lastly, like the other senses, the smell is capable of great im- provement by education. The perfumer arrives, by habit, at an accurate discrimination of the nicest shades of odours; and the chemist and the apothecary employ it constantly to aid them in distinguishing bodies from each other, and in pointing out the changes that take place in them, under the influence of heat, light, moisture, &c. In this way it becomes a useful chemical test. The effect of education is likewise shown, by the difference between a dog kept regularly accustomed to the chase, and one that has not been trained. For the same reason, in man, the sense is more exquisite in the savage than in the civilized state. In the latter, he can have recourse to a variety of means for distinguishing the pro- perties of bodies, and hence he has less occasion for acuteness of smell than in the former; whilst, again, in the civilized state, num- bers destroy the sense, in order to procure pleasure. The use of snuff is one of the most common of these destructive influences. a Wilson's American Ornithology, with biographical sketch, by Geo. Ord Philad. ORGAN OF HEARING. 137 Of the acuteness of the sense of smell in the savage, we have an example, on the authority of Humboldt: he affirms, that the Peru- vian Indians in the middle of the night, can distinguish the different races by their smell,—whether they.are European, American Indian, or negro. To the same cause must be ascribed the delicacy of olfaction generally observed in the blind. The boy Mitchell,1 who was born blind and deaf, and whose case will have to be referred to here- after, was able to distinguish the entrance of a stranger into the room by the smell alone. A gentleman, blind from birth, from some unaccountable impression of dread or antipathy, could never endure the presence of a cat in the apartment. One day, in company, he suddenly leaped up, got upon an elevated seat, and exclaimed that there was a cat in the room, begging them to remove it. It was in vain, that the company, after careful inspection, assured him he was under an illusion. He persisted in his assertion and in his state of agitation; when, on opening the door of a small closet in the room it was found that a cat had been accidentally shut up in it. OF THE SENSE OF HEARING OR AUDITION. Audition makes known to us the peculiar vibrations of sonorous bodies, which constitute sounds. It differs from the senses which have already been described, in the fact that contact is not required between the organ of sense and the sonorous body; or between the organ and any emanation from the body. It is, however, a variety of touch, but produced by a medium acted upon by the vibratory body. 1. ANATOMY OF THE ORGAN OF HEARING. The auditory apparatus is a subject of intricate study to the young anatomist; and unfortunately when he has become acquainted with the numerous minute portions, to which distinct and difficult appella- tions have been appropriated, he has here, as in many other cases, attained a mere tedious detail of names, without having added to his stock of philosophical information. Happily, it is not necessary for our purpose to go thus minutely into the description of the organ of hearing. According to the plan hitherto pursued, allusion will be made to those portions of it only which concern the physiological inquirer. In the ear, as well as in the eye, we have the distinction between the physical and nervous portions of the organs more clearly exhi- bited than in the skin, mouth, or nose. The nervous portion is situate deeply within the organ; and the parts, between it and the exterior, act physically on the sonorous vibrations, in the case of the ear; and on the light, in that of the eye. The organs of the senses hitherto considered are symmetrical. * Wardrop's History of James Mitchell, Lond. 1813; and Dugald Stewart's Elements of the Philosophy of the Human Mind, iii. 401, 3d edit. Lond. 1808. 12* 138 SENSE OF HEARING. Those of audition are two in number, distinct but harmonious, and situate at the sides of the head, in a part of the temporal bone, generally called from its hardness the pars petrosa, and by the French and German anatomists regarded as a distinct bone, under similar appellations—Le Rocher and F e 1 s e n b e i n. This bone is seated at the base of the skull, so that the internal parts of the auditory organ are deeply and securely lodged. For facility of description, the ear may be divided into three dis- tinct portions':—1, the external ear, or that exterior to the membrana tympani; 2, the middle ear—the space contained between the mem- brana tympani and the internal ear; and 3, the internal ear itself, in which the auditory nerve is distributed. 1. The external ear. This portion of the auditory apparatus is commonly looked upon as an acoustic instrument, for collecting the sonorous rays or vibrations, and directing them, in a concentrated state, to the parts within. It is composed of the pavilion, and meatus auditorius externus. Fig. 20. 1. The pavilion. 2. Meatus auditorius externus. 3. Membrana tympani. 4. Malleus; 5. incus; 6. Stapes; Os orbiculare between the incus and stapes. 7. Cavity of the tympanum. 8. Eustachian tube. 9. Meatus auditorius internus. 10,11, 12. The labyrinth. 10. Vestibule. 11, 11, 11. Semi- circular canals. 12. The cochlea. 13. Stapedius muscle. The pavilion varies in size and position in different individuals. It is the fibro-cartilaginous, thin, and expanded portion, which is an appendage, as it were, to the head. It is irregular on its anterior surface; presenting several eminences and depressions. The emi- ORGAN OF HEARING. 139 nences are five in number, and have been called, by anatomists, the helix, anthelix, the tragus, antitragus, and the lobe. The helix forms the rim of the pavilion: the tragus is the small nipple-like projection on the facial side of the meatus auditorius; the antitragus is the projection opposite to this,—forming the lower portion of the anthelix; and the lobule is the fatty, pendulous por- tion, to which ear-rings are attached. The depressions are three in number—the groove of the helix or cavitas innominata; the fossa navicularis or scapha; and the concha. The name of the first suffi- ciently indicates its situation; the second is nearer the meatus auditorius; and the concha is the expanded portion, which joins the commencement of the meatus, and is bounded by the anthelix, tragus, and antitragus. The pavilion is supple and elastic; and, beneath the skin, are numerous sebaceous follicles, which are distinctly perceptible, and give to the skin its polish, and probably a portion of its suppleness. On the different eminences, some muscular fibres are perceptible, which it is not necessary for our purpose to distinguish; for in man at least they are only vestiges—as the French term them—to indi- cate the uniform plan, which appears to have prevailed in the forma- tion of the vertebrated animals; if they have any office it must be extremely unimportant. Numerous vascular and nervous ramifications are distributed on the pavilion. It is attached to the head by different ligaments, called —from their situation or attachments—zygomato-auricular or ante- rior auricular:—temporo-auricular or superior auricular, and mas- toido-auricular or posterior auricular; all of which terminate on the convex part of the concha. Three muscles, in animals at least, are attached to the ear, so as to move the pavilion. These occupy the same position as the ligaments described, and have similar names. In man, these again are mere vestiges; but in many animals—in the horse, for example—they are largely deve- loped, and are capable of moving the pavilion in various directions; and there are men, who possess a degree of voluntary power over it." The meatus auditorius externus extends from the inner extremity of the concha to the membrana tympani. In the adult it is about an inch long; narrower in its middle than at its extremities; longer inferiorly than superiorly, owing to the obliquity of the membrana tympani; and slightly curved upwards about its middle. The outer orifice is furnished with down or hairs, like the orifices of certain other canals. The meatus is partly osseous, for the space of half an inch and penetrates the temporal bone. More externally it is formed of fibro-cartilage,—a prolongation of that of the concha. It is lined by an extension of the skin, which becomes gradually thinner as it proceeds inwards, and is ultimately reflected over the outer surface of the membrana tympani. Beneath this skin, numerous sebaceous follicles are situate, which secrete the bitter humour, » Haller. Elem. Physiol, xv. 1, 4. 140 SENSE OF HEARING. called cerumen. This humour occasionally becomes inspissated; obstructs the canal; prevents the sonorous vibrations from reaching the membrana tympani, and is thus the cause of deafness. Softening the cerumen, by means of warm water* or oil, or soap and water dropped into the meatus, and then removing it by means of the syringe, restores the hearing. The portion, then, of the auditory apparatus—which we have arbitrarily termed the external ear—is a complete cul-de-sac, formed by a prolongation of the common integument. There is no opening communicating with the next portion—the middle ear;—the mem- brana tympani, with its dermoid envelopes, forming at once the medium of union and of separation between the two. A knowledge of this fact would somewhat diminish the alarm, in cases where in- sects or other extraneous bodies get into the meatus auditorius. The pain is excruciating, owing to the great general sensibility of this portion of the auditory apparatus; but, generally, the chief dread entertained is. that the irritating substance may pass into the head. It cannot, of course, proceed further than the membrana tympani, and even were it able to clear this obstacle, insuperable impediments exist to its farther progress. 2. The middle ear includes the cavity of the tympanum, the small bones contained in the cavity, the mastoid cells. Eustachian tube, &c. Like the last, it belongs to the physical portion of the ear. The cavity of the tympanum or drum of the ear has the shape of a portion of an irregular cylinder. Its name is not, indeed, inap- propriate. It has some resemblance to a drum, not only in form, but, as will be seen, in function likewise. The outer extremity of this cylinder is closed, like the drum, by the membrane already re- ferred to—the membrana tympani. This membrane is not situate vertically in the meatus, but obliquely downwards and inwards, so that the cavity is broader above than below. It is very thin and transparent, and consists of three layers,—the outermost formed bv the membrane lining the meatus auditorius externus; the most in- ternal belonging to the membrane of the cavity of the tympanum: and the middle being the membrane proper. On its inner side is distributed the nerve, called chorda tympani, and its centre affords attachment to one extremity of the chain of small bones,—to the handle of the malleus. The proper tissue of the membrana tympani is drv. and it is generally esteemed to be devoid of fibres." vessels and nerves. Sir Everard" Home,b however, asserts, that the membrane is muscular; that its fibres run from the circumference towards the centre, and are attached to the malleus: and that if the membrane of the human ear be completely exposed on both sides, by removing the contigu- ous parts, and the cuticular covering be washed off from its ex- * Haygarth, Medical Observations and Inquiries, vol. br. 2d edit p. 1^5. 1752. b Philos. Transact for 1500, P. i. p. 1, and Lectures on Comp. Anat, ui. 262~ Lond ORGAN OF HEARING. 141 tcrnal surface, and if it be placed in a clear light, the radiated direc- tion of its fibres may be easily detected. Tin's fibrous arrangement, Sir Everard conceives to be muscular, and on this he'founds some ingenious speculations, lo be hereafter noticed, regarding the appre- ciation of sounds. The discovery of a fibrous structure would, however, by no means prove, that the membrane is capable of con- tracting ; or that it is formed of muscular tissue. Many of the liga- ments, which consist of gelatine, and are consequently not contractile like muscles, are distinctly fibrous in their arrangement. The same may be said of the tendons, whose utility, as conductors of the force developed by the muscle, would be materially interfered with, were they possessed of the same degree of contractilitv. Again, Iluysch," Sir Everard Home, and Sir Charles Bellb affirm, that the membrana tympani is very vascular,—Sir Everard assert- ing, that the vessels, in their distribution, resemble those of the iris, and are nearly half as numerous;—their general direction being from the circumference to the handle of the malleus. It is not easy to account for this discrepancy amongst anatomists, as to the struc- ture of the membrana tympani. A part of it is probably referable to some having directed their attention to the membrane proper; others to the membrane with its dermoid coverings, which are highly vascular. The inner extremity of the drum is partly osseous, partly mem- branous. Nearly opposite the centre of the membrana tympani is the foramen ovale or vestibulare, called the fenestra ovalis or vesti- bularis, situate vertically, and forming a communication between the middle and the internal ear. It is closed by a membrane, con- sisting, like the membrana tympani, of three layers, to which is at- tached the base of the stapes—the inner extremity of the chain that stretches across the cavity. Immediately below the foramen ovale is the bony projection, called the promontory; and beneath this again, a second opening, called the foramen rotundum or cochleare or fenestra rotunda or cochlearis, which forms a communication be- tween the middle ear and the external scala of the cochlea. This foramen is closed by a membrane, similar to that of the foramen ovale; but not, like it, parallel, or nearly so, to that of the tympanum, —being situate obliquely. There is no communication by a chain of bones between it and the membrana tympani. These small bones or ossicles are four in number, so connected with each other as to form a bent lever; one extremity of which is attached to the tympanic surface of the membrana tympani,—the other to the membrane of the foramen ovale. These bones are usually termed, from their shape—beginning with the most external, and following their order—malleus, incus, os orbiculare, (by some not considered a distinct bone, but a process of the incus,) and stapes. 1 Epi>t. Anat. octava, p. 10, Amstel. 1724. b Anat and Physiol, edited by J. D. Gcdman, oth Amer. edit. ii. 253, New York, 1-27. 142 SENSE OF HEARING. A small muscular apparatus,—consisting of three muscles, the ante- rior muscle of the malleus; the internal muscle of the same bone; and the muscle of the stapes,—is attached to the chain, which it can stretch or relax; and of course it produces a similar effect upon the membranes to which the chain is attached. They are animated by branches of the portio dura, or facial nerve, which is itself not a nerve of sensibility, but of motion; yet probably acquires this func- tion by its union with the vidian twig of the fifth pair, in its passage through the aqueduct of Fallopius. It is this nerve which furnishes the chorda tympani. Bellingeri1 thinks, that the fifth pair regulates altogether the involuntary motions of the internal ear.b At the anterior and inferior part of the cavity is the tympanic extremity of a canal, through which the drum receives the air it contains. This canal, called the Eustachian tube, i$ about two inches long, and proceeds obliquely forwards and inwards, to the lateral and superior part of the pharynx, into which it opens behind the posterior nares. It is partly osseous, partly fibro-cartilaginous and membranous; and, towards its pharyngeal extremity, it expands, terminating by an oval aperture, resembling a cleft. Throughout its course it is lined by a mucous membrane, which appears to be a prolongation of that of the nasal fossae, and it is capable of being more or less contracted and expanded by the muscles, which com- pose and move the velum palati. The cavity of the tympanum likewise communicates, by a short and ragged canal, with numerous cells contained in the mastoid process. These cells open into each other, and vary in number, size, and arrangement in different individuals, and animals. They are called the mastoid cells. The cavity is larger in those animals, whose sense of hearing is most acute. In man, it is about a quarter of an inch deep, and half an inch broad. It is lined by a prolongation of the same mem- brane, as that which lines the Eustachian tube. This membrane, as we have seen, covers the membrana tympani, and the mem- branes of the foramen ovale, and foramen rotund um. It likewise lines the mastoid cells, and is reflected over the small bones. The middle ear does not exist in every animal endowed with hearing. It does not begin to appear lower in the scale than in reptiles; and is by no means equally complex in all. Frequently, the chain of bones is entirely wanting; and at other times we find one bone only. 3. The internal ear or labyrinth is the most important part of the apparatus. It consists of several irregular cavities in the pars petrosa of the temporal bone, in which the nerve of audition is dis- tributed. It is, consequently, in this portion, that the physical part of audition terminates, and the nervous begins. The labyrinth comprises the vestibule, semicircular canals, and cochlea. a Op. citat. and Edinb. Medical and Surgical Journal, July, 1834, p. 128. b See, on the nerves of the Tympanum, Wistar's Anatomy, by Prof. Horner, 7th edit. by Prof. Pancoast, ii. 438, Philad. 1839. ORGAN OF HEARING. 143 Labyrinth separated from the Solid Bone in which it lies embedded. V. Vestibule. X. Y. Z. Semicir- cular canals. K. Cochlea. O. Fe- nestra ovalis. R. Fenestra rotunda. The vestibule—as its name imports—is the hall, that communi- cates with all the other cavities of the labyrinth. It would appear to be the most essential part of the organ, as it often exists alone. At its inner sur- face are numerous small foramina, which communicate with the bottom of the mea- tus auditorius internus, and through which the filaments of the auditory nerve reach the labyrinth. Externally, it communi- cates with the cavity of the tympanum by the foramen ovale. Posteriorly, it opens into the semicircular canals by five foramina; and, anteriorly, by a single foramen, into the internal scala of the cochlea. There is, also, posteriorly and inferiorly, near the common orifice of the two vertical semicircular canals, the opening of a small, bony duct, which terminates internally at the posterior sur- face of the petrous portion of the tempo- ral bone. This duct is called the aquoe- ductus or diverticulum vestibuli. The semicircular canals are three in number, and occupy the hinder part of the labyrinth. They are called superior vertical, posterior vertical, and horizontal. They are cylindrical cavities, curved semicircularly, and are more expanded at their vestibular origin, which has been therefore called ampulla. They are consti- tuted of a plate bone, situate in the spongy tissue of the pars petrosa, and all of them communicate with the vestibule. The cochlea is the most anterior portion of the labyrinth. It is so called in consequence of its resemblance—in man and in the mammalia—to a snail's shell; hence also, its French and German names, limacon and s c h n e c k e. It is the most intricate part of the organ of hearing, and does not, by any means, admit of easy description. It is a conoidal canal, spirally convoluted, making two turns upon itself and resting on a bony nucleus or pillar, called modiolus. The base of the nucleus is concave; corresponds to the bottom of the meatus auditorius internus, and is pierced by small foramina, through which the filaments of the auditory nerve reach the cochlea. The spiral canal is divided, in its whole length, by a partition, half osseous and half membranous, called the lamina spiralis; so that two distinct tubes are thus formed. These are the scalce of the cochlea. At the apex of the cochlea they run into each other; but, at the base, the one turns into the vestibule, and is hence called the superior or vestibular or internal scala; the other communicates with the cavity of the tympanum by the foramen rotundum, and is called the inferior, tympanic, or external scala. At this scala, near the foramen rotundum, a bony canal begins, which proceeds to- 144 SENSE OF HEARING. wards the posterior surface of the pars petrosa on which it opens. It is the aquceductus or diverticulum cochlea. The cochlea does not exist in all animals that hear. It is not, therefore, of essential importance. It varies, too, greatly, in com- plication, in different animals. In birds, whose hearing is extremely delicate, it merely consists of a short, hollow, bony process, divided into two scalse but without any spiral arrangement. In reptiles, the cochlea is still more imperfect; and in many species it can scarcely be said to exist. In fishes there is no trace of it. Fig. 21. Osseous Labyrinth laid open to show especially the Membranous Labyrinth. X, Y, Z. Semi circular canals. A, A, A. Ampullae. P. Perilymph between the osseous and mem- branous labyrinth. U. The utricle. S. The sacculus. O, O Cretaceous bodies. G, N. Auditory nerve. K. Branch going to the cochlea. L. Lamina spiralis. M. Apex of modiolus. D. Portio dura. The different cavities of the internal ear are lined by an ex- tremely delicate membrane. In many animals this membrane alone exists without any bony parietes. It exhales at its inner surface a limpid fluid, called the liquor or lymph of Cotugno or Cotunnius, the perilymph of Breschet, which, under particular circumstances, can reflow into the aquseductus vestibuli and aquaeductus cochleae. This fluid is contained in all the cavities of the internal ear. Within the cavity of the osseous labyrinth just described are contained membranes having nearly the shape of the vestibule and semi- ORGAN OF HEARING. 145 circular canals, but not extending into the cochlea. These mem- branes, which compose what has been called the membranous labyrinth, form a continuous but close sac, containing a fluid—the endolymph,—termed by De Blainville vitrine auditive, from its sup- posed analogy to the vitreous humour of the eye, perfectly similar in appearance to the perilymph, which surrounds it on the outer side, and intervenes between it and the sides of the osseous laby- rinth so as to prevent any contact. The form of the membranous vestibule requires special notice, as it is not an exact imitation of the osseous cavity, being composed of two distinct sacs which open into each other; one of these is termed the utricle, sinus or alveus utriculosus, sacculus vestibuli, and median sinus; the other, the sacculus. Each sac contains in its interior a small mass of white calcareous matter resembling pow- dered chalk, which seems to be suspended in the fluid contained in the sacs, by means of a number of nervous filaments proceeding from the auditory nerves, (G N. Fig. 21.) From the universal presence of these substances in the labyrinth of all the mammalia, and from their much greater size and hardness in aquatic animals, it is presumable that they perform some office of importance in audition.* They are termed by Breschet, otolithes and oloconies, according as they are of a hard or a soft consistence. The small square figures (p. 144) represent their size and appearance in the dog and the hare. It is in the cavities of the internal ear, and on the different parts of the membranous labyrinth, that the auditory or acoustic nerve is distributed. This nerve is the portio mollis of the seventh pair of most anatomists. It arises, like the other nerves of the senses, from the medulla oblongata, and near the anterior paries of the fourth ventricle. Thence it passes obliquely outwards, forwards, and upwards, and enters the meatus auditorius internus, the foramen of which is situate on the posterior surface of the pars petrosa. The base of this meatus corresponds to the inner surface of the vestibule, and to the base of the cochlea. Through the first foramen, near the base of the meatus, the portio dura of the seventh pair or facial nerve passes, to gain the aqueduct of Fallopius, along which it pro- ceeds, giving off filaments to different parts of the middle ear, and ultimately issuing by the stylo-mastoid foramen, to be lost on the muscles of the face. Below the part of the meatus, where the facial nerve emerges, are several other foramina, through which the filaments of the audi- tory nerve attain the labyrinth. These are distributed to the vesti- bule, semicircular canals, and cochlea; and terminate, by very delicate ramifications, in the tissue and at the surface of the mem- brane that lines the labyrinth. Such are the organs concerned in the function of audition. Be- * Breschet, Memoir, de 1'Academe de Medecin., torn. v. Recherches Anatomiques et Physiologiques sur l'Organe de l'Ouie, &c, Paris, 1836, and Roget's Animal and Vegetable Physiology, ii. 305, Amer. Edit. Philad. 1836. VOL. I. 13 146 SENSE OF HEARING. fore proceeding to the physiology of these different parts, and the assistance afforded to the mind by this sense, it js necessary to enter into a brief physical disquisition on the subject of sound. 2. OF SOUND. If a body, by percussion or otherwise, be thrown into vibration, every vibration will excite a corresponding wave in the air; and these oscillations will be propagated, in all directions, until they are gradually lost in distance; but if they strike on the organ of hear- ing with the necessary force, a sensation is produced, which is called sound or noise. The term, however, is frequently used to signify, not only the sensation, but likewise the affection of the air, or of the sonorous body, by which the sensation is effected. That bodies move or oscillate, when they produce sound, admits of easy detection. We can see it in drums, bells, musical strings, &c, whose vibrations, being extensive, are more perceptible; and we can arrest them, and with them the sound, by putting the hand upon the body, or by muffling it. Whenever a sonorous body is struck, a change in the relative position of its molecules is produced. These, by virtue of their elas- ticity, tend to return to their former condition. This is done by a series of oscillations, which are, at first, more extensive, but become gradually less, until they finally cease. The rapidity of these oscil- lations is greater in bodies that are hard and elastic; and hence it has been concluded, that these two qualities render a body sonorous. It is not, however, a matter of facility to say, what is the precise cause of the difference of sound in analogous bodies. It must, of course* be dependent upon intimate composition, but of a character not easily intelligible to us. There are but one or two individuals in Great Britain, who have been celebrated for the fabrication of the larger order of bells—for churches, colleges, &c.—and in certain countries the art is comparatively unknown. The resonance is entirely owing to the intimate composition of the body, and is beautifully and sin- gularly exhibited in the Chinese gong, the sound of which will con- tinue to rise for some time after a succession of rapid and forcible blows has been inflicted. But, in order that the oscillations of a sonorous body may affect the organ of sense, an intermediate body is necessary to repeat and transmit them. This body is called the vehicle of sound, and it is usually the air. Lamarck supposes the existence in the atmo- sphere of a vibrative fluid, of great subtilty, which penetrates the globe invisibly as well as the bodies on its surface; and Geoffroy St. Hilaire affirms, that sound " is a matter resulting from the com- bination of the external air with the polarized air of the sonorous body!"—but these are topics that belong to works on higher physics." The air, by virtue of its elasticity, is admirably adapted as a vehicle • Adelon, Physiologie de I'Homme, 2de edit. i. 355, Paris, 1829, and Lepelletier, .Physiologie, iii. Ill, Paris, 1832. SOUND. 147 for sound. The loudness of the sound conveyed by it is dependent upon the density of the medium. If we put a bell under the receiver of an air pump, and exhaust the air, the sound will become gradually more and more faint, and when the air is exhausted will not be heard at all. For the same reason a pistol fired on the top of the Himala mountains gives a much feebler report than in the valleys beneath.* Sympathetic sounds afford additional evidences of the carrying power of air. Every sonorous, elastic body can be thrown into oscillations, provided the air around it be made to tremble in any manner. Thus, if we sound a note near a piano-forte, whose dampers are raised so as to admit of free vibration, the string, that is in unison with the tone produced, will vibrate; and a wine- glass or goblet may, according to Arnott, be made to tremble, and even to fall from a table, by sounding on a violoncello near it, the note that accords with its own. The strata of air, in proximity with the sonorous body, receive the first impulses ; and from these they are successively propagated to others; much in the same manner as the undulations extend from the place in which a stone is cast on a surface of smooth water; except that the aerial undulations usually extend in every direction, whilst the aqueous proceed only horizontally. In this propagation from stratum to stratum a portion of the sound is necessarily lost; so that the loudest sounds are heard only within certain limits; and, in all cases, the intensity of the sound is inversely as the square of the distance from the sonorous body. By causing the sonorous undulations to proceed entirely in one direction, and preventing their escape in every other, a sound may be rendered audible at a much greater distance. Biot found, that when he spoke in a wdiisper at one extremity of a cylinder upwards of one thousand yards long, he was distinctly heard at the other. In many large manufactories the knowledge of this fact is turned to good account. By having numerous tubes communicating with the different rooms of the establishment, and terminating in his office, the principal is enabled to have his directions readily conveyed, and to receive any information he may require, without the slightest inconvenience. The velocity, with which sound proceeds, admits of easy calcu- lation. Light passes with such rapidity, that it may be regarded as proceeding from objects on the earth instantaneously to the eye. The velocity of sound is incomparably less. We see the flash of a gun at a distance; and, some time afterwards, we hear the report. Considering the light then to have reached the eye instantaneously, if we know the distance of the gun, and note the time that elapsed between the appearance of the flash and the report, we can calcu- late accurately the rapidity of sound. This is found to be about eleven hundred and forty-two feet in a second. We can tell, in a Pouillct, Elemens de Physique Experimentale, iii. 198, Paris, 1832; and Art. Schall, in Picrer's Anat. Physiol. RealwOrterb. vii. p. 205, Altenb. 1827. 148 SENSE OF HEARING. this manner, the distance of a thunder cloud, by noting the time of the flash, and the time that elapses before hearing the clap. If it be thirty seconds, the cloud is at the distance of thirty times eleven hundred and forty-two feet, or of six miles and a half. The velocity is the same for all kinds of sounds. Biot found, on playing a flute at the end of the tube, above referred to, that the tones arrived at the ear placed at the other extremity in due suc- cession ; so that their velocity must have been uniform. When the aerial oscillations meet with a resisting body of a regular surface, as A B, Fig. 22, they are reflected at an angle equal to the angle of incidence: consequently an ear, placed in the course of these reflected waves as at C, will refer the sound to a distance as far behind the point of reflection, and in the direction of the reflected ray, as the sonorous body is from the point of re- flection. It will seem to be at E. The ear at C will, however, receive the direct oscillations from the bell D, as well as those that proceed along the lines D F and F C ; or in other words, it will hear both the sound and its echo; and, if the surfaces on which the sonorous undulations impinge be favourably disposed, these echoes may be very numerous. The utility of the ear trumpet, and of the speaking trumpet is to be explained by this law of the reflection of the aerial undulations : and some physiologists are of opinion, that the external ear is inser- vient to audition on similar principles. The ear trumpet is a tube, narrow at one extremity, so as to enter the concha; and expanded at the other like a trumpet. It is also curved, so that it may be easily directed to objects. All the sonorous rays, which enter the expanded extremity, after various reflections, are brought to a focus in the auricular end; and the intensity of the sound is, in this way, so much augmented, that a person who, without it, is entirely deaf to common conversation, may be able to enjoy it. A sheet of paper, folded like a cone, the apex of which is placed in the concha, serves a like purpose; and, to a less extent, the hand held concavely behind the ear. Air is not the only, or the most perfect, vehicle of sound. The personal experiments of divers show, that it can be conveyed through water. The blows of workmen around a diving-bell are distinctly heard above; and fishes have manifestly an acute sense of hearing, although this was at one time denied. An experiment, made by the SOUND. 149 Abbe Nollet, and repeated by Franklin, proves, that water transmits a much stronger vibration than air. When two stones were struck together under water, a shock was given to the ear, which was almost insupportable. The latter philosopher found by experiment, that sound, after travelling above a mile through water, loses but little of its intensity. According to Chladni, the velocity of sound in water is about 4900 feet in a second, or between four and five times as great as in air. Solids, too, are much better conductors of sound than air. If we scratch one end of a wooden rod, the sound will be distinctly heard by the ear applied to the other, although it may be inaudible through the air. Savage tribes are in the habit of discovering the advance of enemies, or of their prey, by applying the ear to the ground; and the watchmen, in some of the towns, instead of springing a rattle, and alarming offenders, strike the pavement with a staff, the sound of which is heard by their fellow watchmen at a considerable dis- tance. It is a common practice to ascertain, whether a kettle boils, by putting one end of a poker on the lid, and the other to the ear. The difference between simmering and boiling is in this way easily detected. A knowledge of this fact, and of the ready communi- cation of sound through solids, has given rise to a valuable suggestion for the discrimination of diseases of the chest, and of various physiological and pathological conditions. By putting the ear to the chest we can hear the rush of the air along the bronchial tubes, the pulsations of the heart, &c. and can discover any aber- ration that takes place in the execution of their functions. This is what has been called, by the late distinguished Laennec, of Paris— the proposer of the method—immediate auscultation. The direct application of the ear to the chest is, however, frequently inadmis- sible. In these cases Laennec used a hollow cylinder, called a stethoscope, one end of which he applied to the chest—the other to the ear. This plan he termed mediate auscultation? The suggestion has led to most valuable improvements in diagnosis. Hassenfratz and Biot have made some accurate experiments on the comparative rapidity of the progress of sound through air and solid bodies. The latter found, in the aqueducts of Paris, that a blow, struck upon a pipe nine hundred and fifty-one metres, or about ten hundred and forty yards, in length, was heard two seconds and a half sooner through the sides of the pipe than through the air; but the sound did not extend so far. Ice conveys sound even better than water; for if cannon be fired from a distant post—a frozen river intervening—each flash is followed by two distinct reports, the first conveyed by the ice,—the second by the air. It has been already observed, that the vibrations of the air, caused by a sonorous body, are capable of exciting corresponding or sym- pathetic vibrations in solid bodies within their sphere of action. It * A Treatise on Diseases of the Chest, and on Mediate Auscultation, from the French of Laennec, by Dr. Forbes, 4th edit. Lond. 1834, reprinted in this country. 13* 150 SENSE OF HEARING. was an old observation, that such vibrations are excited only in bodies in unison with the sonorous body; in other words, in those that are capable of producing the same tone with the latter. M. Savart has, however, found, that unison is not necessary; and that when a sound is produced in the air, every body receives a vibra- tion, which is a repetition of the one that occasions the sound. This he proved by using small membranes, on which he placed fine sand. These were agitated, and the sand assumed various regular arrange- ments, whenever a sound was produced in their vicinity. This law of physics is important in its physiological relations. The apparatus of audition consists of several membranous structures, which are thrown into oscillations, whenever the ear receives the impressions of sound. The vibrations, which produce sound, differ much as regards their extent and rapidity; and on these differences are dependent two of the qualities of sound—strength and tone. The strength or intensity of sound depends on the extent of the vibrations of a sonorous body. This is easily seen in a musical string; the sound of which becomes weaker as the extent of the oscillations diminishes. The tone, on the other hand, is dependent on the rapidity of the oscillations;—on their number in a given time. The tone, produced by a string or other sonorous body that vibrates quickly, is termed acute or sharp, when compared with the tone of one that vibrates more slowly. The latter is called grave, when compared with the former. The gravest sound that the ear can appreciate, is ordinarily con- sidered to result from thirty-two vibrations per second; the most acute, from eight thousand one hundred and ninety-two vibrations, according to some;—twelve thousand, according to others. Some well-devised experiments, made by Savart, largely extend these limits, and appear to indicate, that they cannot yet be rigidly fixed. In his experiments, the ear distinctly appreciated fourteen or sixteen vibrations per second; and the acutest note, that was audible, proceeded from upwards of forty thousand simple oscillations, per second. The duration of the impression of a sonorous vibration on the ear is about the sixteenth part of a second. If a sonorous body be struck, and the vibrations excited be all performed in equal times, a simple and uniform sensation will be produced on the auditory nerve, and one musical tone will be heard. But if the vibrations be various and irregular, they will fall irregu- larly on the organ of hearing, and will excite a harsh impression, as if various sounds were heard together. In other words, a noise or discord will be produced. If two notes, sounded together, afford pleasure, they produce har- mony or concord. This arises from the agreement of the vibrations of the two sonorous bodies, so that some of the vibrations of each strike upon the ear at the same time. If, for example, the vibrations PHYSIOLOGY OF THE EXTERNAL EAR 151 of one sonorous body take place in double the time of another, the second vibration of the latter will strike upon the ear at the same instant as the first vibration of the former. This is the concord or harmony of an octave. Between a note and its octave, there are six intermediate notes, constituting the diatonic scale or gamut. If the vibrations of two strings are as two to three, the second vibration of the former will correspond with the third vibration of the latter, pro- ducing the harmony called a fifth. There are other tones, which, although they cannot b$ struck together without producing discord, if struck in succession, may give the pleasure called melody. Melody is, in truth, nothing more than the effect produced on the brain by pleasing musical tones, sounded in succession. There is another quality of sound which the French call timbre. By some of the translators of the works of the French physiologists, this word has been inaccurately rendered note. It is essentially dif- ferent from note or tone, and is peculiar. By English philosophers it is termed the quality of sound. It is this quality that enables us to recognise various instruments, although sounding the same note or tone; and to distinguish the voices of individuals from each other. Its cause is not evident. By most, it is conceived to depend upon the nature of a sonorous body, if it be a surface,—and at the same time on its shape, if a tube. Biot conjectures, that it is owing to the series of harmonic sounds forming part of every appreciable sound. When any sonorous body is made to vibrate, a distinct sound is heard, which is the fundamental; but, if attention be paid, others will be heard at the same time. These are called harmonics. It is not improbable but that the timbre or quality may be depen- dent as well upon the nature of the sonorous body, as upon the greater or less number of harmonics, that accompany the funda- mental sound.1 3. PHYSIOLOGY OF AUDITION. In tracing the progress of the sonorous vibrations to the internal ear, we shall follow the order of parts described in the anatomical sketch of the auditory apparatus;—commencing with the external ear. The meatus auditorius externus being always open, sonorous vibrations can readily attain the rriembrana tympani. Some of these pass directly to the membrane without experiencing reflection, and communicate their oscillations to it. The pavilion, by most physiologists, has been regarded as a kind of ear-trumpet, for col- lecting the aerial undulations, and directing them, after various reflections, to the bottom of the auditory canal. In the horse, and in those animals which have the power of pricking the ears, or of moving them in various directions, this is doubtless the case; but in man we cannot expect any great effect of the kind, if we regard its 1 See, on undulations in general, Midler's Elements of Physiology, by Baly, Pt v. p. 1215, Lond. 1839. 152 SENSE OF HEARING. particular arrangement, and the incapability of moving it from its fixed direction, which is nearly parallel to the head. Boerhaave,8 indeed, pretended to have proved by calculation, that every sonorous ray, which falls upon the pavilion, is ultimately directed towards the meatus auditorius externus.b Simple inspection of the pavilion will show that this cannot be universally true. Some part of the anthelix is, in almost every individual, more prominent than the helix; and it is therefore impossible for the undulations, that fall upon the posterior surface of the former, to ke reflected towards the concha. M. Itard,c a distinguished physiologist and aurist of Paris, asserts, that he has never seen the loss of the pavilion affect the hearing; and that, as is well known, many animals, whose sense of hearing is extremely acute,—the mole and birds, for example,—are devoid of it. Hence he concludes, that it is perhaps rather injurious than favourable to audition, and is more inservient to the expression than to the hearing of the animal. M. Itard's view is doubtless too exclusive.*1 The pavilion may have but little agency as an ear- trumpet, but it must have some. The concha, being the expanded extremity of the meatus auditorius, must receive more sonorous vibrations than could be admitted by the meatus itself. These are reflected towards the membrana tympani, and reach that expansion in a state of concentration—but to no great extent, it is true. In this way, and perhaps in that suggested by M. Savart,6 the pavilion is useful in audition. That gentleman is of opinion, that the whole of the external ear, the elasticity of which he considers to be capa- ble of slight modification by the action of its proper muscles, is an apparatus for repeating sonorous vibrations, and transmitting them along its own parietes to the membrane of the tympanum. Accord- ing to this view, the different inequalities of surface in the pavilion admit of explanation. When the membrane is stretched in a direc- tion parallel to a sonorous surface, the oscillations, impressed upon it, are most marked; and, accordingly, as sounds impinge upon the pavilion from various quarters, the inequalities of surface always admit of some being disposed in the most favourable way for the reception of the vibrations. It is true, however, that the pavilion is not essential to audition; the hearing not suffering by its removal for more than a few days; so that its physiological influence is much more limited than might be conceived. It is probable, that it contributes to a knowledge of the direction of sounds, and it is certainly calculated to protect the membrana tympani/ a Praelect. torn. iv. p. 317; and Buchanan, Physiological Illustrations of the Organ of Hearing, &.c. p. 77, London, 1828. b Magendie, Precis. Elementaire, i. 115. c Traite des Maladies de l'Oreille et de 1'Audition, i. 131. Paris, 1821. d Kramer, on the Nature and Treatment of Diseases of the Ear, translated from the German, by Dr. J. R. Bennet, Lond. 1837; and Dunglison's Amer. Med. Library Edi- tion, p. 17, Philad. 1838. e Annales de Chimie, xxvi. 5; and Journal de Physiologie, iv. 183, and v. 367 f Dr. Sym, Edinb. Med. and Surg. Journal, Jan. 1841, p. 48. PHYSIOLOGY OF THE MIDDLE EAR. 153 The meatus auditorius externus conducts the sonorous vibrations directly, and by reflection, to the membrana tympani, as well as by its parietes. It is probable, too, that it is useful in protecting the membrane from the direct action of the air and extraneous bodies. This is perhaps the cause of its tortuous character in all animals. If too tortuous, the sense of hearing becomes impaired,—the sono- rous oscillations not being properly directed towards the membrane. Baron Larrey has published some cases of deafness produced in this manner, which were removed by wearing an artificial concha and meatus, of the natural curvature, made of gum elastic. The down or hairs, at the entrance of the meatus, have also been re- garded as protecting agents against the intrusion of extraneous bodies; whilst the cerumen has been looked upon as a fit material for entrapping insects in the slough formed by it, or for destroying them by its poisonous influence. It is probable, however, that the most important function of the cerumen is to keep the lining mem- brane of the meatus in a physical condition adapted for the proper fulfilment of its functions. Middle Ear.—In the mode described, the vibrations of a sonorous body attain the membrana tympani. An experiment by Savart would seem to show, that this membrane is thrown into vibrations chiefly by the air contained in the meatus. He made a small truncated cone of pasteboard, and closed the smaller extremity by a tense membrane, nearly as the membrana tympani closes the inner extremity of the meatus auditorius; and he found, that when sounds were produced near the parietes of the cone, the membrane vibrated but little; whilst, if they were occasioned opposite the base of the cone, so that they could be transmitted to the mem- brane by the air within the canal, the vibrations were very distinct, even at a distance of thirty yards and upwards. The membrane of the tympanum, then, receives and repeats the sonorous vibrations. It has, however, been supposed to be possessed of other functions. Dumas,b for example, conceived it to be com- posed of numerous cords, and each of these to correspond to some particular tone. But of this arrangement we have not the slightest evidence from observation or analogy. By others, it has been supposed, and with every probability, that the membrane is capable of being rendered tense, or the contrary, by the bent lever, formed by the chain of small bones. They have farther stated, that this tension or relaxation is adapted to the sounds, which the membrane has to transmit. The ancients believed, that the adaptation was produced by the stretching of the membrane, so as to put it in unison with the sound produced. Independently, however, of the experiments of Savart, which show, that unison is not necessary for the production of vibrations, the fact, that we are capable of distinguishing several sounds at the same time, would be sufficient to negative the suppo- 1 Principes de Physiologie, 2de edit., Paris, 1806. 154 SENSE OF HEARING. sition. Nor can we easily conceive, that the membrane could admit of as many distinct vibrations as the ear is capable of accu- rately appreciating tones, which amount to about eight octaves. Bichat thought, that the degree of tension of the membrane cor- responded with the intensity of sounds; and that its effect was to cause the sonorous vibrations to attain the internal ear, in a degree sufficiently strong to excite the appropriate impression, but not so strong as to cause pain,—the membrane becoming more tense for a feeble sound, and relaxed for one too strong. In support of this view, Bichat cites the case of several persons, who could not hear ordinary sounds, until the ear had been impressed by louder, which, according to him, roused the membrane to tension. Savart, on the other hand, from the fact, that every membrane vibrates with more difficulty, and less extensively, according to its tension, conjectures, that the membrane is relaxed in the case of very feeble or agreeable sounds, and that it is rendered tense to transmit the too powerful or the disagreeable. Again, it has been conceived that the tension varies with the tone of the sound,—being augmented, according to some physio- logists, in the case of acute, according to others, in that of grave, sounds. Sir Everard Home,a it has been remarked, esteems the mem- brana tympani to be muscular: and he affirms, that it is chiefly by means of this muscle, that accurate perceptions of sound are made by the internal organ; and that by it the membrane can alter its degree of tension. It has been already observed, that the muscles, attached to the small bones, are capable of varying this tension; that the internal muscle of the malleus or tensor tympani, for example, by its contraction, renders it more tense. Sir Everard admits, " that the membrana tympani is relaxed by the muscles of the malleus, but not for the. purpose alleged in the commonly re- ceived theory. It is stretched in order to bring the radiated muscle of the membrane itself into a state capable of acting, and of giving those different degrees of tension to the membrane, which em- power it to correspond with the variety of external tremors: when the membrane is relaxed, the radiated muscle cannot act with any effect, and external tremors make less accurate impressions." The reader is referred to the remarks already made on the views of Sir Everard in their anatomical relations. His speculations do not, however, end here. He employs the discovery to account for the difference between a "musical ear," as it is usually termed, and one which is incapable of discriminating, or feeling pleasure from, the succession of musical tones,—with what success we shall inquire presently. The truth is, that none of the conjectures, which have been pro- posed, regarding the precise effects of tension or relaxation of this membrane, can be looked upon in any other light than as ingenious » Lect, on Comp. Anat, iii, 265, PHYSIOLOGY OF THE MIDDLE EAR. 155 speculations, based, generally, upon the fact, that the membrane seems certainly capable of being varied in its tension by the move- ments of the chain of bones, but leading us to no certain knowledge of the precise effect on audition of such tension or relaxation.* In fact, although the integrity of the membrana tympani is neces- sary for perfect hearing, its perforation or destruction does not induce deafness. We have numerous cases of perforation from accident and otherwise, related by Valsalva,1' Willis,0 Riolan,d Flourens, and others, in which the hearing continued; and, in cer- tain cases of deafness, the membrane is actually punctured for the purpose of restoring the hearing.e The communication of sonorous oscillations from the membrana tympani across the cavity of the tympanum to the internal ear is effected in three different ways; 1, by the air, contained in the cavity of the tympanum; 2dly, by the chain of bones to the mem- brane of the foramen ovale; and 3dly, by the parietes of the tym- panum. So that, if the membrana tympani should be punctured or destroyed, the aerial undulations, caused by a sonorous body, and which enter the meatus auditorius, may extend into the cavity of the tympanum, and excite corresponding oscillations in the mem- branes of the foramen ovale, and foramen rotundum. The chorda tympani—composed, as we have seen, of a branch of the fifth pair and of the portio dura of the seventh, and distributed on the interior surface of the membrana tympani—probably conveys no acoustic impression to the brain. To it is owing the excessive pain, caused by the contact of an extraneous body with the mem- brane, and that occasioned by a loud noise, or by compressing the air forcibly in the meatus by passing the finger suddenly and strongly into the concha. The uses of the mastoid cells, which communicate with the middle ear, are not known. It would seem, that the strength of audition is in a ratio with their extent. In no animals are they more ample than in birds, which are possessed of great delicacy of hearing. This effect may be induced either by their enlarging the cavity of the tympanum, and allowing the sonorous oscillations to come in contact with a larger surface; or by the plates, wrhich compose them, being thrown into vibration. It has been conceived, too, that they may serve as a diverticulum for the air in the middle ear, when subjected by the membrana tympani to unusual compression. Sir Charles Bell/ with more warmth than is judicious or cour- teous, combats the idea of the foramen rotundum receiving the undulations of air. The oblique position of the membrane of the foramen, with regard to the membrana tympani, satisfactorily, he * For the fancied uses of this membrane, see Haller, Element. Physiol, v. 198. & Op. Anat. de Aure Humana, &c. Ed. J."A. Morgagni, Venet. 1740. c Oper. Omn. Venet. 1720. d Enchirid. Anat. 1. iv. c. 4, Lugd. Bat. 1649. e Deleau (le jeune), Memoire sur la Perforation du Tympan, &c, Paris, 1822; Itard, in Mem. de 1'Academ. Royale de Medecine, torn. v. Fascic. 4, Paris, 1836; and a translation, by the author, in his American Medical Library and Intelligencer, for May 1, 1837 ; also Kramer, op. citat. {Op. citat. i. 269. 156 SENSE OF HEARING. thinks, opposes this doctrine. The function which, with Savart, he assigns to it—if not accurately, at least ingeniously—is the follow- ing. As the membrane of the foramen ovale receives the vibrations from the chain of small bones, these vibrations circulate through the intricate windings of the labyrinth and are again transmitted to the air in the tympanum by the foramen rotundum. The different cavities of the labyrinth being filled with an incompressible fluid, no such circulation, he insists, would occur, provided the parts were entirely osseous. As it is, the membrane of the foramen rotundum gives way, "and this leads the course of the undulations of the fluid in the labyrinth in a certain unchangeable direction." The explanation of Sir C. Bell is not as convincing to us as it seems to be to himself. The membrane of the foramen rotundum does not appear to be required for the undulation in the cavities of the labyrinth, which he describes, as the liquor of Cotunnius can readily reflow into the aqueducts of the vestibule and cochlea. The principal use of these canals would seem, indeed, to be, to form diverticula for the liquor, when it receives the aerial impulses. Sir C. Bell cites the case, often quoted from Riolan, of an indivi- dual, who was deaf from birth, and who was restored to hearing by accidentally rupturing the membrana tympani, and breaking the ossicles with an ear-pick—" disrupit tympanum, fregitque ossicula, et audivit." In these and other cases, in which the membrana tympani and ossicles have been destroyed, and the hearing has still persisted, the vibrations must have been conveyed to the parietes of the internal ear through the air in the cavity of the tympanum, and, notwithstanding the charge of "absolute confusion of ideas," adduced against such individuals as Scarpa," Magendie, Adelon, and others, who believe that the foramen rotundum receives the undulations of the air, we must confess, that the idea of the com- munication of vibrations through that medium, as well as through the membrane of the foramen ovale, and the osseous parietes of the labyrinth, appears to us most solid and satisfactory. The ossicles or small bones have given occasion to the wildest speculations. At the present day, they are considered to fulfil one of two functions;—either to conduct the vibrations from the mem- brana tympani, or to stretch the membranes to which the extremi- ties of the chain are attached. Both these offices are probably executed by them, the malleus receiving the vibrations from the membrana tympani, and conveying them t© the incus,—the incus to the os orbiculare,—the os orbiculare to the stapes, and the stapes to the membrane of the foramen ovale, by which they are transmitted to the liquor of Cotunnius. Savart conceives, that the chain of ossicles is to the ear what the bridge is to the violin. It has been already observed, that the ossicles are not essential to hearing, although they may be required to perfect it; and that they may be a Anat. Disquis. de Auditu et Olfactd., Ticin, 1789 ; and De Structura Fenestra Rotunda? Auris, &c. Mutin. 1772. PHYSIOLOGY OF THE MIDDLE EAR. 157 destroyed, without deafness being produced, provided the membrane of the foramen ovale remains entire, and the parts within the laby- rinth retain their integrity. If, in the removal of the stapes by ulceration or otherwise, the membrane of the foramen were to be ruptured, the liquor of Cotunnius would of course escape, and partial or total deafness be the result. In some experiments, instituted" by Flourens on pigeons, he found, that the removal of the malleus and incus did not have much effect upon the hearing; but when the stapes was taken away it was greatly diminished, and still more so when the membranes of the fenestra ovalis and fenestra rotunda were destroyed. The Eustachian tube is an important part of the auditory appa- ratus, and an invariable accompaniment of the membrana tympani, in animals. Without the tube, the membrane would be devoid of function. Pathology shows us, in the clearest manner, that its inte- grity is necessary to audition; and that deafness is the consequence of its closure. Dr. Bostock* thinks, " it is perhaps not very easy to ascertain in what mode it acts, but it may be concluded that the proper vibration of the membrana tympani is, in some way, con- nected with the state of the air in the tube." The name of the cavity to which the tube forms a communication with the external air might have suggested an easy and sufficient explanation of its use. The drum of the ear, like every other drum, requires an aperture in some part of its parietes, in order that its membranes may vibrate. The Eustachian tube serves this purpose, and its closure produces the same effect upon the membrana tympani at one end of the cylinder, and on the membrane of the foramen ovale at the other, as would be produced on the parchments of the ordi- nary drum by the closure of its lateral aperture. We can, in this way, account for the temporary deafness, which accompanies severe cases of inflammation of the throat: the swelling obstructs the Eustachian tube. During the constant efforts Of deglutition the air is renewed in the cavity of the tympanum; and, as the extremities of the Eusta- chian tube terminate in the pharynx, it always enters at a modified temperature. By closing the nose and mouth, and forcing air from the lungs, we can feel a sensation of fulness in the ear, produced by the pres- sure of the air against the internal surface of the membrana tym- pani; and they, who have the membrane perforated, can send tobacco smoke copiously out of the external ear. Besides this necessary function, the Eustachian tube has been supposed to possess another,—that of serving as a second meatus auditorius, by permitting sonorous vibrations to enter through the pharyngeal extremity, and, in this way, to attain the internal ear. A simple experiment, first described by Perolle,b exhibits the fallacy » Physiology, 3d edit., p. 721, Lond. 1836. b Hist, et Mem. de la Societe Royale de M^decine, torn. iii. VOL. I. 14 158 SENSE OF HEARING. of this notion. If we carry a watch far back into the mouth, taking care not to touch the teeth, little or no sound will be heard, but if we draw the watch forward, so as to touch the teeth, the ticking becomes distinctly audible. If the pharyngeal extremity acted as a second meatus, the sound ought to be heard better when the watch is placed nearer to it; but this is not the case. On the contrary, it is not until the sonorous body is put in contact with the teeth, that the sound is appreciated. This is effected by the vibrations of the watch being conveyed along the bony parietes until they reach the auditory nerve. Again; if the meatus auditorius externus be completely closed, we cannot hear the voice of one who speaks into the mouth; and can hear but imperfectly our own. The fact of our gaping, when desirous of hearing accurately, has partly led to the belief, that the Eustachian tube acts as a second meatus. It has been properly remarked, however, that this may be merely an act of expression; and, also, that the meatus auditorius is rendered more open, when we depress the lower jaw, than when it is raised, as can be readily perceived by inserting the little finger into the meatus, when the jaw is in either situation. In addition to these functions, it is probable, that the Eustachian tube acts as a diverticulum for the air in the cavity of the tympa- num, when it is agitated by too powerful sounds. The closure of the Eustachian tube is the cause of that form of deafness, which is relieved by the injection of air or other fluids into the tube8—a fact, the knowledge of which has been the foundation of much empiricism. Internal Ear.—In the various ways mentioned, the vibrations of a sonorous body reach the internal ear. The membranes of the foramen ovale and foramen rotundum resemble the membrana tym- pani in their physical characteristics; and when thrown into vibra- tions communicate the impression to the liquor of Cotunnius, which fills the cavities of the internal ear. By this medium, the vibrations are conducted to the auditory nerve, which conveys the impression to the brain. The views entertained regarding the sympathetic vibrations of the membrana tympani, have almost all been applied to the mem- brane of the foramen ovale: our knowledge, however, is restricted to the fact, that its tension can be varied by the chain of bones, without our being able to specify the circumstances under which this takes place. Adelon asserts, that the membrane may be torn, and yet the sense of hearing may not be destroyed. This seems scarcely possible, as the liquor of Cotunnius must necessarily escape, and so much morbid action be induced as to render audition appa- rently impracticable. a Deleau (le jeune), sur le Cath6t6risme de la trompe d'Eustache, et sur les Experi- ences de M. Itard, &c. Paris, 1828; also, Itard, and Kramer, in oper. citat.; Pilcher, a Treatise on the Structure, Economy and Diseases of the Ear, Lond. 1838; Dr. Jos. Williams, Treatise on the Ear, Lond. 1840; and the author's New Remedies, p. 515, 3d edit. Philad. 1841. PHYSIOLOGY OF THE INTERNAL EAR. 159 The membrane of the foramen rotundum, which forms the medium of communication between the cavity of the tympanum and the cochlea, has, of course, no chain of bones to modify its tension. Both the vibrations into which it is thrown, and those of the vestibular membrane, are imparted, as we have seen, to the liquor of Cotunnius, which is present in every ear, and appears essential to audition. Of the precise uses of the vestibule, semicircular canals, and cochlea, we have very limited notions. The beauty and complexity of their arrangement, has, however, given rise to various conjec- tures. Le Cata considered the lamina spiralis to consist of numerous minute cords, stretched along it, and capable of responding to every tone. Magendieb affirms, that no one at the present day admits the hypothesis regarding the use of this osseo-membranous septum; but he is in error. Sir C. Bell0 asserts, that the cochlea is the most important part of the organ of hearing; or rather, that it is " the refined and higher part of the apparatus;" and he considers the lamina spiralis as the only part adapted to the curious and ad- mirable powers of the human ear, for the enjoyment of melody and harmony. The subject of the musical ear will engage us presently. It may be sufficient to remark, in this place, that there is no ratio in animals, between the delicacy of the hearing, and the degree of complication of the cochlea. The cochlea of the Guinea pig is more convoluted than that of man, yet we can hardly conceive it to have a better appreciation of musical tones; whilst in birds, whose hearing is unquestionably delicate, the organ is, as we have remarked, extremely simple, and has no spiral arrangement. Again; the semicircular canals have been compared to organ pipes, adapted for producing numerous tones; and Dr. Youngd sup- posed them to be " very capable of assisting in the estimation of the acuteness or pitch of a sound, by receiving its impression at their opposite ends; and occasioning a recurrence of similar effects at different points of their length according to the different character of the sound; while the greater or less pressure of the stapes must serve to moderate the tension of the fluid within the vestibule, which serves to convey the impression." "The cochlea," he adds, "seems to be pretty evidently a micrometer of sound." All these are mere hypotheses;—ingenious, it is true, but still hypotheses; and, in candour, we must admit, that we have no positive knowledge of the precise functions of either vestibule, cochlea, or semicircular canals. Our acquaintance with them is limited to this; that they contain the final expansions of the auditory nerve; and that it is within them, that this nerve receives its impressions from the oscillations of sonorous bodies. It has been observed, that these vibrations may reach the nerve * Traite des Sens, Paris, 1767, and English translation, Lond. 1750. b Precis, &c. i. 121. c Op. citat. ii. 273. d Med. Literature, p. 98, Lond. 1813 160 SENSE OF HEARING. by the bony parietes, and that the ticking of a watch, held between the teeth, is, in this way, heard. A blow upon the head is distinctly audible; and Ingrassiasa relates the case of a person, who had become deaf in consequence of obstruction of the meatus auditorius externus, and yet could hear the sound of a guitar, by placing the handle between his teeth, or by making a communication between his teeth and the instrument by a metallic or other rod. The physi- cian has recourse to a plan of this kind for detecting whether a case of deafness be dependant upon obstructed Eustachian tube— upon some affection of the meatus auditorius externus—or upon insensibility of the auditory nerve, or of the part of the brain that effects the sensation. If the latter be the case, the ticking of a watch, applied to the teeth, will not be audible, and the case may necessarily be one of a hopeless character. If, on the other hand, the sound be perceived, the attention of the physician may be directed, with well founded expectation of success, to the physical parts of the organ, or to those concerned in the transmission of vibrations. Frequently, it will happen, in such cases, that the Eustachian tube is impervious, and properly directed efforts may succeed in removing the obstruc- tion ; or if this be impracticable, temporary, if not permanent, relief may be obtained by puncturing the membrana tympani, and allowing the aerial undulations, in this way, to reach the middle and internal ear. Lastly;—as regards the precise nerve of hearing. In this sense we have the distinction between the nerve of general, and that of special sensibility, more clearly observed. The experiments of Magendieb have shown, that the portio mollis of the seventh pair is the nerve of special sensibility;—that it may be cut, pricked, or torn, without exhibiting any general sensibility, and that it is inservient only to the sense of hearing. The same experiments demonstrate, that this nerve cannot act, unless the fifth pair or nerve of general sensibility be in a state of integrity. If the latter nerve be divided within the cranium, the hearing is always enfeebled, and frequently destroyed. The experiments of Flourens,0 to which allusion has been made, led him to infer, that the rupture of the cochlea was of less consequence than that of the semicircular canals. Laceration of the nerve, dis- tributed to the vestibule, enfeebled the hearing, and its total de- struction was followed by irreparable deafness. For these, and other reasons furnished by comparative anatomy, Lepelletier infers,d that, in the higher organisms, the vestibule and its nerve constitute the essential organ of impression, the other parts being superadded to perfect the apparatus. * De Ossibus, p. 7. See, also, Boerhaave, Preelectiones, iv. 415, and Haller, Element. Physiol, torn. v. p. 253, Lausann. 1763. h Precis, &c. 2de edit. i. ] 14. c Experiences sur la Systeme Nerveux, p. 42, Paris, 1825. d Traite de Physiologie Medicale et Philosophique, iii. 143, Paris, 1832. See, on the Comparative Physiology of Hearing, Roget's Animal and Vegetable Physiol, edit. cit. ii. 308. IMMEDIATE FUNCTION OF HEARING. 161 An interesting case of malformation has been related by Pro- fessor Mussey,* of Cincinnati, which shows, that other nerves, besides the portio mollis of the seventh pair, may, under unusual circum- stances, be inservient to audition. In this case there was no appear- ance whatever of meatus auditorius externus in either ear, and yet the man, twenty-seven years of age, although his sense of hearing was too obtuse for low conversation, could hear sufficiently well to prose- cute his business—that of a bookseller—without material inconve- nience. By covering the head with layers of cloth, it was found that the hearing was manifestly obscured. On speaking to him with one' end of a stick in the listener's mouth, whilst the other end was applied in succession to different parts of the head and face, it was found, that the part over the mastoid process conducted sound most readily; and that the parts corresponding with the upper two- thirds of the occipital, the mastoid plate of the temporal, and the posterior half of the parietal bone, transmitted sounds more readily than the anterior half of the scalp, the forehead, temples, or any other part of the face. Professor Mussey infers, from the results of his observations on this case, that the nerves, derived from the spinal cord below the foramen magnum of the occipital bone, and re- flected in profusion over the scalp, were concerned in this unusual function, and that the branches of the fifth pair were probably the seat of the peculiar faculty on the face.b The immediate function of the sense of hearing is to appreciate sound; and we may apply to it what has been said of the other senses, that, in this respect, it cannot be supplied by any other— that it is instinctive, requires no educatiun, and is exerted as soon as the parts have attained the necessary degree of developement. Amongst the advantages afforded by the possession of this sense, which has been properly termed intellectual, are two of the highest gratifications we enjoy—the appreciation of music, and the plea- sures of conversation. It is to it that we are indirectly indebted for the use of verbal language—the happiest of all inventions—as it has been properly termed, and to which we shall have to advert in the course of our inquiry into the animal functions. Metaphysicians and physiologists have differed considerably in their views regarding the organs more immediately concerned in the appreciations in question. Many, for example, have referred the faculty of music to the ear; and hence, in common language, we speak of an individual, who has a " musical ear," or the con- trary. Others, more philosophically we think, have considered, that the faculty is seated in the encephalon; that the ear is merely the instrument for conveying the sonorous undulations, which, in due order, constitute melody, but that the appreciation is ultimately effected in the brain, " that it," (the power of distinguishing the * American Journal of the Medical Sciences, Feb. 1838, p. 378. b See a similar case by Mr. Swan, in Medico-Chirurgical Transactions, vol. xi. 14* 162 SENSE OF HEARING. musical relations of sounds,) says Dr. Brown,a " depends chiefly or perhaps entirely, on the structure or state of the mere corporeal organ of hearing, which is of a kind, it must be remembered, peculiarly complicated, and therefore susceptible of great original diversity in the parts, and relations of the parts that form it, is very probable; though the difference of the separate parts themselves, or of their relations to each other, may, to the mere eye, be so minute, as never to be discovered by dissection." Many physiolo- gists of eminence have regarded the complex internal ear as the seat of the faculty; some looking to the cochlea; others to the semicircular canals; but few referring it to the brain. Sir C. Bell, indeed, asserts, that " we are not perhaps warranted in concluding, that any one part of the organ of hearing bestows the pleasures of melody and harmony, since the musical ear, though so termed, is rather a faculty depending on the mind." Yet afterwards he adds— " we think that we find in the lamina spiralis (of the cochlea) the only part adapted to the curious and admirable powers of the human ear, for the enjoyment of melody and harmony. It is in vain to say, that these capacities are in the mind and not in the outward organ. It is true, the capacity for enjoyment or genius for music is in the mind. All we contend for is, that those curious varieties of sound, which constitute the source of this enjoyment, are communicated through the ear, and that the ear has mechanical provisions for every change of sensation."b A cherished opinion of Sir Everard Homec on this subject has been referred to. Conceiving the membrane of the tympanum to be muscular, he considers the membrani tympani, with its tensor and radiated muscles, to resemble a monochord, " of which the membrani tympani is the string; the tensor muscles the screw, giving the necessary tension to make the string perform its proper scale of vibrations; and the radiated muscle acting upon the mem- brane, like the movable bridge of the monochord, adjusting it to the vibrations required to be produced;" and he adds, " the diffe- rence between a musical ear and one which is too imperfect to dis- tinguish the different notes in music, will appear to arise entirely from the greater or less nicety with which the muscle of the malleus renders the membrane capable of being truly adjusted. If the ten- sion be perfect, all the variations produced by the action of the radiated muscle will be equally correct, and the ear truly musical." In this view,—as unsatisfactory in its basis as it is in some of the details,—Sir Everard completely excludes, from all participation in the function, the internal ear, to which the attention of physiologists, who consider the faculty to be seated in the ear, has been almost exclusively directed. A single case, detailed by Sir Astley Cooper,d prostrates the a Lectures on the Philosophy of the Human Mind, Edinb. 1820 ; and Amer. Edit., vol. i. p. 207, Boston, 1826. b Anat. and Physiol. 5th Amer. Edit, by Godman, ii. 273, New York, 1829. c Lect. on Comp. Anat. iii. 268. d Philosoph. Transact, for 1800, p. 151, and for 1801, p. 435. MUSICAL EAR. 163 whole of the ingenious fabric, erected by Sir Everard. Allusion has already been made to the old established fact, that the mem- brane of the tympanum may be destroyed without loss of hearing necessarily following. Sir Astley was consulted by a gentleman, who had been attacked, at the age of ten years, with an inflamma- tion and suppuration in his left ear, which continued discharging matter for several weeks. In the space of about twelve months after the first attack, symptoms of a similar kind took place in the right ear, from which matter issued for a considerable time. The discharge, in each instance was thin, and extremely offensive; and in it, bones or pieces of bones were observable. In consequence of these attacks he became deaf, and remained so for three months. The hearing then began to return; and in about ten months from the last attack, he was restored to the state he was in when the case was published. Having filled his mouth with air, he closed his nostrils and contracted the cheeks; the air, thus compressed, was heard to rush through the meatus auditorius with a whistling noise, and the hair, hanging from the temples, became agitated by the current of air, that issued from the ear. When a candle was applied, the flame was agitated in a similar manner. Sir Astley passed a probe into each ear, and thought the membrane of the left side was totally destroyed, as the probe struck against the petrous portion of the temporal bone. The space, usually occupied by the membrana tympani, was found to be an aperture without one trace of mem- brane remaining. On the right side, also, a probe could be passed into the cavity of the tympanum; but, on this side, some remains of the circumference of the membrane could be discovered, with a circular opening in the centre, about a quarter of an inch in diame- ter. Yet this gentleman was not only capable of hearing every thing that was said in company, but was nicely susceptible to musical tones; " he played well on the flute, and had frequently borne a part in a concert; and he sung with much taste and per- fectly in tune." But, independently of these partial objections, the views, that assign musical ear and acquired language to the auditory apparatus, appear liable to others that are insuperable. The man who is totally devoid of musical ear, hears the sound distinctly. His sense of hear- ing may be as acute as that of the best musician. It is his apprecia- tion that is defective. He hears the sound but is incapable of com- municating it to others. The organ of appreciation is—in this, as in every other sense—the brain. The physical part of the organ may modify the impression, which has to be made upon the nerve of sense; the latter is compelled to transmit the impression as it receives it; and it is not until the brain has acted, that perception takes place, or that any idea of the physical cause of the impres- sion is excited in the mind. If, from faulty organization, such idea is not formed in the case of musical tones, the individual is said not to possess a musical ear, but the fault lies in his cerebral conforma- tion. We do not observe the slightest relation between musical 164 SENSE OF HEARING. talent and delicacy of hearing. The best musicians have not neces- sarily the most delicate sense; and, for the reasons already assigned, it will be manifest, why the idiot, whose hearing may be acute, is incapable of singing, as well as of speaking. Again, we do not see the least ratio in animals between the power and character of their music, and the condition of their auditory sense. We are com- pelled then to admit, that the faculties of music and speech are dependent upon the organization of the brain; that they require the ear as a secondary instrument; but that their degree of perfection is by no means in proportion to the delicacy of the sense of hearing. In these opinions, Gall,* Broussais,b Adelon,c and other distinguished physiologists concur. " Speech," says Broussais, " is heard and repeated by all men, who are not deprived of the auditory sense, because they are all endowed with cerebral organization fit to pro- cure for them distinct ideas on the subject. Music, when viewed as a mere noise, is also heard by every one; but it furnishes ideas, sufficiently clear to be reproduced, to those individuals only, whose frames are organized in a manner adapted to this kind of sensation." Yet, although we must regard the musical faculty to be intel- lectual, and consequently elevated in the scale, it is hardly necessary to say, that the want of it is no evidence of that mental and moral degradation, which has been depicted by poets and others.d In the classification of the objects of human knowledge, music has been ranked with poetry; but we meet with striking evidences of their wide separation. Whilst the professed musician is frequently devoid of all poetical talent, many excellent poets have no musical ear. Neither does the power of discriminating musical tones indi- cate that the possessor is favoured with the finer sensibilities of the mind; nor the want of it prove their deficiency. It has been a com- mon remark, that, amongst professed musicians, the intellectual a Sur les Fonctions du Cerveau, v. 96, Paris, 1825. b Traite de Physiologie appliquee a la Pathologie, Paris, 1822; translation by Drs. Bell and La Roche, p. 84, 3d Amer. Edit. Philad; 1832. c Op. citat. i. 383. See, also, Elliotson, Human Physiology, p. 548, Lond. 1840. d " The man that hath no music in himself, Nor is not mov'd with concord of sweet sounds, ' Is fit for treasons, stratagems and spoils; The motions of his spirit are dull as night, And his affections dark as Erebus: Let no such man be trusted." Shakspeare, "Merchant of Venice" v. i. " Is there a heart that music cannot melt ? Alas! how is that rugged heart forlorn; Is there, who ne'er those mystic transports felt Of solitude and melancholy born ! He needs not woo the muse; he is her scorn. The sophist's rope of cobweb he shall twine; Mope o'er the schoolman's peevish page; or mourn, And delve for life in mammon's dirty mine; Sneak with the scoundrel fox, or grunt with glutton swine." Beattie, " Minstrel." JUDGMENT OF DISTANCE, ETC. BY SOUND. 165 manifestations have been singularly and generally feeble; a result partly occasioned by their attention having been almost entirely engrossed from childhood by their favourite pursuit, but not perhaps to be wholly explained by this circumstance; and, whilst we find them often unmarked by any of the kindlier sympathies, we see those, that are " not moved with concord of sweet sounds," alike distinguished as philosophers and philanthropists. The defect, in these cases, differs probably in an essential manner, from one to which attention has been drawn by the late Dr. Wol- laston.a In that communication he describes many curious facts, regarding what he terms a peculiarity in certain ears, which seem to have no defect in the general capacity of receiving sound, or in the perception of musical tones, but are insensible to very acute sounds. This insensibility commences when the vibrations have attained a certain degree of rapidity, beyond which all sounds are inaudible to ears thus constituted. Thus, according to Wollaston, certain persons cannot hear the chirp of the grasshopper; others the cry of the bat; and he refers to one case in which the note of the sparrow was not audible. Dr. Wollaston himself was incapable of hearing any sound higher than six octaves above the middle E of the piano forte. The defect would, at first sight, appear to be referable to the physical part of the ear, rather than to the auditory nerve, or to the part of the brain concerned in the appreciation of sounds; the vibrations, that are performed with great rapidity, not being re- sponded to by the parts of the organ destined for this purpose; and, consequently, never reaching the auditory nerve. Researches, however, by Savart,b—one of the most dexterous and ingenious experimenters of the day,—seem to show, that the defective appre- ciation of acute sounds, in such cases, is not owing to their acute- ness, but to their feebleness; that if the sound can be made suffi- ciently intense, the ear is capable of hearing a note of upwards of forty thousand simple oscillations in a second; and that the cases referred to by Wollaston are, consequently, owing to defective hearing, rather than to insensibility to very acute sounds. Another acquired perception of the ear is that of forming a judgment of the distance of bodies. This we do by attending to the loudness of the sound; for we instinctively lay it down as a principle, that a loud sound proceeds from a body that is near us, and a feeble sound from one more remote. This is the cause of numerous acoustic errors, in spite of reason and experience. In the theatres, the deception is often well managed, when the object is to give the idea of bodies approaching. The sound—that of martial music, for example—is rendered faint and subdued; and, under such circumstances, appears to proceed from the remote distance; and, by adding gradually and skilfully to its intensity, a Philosophical Transactions for 1820, p. 306. b Magendie's Journal de Physiologie, v. 367. * 166 SENSE OF HEARING. we are irresistibly led to the belief, that the army is approaching; and the illusion is completed by the appearance of the military band on the stage, allowing its soul-inspiring strains to vibrate freely in the air. In like manner we are deceived by the ventriloquist. He is aware of the law that guides us in our estimation of distance, and, by skilfully modifying the intensity of his voice, according as he wishes to make the sound appear to proceed from a near or a distant object, he irresistibly leads us into an acoustic error. It requires education or experience to enable us to appreciate dis- tances accurately by this sense, as well as to judge of their position. In the case, detailed by Magendie,1 of a boy, who, after having been entirely deaf until the age of nine, was restored to hearing by M. Deleau, by means of injections thrown into the cavity of the tympanum through the pharyngeal extremity of the Eustachian tube, one of the most remarkable points was, his difficulty in acquiring a knowledge of the position of sonorous bodies. In forming our judgment on this subject we require the use of both ears. In all other cases an impression made upon one only would perhaps be sufficient. The common opinion is, that to judge of the direction of a sound we compare the intensity of the impres- sion on each ear, and form our deductions accordingly; and that if we close one ear we are led into errors, which are speedily dissi- pated by employing both. Still we are often deceived even under these last circumstances, and are compelled to call in the aid of sight. The blind afford us striking examples of accuracy, in this respect, in their acquired perceptions by the ear. In the B e 1 i s a r of Zeune, the case of a blind man is cited from Diderot; who, guided by the direction of the voice, struck his brother in a quarrel on the forehead, with a missile, which brought him to the ground.b Mr. Wheatstone supposes, that the perception we have of the direc- tion of sounds arises solely from the portion which is transmitted through the solid parts of the head, and which, affecting the three semicircular canals, situate in planes at right angles with each other, with different degrees of intensity, according to the direction in which the sound is transmitted, suggests to the mind the corre- sponding direction. If the sound is transmitted in the plane of either of the semicircular canals, the nervous matter in that canal will be more strongly acted on than that in either of the other two; and if it be transmitted in any plane intermediate between any two of the rectangular planes, the relative intensities in these two canals cor- responding therewith will vary with the direction of the intermediate plane.0 If the sonorous vibrations before reaching the ear are deflected from their course we are liable to deception, mistaking the echo for the direct or radiant sound. a Magendie's Journal de Physiologie, v. 223. b Rudolphi, Grundriss, u. s. w. Berlin, 1821, &c. c Journal of Science, New Series, ii. 67, Lond. 1827, and Elliotson's Human Phy. siology, p. 554, Lond. 1840. JUDGMENT OF MAGNITUDE, ETC. 157 The ideas of magnitude acquired by the ear are few, and to a trifling extent only. They occasionally enable the blind to judge of the size of apartments, and this they can sometimes do with much accuracy/ It is well known, that if a sound be confined within a small space, it appears much louder than when the sonorous undu- lations can extend farther; hence the greater noise, caused directly by a pistol fired in a room than in the open air. The sound indi- rectly produced will necessarily be modified by the different reflec- tions or echoes, that may be excited. By attending to these cir- cumstances—to the loudness of the voice and to the intensity of the reverberations occasioned by the wTalls, and by calling into their aid the experience they have had under similar circumstances—in other words, by effecting a strictly intellectual process—the blind attain the knowledge in question. The velocity of a body is indicated by the rapid succession of the vibrations that impress the ear, as well as by the change in their intensity if the body be moving along a surface or through the air. A carriage, approaching us with great velocity, is detected by the ear, from the rapidity with which the wheels strike against inter- vening obstacles ; and by the gradual augmentation in the intensity of the sound thus produced. When opposite to us the intensity is greatest; and a declension gradually takes place until the sound is ultimately lost in the distance. Lastly;—by audition we can form some judgment of the nature of bodies from the difference in the sounds emitted. It has been already remarked, that the timbre or quality of sound can be accurately appreciated. By this quality we can distinguish be- tween the sound of wood or of metal; of hollow or solid bodies, &c.; but in all these cases we are compelled to call into aid our experience—without which we should be completely at a loss—and to execute a very rapid, but often a very complicated intellectual operation. To conclude:—audition may be exercised passively as well as actively; hence the difference between simply hearing, and listening. We cannot appreciate, in man, the precise effects produced on the different portions of the ear by volition;—whether, for example, the advantage be limited to the better direction given to the ear, as regards the sonorous body, and to the avoiding of all distraction, by confining the attention entirely to the impressions made on this sense; or whether, by it, the pavilion may not be made somewhat more tense by the contraction of its intrinsic and extrinsic muscles; —the membrana tympani, and the membranes of the foramen ovale be modified by the contraction of the muscles of the ossicles; or, in fine, the auditory nerve be rendered better adapted for the recep- tion of the impression, and the brain for its appreciation. All these points are insusceptible of direct observation and experiment, and 1 Darwin's Zoonomia, vol. ii., and Manchester Memoirs, 2d edit. v. 622, Lond. 1789. 168 SENSE OF SIGHT. are, therefore, enveloped in uncertainty. In some animals—as the horse—the outer ear becomes an acoustic instrument under the guidance of volition; and is capable of being turned in every direc- tion in which a sonorous body may be placed. Like the other senses, that of hearing is largely improved by edu- cation or cultivation. The savage, who is accustomed, in the still- ness of the forest, to listen to the approach of his enemies or of his prey, has the sense so delicate as to hear sounds, that are inaudible to one brought up in the din of the busy world. The blind,* for reasons more than once assigned, afford examples of extreme delicacy of this as well as of their other remaining senses. They are necessarily compelled to cultivate it more ; and, lastly, the musician, by education, attains the perception of the nicest shades of musical tones. The aptitude is laid in cerebral organization, and is developed by the education of the instrument— the ear—as well as of the encephalic or intellectual organ, without which, as we have seen, no such appreciation could be accomplished. OF THE SENSE OF SIGHT OR VISION. The immediate function of the sense of sight is to give us the notion of light and colours. Like the other senses, it is a modifica- tion of that of touch, whether we regard the special irritant—light— as an emanation from luminous bodies, or as the vibration of a subtile, ethereal fluid, pervading all space. Under the latter theory it would most strongly resemble the sense last considered. The pleasures and advantages, derived by the mind through this inlet, are of so signal a kind as to render the organ of vision a sub- ject of universal interest. Every one, who lays the slightest claims to a general education, has made it more or less the subject of study, and is frequently better acquainted with its structure and properties than the medical practitioner. Complicated as its organization may seem, it is, in action, characterized by extreme simplicity; yet, " in its simplicity," as Arnotta has remarked, " so perfect, so unspeakably perfect, that the searchers after tangible evidences of an all-wise and good Creator, have declared their willingness to be limited to it alone, in the midst of millions, as their one triumphant proof." Into this structure we shall inquire, so far as is necessary for our purpose, after having described fhe general properties of light; and then detail the mode in which its various functions are effected, and the knowledge derived by the mind through its agency. The eye is the organ of vision. It varies materally in different animals: in some consisting of a simple capsule, with the final ex- pansion of the nerve of sight distributed on its interior, and com- municating externally by means of a transparent cornea, which admits the light. It is in this simple state, that M. de Blainvilleb » Elements of Physics, 2d Amer. Edit. vol. ii. P. i. p. 161, Philad. 1836. b De l'Organization des Animaux, Paris, 1825. LIGHT. 169 assimilates it to a bulb of hair, modified for the new function it has to perform. In man, and in the upper classes of animals, the organ is much more complicated in its structure; and in it we have a still clearer example of the distinction between the physical, and ner- vous or vital part of the apparatus, than in any of the other organs of sense—the former consisting of transparent tunics, and humours, which modify the light according to the laws of optics—the latter being a production or expansion of the nervous system, for the re- ception of the impression of light, and for conveying such impression to the proper part of the encephalon. There is, besides, attached to the organ, a number of accessory parts or tutamina, which are more or less concerned in the proper performance of the function. It will be necessary, therefore, to give a succinct view, not only of the eye, properly so called, but also of these accessory organs, which serve to lodge, move, protect, and lubricate it. The descrip- tion will not, however, be clearly understood, without premising some general observations on the properties of light, especially as regards its refraction, on which the phenomena of vision are greatly dependant. 1. OF LIGHT. The sun and the fixed stars are the great sources of light. It is given off also from substances in a state of combustion, and from phosphorescent bodies; and, by entering the eye directly, or after various reflections or refractions, impinges on the optic nerve, and gives the sensation of light. Two great opinions have been entertained regarding the nature of light; the one, propounded by Newton—that it consists of extremely minute particles, emanating from luminous bodies; the other—that of Descartes, Hook, Huygens, Euler,a and others,—that it is a subtile, eminently elastic fluid—an ether—pervading all space, the elastic molecules of which, when put in motion by the oscillations of bodies, impress the eye as sonorous vibrations affect the ear. It is not for us to discuss this question of higher physics. We may merely remark, that difficulties attend both hypotheses. According to that of Descartes, it is not easy to explain, why an opaque body should prevent the undulations from reaching the eye—or the change of direction, which the light experiences in passing from one medium into another; whilst, according to that of Newton, it is difficult to conceive, how a luminous body, as the sun, can shed its immense torrents of light incessantly, without undergoing rapid diminution; and how, with the extreme velocity of light, these particles should not be possessed of sensible momentum ; for it has been found, that a large sunbeam, collected by a burning-glass, and thrown upon the scale of a balance of extreme delicacy, is insufficient to disturb the * Letters of Euler on different subjects of Natural Philosophy; with Notes, &c. by Sir David Brewster, Amer. Edit, by Dr. Griscom, New York, 1833, vol. i. 87. VOL. I. 15 170 SENSE OF SIGHT. equilibrium. To the hypothesis of Newton it has also been objected, that the particles, being reflected by thousands of bodies, and in in- numerable directions, would necessarily jostle and interfere greatly with each other. This objection is not, however, as valid as it appears at first sight. It will be seen hereafter, that the impression of a luminous object remains upon the retina for the sixth part of a second. Admitting it, however, to impress the eye for the -jo-^h part, three hundred particles, per second, would be sufficient to excite a constant and uniform sensation of the presence of light; and since, as we shall find, it traverses sixty-seven thousand leagues in a second of time, if we divide this by three hundred, we shall find a space of six hundred and seventy miles between each par- ticle ; a distance equal to that—in a straight line—between New York and Savannah; and if we suppose six particles to be sufficient per second, each will be separated from the other by a space of thirty-three thousand five hundred miles ! Without deciding in favour of either of the great theories, that of Newton admits of more easy application to our subject, and will, therefore, be employed in the various explanations that may be required. The light, then, proceeding from a luminous body, impinges on the substances that are within its sphere; and these, by reflecting the whole or a part of it to the eye, become visible to us. In its course, direct or reflected, its velocity is almost inconceiv- able. From observations made on the eclipses of Jupiter's satel- lites, by Romer, Cassini, and other astronomers, it has been calcu- lated, that the light of the sun is eight minutes and thirteen seconds in its passage from that luminary to the earth. The distance be- tween the earth and the sun is thirty-three millions of leagues so that the velocity of light is sixty-seven thousand leagues, or two hun- dred thousand miles per second; in other words, in the lapse of a single second it could pass between Washington and Albany—sup- posing the distance to be three hundred miles—seven hundred times; and could make the tour of the globe in the time it takes us to wink. In consequence of this extreme velocity,—in all calculations, regard- ing the light from bodies on the surface of the globe, it is presumed to reach the eye instantaneously; for, granting that a luminous body at Albany could be seen at Washington, the light from it would reach the eye in the -^th part of a second. Inconceivable as this velocity is, it is far surpassed by that of the attractive power exerted between the heavenly bodies. " I have ascertained," says La Place, " that between the heavenly bodies all attractions are* transmitted with a velocity, which, if it be not infinite, surpasses several thou- sand times the velocity of light; and we know that the light of the moon reaches the earth in less than two seconds." An annotator on the works of this distinguished mathematician is more definite, affirming, " that the gravific fluid passes over one million of the earth's semi-diameters in a minute of time." Its velocity is eight millions of times greater than that of light. LIGHT. 171 A series of particles, succeeding each other in a straight line, is called a ray of light. The light wThich proceeds from a radiant point, forms diverging cones, which would be prolonged indefinitely did they not meet with obstacles. In its course, it loses its intensity according to a law, which seems applicable to all influences radiating from a centre. If a taper be placed in the middle of a box, each of whose sides is a foot square, all the light must impinge upon the sides of the box; if it be placed in a box, whose sides are two feet square, the light will shine upon them from double the distance, but it will be distributed over four times the surface. The intensity of the light, then, in this case, as in every other, diminishes according to the square of the distance from the luminous body. According to this rule, those planets, which are nearer the sun than we are, must receive the light and also the heat—for the same law applies to caloric—in much greater inten- sity; whilst the more distant luminaries can receive but little caloric, or light, in comparison with our earth; hence, perhaps, the neces- sity of the satellites by which they are accompanied, and by whose agency the light of the sun is reflected to the planet, and the defi- ciency is, in some measure, compensated. In proceeding from a luminous body, the rays, cones, or pencils of light must traverse intermediate bodies, in order to reach the eye. These bodies are called media. Air is the common medium; and when, in this way, the light has reached the exterior of the organ, the farther transmission is effected through different transparent humours, which consequently form so many media. In its course through the different media, the light may remain unmodified: it may proceed in the same straight line; or it may meet with an obstacle which arrests it altogether, or reflects it; or, again, it may traverse media of different natures and densities, and be made to deviate from its original course, or be refracted. When a ray of „. „„ light falls upon an t°' 172 SENSE OF SIGHT. Suppose I J, (Fig. 23,) to represent a plate of polished metal, or of glass, rendered opaque by a metal spread upon its posterior surface, as in the common looking-glass. The rays, proceeding from an observer at K, will be reflected back to him in the same line K C; that is, in a line perpendicular to C, the point of incidence. The observer will, therefore, see his own image; but for reasons to be mentioned hereafter, under the head of optical illusions, he will seem to be as far behind the mirror as he really is before it, or at E. Suppose, on the other hand, that the observer is at A, and that a luminous body is placed at B; in order that the rays, proceeding from it, shall impinge upon the eye at A, it is necessary that the latter be directed to that point of the mirror from which a line, drawn to the eye, and another to the object, will form equal angles with the perpendicular; in other words, the angle B C K, or angle of incidence, must be equal to the angle of reflection, A C K. In this case, again, the object will not appear to be at B, but in the prolongation of the line A C, at H, as far from the point of incidence, C, as B is. Except in the case of illusions, the study of the reflection of light or catoptrics does not concern vision materially. It is on the prin- ciples of dioptrics, that the chief modifications are effected on the progress of the light through the physical part of the organ; and, without some knowledge of these principles, the subject would be totally unintelligible. It is necessary, therefore, to dwell at some length on this topic. Whenever a ray of light passes through diaphanous or trans- parent bodies of different densities, it is bent or made to deviate from its course, and such deviation is called refraction; the ray is said to be refracted; and, owing to its being susceptible of such refraction, it is held to be refrangible. The point, at which a ray of light enters a medium, is called the point of immersion; and that, by which it issues from such medium, the point of emergence. Instead of considering the medium I J opaque, let us regard it as transpa- rent. C, in this case, will be the point of immersion for the incident rays that meet there ; and L and F will be the points of emergence for the rays K E and A C F G, respectively. If a ray of light, as K C, falls perpendicularly on the surface of any medium, it con- tinues its course through the medium without experiencing any modification, and emerges in the same straight line. Hence a body at L will appear in its true direction and distance to an observer at K looking directly downwards on a pool of water, I J. If, on the other hand, a ray of light, as A C, after having passed through air, falls obliquely upon the surface of the water at C; by entering a medium of different density, it is deflected from its course; and, instead of proceeding in the direction C H, it is refracted, at the point of immersion, in the direction C F—that is, towards the per- pendicular K E. If, again, the ray emerges at F into a medium of the same density as that through which it passed in the course A C, it will proceed in a line parallel to A C, or in the direction F G, or it LIGHT. 173 will wander from the perpendicular. The cause of this difference in the deflections, produced by different media, is not easy of expla- nation. The fact alone is known to us, that bodies refract light differently according to their densities and nature. If the light pro- ceeds from a rarer to a denser medium it is attracted or refracted towards the perpendicular; if on the contrary, it passes from a denser to a rarer medium, it is refracted from the perpendicular. The ray A C passed from a rarer medium,—the air,—into a denser, I J—water: it was refracted in the direction C F, towards the per- pendicular K E. On emerging at F, circumstances were reversed; it wandered from the perpendicular M N, and in the direction F G, parallel to A C, because the media, above and below I J, were identical. We can now understand, why water, saline solutions, glass, rock-crystal, &c. have higher refractive powers than air. They are more dense. The nature or character of bodies also influences greatly their refractive powers. Newton observed this, in his experiments upon the subject, and has furnished science with one of its proudest tro- phies, by his prognostic, in the then infant state of chemistry, that water and the diamond would be found to contain combustible ingre- dients. The diamond or brilliant is one of the most refractive of known substances, and this is one of the sources of its brilliancy. The opinion of Newton, it is hardly necessary to say, has been triumphantly confirmed. This refraction of the rays, that fall obliquely upon a medium, gives rise to numerous optical illusions. The ray proceeding from F, in the bent course F C A, will impinge on an eye at A; and the object F will appear to be at/. The pool will consequently seem shallower. In like manner, an object O in the air would not be per- ceptible to an eye in the water at F, in the direction O C F; whilst one at A would be distinctly visible,—the ray from it proceeding in the direction A C F, but appearing to come straight to the eye in the direction O C F. All transparent bodies, at the same time that they refract light, reflect a portion of it. , This is the cause of the reflections we no- tice on the glass of our windows, and of the image perceptible in the eye. The same substance has always the same refractive power, what- ever may be its shape:—in all cases, the sine of the angle of refrac- tion, holding the same ratio to the sine of the angle of incidence, whatever may be the incidence. The angle of incidence is the angle formed by the incident ray with a perpendicular raised from the point of immersion; the angle of refraction, that formed by the re- fracted portion of the ray with the same perpendicular. In Fig. 23, A C K is the angle of incidence of the ray A C; and L C F the angle of refraction. The sines of these angles respectively are the lines PQandLF. But although the media may refract the rays of light equally, the form of the refracting body will materially modify their arrange- 15* 174 SENSE OF SIGHT. ment. The perpendiculars to the surface may approach or recede from each other; and if this be the case the refracted rays will ap- proach or recede from each other likewise. Where the body has plane and parallel surfaces, as in the glass of our windows, the refraction, experienced by the ray on entering the glass, is corrected by that which occurs on its emergence; and although the light may not pass in one straight line, it proceeds in parallel lines, separated by a space dependent upon the thickness of the refracting body and the obliquity of the incident ray. If the medium be very thin, as in a pane of glass, the rays do not appear deflected from their original direction. In Fig. 23, the interval be- tween the direct ray and the ray A C F after its emergence is that between G and H. If the surfaces of the diaphanous body are plane, but inclined to- wards each other, Fig. 24. as in the common H prism, the refrac- tion, experienced by the ray on emerg- ing, instead of cor- recting that expe- rienced during its (2 -«-< "-^«^. passage through the body, is added to it; and the rays are deflected from their course to an extent equal to the sum of the two refractions. The ray A B, Fig. 24, after impinging upon the side D L of the prism, at B, instead of continuing its course in the direc- tion B J, is refracted towards the perpendicular C B F; the medium being denser than air; and on emerging into the rarer medium, in- stead of continuing its course in the direction G I, it is refracted in the line G H or from the perpendicular K J. Again, if the surfaces of the medium be convex, the rays are so situate, after refraction, as to converge behind the refracting body into a point called the Fig. 25. focus, which is nearer to \ the medium the less the divergence of the rays, or in other words, the more distant the lumi- B nous object. Fig. 25 ex- hibits a pencil of rays, proceeding from a ra- diant point at A, and meeting at a focus at B; the dotted lines being the perpendiculars drawn to the surface at the points of immersion and emergence. Lastly, if the surfaces of the medium be concave, as in Fig. 26, the luminous rays, proceeding from a radiant point as at A, are ren- LIGHT. 175 dered so divergent, that if we look for a focus here it must be ante- rior to the medium or at G. A knowledge of these facts has given occasion to the construction of numerous invaluable optical instruments, adapted to modify the luminous rays, so as to change the situation in which bodies are seen, to augment their dimensions, and to render them more lumi- nous, and visible, when remote and minute. It is, indeed, to this branch of science that we are indebted for some of the most im- portant information and advantages, that we possess in the domains of science and art. The simplest of these instruments are bodies, shaped like a lentil, and hence called lenses. They are composed of two segments of a sphere. The medium in Fig. 25 is a double convex lens; that in Fig. 26, a double concave. The manner in which they modify the course of the luminous rays passing through them has been sufficiently described. Fig. 26. The study of the refraction of light leads us to the knowledge of an extremely important fact; which, when it was first made known by Newton, excited universal astonishment;—viz. that a ray of light is itself composed of several coloured rays differing from each other in their refrangibility. If a beam of the sun's light be admitted through the hole of a window-shutter, E F, into a dark chamber, it will proceed in a direct line to P, and form a white spot upon the wall, or on a whitened screen placed there for the purpose. But if a glass prism, B A C, be placed, so that the light may fall upon its surface, C A, and emerge at the same angle from its second surface, B A, in the direction g G, the beam will expand; and if, after having emerged, it be received on the whitened screen, M N, it will be found to occupy a considerable space; and, instead of the white spot, there will be an oblong image of the sun, K L, consisting of seven colours;—red, orange, yellow, green, blue, indigo, and violet. Each of these colours admits of no farther decomposition, when again 176 SENSE OF SIGHT. passed through the prism; and the whole lengthened image of the sun is called the prismatic or solar spectrum. In this dispersion of the coloured rays, it will be observed, that the red ray is the least turned from its course; and is hence said to be the least refrangible; whilst the violet is the most so. Fig. 27. White Such is the spectrum, as depicted by Newton: since his time it has, by some, been considered to consist of three colours,—red, yellow, and blue; as certain of the colours can be composed from others,—the green, for example, from the blue and the yellow. Wollaston made it to consist of four ; red, green, blue, and violet: Sir J. Herschel of four; red, yellow, blue, and violet: and, more recently, Sir David Brewster has restricted it to three ; red, yellow, and blue. The causes which have led to these various divisions, it is not our province to explain. Each of the rays, of which the spectrum is composed, appears to have a different calorific and chemical action; but this is a subject, that nowise concerns the function we are considering. The decomposition of light into its constituent rays enables us to explain the cause of the colour of different substances. When white light impinges upon a body, the body either absorbs all the rays that compose it; reflects all; or absorbs some, and reflects others. If it reflects the whole of the light to the eye, it is of a white colour; if it absorbs all, or reflects none, it is black; if it reflects only the red ray, and absorbs all the rest, it is red, and so of the other colours. The cause, why one body reflects one ray, or set of rays, and absorbs others, is totally unknown. It is conceived to be owing to the nature and particular arrangement of its molecules. This is probable. But we are still as much in the dark as ever. It is ac- counting for the ignotum per ignolius. Two other points require a brief notice, being intimately con- cerned in vision;—the aberration of sphericity, and the aberration of refrangibility. LIGHT. 177 It has been remarked, that the rays of light—after passing through a convex lens, or medium whose surfaces are convex—converge, and are brought to a focus behind it. The whole of the rays do not, however, meet in this focus. The rays that are nearest the axis, R" F of the lens, Fig. 28, are refracted to a focus more remote from the lens, than those that fall on the lens at a distance from the axis. The rays R', pi„ 28 R", and R'", are brought to a focus at F, whilst the rays R L, and R"", L' converge at the point I, much nearer the lens. In like manner, rays which fall upon the lens intermediate between the rays R and R', will have their foci intermediate between / and F. This diversity of focal distances is called the spherical aberration, or the aberration of sphe- ricity: the distance I F is the longitudinal spherical aberration; and B A the lateral spherical aberration, of the lens. This aberration is the source of confusion in common lenses; and, as it is dependant upon the shape of the lens, it has been obviated, by forming these instruments of such degrees of curvature, that the rays, falling upon the centre or margins of the lens, may all be refracted to the same focus. This is effectually accomplished by lenses, whose sections are ellipses or hyperbolas. In a common lens, the inconvenience is obviated by employing lenses of a small number of degrees, or by interposing an opaque body—called, by the opticians, a diaphragm —anterior to the lens, so that the rays of light can only impinge upon the central part, and consequently be refracted to the same focus. This diaphragm is present in all telescopes, and occupies the situation of the curves D and D' in Fig. 28, so as only to admit the rays R', and R", and R'", to fall upon the lens. Such an appa- ratus, we shall find, exists in the human eye. Lastly,—it has been already observed, that the different rays, constituting the solar spectrum, are unequally refrangible,—the red being the least, the violet the most so; hence the cause of their dis- persion in the spectrum. It follows from this fact, that, whenever light experiences refraction, there must be more or less dispersion of its constituent rays; and the object, seen by the refracted ray, will appear coloured. This must, of course, occur more particu- larly near the margins of the lens, where the surfaces become less and less parallel until they meet. The inconvenience, resulting from this dispersion, is called the aberration of refrangibility, and it has been attempted to be obviated by glasses, which have been 178 SENSE OF SIGHT. ABO termed, in consequence, achromatic. These are made by combining transparent bodies of different dispersive powers, in such sort, that they may compensate each other, and thus the object be seen in its proper colours, notwithstanding the refraction. Dr. Blair found, for example, that by Fig. 29. enclosing muriate of antimony B E, between two con- vex lenses of crown glass, A D and C F, the parallel rays R, R and R were re- fracted to a single focus at P without the slightest trace of secondary colour. Newton was of opi- nion, that the light, in traversing a refracting medium, always experiences a dispersion of its rays, proportional to its refraction. He therefore believed, that it would be impossible to fabricate an achromatic glass. This is one of the rare cases in which that illustrious philosopher erred. Since his time—and chiefly by the labours of Dollond—such in- struments have been formed on the principles above mentioned; so as to greatly diminish the inconveniences sustained from the use of common lenses; although still not perfectly achromatic. The in- convenience is farther obviated by the diaphragm in telescopes, already referred to. As the dispersion is most experienced near the margin of the lens, it shuts off the rays, which would otherwise fall upon that portion, and diminishes the extent of aberration. The human eye is achromatic. It is obviously essential that it should be so; and this result is probably owing to a combination of causes. It is formed of media of different dispersive powers. Its lens is constituted of layers of different densities, and it is provided with a diaphragm of singularly valuable construction. Such are the prominent points of the beautiful science of optics, that chiefly concern the physiologist, as an introduction to vision. Others will have to be adverted to, when we consider the eye in action.* 2. ANATOMY OF THE ORGAN OF VISION. The human eye is almost spherical, except for the prominence at its anterior and transparent part—the cornea. It has been com- pared to a telescope, and with much propriety; as many of the * Pouillet, Elemens de Physique, iii. 202, Paris, 1832; Sir David Brewster's Treatise on Optics, Amer. Edit., by A. D. Bache, Philad. 1833; Turner's Elements of Che- mistry, by F. Bache, 6th edit, Philad. 1840; Young's Lectures on Natural Philosophy, Lond. 1807 ; Ficinus, art. Licht, in Pierer's Anat. Phys. Real Wc-rterb. iv. 776, Leipz. 1821; and J. Mailer's Elements of Physiology, by Baly, P. v. p. 1088, Lond, 1839. ORGAN OF VISION. 179 a. Aqueous humour, b. Cornea, c. Iris. d. Lens. e. Ciliary processes. /. Vitreous humour, g. Optic nerve, h.i. Muscles above and below. parts of that instrument have been added to execute particular offices, which are admirably performed by the eye—the most per- fect of all optical instruments. Every telescope Fig. 30. consists, in part, of a tube, which always comprises pieces, capable of readily entering into each other. Within this cylinder are several glasses or lenses, placed in succession from one extremity to the other. These are intended to re- fract the rays of light and to bring them to determinate foci. Within the telescope is a kind of partition of paper or metal, having a round hole in its centre, and usually placed near a convex glass, for the purpose of diminishing the surface of the lens accessible to the rays of light, and obviating the spherical aber- ration. The interior of the tube and of the diaphragm is coloured black, to absorb the oblique rays, which are not inservient to vision, and thus to prevent them from causing confusion. This arrangement is nearly a counterpart of that which exists in the eye. The tube of the instrument is represented by three mem- branes in superposition,—the sclerotic, choroid, and retina; the latter being the one, that receives the impression of light. Within this case are four refracting bodies, situate one behind the other; and all intended to bring the rays of light to determinate foci, viz.— the cornea, aqueous humour, crystalline lens, and vitreous humour. Lastly, in the interior of the eye, near the anterior surface of the crystalline lens, is a diaphragm—the iris, having an aperture in its centre—the pupil. These different parts will demand a more de- tailed notice. 1. Coats of the Eye, &c.—The sclerotic is the outermost coat. It is that which gives shape to the organ, and which constitutes the white of the eye. It is of a dense, resisting, fibrous nature, belong- ing to what Chaussier calls the albugineous tissue. Behind, it is penetrated by the optic nerve; and before, the cornea is dovetailed into it. It has, by some anatomists, been considered a prolongation of the dura mater, accompanying the optic nerve; whilst the cho- roid has been regarded as an extension of the pia mater, and the retina, of the pulp of the nerve. The sclerotic is the place of inser- 180 SENSE OF SIGHT. tion for the various muscles that move the eyeball, and is manifestly intended for the protection of the internal parts of the organ. Immediately within the sclerotica—and feebly united with it by vessels, nerves and cellular tissue3—is the choroid coat;—a soft, thin, vascular, and nervous membrane. It com- pletely lines the scle- rotic, and has conse- quently the same shape and extent. Behind, it is perforated by the optic nerve; before, it has the iris united with it; and within, it is lined by the retina, which does not how- ever adhere to it,— the black pigment se- parating them from each other. It is chiefly composed of the ciliary vessels and a. Iris. b. White of the eye. P. Plica semilunaris. C Carun- nerves, and COnSlStS 01 cula lachrvmalis. S S S. Supercilium. T. Under surface of upper tWO distinct lamina?, eyelid, t. Under surface of lower eyelid, p. Punctum lachrymale . . c in the tarsus of each eyelid. to the innermost Ot which Ruysch—the son—gave the name membrana Ruyschiana. In fishes these laminse are very perceptible, being separated from each other by a, substance, which Cuvier considers to be glan- dular. The choroid is impregnated and lined by a dark-coloured mucous pigment, called pigmentum nigrum. In some cases, as in the albino, this substance, which is exhaled from the cho- roid, is light-coloured, approximating to white. Leopold Gmelin,b conceives, that it approaches the nature of indigo; Dr. Youngc regards it as a mucous substance, united to a quantity of car- bonaceous matter, upon which its colour depends, and Berzelius,d from his chemical investigations, considers it to consist chiefly of carbon and iron; but Professor Jacob thinks it obviously an animal principle sui generis, its elements being oxygen, hydrogen, carbon, and nitrogen. Dr. Apjohn found 100 parts, in a dry state, leave, when incinerated, 4.46 of a calx consisting of chloride of *■ In the situation of this cellular tissue, Arnold describes a serous membrane, Spinnwebenhaut, Arachnoidea oculi, Lamina fusca scleroticse.—Arnold ilber das Auge, Tab. iii. Fig. 2, and Weber's Hildebrandt's Handbuch der Anatomie, iv. 68, Braun- schweig, 1832. b Dissert. Sistens Indagationem Chemicam Pigmenti Nigri Oculorum Taurorum. Gotting. 1812. c Medical Literature, p. 521, Lond. 1813. d Medico-Chirurg. Trans, iii. 255 ; see also, Prof. Schlemm, in Art. Augapfel, in Enyclopad. Worterbuch des Medicinisch. Wissenchaft. B. iv. s. 28, Berlin, 1830. ORGAN OF VISION. 181 calcium, carbonate of lime, phosphate of lime, and peroxide of iron. Mr. T. W. Jones has examined microscopically the layer of black pigment on the inner surface of the choroid. He states that it possesses organization, and constitutes a real membrane, consisting of very minute flat bodies of an hexagonal form, joined together at their edges." On the outer side of the bottom of the cavity of the eye, there is a small shining space, destitute of this pigment, through which the colours of the membrana Ruyschiana appear. This spot is termed the tapetum. It is met with only in quadrupeds. The retina is the last coat, if we except a highly delicate serous membrane—discovered by Dr. Jacob,b of Dublin, and called after him Tunica Jacobi,—which is interposed between the retina and the choroid coat.c Mr. George H. Fielding, of Hull,d has also affirmed, that immediately behind the retina, and in connexion with it, there is a peculiar membrane, separable into distinct layers from the choroid, and supplied with blood-vessels, which he proposes to name membrana versicolor. He presumes, that it receives the vibrations of light, and communicates them to the retina. The eyes, used for ex- periment, were those of the ox and the sheep. The retina lines the choroid ; and is a soft, thin, pulpy, and grayish membrane, formed chiefly, if not wholly, by the final expansion of the optic nerve. Ribes,e indeed, esteems it a distinct membrane, on which the optic nerve is distributed;—a structure more consistent with analogy. On its inner surface, it is in contact with the membrane of the vitreous humour, but they are not adherent. Anteriorly, it terminates near the anterior extremity of the choroid, forming a kind of ring, from which an extremely delicate lamina is given off. This is reflected upon the ciliary processes, dips into the intervals separating them, and, according to some anatomists, passes forward as far as the crystalline. Recent observers—B. C. R. Langenbeck, Treviranus, Gottsche, Volkmann, E.H.Weber, Michaelis, and others have exa- mined minutely into the anatomy of the retina, and have shown that it consists of several layers :—Langenbeck says three; Michaelis, four/ About a sixth of an inch on the outside of the optic nerve, and in the direction of the axis of the eye, or of a line drawn per- pendicularly through the centre of the cornea, is a yellow spot, about a line in extent, having a depression in its centre. These are the limbus luteus or macula lutea, and foramen centrale of Sommering.s a See Art. Eye, by Dr. Jacob, in Cyclop, of Anat. and Physiol. Part x. for June, 1837, p. 181. b Philosoph. Transact, for 1819 ; Medico-Chirurg. Transactions, xii. Lond. 1823, and Art. Eye, in Cyclop, of Anat. and Phys. p. 186. c Philosophical Transactions, for 1829, p. 300. d Second Report of the British Association, for the Advancement of Science; and Amer. Journal of the Med. Sciences, Nov. 1833, p. 220. e Memoir, de la Societe Medicale d'Emulation, vii. 86. f J. Milller's Report on the Progress of Anatomico-Physiological Science, for the year 1836, in Midler's Archiv. 1837, Heft 3; and Brit, and For. Med. Rev. Jan. 1838, p. 298; also, W.Clay Wallace, Treatise on the Eye, &c. 2d edit. New York, 1839; and Lond. Med. Gaz. Oct. 20, 1838. s Sommering, in Comment. Societ. Gotting." torn. xiii. 1795-98; A. ab Ammon, de VOL. I. 16 182 SENSE OF SIGHT. The yellow spot does not exist in the fetus ;a and the folds, described by Sommering as surrounding the yellow spot, would appear to be a post mortem appearance. In the examination of two convicts, three hours after execution, the foramen was not seen satisfactorily.b The retina receives many blood-vessels, which proceed from the central artery of the retina, or of Zinn. This vessel—it is important to observe—enters the eye through the centre of the optic nerve, the porus opticus—and, before passing directly through the vitreous humour, sends off lateral branches to the retina. 2. Diaphanous parts of the Eye.—The parts, which act as re- fracting bodies, are either transparent membranes, or fluids con- tained in capsules, which give them a fixed shape. These parts are the cornea, aqueous humour, crystalline, and vitreous humour. The cornea is the convex transparent part of the eye, advancing in front of the rest of the organ, as a watch-glass does before the case, and appearing like the segment of a smaller sphere superadded to a larger. It was, for a long time, considered to be a prolongation of the sclerotic ; but they are manifestly distinct membranes, being separable by maceration. The posterior surface is concave, and, between it and the iris, is the small space occupied by the aqueous humour, called the anterior chamber of the eye. The cornea is gene- rally considered to be composed of several thin laminae in super- position, which have been compared to horn, and hence the name of the membrane; but Mr. T. Wharton Jonesc denies this, and describes it as consisting merely of interweaving bundles of fibres. Like the corneous tissue in general, it possesses neither blood-vessels nor nerves. In animals, the density and convexity of the cornea vary with the media in which they exist, and with the condition of the other refractive parts of the eye. In old age, the cornea is harder, tougher, and less transparent than in youth, and it frequently becomes completely opaque in its circumference, presenting the appearance called arcus senilis, in German, greisenbogen. The aqueous humour is a slightly viscid fluid, which occupies the whole of the space between the posterior surface of the cornea and the anterior surface of the crystalline. This space is divided by the iris into two chambers—an anterior and a posterior—the latter being the small interval between the hinder surface of the iris, and the anterior surface of the crystalline. Sir David Brewsterd erroneously asserts that the posterior chamber contains the crystalline and vitre- ous humours; and Dr. Arnott,e that the anterior and posterior Genesi et Usu Maculae Luteae, &c. Vinar. 1830; Sir E. Home, in Lect. on Comp. Anat. iii. 205, Lond. 1823; J. Midler's Report, in op. cit. and Grube, in Midler's Arcluv. 1840, Heft i.; and Brit, and For. Med. Rev., July, 1840, p. 254. 1 Rudolphi, Grundriss der Physiologie, B. ii. Abtheil, 1, s. 176, Berlin, 1823. b W. E. Horner, Special and General Anatomy, 5th edit. p. 426, Philad. 1839 ; and J. Pancoast, in Wistar's Anatomy, 7th edit. p. 395, Philad. 1839. c W. Mackenzie, Practical Treatise on Diseases of the Eye, with an Anatomical Introduction by Thomas Wharton Jones, Lond. 1840. d A Treatise on Optics, edit. cit. p. 241. e Elements of Physics, &c. 2d Amer. Edit. vol. ii. P. i. p. 162, Philad. 1836. ORGAN OF VISION. 183 chambers of the eve are the compartments before and behind the crystalline. Anatomists are not agreed, whether the aqueous hu- mour has a proper membrane, which secretes it, or whether it is not an exhalation from the vessels of the iris and ciliary processes. Ribes, indeed, derives it from the vitreous humour. Howsoever secreted, it is very rapidly regenerated, when evacuated; as it must be in every operation for the cataract by extraction. It is not lodged in cells, and hence readily flows out when the cornea is punctured. The quantity of aqueous humour, in the adult, is about five or six grains. Its specific gravity is not rigidly established, but it differs slightly from that of water, being a"little greater. According to Berzelius,it is composed of water, 98.10; a little albumen; muriates, and lactates 1.15; soda, with.a substance soluble in water, 0.75.a Fig. 32. Section of the Eye magnified three diameters. The crystalline lens is a small body, of a crystalline appearance, and lenticular shape, whence its name. It measures in the adult, about 1.33 of an inch in its greatest circumference; and is about 2^ lines thick at its centre. It is situate between the aqueous and vitreous humours, and at about one-third of the antero-posterior diameter of the organ. A depression, at the anterior surface of the a Magendie, Precis de Physiologie, edit. cit. p. 57. For some Microscopical Observa- tions on the Anatomy of the Aqueous Capsule, by Dr. Werneck, see Von Amnion's Zeitschrift fur Ophtha'lmolog. B. iv. und v. 1837; and British and Foreign Medical Re- view, July, 1838, p. 205. 184 SENSE OF SIGHT. vitreous humour, receives it, and a reflection of the proper mem- brane of this humour passes over it. The crystalline is surrounded by its capsule, the interior of which is bathed'by a slightly viscid and transparent secretion, called liquor Morgagnii. The lens is more convex behind than before; the radius of its anterior surface being, according to Brewster,8 0.30 of an inch ; and that of its posterior surface 0.22 of an inch. It consists of a number of concentric ellipsoid lamina?, increasing in density from the circumference to the centre. Some fibres detach them- selves from the different laminae to those immediately beneath, con- stituting the sole bond of union that exists between them. Of old, it was believed, that the crystalline was of a muscular structure, and capable of modifying its own convexity, so as to adapt the eye to distances. This was the opinion of Descartes; and it has more recently been revived, with modifications, by Dr. Young.b Its muscularity is, however, by no means established, although its fibrous character is unquestionable. The specific gravity of the human crystalline is said by Chene- vixc to be 1.0790. He considered it to be composed chiefly of albumen: according to an analysis, however, of Berzeliusd it would appear to contain 35.9 parts, in the hundred, of a matter very analo- gous to the colouring matter of the blood.6 The vitreous humour, so called in consequence of its resemblance to melted glass, occupies the whole of the cavity of the eye behind the crystalline. It is convex behind, and concave before, and is invested by a delicate, thin transparent membrane, called tunica hyaloidea, which furnishes prolongations internally, that divide it into cells. It is owing, indeed, to this arrangement of the membrane, and not to the density of the humour, that it'has the tenacity of the white of egg. Its density does not differ materially from that of the aqueous humour:—their specific gravities being stated at 1.0009, and 1.0003 respectively. The cells, formed by the hyaloid mem- brane, are not all of the same shape and size. They communicate freely with each other, and are well represented in Fig. 32. At the anterior part, where the hyaloid membrane reaches the margin of the crystalline, it is separable into two laminae; one of which is reflected over the anterior, the other over the posterior surface of the lens. Between these laminae, and at their junction round the crystalline, a canal exists, into which air may be in- troduced : it then exhibits a plaited arrangement, and has been called the bullular canal of Petit ;f and, by the French writers, the canal godronne, or simply the canal of Petit. This canal is gene- rally conceived to be devoid of aperture; but Jacobson affirms, that a Op. citat. p. 242. See, also, Philos. Transact, for 1835, p. 366. b Philos. Transact, for 1793, p. 169; and Med. Literature, p. 521, London, 1813. c Philosoph. Trans, for 1803, p. 195. <■ Medico-Chirurgical Transact, iii. 253. e Werneck, op. cit. f Memoir, de l'Academie des Sciences, Paris, 1723 and 1728, and Haller. Element. Physiol, xvi. 2, 18. ORGAN OF VISION. 185 it has, in its sides, a number of minute foramina, which admit the entrance and exit of the aqueous humour. The composition of the vitreous humour, according to Berzelius,1 is as follows:—water, 98.40; albumen, 0.16; muriates and lac- tates, 1.42; soda, with an animal matter, soluble only in water, 0.02. Its absolute weight is fifteen or twenty times greater than that of the aqueous humour. 3. It was remarked, in the comparison drawn between the eye and the telescope, that a diaphragm exists in the former, called the iris; and sometimes the uvea. Generally, however, the latter term is appropriated to the posterior lamina of the iris. By some anato- mists, the iris is conceived to be a prolongation of the choroid: by others, to consist of a proper membrane, of a muscular character; and, by others again, to be essentially vascular and nervous; the vessels and nerves being distributed on an erectile tissue.1* There is, in the views of both anatomists and physiologists, much dis- crepancy regarding the structure and functions of this portion of the eye. Edwards,0 of Paris, affirms, that it consists of four laminae, two of which are extensions of the laminae composing the choroid ; a third belongs to the membrane of the aqueous humour, and is reflected over its anterior surface; and the fourth is the proper tissue of the iris. Magendie4 asserts, that the most recent anatomical investigations prove the membrane to be muscular; and to be com- posed of two sets of fibres;—the outermost radiating, whose office is to dilate the pupil; the innermost circular and concentric, for the purpose of contracting it. The arrangement of these fibres is re- presented in Figs. 33 and 34; the former of which is an internal view of the human iris, magnified three diameters; and the latter, an external view, exhi- biting the surface to consist essentially of a plexus of blood-vessels; both are taken from the microscopic investiga- tions of Mr. Bauer, and Sir Everard Home.6 These vessels, and nerves, are ramifications of the ciliary,—the nerves arising from the ophthalmic gan- glion and nasal branch of the fifth pair. Berzelius/ too, affirms, that the iris has all the chemical characters of muscle. Fig. 33. a Medico-Chirurgical Transactions, iii. 253. b Lepelletier, Physiologie Medicale et Philosophique, Paris, 1832, torn. iii. p. 158. c Bullet, de la Societe Philom. etc. 1814, p. 81. * Op. citat. i. 61. e Lectures on Comparative Anatomy, Lond. 1814-1828. See, on the Structure of the Iris. art. Eye, by Dr. Jacob, in Cyclop, of Anat. and Physiol, for June, 1837; We- ber's Hildebrandt's Handbuch der Anatomie, iv. 18, Braunschweig, 1832; Dr. Bolton, in Dunglison's Medical Intelligencer, Dec. 1, 1838; Mackenzie, Practical Treatise on the Diseases of the Eye, 3d edit, by T. Wharton Jones, Lond. 1840; and Rognetta, Cours d'Ophthalmologie, Paris, 1839. 1 View of the Progress of Animal Chemistry, p. 86, Lond. 1813. 16* 186 SENSE OF SIGHT. The iris is the coloured part of the eye, seen through the trans- parent cornea; and, according to the particular colours reflected from it, the eye is said to be blue, gray, Fig. 34. hazel, &c. In its centre, is an opening, called the pupil, through which alone the rays of light can reach the lens. This opening can be enlarged or con- tracted by the contraction or dilatation of the iris; and in this respect it is per- petually varying, according to circum- stances. In man, the pupil is circular, but it differs greatly in its dimensions and shape in different animals. On the posterior surface of the iris, or on the uvea, the pigmentum nigrum exists, as on the choroid. This layer has likewise some effect in giving colour to the eye; in blue eyes, for instance, the tissue of the iris is nearly white; the pigmentum nigrum, which appears through it, being the chief cause of its colour. At the point of junction between the iris and the choroid coat, they are united to the sclerotica by a band of cellular substance, called the ciliary ligament; and, from the anterior margin of the choroid, where it unites with the base of the iris, numerous vasculo- membranous appendages arise, which appear to be prolongations of the anterior margin of the choroid, turning inwards towards the margin of the crystalline lens, and terminating abruptly, without being attached to that body. They are the ciliary processes. These beautiful appendages are from sixty to eighty in number; and resemble the disk of a radiated flower. On their posterior sur- face, they are covered" by the same kind of pigment as that of the choroid and uvea; and they impart the stain to the membranes of the crystalline and vitreous humours. The greatest diversity of opinion, here again, exists regarding both structure and function. By some, these processes have been esteemed nervous ; by others, muscular, glandular, and vascular. Sir Everard Home asserts, on the autho- rity of microscopic observations by Mr. Bauer,* that between the processes are bundles of muscular fibres of considerable length, which originate all around from the capsule of the vitreous humour, pass forward over the edge of the lens, are attached firmly to its capsule, and there terminate. They are unconnected with the ciliary processes, or iris, and he conceives that their contraction will pull the lens towards the retina. In appearance they resemble the choroid, and are probably identical with it in structure. Such is an anatomical view of the physical part of the eye proper, so far as is necessary for the physiological inquirer. We * Op. citat., and Philosoph. Transact, for 1822, p. 78. ORGAN OF VISION. 187 have yet to consider the most important part of the organ;—that which is essentially nervous and vital in its action; and which, as we have seen, goes to constitute one of the membranes of the eye- ball—the retina. The optic nerves—the second pair of Willis—arise from the ante- rior part of the corpora quadrigemina,8 and not, as was at one time universally believed, from the thalami nervorum opticorum. Setting out from this point, they proceed forwards towards the thalami, to which they adhere; receiving filaments from the corpus geniculatum externum, an eminence a little anterior to, and on the outside of, the corpora; and from a layer of cineritious substance, situate between the point of junction of the nerve of each side and the eminentiae mammillares—called the tuber cinereum.b Proceeding for- ward towards the eye, the nerves approach, and form a junction at the sella turcica or on the upper surface of the sphenoid bone. Anterior to this point, they diverge, each passing through the optic foramen to the corresponding eye; piercing the sclerotic and choroid at a point about one-tenth of an inch from the axis of the eye on the side next the nose, where it has a button-like appearance, and expanding, to form the whole, or a part of the retina. When the optic nerve is regarded from the inside, after removing the retina and choroid, it appears in the form of a circular spot, perforated with small holes, from which the medullary matter may be expressed. This is the lamina cribrosa of Albinus. M. Lassaigne has examined the chemical composition of the optic nerve and retina; and concludes, from his experiments, that the retina is formed of the same elements as the cerebral and nervous substance; differing only in the proportion of the constituents. It is a question that has often been agitated, whether the optic nerves, at their junction on the sella turcica, simply lie alongside each other; or whether they decussate, so that the root of the nerve of the left eye is on the right side; and that of the right on the left. Anatomical investigations have hitherto left the question unsettled, and pathology appears to have furnished proofs on both sides. Thus, where the right eye has been lost for a considerable time, the optic nerve of the same side has been found in a state of atrophy through its whole extent. In other cases of the kind, the posterior portion of the left nerve has been found in this condition.0 Fishes have the nerve arising from one side of the brain, and passing to the eye of the other side; hence crossing, but not uniting. On the other hand Vesaliusd gives a plate of a case in which he found the optic nerves passing to the eyes of the same side from which they originate without touching at all; and yet without any disturbance of vision. It is not necessary, however, to adduce the numerous cases that have been published in favour of one view or a See a Pathological case illustrating this origin; by G. Kennion, M.D., in Lond. Med. Gaz. Sept. 1838. •» Solly, Lond. Med. Gazette, Sept. 24, 1838. c Rudolphi, Grundriss der Physiologie, B. ii. Abth. 1, s. 203. d De Corp. Human. Fabric, lib. iv. c. 4. 188 SENSE OF SIGHT. the other. It is impossible to sift those that are entitled to implicit confidence from those that are not. We may merely remark, that certain observations of Valsalva, Cheselden,a and Petitb appear to show, that where the brain is injured, it is the eye of the opposite side that is affected, and, in cases of hemiplegia or paralysis of one side of the body, we certainly have too many instances for testing the accuracy of this opinion. Sommering0—whose correctness as an observing anatomist has never been disputed—affirms, that he had an opportunity of exa- mining seven blind persons, in all of whom the atrophy of the nerve was on the side or root opposite to the eye affected.d Some, again, have advanced an opinion, that the decussation is partial, and con- cerns only the internal filaments; that the other filaments pass directly on to half the corresponding eye; so that one-half of each eye is sup- plied by straight fibres proceeding directly from the root of the same side; the other half by those resulting from the decussation of the internal fibres. Messrs. Wollaston,6 Berard, Pravaz,f Gall and Spurzheim, Cuvier, Serres, Vicq-d'Azyr, Caldani, Ackermann, the brothers Wenzel; G. R. Treviranus; J. Miiller,s and others, embrace this opinion for the purpose of explaining the anomaly of vision called hemiopia, in which only one-half the object is seen. Cuvier, Serres, and Caldani also assert, that they have noticed this arrange- ment in the nerves of the horse, when subjected to appropriate maceration. These views are, however, opposed by the direct experiments of Magendie.h He divided, in a rabbit, the right optic nerve, behind the point of decussation, or what has been called the chiasma of the nerves;—the sight of the left eye was destroyed. On cutting the left root, the sight of the right eye was equally destroyed; and on dividing the bond of union, in another rabbit, by a longitudinal incision, made between the nerves, vision was entirely abolished in both eyes;—a result, which, as he properly remarks, proves not only the existence ofaecussation, but, also, that it is total, and not partial as Wollaston had supposed. Another experiment, which he insti- tuted, led to a similar result. Fifteen days before examining a pigeon he destroyed one eye. The nerve of the same side, as far as the chiasma, was wasted; and, behind the chiasma, the root of the opposite side. Rolando and Flourens,1 too, found in their experi- * Anatomy of the Human Body, 13th edit. Lond. 1792. "> Memoir, de l'Acad. 1723 & 1728. c Blumenbach, Med. Bibl. ii. 2. s.368; and De Decussatione Nervorum Opticorum. Mogunt. 1786. d See a case elucidative of this point in Lallemand, Sur les Pertes Seminales, and in Dr. Wood's Translation in Dunglison's American Med. Library for 1839, p. 30. e Philosophical Transact. 1824, p. 222. f Archives Generates de Medecine, Paris, 1825, Mai, p. 59; also Nelaton, ibid. Fevrier, 1834. « Hildebrandt's Handbuch der Anatomie, von E. H. Weber, Band. iii. s. 438, Braunsch- weig, 1832: Blumenbach op. citat.; Sir D. Brewster's Natural Magic, Amer. Edit., p. 36, New York, 1833; and Pouillet, Elemens de Physique, iii. 338, Paris, 1832. h Precis, &c. edit. cit. i. 64. > Recherches Experimentales sur le Systeme Nerveux, Paris, 1824. ORGAN OF VISION. 189 ments, that when one cerebral hemisphere was removed, the sight of the opposite eye was lost. We may conclude, then, in the present state of our knowledge, that there is not simply a junction, or what the French call adossement, of the optic nerves; but that they de- cussate at the sella turcica.* The eye proper receives numerous vessels,—the ciliary arteries and veins—and several nervous ramifications, the greater part of which proceed from the ophthalmic ganglion of the fifth pair. The following are the dimensions, &c. of the organ, on the autho- rities of Petit, Young, Gordon, and Brewster. Eng. Inch. Length of the antero-posterior diameter of the eye - - - 0.91 Vertical chord of the cornea ------ 0.45 Versed sine of the cornea - - - - - - 0.11 Horizontal chord of the cornea ..... 0.47 Size of pupil seen through the cornea .... 0.27 to 0.13 Size of pupil diminished by magnifying power of cornea to - 0.25 to 0.12 Radius of the anterior surface of the crystalline .... 0.30 Radius of posterior surface ...... 0.22 Principal focal distance of lens ...... 1.73 Distance of the centre of the optic nerve from the foramen centrale of Sommering - - - - - - - 0.11 Distance of the iris from the cornea - - - ... 0.10 Distance of the iris from the anterior surface of the crystalline - 0.02 Field of vision above a horizontal line - - - 50° ? , qno Field of vision below a horizontal line - - - 70° \ Field of vision in a horizontal plane ... 150ob Diameter of the crystalline in a woman above fifty years of age - 0.378 Diameter of the cornea ....... 0.400 Thickness of the crystalline v - - - - - - . 0.172 Thickness of the cornea - - - - - - - 0.042c It is proper to remark, that all these measurements were neces- sarily taken on the dead organ, wrhen the parts are by no means in the same relative situation as when alive; and this is a cause, why many of the phenomena of vision can never be determined with mathematical accuracy. 3. ACCESSORY ORGANS. The visual organs, being of an extremely delicate texture, it was of obvious importance, that they should be guarded against deranging influences. They are accordingly provided with numerous parts, which afford them protection, and enable them to execute the func- tions for which they are destined. They are, in the first place, securely lodged in the bony cavities called the orbits, which are of a conical figure, with the apices directed inwards. In the trun- cated apex the foramen opticum is situate, by which the optic nerve a See also, on this subject, Adelon, Physiologie de I'Homme, i. 402, 2de edit. Paris, 1829 ; and Bostock's Physiology, edit. cit. p. 709. b According to Young, Philos. Transact. P. i. p. 46, Lond. 1801, the field of vision internally is 60°, externally 90°; according to Purkinje, (Rust's Magazine B. xx. Berlin, 1825,) internally 60°, externally 100°. c For more detailed dimensions of the organ and its various parts, see Weber's Hil- debrandt's Handbuch der Anatomie des Menschen, iv. 101, Braunschweig, 1832. 190 SENSE OF SIGHT. enters the orbit. Here are, also, the superior orbilar and spheno- maxillary fissures, through which many vessels and nerves proceed to the eye or its appendages. The base of the orbits is not directly opposite to the apices, but tends outwards; so that the axes of these cavities, if prolonged, would meet at the sella turcica. The eye, however, is not placed in the direction of the axis of the orbit, but straight forward; and as it is nearly spherical, it is obvious that it cannot completely fill the conical cavity. In Fig. 30, the muscles h and i indicate the shape of the upper and lower surfaces of these cavities;—the whole of the space, between the posterior part of the orbit and these muscles, which is not occupied by the optic nerve, being possessed by an adipous, cellular tissue, on which the eye is placed, as it were on a cushion. Under particular morbid circum- stances, this deposit becomes greatly augmented, so as to cause the eye to start from its socket; constituting the disease called exoph- thalmos. The parts, however, that are more immediately reckoned amongst the protectors of the organ—the tutamina oculi—are the eyebrows, eyelids, and the lachrymal apparatus. The eyebrows or supercilia, (Fig. 31, S S S.) are situate imme- diately on the superciliary ridge of the frontal bone. They consist of hair, varying in colour according to the individual, and turned towards the outer angle of the eye—of common integument—of sebaceous follicles, situate at the root of each hair—and of muscles to move them, namely, the frontal portion of the occipito-frontalis, the upper edge of the orbicularis palpebrarum, and the corrugator supercilii. The palpebrcB or eyelids are, in man, two in number, an upper and a lower, or a greater and a less—the palpebra major vel supe- rior, and the palpebra minor vel inferior—the former covering three- fourths of the eye; hence the transverse diameter of the eye is not represented by their line of union, the latter being much below it, and therefore improperly termed, by Haller, JEquator oculi. By the separation of the eyelids, we judge, but inaccurately, of the size of the eye—one, who is capable of separating them more largely from each other, appearing to us to have a larger eye,—and con- versely. The edge of the eyelids is thick, rounded, and furnished with hairs, resembling generally, in colour, those of the head. These are the eyelashes or cilia. On the upper eyelid they are curved up- wards; on the lower downwards, as in Fig. 30. The eyelids are formed of four membranous layers, in superposition, and of a fibro- cartilage, which extends along the whole of the edge and keeps them tense. The outermost of these layers is the common integu- ment, the skin of which is very delicate and semi-transparent, yielding readily to the motions of the eyelids, and having nume- rous transverse folds. The cellular tissue, beneath the skin, is very- loose, and, under particular circumstances, is infiltrated by a serous fluid, giving the eyelid, especially the lower, a dark appearance; but it never contains fat. Beneath the common integument is the ACCESSORY ORGANS OF VISION. 191 muscular stratum, formed by the orbicularis palpebrarum, in the lower eyelid; in the upper, by the same muscle, and the levatorpal- pebrce superioris, (Fig. 35, 15,) which arises from above the foramen opticum, and is inserted into the superior edge of the fibro-cartilage of the tarsus. Beneath the orbicularis palpebrarum, again, there is a fibrous layer, which occupies the whole of the eyelids, passing from the edge of the orbit to the tarsal margin, and seems intended to limit the motion of the eyelids, when they approximate each other. The last layer, and that which forms the posterior surface of the eyelids, is a fine, delicate, transparent, mucous membrane, called tunica conjunctiva or tunica adnata; so named because it joins the eye- lids to the globe of the eye. It lines, in fact, the eyelids, and is re- flected over the ball; but it has been a matter of contention, whether it passes over the transparent cornea. The generality of anatomists say it does; Ribes,a however, maintains the opinion, that it extends only as far as the circumference of the cornea, and that the cornea itself is covered by a proper membrane. Physiologically, this dis- pute is of no moment. At its outer surface, a humour is constantly exhaled, which keeps it moist, and facilitates the motions of the eye- lids over the eyeball. Its loose state also favours these motions. Both eyelids are kept tense by the aid of a fibro-cartilage, situate along the edge of each, and called tarsus. That of the upper eyelid is much more extensive than that of the lower; and both seem as if cut obliquely, at the expense of their inner surface; so that, in the opinion of most anatomists, when the eyelids are brought together, a triangular canal is formed between them and the ball of the eye, which has been conceived useful in conducting the tears towards the lachrymal puncta. Magendieb denies that any such canal exists; and there seems but little eviderice of it, when we examine how the tarsal cartilages come in contact. Such a canal, destined for the purposes mentioned, would, indeed, seem superfluous. Besides the eyelashes, certain compound follicles, called Meibomian, are situate in the substance of the tarsal cartilages. These are thirty or forty in number in the upper eyelid, and twenty-five or thirty in the lower. They are in particular furrows between the tarsal fibro-cartilages and the conjunctiva, (Fig 31, T, t) and secrete a sebaceous fluid, called by the French chassie, in the dry state; by the Germans augenbutter, ("eyebutter") and by us, gum of the eye, which serves the purposes of the follicular secretions in general. The arrangement of the eyelids differs in different animals. In several, both eyelids move; but, in others, only one; either the lower rising to join the upper, or the upper descending to meet the lower. In the sunfish—tetraodon mola—the eyelid is single and cir- cular, with a perforation in the centre, which can be contracted or enlarged, according to circumstances. In many animals, again, » M^moires de la Soci^te" Medicale d'Emulation, vol. vii., Paris, 1817. b Precis Elementaire, i. 52. 192 SENSE OF SIGHT. there is a third eyelid, called the nictitating membrane, which is of a more delicate texture and more largely supplied with blood-ves- sels; and in some animals is transparent. In birds it exists, and is well seen in the owl. It is at the inner angle of the eye, and is capable of being drawn over the ball like a curtain, by two particu- lar muscles, and of thus freeing the surface of the eye from extra- neous substances. In man, it is only a vestige, destined to no apparent use. It is represented in Fig. 31, and is called valvula or plica semilunaris.* The eye has its proper muscles, capable of moving it in various directions. Their arrangement is readily understood. They are six in number:—four recti or straight muscles, and two oblique. 1. The rectus superior or levator. 2. The rectus inferior or depressor. 3. The rectus internus or adductor; and 4, the rectus externus or abductor. They all arise from the base of the orbit, around the optic foramen; pass forward to vanish on the sclerotica; and, ac- cording to some anatomists, extend over, and form a layer to the cornea. Fig. 35. 1. Globe of the eye. 2. Optic nerve. 3. Aponeurosis of the rectus externus. 4. Posterior ex- tremity of do. 5. One of the origins of do. on the outside of the optic nerve. 6. Inner origin of do. from an aponeurosis. 7. Aponeurosis common to it and the rectus inferior and rectus internus. 8. Rectus superior. 9. Posterior extremity of do. 10. Rectus inferior. 111111. Obliquus superior. 12. Trochlea. 13. Obliquus inferior. 14. Rectus internus. 15. Levator palpebra superioris. 16. Upper eyelid. The oblique muscles are, 1. The greater oblique, obliquus supe- rior, patheticus or trochlearis, which arises from the inner side of the foramen opticum, passes forwards to the internal orbitar pro- cess of the frontal bone, where its tendon is reflected over a pulley a T. W. Jones, Art, Lachrymal Organs, Cyclop. Anat. and Physiol. Sept. 1840. PHYSIOLOGY OF VISION. 193 or trochlea, and crosses the orbit to be inserted into the upper, pos- terior, and outer part of the globe of the eye. 2. The lesser oblique or obliquus inferior, whose fibres arise from the anterior and inner part of the floor of the orbit, near the lachrymal groove, pass under the eyeball, and are inserted between the entrance of the optic nerve and insertion of the abductor oculi, and opposite the insertion of the obliquus superior. These muscles have their proper nerves. The third pair—motores oculorum—or common oculo-muscular, are distributed to all the mus- cles except the trochlearis and abductor. The fourth pair or pathetic or internal oculo-muscular, to the trochlearis singly; and the sixth pair or external oculo-muscular, to the abductor. Lastly, the office of tutamina oculi is not wholly engrossed by the parts, that have been mentioned. The apparatus for the secre- tion of the tears participates in it, by furnishing a fluid, which lubricates the surface of the eye, and keeps it in the necessary degree of humidity for the proper performance of its functions. It is a beautiful, and ingenious little apparatus, the structure of which can easily be made intelligible. It consists of the lachrymal gland, the excretory ducts of the gland, the caruncula lachrymalis, the lachrymal ducts, and the nasal duct; in other words, of two sets of parts—one, forming the fluid and pouring it on the anterior surface of the eye; the other comprising the organs for its excretion. The lachrymal gland is situate in a small fossa or depression at the upper, anterior, and outer part of the orbit. It is an oval body of the size of a small almond; of a grayish colour, and composed of small, whitish, granular bodies collected into lobes. From these, six or seven excretory ducts arise, which run nearly parallel to each other and open on the inner side of the upper eyelid, near the outer angle of the eye and near the tar- sal cartilage. Through these ducts, the tears, secreted by the lachry- mal gland, are spread over the tu- nica conjunctiva. They are com- posed, according to Fourcroy and Vauquelin,* of water, mucus, mu- riate of soda, soda, phosphate of lime, and phosphate of soda; and their taste is manifestly saltish, al- though the saline ingredients are described as not exceeding a hundredth part of the whole. They are not secreted by those animals that live in the water. Fig. 36. abed. The lachrymal canals. a a. The puncta lachrymalia. efg h i. The lachrymal duct. k I. The lachrymal gland. " Journal de Physique, xxxix. 256. vol. I. 17 194 SENSE OF SIGHT. At the inner angle of the eye is the caruncula lachrymalis. It is a collection of small mucous follicles, which secrete a thick, whitish humour, to fulfil a similar office with the secretion of the meibo- mian follicles. It completes the circle formed by the meibomian glands around the eyelids. (Fig. 31.) The rosy or pale colour of this body is supposed to indicate strength or debility. This it does, like other vascular parts of the system, and in a precisely similar manner. The puncta lachrymalia are two small orifices, situate near the inner angle of the eye (Figs. 31 and 36); the one in the upper, the other in the lower eyelid, at the part where the eyelids quit the globe to pass round the caruncula lachrymalis. They are continually open, and directed towards the eye. Each punctum is the com- mencement of a lachrymal duct, which passes towards the nose in the substance of the eyelids, between the orbicularis palpebrarum and the tunica conjunctiva. These open, as represented in Fig. 36, into the lachrymal sac, which is nothing more than the commence- ment of the nasal duct or ductus ad nasum. The bony canal is formed by the anterior half of the os unguis, and by the superior maxillary bone, and opens into the nose behind the os spongiosum inferius. Through these excretory ducts, all of which are lined by a prolongation of the mucous membrane, the tears pass into the nasal fossae. Dr. Horner,1 the able professor of anatomy in the University of Pennsylvania, has best described a small muscle, which is evidently a part of the lachrymal apparatus, and to which he gives the name tensor tarsi. It is on the orbital face of the lachrymal sac; arises from the superior posterior part of the os unguis; and, after having advanced a quarter of an inch, bifurcates; one fork being inserted along each lachrymal duct, and terminating at or near the punctum. It is probable, that the function of this muscle is to keep the punctum properly directed towards the eyeball, or, as Dr. Physick has suggested, to keep the lids in contact with the globe. The office, assigned to it by Dr. Horner, of enlarging, by its contraction, the cavity of the lachrymal sac, and thus producing a tendency to a vacuum, which vacuum can be more readily filled through the puncta than through the nose, owing to the valves or folds of the internal membrane of the sac—is ingenious, but apocryphal. The tensor tarsi muscle is now commonly associated with the name of Dr. Horner.b 4. PHYSIOLOGY OP VISION. The preceding anatomical sketch will enable the reader to com- prehend this important organ in action. In describing the office a Lessons in Practical Anatomy, 3d edit., p. 116, Philad. 1836; and Special and General Anatomy, 5th edit. ii. 407, Philad. 1839. See, also, RosenmoUer's Handbuch der Anatomie, dritte Auflage, Leipz. 1819. b T. W. Jones, art. Lachrymal Organs, Cyclop, of Anat and Physiol., July, 1840. PHYSIOLOGY OF VISION. 195 executed by its various^components, we shall follow the order there observed, premising some general considerations on the mechanism of vision; and afterwards depict the protecting and modifying in- fluences exerted by the various accessory parts:—the different phenomena of vision will next be explained, and lastly, the infor- mation conveyed to the mind of this sense. In tracing the progress of luminous rays through the purely physical part of the organ, we shall, in the first instance, suppose a single cone to proceed from a radiant point in the direction of the axis of the eye; or, in other words, of the antero-posterior diameter of the organ, B b. Fig. 37. It is obvious, that the rays, which fall upon the transparent cornea can alone be inservient to vision. Those, which impinge upon the sclerotica, are reflected; as well as a part of those that fall upon the cornea, giving occasion, in the latter case, to the image observed in the eye, and to the brilliancy of the organ. Nor does the whole of the cornea admit the rays, for it is commonly more or less covered, above and below, by the free edge of the eyelids. Again, the whole of the light, that enters the cornea, does not impinge upon the retina. A portion falls upon the iris, and is re- flected back to the eye, in such manner as to give us the notion of the colour of the organ. It is, consequently, the light, which passes through the pupil, that can alone attain the retina. Some interesting points of diagnosis are connected with the reflection which takes place from the humours of the eye. If a lighted candle be held before an eye, the pupil of which has been dilated by belladonna, and in which there is no obscurity in the humours or their capsules, three distinct images of the flame are perceptible—two upright, and one inverted—one of the former reflected from the cornea, and the other from the anterior part of the crystalline; the third inverted image being caused by the 196 SENSE OF SIGHT. reflection from the posterior concave surface of the crystalline. M. Sanson has proposed this catoptric method of examining the eye as a means of diagnosis between cataract and amaurosis; and Dr. Hays, who has employed it to some extent, regards it as a most valuable mode of investigating various conditions of the eye, which might not be readily understood without its agency.* If we suppose a luminous cone to proceed from a radiant point B, Fig. 36, directly in the prolongation of the antero-posterior diameter of the eye, the axis of this cone will also be the axis of the organ; so that a ray of light, impinging upon the humours in the direction of this axis, will, as in the case of the lenses previously referred to, pass through the humours without undergoing deflection, and will fall upon the retina at b. This, however, is not the case with the other rays composing the cone. They do not fall perpen- dicularly upon the cornea, and are, consequently, variously refracted in their passage through the cornea, aqueous humour, crystalline, and vitreous humour; but so that they join their axes in a focus at the point where it strikes the retina. The transparent parts of the eye, as has been seen, are of different densities, and are consequently possessed of different refractive powers. These powers it has been attempted to estimate; and the following is the result of the somewhat discordant evaluations of dif- ferent experimenters: the power of air being 1.000295. Cornea. Aqueous Humour. CRYSTALLINE LENS. Vitreous Humour. Capsule. Outer Layers. Centre. Mean. Hawksbee -Jurin, - -Rochon, Young, - -Chossat, Brewster, - 1.339 1.33595 1.3333 1.329 1.3333 1.338 1.3366 1.339 1.3767 1.338 1.393 1.3990 1.384 1.3839 1.33595 1.332 1.339 1.3394 A ray of light, impinging obliquely on the surface of the trans- parent cornea, passes from a rarer to a denser medium. It will, con- sequently, be refracted towards the perpendicular raised from the point of impact. It will, from this cause, as well as from the con- vexity of the cornea, be rendered more convergent; or, in other words, will approach the axis of the cone. (See Fig. 25.) In pro- ceeding through the aqueous humour, little variation will be pro- duced, as the densities of it and the cornea differ but little: the latter is slightly more refractive, according to the table, and therefore the tendency, that exists, will be to render the ray less convergent. a Proceedings of the American Philosophical Society, i. 97, 102, Philad. 1840; and American Journal of the Medical Sciences, Aug. 1838, p. 494, May, 1839, p. 255, and Aug. 1839, p. 513. PHYSIOLOGY OF VISION. 197 This convergence gives occasion to the entrance of a greater num- ber of rays through the pupil, and necessarily adds to the intensity of the light that impinges on the crystalline. Pursuing the ray through the two chambers of the eye, we find it next impinging on the surface of the crystalline, which possesses a much higher re- fractive power than the cornea or aqueous humour; in the ratio of 1.384 to 1.336. From this cause, and from the convexity of the anterior surface of the lens, the ray is rendered still more conver- gent or approaches still more the axis of the cone. It is probable, however, that even here some of the light is reflected back, and goes towards the formation of the image in the eye, and the bril- liancy of the organ ; other reflected rays perhaps impinge upon the pigmentum nigrum lining the posterior surface of the iris, and are absorbed by it. From the crystalline the ray emerges into a medium possessing less refractive power; and, therefore, is deflected from the perpendicular. The shape, however, of the posterior surface of the lens so modifies the perpendiculars, as to occasion such a degree of convergence, that the oblique ray meets the axis at a focus on the retina. (See Figs. 25 and 36.) In this manner two cones are formed; the one having its apex at the radiant point, and its base on the cornea—the objective cone,—the other having its apex on the retina, and termed the ocular cone. These remarks apply chiefly to the cone proceeding in the direc- tion of the axis of the different humours, from a single radiant point. It is easy to understand, that every portion of the object ABC, Fig. 36, must be a radiant point, and project so many cones in an ana- logous manner, which, by impinging upon the retina, form a picture of the object upon that expansion, at g b h. It is important, how- ever, to observe that the rays proceeding from the upper part of the object, fall, after refraction, upon the, lower part of the retina; and those from the lower part of the object upon the upper; so that the picture or representation of the object on the retina is inverted. How the idea of an erect object is excited in the mind will be the subject of after inquiry. When rays fall obliquely on a lens, as A g and C //, and pass through the centre of the lens, they suffer refraction at each of its surfaces, but as the two refractions are equal and in opposite direc- tions, the rays may be esteemed to pursue their course in a straight line. The point a, at which these various rays cross, is called the optic centre of the crystalline. Each of these straight rays, pro- ceeding from a radiant point, may be assumed as the axis of all the rays proceeding obliquely from the same point, and the common focus must fall on some part of this axis. In this way the object is represented, in miniature and inverted, on the retina. As, however, the oblique ray has to pass through the cornea and aqueous humour, before it impinges on the crystalline, it undergoes considerable de- flection, and consequently it is not accurate to represent it as pur- suing a straight course through the different humours, in its way to the retina. The main deflection—as in the case of the rays D t s, 17* 198 SENSE OF SIGHT. and E t r, Fig. 36—occurs at the entrance of the rays into the cornea. That an inverted representation of external objects is formed within the eye is in accordance with sound theory, and is supported not only by indirect, but by direct experiment. If a double convex lens be fitted into an opening made in the window-shutter of a darkened chamber, luminous cones will proceed from the different objects on the outside of the house, and will converge within; so that if they be received on a sheet of paper, a beautiful and distinct image of the object will be apparent. This is the well-known instrument, the camera obscura (Fig. 37*), of which the organ of sight may be re- garded as a modification. Making abstraction, indeed, of the cornea, and of the aqueous and vitreous humours, the representation of the eye in Fig. 36, with the object, ABC and its image on the retina, is the common camera obscura. The eye is, therefore, more complica- ted and more perfect than this simple instrument; the cornea with the aqueous and vitreous humours being added for the purpose of con- centrating the light on the retina; the latter, in addition, affording a large space for the expansion of the retina, and preventing the organ • from collapsing. In the operation for cataract by extraction, which consists in removing the lens through an opening, made in the lower part of the cornea, the aqueous humour escapes, but is subsequently regenerated. If, however, too much pressure be exerted on the ball, to force the crystalline through the pupil and the opening in the cornea, the vitreous humour is sometimes pressed out, when the eye collapses and is irretrievably lost. Fig. 37*. Experiments have also been instituted on this subject, the results of which are even more satisfactory than the facts just mentioned. These have been of different kinds. Some experimenters have formed artificial eyes of glass, to represent the cornea and crys- talline, with water in place of the aqueous and vitreous humours. Another mode has been to place the eye of an ox or sheep in a hole in the shutter of a dark chamber, having previously removed the PHYSIOLOGY OF VISION. 199 posterior part of the sclerotica, so as to permit the images of objects on the retina to be distinctly seen. Malpighi and Haller employed a more easy method. They selected the eyes of the rabbit, pigeon, puppy, &c. the choroid of which is nearly transparent; and, direct- ing the cornea towards luminous objects, they saw them distinctly depicted on the retina. More recently, Magendie3 has repeated these experiments by employing the eyes of albino animals, as those of the white rabbit, the white pigeon, the white mouse, &c. which afford great facilities for accomplishing the experiment; the sclero- tica being thin, and almost transparent; the choroid, also, thin, and when the blood, which gives it colour, has disappeared after the death of the animal, offering no sensible obstacle to the passage of light. In every one of these experiments, external objects were found to be represented on the natural or artificial retina in an in- verted position; the image being clearly defined, and with all the colours of the original. Yet how minute must these representations be in the living eye; and how accurate the mental appreciation, seeing that each impression from myriads of luminous points is transmitted by the retina to the encephalon, and perceived with unerring certainty! In the prosecution of his experiments—in some of which he was assisted by M. Biot—Magendie found, as might have been expected, that any alteration in the relative proportion or situation of the dif- ferent humours had a manifest effect upon vision. When a minute opening was made in the transparent cornea, and a small quantity of the aqueous humour permitted to escape, the image had no longer the same distinctness. The same thing occurred when a little of the vitreous humour was discharged by a small incision made through the sclerotica. He farther found that the size of the image on the retina was proportionate to the distance of the object from the eye. When the whole of the aqueous humour was evacuated, the image seemed to occupy a greater space on the retina, and to be less distinct and luminous, and the removal of the cornea was attended with similar results. When the crystalline was either depressed or extracted, as in the operation for cataract, the image was still formed at the bottom of the eye; but it was badly defined, slightly illuminated, and at least four times the usual size. Lastly,—when the cornea, aqueous humour, and crystalline were removed, leaving only the capsule of the crystalline, and the vitre- ous humour, an image was no longer formed upon the retina; the light from the luminous body reached it, but it assumed no shape similar to that of the body from which it emanated. The greater part of these results—as Magendieb remarks—accord very well with the theory of vision. Not so, the distinctness of the a Precis Elementaire, i. 70. »> Ibid. i. 73. 200 SENSE OF SIGHT. image under these deranging circumstances. According to the commonly received notions on this subject, it is necessary, in order to have the object depicted with distinctness on the retina, that the eye should accommodate itself to the distance at which the object is placed; otherwise indistinct vision must result. This is a subject, however, that will be discussed presently. Such are the general considerations relating to the progress of luminous rays from an object through the dioptrical part of the organ of sight to the nervous portion—the retina. We shall now inquire into the offices executed by the separate parts, that enter into its composition, where they have not already engaged attention. We have shown, that the cornea, aqueous humour, crystalline, and vitreous humour are a series of refractive bodies, to concentrate the luminous rays on the retina; to keep the parietes of the eye distended, and to afford surface for the expansion of the retina;— thus enlarging the field of vision. It is probably owing to their different refractive powers, that the eye is achromatic; or, in other words, that the rays, impinging upon the retina, are not decomposed into their constituent colours,—an inconvenience which appertains to the common lens. (Fig. 28.) The eye is strictly achromatic; and it has been an object of earnest inquiry amongst philosophers, to determine how the aberration of refrangibility is corrected in it. Euler,a first perhaps, asserted, that this is owing to the different refractive powers of the humours; and he conceived, that, by imitating this structure in the fabrication of lenses, they might be rendered achromatic. Experience has shown the accuracy of this opinion. (Fig. 29.) Others have believed that the effect is produced by certain of the humours—as the aqueous and the vitreous—which they have considered capable of correcting the dispersion produced by the cornea and crystalline. Others, again, have placed it in the crystalline, the layers of which being of different dispersive powers might correct each other. Lastly,—some have denied altogether the necessity for the eye's being achromatic; asserting, that the depth of the organ is so inconsiderable, that the dispersion of the rays, by the time they reach the retina, ought to be inappreciable. Such was the opinion of D'Alembert. Maskelyneb calculated the amount of the aberration, that must necessarily take place in the eye, and concluded that it would be fourteen or fifteen times less than in a common refracting telescope, and therefore imperceptible. Uncertainty still rests on this subject; and it cannot be removed until the dispersive and refractive powers of the transparent parts of the organ be mathematically determined; as well as their exact curvatures. It has been already shown, that the data we possess on this subject from different observers are sufficiently imprecise.0 * Memoir. Berlin, pour 1747, p. 279; and Letters of Euler, by Sir D. Brewster, Amer. Edit. i. 163, New York, 1833. b Philosoph. Transactions for 1789, lxix. 256. c Bostock's Physiology, 3d edit. p. 692, Lond. 1836. PHYSIOLOGY OF THE COATS OF THE EYE. 201 Our knowledge, then, is restricted to the fact, that the eye is per- fectly achromatic, and that, in this respect, it exceeds any instrument of human construction. The views of Euler are the most probable; and the effect doubtless is much aided by the iris or diaphragm, which prevents the rays from falling upon the margins of the lens, where, by the surfaces meeting at an angle, the aberration must necessarily be greatest. Of the coats of the eye,—the sclerotic, as has been remarked, gives form to, and protects the organ. The choroid is chiefly useful by the black pigment, which lines, and penetrates it. It will be seen, indeed, that some individuals, on insufficient grounds, have esteemed it the seat of vision. Leaving this question for the moment, and granting, as we shall endeavour to establish, that the impression is received upon the expansion of the optic nerve—the retina,—the use of the choroid would seem to be, in ordinary circumstances, to afford surface for the pigmentum nigrum, whose function it is to absorb the rays after they have passed through the retina, and thus to obviate the confusion that would arise from varied reflections, were the choroid devoid of such dark cover- ing. In albinos or white animals, in which the pigment is wanting, this inconvenience is really experienced, so that they become nyclalopes, or at least see but imperfectly during the day.a In the night, however, or when the light is feeble, their vision is unimpaired; and hence the albinos of our species have been called by the Ger- mans and Dutch, ka k er 1 aken, or cockroaches* Sir Everard Homec is of opinion, that the pigmentum nigrum of the eye is provided as a defence against strong light, and hence it is lightest in those countries least exposed to the scorching effects of the sun. In confirmation of this, he remarks, that it is dark in the monkey, and in all animals that look upwards, and in all birds ex- posed to the sun's rays; whilst the owl, that never sees the sun, has no black pigment. The function, assigned to it by Sir Everard, it doubtless possesses. The use of the shining spot on the outside of the optic nerves, in the eyes of quadrupeds, called the tapetum, has been an interesting theme of speculation, and has given rise to much ingenious, and to not a little ridiculous, hypothesis amongst naturalists. The absence of the black pigment necessarily occasions the reflection of a por- tion of the rays from the membrana Ruyschiana; and it has been presumed, that these reflected rays, in their passage back through the retina may cause a double impression, and thus add to the a Von Ammon, Art. Blindheit bei Tagc, in Encycl. Worterb. der Med. Wissensch. B. v. S. 590, Berlin, 1830. b Rudolphi, Art. Albinos, in EncyclopSd. Worterbuch, B. ii. S. 17, Berlin 1828— Lawrence's Lectures on Physiology, Zoology, and the Natural History of Man, p. 287, Lond. 1819 ; Picrer, art. Kakerlack, in Anat. Phys. Real. Worterb. iv. 252, Lcipz. 1821; and Dunglison's American Medical Intelligencer, i. 225, Philad. 1838. c Lectures on Comparative Anatomy, iii. 220, Lond. 1823. 202 SENSE OF SIGHT. intensity of vision. Another view has been, that the reflected rays may pass outwards through the retina without exciting any action, to be thrown on the object in order to increase the distinctness of the image on the retina, by an increase of its light. Dr. Fleming,8 who usually exhibits much philosophical acumen, and physiological accuracy, thinks it not probable, that both surfaces of the retina are equally adapted for receiving impressions of external objects, and is of opinion, that the rays, in their passage inwards, alone produce the image. More recently, however, M. Desmoulinsb has adduced many facts and arguments to show, that the tapetum really does act the part of a mirror, and, by returning the rays through the retina, subjects it to a double contact. He affirms, that in nocturnal animals, and in many fishes and birds, which require certain advan- tages to compensate for the conditions of the media in which they are situate, the tapetum is of great extent, and always corresponds to the polar segment of the eyeball, or to the visual axis; that in many animals, as in the cat, the pigmentum nigrum is wholly want- ing; and that it is only necessary for the vision of diurnal animals. He farther remarks, that, in man, the pigment diminishes according to age ; and that in advanced life it becomes white ; and he inge- niously presumes, that this is a means employed by nature to compen- sate, in some measure, for the gradual diminution in the sensibility of the retina,—the choroid beneath reflecting more and more of the rays, according as the pigment is removed from its surface. The views of M. Desmoulins are the most satisfactory of any that have been propounded, and they are corroborated by the experi- ments of Gruithuisen, Esser, and Tiedemann,c which show, that the phenomenon never occurs when the light is totally excluded. Gruit- huisen observed it in the dead as well as in the living animal. Tiede- mann perceived it in a cat, which had been decapitated for twenty hours, and it did not cease until the humours had become turbid. The views of these observers impress us the more forcibly, when we compare them with some other fanciful speculations, such as that of M. Richerand,d who supposes, that the use of the tapetum is to cause animals to have an exaggerated opinion of man! As if the same exaggerated effect would not be produced whatever were the object that impressed the organ. The iris has been compared, more than once, to the diaphragm of a lens or telescope. Its function consequently must be,—to cor- rect the aberration of sphericity, which would otherwise take place. This it does by diminishing the surface of the lens on which the rays impinge, so that they meet at the same focus on the retina. Biot has remarked, that this diaphragm is situate in the eye precisely a Philosophy of Zoology, i. 192, Edinb. 1822. b Magendie's Journal de Physiologie, iv. 89. c Traite Complet de Physiologie de I'Homme, &c, traduit par A. J. L. Jourdan, p. 550—Beytragen zur Physiognosie und Eautognosie, Munich, 1812, p. 199; and Kastner, Archiv. filr die gesammte Heilkunde, viii. 394. d Adelon, Physiologie de I'Homme, 2de edit. i. 443; and Sir E. Home's Lectures on Comp. Anat. iii. 243. ACTION OF THE IRIS. 203 at the place where it can best fulfil the office, and yet admit the greatest possible quantity of light. The iris is capable of contracting or dilating, so as to contract or dilate the pupil. It has been already observed, that the views of anatomists, regarding the muscular structure of the iris, have been very discrepant, and that some esteem it to be essentially vascular and nervous, the vessels and nerves being distributed on an erectile tissue. The partisans of each opinion explain the motions of the iris differently. They who admit it to consist of muscular fibres affirm, that the pupil is contracted by the action of the circular fibres, and dilated by that of the radiated. Those, again, that deny the muscularity of the organ say, that contraction of the pupil is caused by the afflux of blood into the vessels, or by a sort of tume- scence similar to what occurs in erectile parts in general, and dilata- tion by the withdrawal of the surplus fluid." Admitting, (and we think this must be conceded,) that the iris is really muscular, we meet with the singular anomaly in its physio- logy—that no ordinary stimulus, applied directly to it, has any effect, in exciting it to contraction. It may be pricked with the point of a cataract needle without the slightest motion being excited; and, from the experiments of Fontanab and Caldani,c it seems equally insensible, when luminous rays are made to impinge upon it; yet MM. Fowler, Rinhold, and Nysten,d have proved, that it contracts like other muscular parts, on the application of the galvanic stimulus. Like them, too, it is under the nervous influence, its movements being generally involuntary; but, there is some reason to believe, occasionally voluntary. Dr. Roget asserts, that this is the case with his own eye.e In the parrot, and in certain nocturnal birds, its motions are manifestly influenced by volition ;f and, when the cat is roused to attention, the pupil dilates, so as to allow a greater quantity of light to reach the retina. Magendie^ affirms, that the attention and effort, required to see minute objects distinctly, occasion contraction of the human pupil. He selected an individual whose pupil was very movable; and placing a sheet of paper in a fixed position, as regarded the eye and the light, he marked the state of the pupil. He then directed the person to endeavour, without moving the head or eyes, to read very minute characters, traced on the paper. The pupil immediately contracted, and continued so, as long as the effort was maintained. a See, on this contested subject, Dr. Bolton, in Dunglison's American Medical Intelli- gencer, Dec. 1,1838; Dr. Horner, Special and General Anatomy, 5th edit. ii. 422, Philad. 1839; T. Wharton Jones, in Introd. to Mackenzie's Practical Treatise on the Diseases of the Eye, 3d edit. Lond. 1840, and Rognetta, Cours d'Ophthalmologie, Paris, 1839. b Dei moti dell' Iride, cap. i. p. 7, Lucca, 1765. c Institutions Physiologicae, &c. Lips. 1785. d Magendie, ibid. i. 75. e Outlines of Physiology, Amer. Edit, by the author, p. 285, Philad. 1839 ; Bostock, Physiology, 3d edit. p. 102, Lond. 1836; and Travers, Synopsis of the Diseases of the Eye, p. 72, Lond. 1820. { Mayo, Outlines of Physiology, 4th edit. p. 286, Lond. 1837. « Precis Elementaire, 2de edit. i. 74. 204 SENSE OF SIGHT. Many experiments have been made to discover the nerve, which presides over the movements of the iris. These experiments have demonstrated, that if, instead of directing a pencil of rays upon the iris, we throw it upon the retina, or through the retina on the choroid, contraction of the pupil is immediately induced. The movements of the iris must, then, be to a certain extent under the influence of the optic nerve. It is found, indeed, that if the optic nerve be divided, in a living animal, the pupil becomes immovable and expanded. Yet, that the motions of the iris are not solely influenced by this nerve is evinced by the fact, that in many cases of complete amau- rosis of both eyes, there has been the freest dilatation and contraction of the pupil; "and also, that the section of the nerve of the fifth pair, which chiefly supplies the iris, equally induces immobility of the pupil. The same effect is produced, according to Mr. Mayo,a by dividing the third pair; and, according to Desmoulins,b in the eagle, whose iris is extremely movable, the third pair is the only nerve distributed to the organ. The general remark, made by Broussaisc on the organs that com- bine voluntary and involuntary functions, is applicable here;—that they will be found to possess both cerebral and ganglionic nerves. Accordingly, Magendie*1 conjectures, that those of the ciliary nerves, which proceed from the ophthalmic ganglion, preside over the dila- tation of the pupil, or are the nerves of involuntary action; and that those, which arise from the nasal branch of the fifth pair, pre- side over the contraction of the pupil. We might thus understand why, in apoplexy, epilepsy, &c, the pupil should be immovably dilated. All volition and every cerebral phenomenon are abolished by the attack: the nerve of the fifth pair, therefore, loses its influ- ence; and the iris is given up to the agency of the ganglionic nerves or nerves of involuntary action, proceeding from the ophthal- mic ganglion. On the whole, our notions, regarding the motions of the iris, and the nerves that preside over them, must be esteemed vague and unsatisfactory; and the obscurity is not diminished by a remark of Bellinger!.6 The iris, he observes, derives its nerves from the oph- thalmic ganglion, which is formed by the fifth in conjunction with the third pair, and its involuntary motions, he thinks, are regulated by the fifth pair. In those instances, in which the motions of the iris have been found dependent on the will, Bellingeri argues, that the ciliary nerves received no branches from the fifth—a fact, which has been proved by dissection, as well as by the circum- a Commentaries, P. ii. p. 5, and Outlines of Human Physiology, &c. 4th edit. p. 287, Lond. 1837. b Anatom. des System. Nerveux; Paris, 1825. c Traite de Physiologie appliqu6e a la Pathologie, and translation by Dr. Bell and La Rcche, 3d edit. p. 77, Phil., 1833. d Piecis, &c. ed. cit. i. 77. e Dissert. Inaugural. Turin, 1823; and Edinb. Med. and Surg. Journal, for July, ACTION OF THE RETINA. 205 stance that in the parrot, the owl, and the ray genus among fishes —in which the iris is under the will of the animal—there is no ophthalmic ganglion. The iris contracts or dilates according to the intensity of the light that strikes the eye. If the light from an object be feeble, the pupil is dilated to admit more of the luminous rays; on the con- trary, if the light be powerful, it contracts. We see this very manifestly on opening the eyes, after they have been for some time closed, and bringing a candle suddenly near them. It is one of the means we frequently employ in cerebral disease to judge of the degree of insensibility. We shall presently inquire into the effect of contraction or dilata- tion of the pupil on distinct vision; and show, that they are actions for accommodating the eye to vision at different distances. We may conclude, then, that the iris is one of the most important parts of the visual apparatus; and that its functions are multiple:— that it is partly the cause of the achromatism of the organ, by pre- venting the rays of greatest divergence from falling near the mar- ginal parts of the crystalline:—that it corrects the aberration of sphericity—regulates the quantity of light admitted through the pupil, and accommodates the eye, to a certain extent, to vision at different distances. An enumeration of the multiform sentiments, entertained regard- ing the functions of the ciliary processes, will show how little we know, that is precise, on this matter also. They have often been considered contractile; some believing them connected with the motion of the iris, others to vary the distance of the crystalline from the retina. Jacobsona makes them dilate the apertures, which he conceives to exist in the canal godronne, so as to cause the admis- sion of a portion of the aqueous humour into the canal, and thus to change the situation of the crystalline. Others believe, that they secrete the pigmentum nigrum ; and others—the aqueous humour. But the processes are wanting in animals, in which the humours, notwithstanding, exist. There is no opinion, perhaps, more proba- ble than that of Haller ;b—that they are destined to assist mechani- cally in the constitution of the eye, and have no farther use. The function of the retind remains to be considered. It is the part that receives the impression from the luminous rays, which im- pression is by the optic nerve conveyed to the brain. This nervous expansion was, at one time, universally believed to be the most delicately sensible membrane of the animal frame. Of late, it has been shown by the experiments of Magendie,0 that the sensibility of both it and the optic nerve is almost entirely special, and limited to the appreciation of light;—that the general sensibility is exclu- sively possessed by the fifth encephalic pair, and that the nerve of special sensibility is incapable of executing its functions, unless that a Magendie, Precis., edit. cit. i. 78. ° Op. cit. i. 83. VOL. I. b Element. Physiol, xvi. 4, 20. 18 206 SENSE OF SIGHT. of general sensibility be in a state of integrity. That distinguished physiologist found, when a couching needle was passed into the eye at its posterior part, that the retina might be punctured and lace- rated without the animal exhibiting evidences of pain. The same result attended his experiments on the optic nerves. These nerves, both anterior and posterior to their decussation, as well as the thalami nervorum opticorum, the superficial layer of the tubercula quadrigemina, and the three pairs of motor nerves of the eye gave no signs of general sensibility. On the other hand, the general sen- sibility of the anterior part of the eye—of the conjunctiva—is well known. It is such, that the smallest particle of even the softest substance excites intense irritation. This general sensibility Ma- gendie1 found to be totally annihilated by the division of the fifth pair of nerves within the cranium ; so that hard-pointed bodies and even liquid ammonia made no painful impression on the conjunctiva. Nictation was arrested, and the eye remained dry and fixed like an artificial eye behind the paralysed eyelids. The sight, in this case also, was almost wholly lost; but by making the eye pass rapidly from obscurity into the vivid light of the sun, the eyelids approxi- mated, and, consequently, some slight sensibility to light remained; but it was extremely slight. In this sense, then, as in the senses of hearing and smell, we have the distinction between a special nervous system of sense, and a nervous system of general sensibility, without which the former is incapable of executing its elevated functions. The expansion of the retina occupies at least two-thirds of the circumference of the eyeball. It is of obvious importance, that it should have as much space as possible; and, in certain animals, in which the sense is very acute, the membrane is plaited, so as to have a much larger surface than the interior of the eyeball; and thus to allow the same luminous ray to impinge upon more than one point of the membrane. This is seen in the eyes of the eagle and vulture, and in nocturnal animals. The inconceivable acuteness of the sense of sight in birds of prey, has been already referred to, under the sense of smell. (Page 135.) It was there stated, that the strange facts regarding the condor, vulture, turkey-buzzard, &c, which meet in numbers in the forests, when an animal is killed, ought rather, perhaps, to be referred to acuteness of the sense of sight than of smell. Sir Everard Homeb affords an additional illustration of this subject. In the year 1778, Mr. Baber, and several other gentlemen, were on a hunting party in the island of Cassimbusar, in Bengal, about fifteen miles north of the city of Marshedabad; they killed a wild hog of uncommon size, and left it on the ground near the tent. An hour after, walking near the spot where it lay, the sky perfectly clear, a dark spot in the air, at a great distance, attracted their attention; it appeared to increase in size, and to move directly towards them ; * Ibid. i. 494. * Lectures on Comparative Anatomy, Lond. 1814-1828. ACTION OF THE RETINA. 207 as it advanced it proved to be a vulture flying in a direct line to the dead hog. In an hour, seventy others came in all directions, which induced Mr. Baber to remark,—"this cannot be smell." How inconceivably sensible to its special irritant must this mem- brane be in the human eye, when we consider that every part of an extensive landscape is depicted upon its minute surface; not only in its proper situation, but with all its varied tints! and how impracticable is it for us to comprehend, how the infinitely wider range of country can be so vividly depicted on the diminutive eye of the vulture, as to enable it to see its prey from such a remote distance! If pressure be made on the eyeball, behind the cornea so as to affect the retina, concentric luminous circles will be seen, opposite to the part on which the pressure is applied ; and, if the pressure be continued for twenty or thirty seconds, a broad undefined light, which increases in intensity every moment, rises immediately before the eye, If the eyelids be open, and light be present, on the repeti- tion of the last experiment, a dense cloud arises, instead of the broad undefined light, and the eye becomes in a few seconds, perfectly blind, but in the course of three or four seconds after the finger is removed, the cloud appears to roll away from before the eye. From this, it seems, that sensations of light may be produced by mechanical pressure made on the retina; in other words, the retina becomes phosphorescent by pressure. The same thing too, is observed, if a sudden blow be given on the eye, or if we place a piece of zinc under the upper lip, and a piece of copper above the eye. A flash of light is seen; produced, doubtless, by the galvanic fluid impressing directly, or indirectly, the optic nerve. The same thing occurs in the act of sneezing, and in forcing air violently through the nostrils. On repeating the experiment of pressing the eyeball, Sir David Brewster" observed, that when a gentle pressure was first applied, so as to compress slightly the fine pulpy substance of the retina, a circular spot of colourless light was produced, though the eye was in total darkness, and had not been exposed to light for many hours; but if light be now admitted to the eye, the compressed part of the retina is found to be more sensible to the light than any other part, and consequently it appears more luminous. If the pressure be increased, beyond the point mentioned above, the circular part of light gradually becomes .darker, and, at length, black, and is sur- rounded with a bright ring of light. By augmenting the pressure still more, a luminous spot appears in the middle of the central dark one, and another luminous spot diametrically opposite, and beneath the point of pressure. Now, considering the eye, says Sir David, as an elastic sphere, filled with incomprehensible fluids, it is obvious, that a ring of fluids will rise round the point depressed by the finger, and that the eyeball will protrude all around the point of pressure, and consequently the retina, at the protruded part, will be com- » Letters on Natural Magic, Amer. Edit. p. 27, New York, 1832. 208 SENSE OF SIGHT. pressed by the outward pressure of the contained fluid, while the retina on each side,—that is, under the point of pressure, and beyond the protruded part,—will be drawn towards the protruded or be dilated. Hence the part under the finger, which was origi- nally compressed, is now dilated, the adjacent parts are compressed, and the more remote parts, immediately without this, dilated also. "Now," continues Sir David, "we have observed, that when the eye is, under these circumstances, exposed to light, there is a bright luminous circle shading off externally and internally into total darkness. We are led therefore to the important conclusions, that when the retina is compressed in total darkness it gives out light; that when it is compressed, when exposed to light, its sensibility to light is increased; and that when it is dilated under exposure to light, it becomes absolutely blind or insensible to all luminous impressions." Having traced the mode in which the general physiology of vision is effected, and the part performed by each of the constituents of the eye proper, we shall briefly consider the functions of the rest of the visual apparatus, the anatomical sketch of which has been given under the head of accessory organs; and afterwards inquire into the various interesting and important phenomena exhibited by this sense. These organs perform but a secondary part in vision. The orbit shelters the eye, and protects it from external violence. The eye- brows have a similar effect; and, in addition to this, the hair, with which they are furnished, by virtue of its oblique direction towards the temple, and by the sebaceous secretion that covers it, prevents the perspiration from flowing into the eye, and directs it towards the temple or the root of the nose. By contracting the eyebrows, they can be thrown forwards and downwards in wrinkles; and can thus protect the eye from too strong a light, especially when coming from above. The eyelids cover the eye during sleep, and preserve it from the contact of extraneous bodies. During the waking state, this pro- tection is afforded by the instantaneous occlusion of the eyelids, on the anticipation of danger to the ball. The incessant nictation likewise spreads the lachrymal secretion over the surface of the conjunctiva, and cleanses it; whilst the; movement, at the same time, probably excites the gland to augmented secretion. The chief part of the movement of nictation is performed by the upper eyelid ; the difference in the action of the eyelids being esti- mated, by some physiologists, as four to one. Under ordinary cir- cumstances, according to Adelon8 it is the levator palpebral supe- rioris, which, by its contraction or relaxation, opens or closes the eye: the orbicularis palpebrarum not acting. If the levator be con- a Physiologie de I'Homme, 2de edit. i. 419, Paris, 1829. Sec, also, Lawrence on the Diseases of the Eye, Amer. Edit. p. 40, Washington, 1834. ACTION OF THE MUSCLES OF THE EYE. 209 traded, the eyelid is raised and folded between the eye and orbit, and the eye is open; if, on the other hand, the levator be relaxed, or spread passively over the surface of the organ, the eye is closed. In this view, the orbicularis muscle is not contracted, except in extraordinary cases, and under the influence of volition; whilst the closure of the eye, during sleep, is dependent upon simple relaxation of the levator. The views of Broussais* on this subject are, we think, more satisfactory. He considers, that the open state of the eye, in the waking condition, requires no effort; because the two muscles of the eyelids are so arranged, that the action of the levator is much more powerful than that of the orbicularis; and he adduces, in proof of this, that the eyelids are, at the time of death, half open. On the other hand, the closure of the eye in sleep, he conceives to be owing to the contraction of the orbicularis muscle, which acts whilst the others rest. If the opening of the eye were wholly dependent upon the action of the levator palpebra? superioris muscle, its relaxation, during insensibility and death, ought to be sufficient to close the eye completely; and the orbicularis palpebrarum would be comparatively devoid of function; being only necessary for the closure of the organ under the influence of volition. It has been found by experiments, instituted by Sir Charles Bell,b and by Magendie,c that nictation is effected under the influence chiefly of the portio dura of the seventh pair, or facial nerve,—one of the respiratory nerves of Sir Charles Bell's system—the respira- tory of the face. When this nerve is cut, nictation is completely arrested; and when the nerve of the fifth pair, also distributed to these parts, is divided, it ceases likewise, but less thoroughly; a very vivid light exciting it, but only at considerable intervals, and im- perfectly. We see here something very analogous to the partition of the nerves of the senses into those possessing general, and those con- veying special sensibility. Like the latter functionaries, the nerve of the seventh pair appears to be specially concerned in nictation, and not to be capable of executing its office, unless the fifth pair—the nerve of general sensibility—be in a state of integrity. The eyelids, by their approximation, can regulate the quantity of light that enters the pupil, when it is injuriously powerful; when feeble, they are widely separated, to allow as much as possible to penetrate the organ. By their agency, again, the most diverging rays from an object can be prevented from falling upon the cornea; and the vision of the myopic or short-sighted can, in this way, be assisted. It is a means of which they often avail themselves. The cilia or eyelashes, it is probable, are of similar advantage as regards the admission of light into the eye, and have some part, probably, in preventing extraneous bodies, borne about in the air, from reaching the sensible conjunctiva. a Edit, citat. p. 188. b The Nervous System of the Human Body, Amer. Edit. p. 48, Washington,. 1833. c Precis Elementaire, i. 309. 18* 210 SENSE OF SIGHT. The muscles of the eyeball have acquired the chief portion of their interest of late years, and largely through the investigations of the eminent physiologist—of whose labours we have so frequently had occasion to speak—Sir Charles Bell.1 The arrangement of the four straight muscles, and especially their names—sufficiently indi- cate the direction in which they are capable of moving the organ, when acting singly. If any two of them contract together, the eye- ball will, of course, be moved in the direction of the diagonal be- tween the two forces; and if each muscle contracts rapidly after the other, the organ will execute a movement of circumduction. The oblique muscles are antagonists to each other, and roll the eye in opposite directions; the superior oblique directing the pupil downwards and inwards; the inferior upwards and inwards. But as the different straight muscles are capable of carrying the eye in these directions, were we to regard the two sets of muscles as pos- sessing analogous functions, the oblique would appear to be super- fluous. This, along with other reasons, attracted the attention of Sir Charles Bell to the subject; and the result of his experiments and reflections was:—that the straight muscles are concerned in the motions of the eye excited by volition: and that the oblique muscles are the organs of its involuntary motions; and, in this manner, he accounts for several phenomena, connected with the play of these organs in health and disease. Whilst the power of volition can be exerted over the recti mus- cles, the eye is moved about, in the waking state, by their agency; but, as soon as volition fails from any cause, the straight muscles cease to act, and the eye is turned up under the upper eyelid. Hence this happens at the approach of, and during sleep; and when- ever insensibility occurs from any cause, as in faintness, or on the approach of dissolution ; and that turning up of the eyeball, which we have been accustomed to regard as the expression of agony, is but the indication of a state of incipient or total insensibility. Whenever, too, the eyelids are closed, the eyeball is moved, so that the cornea is raised under the upper eyelid. If one eye be fixed upon an object, and the other be closed, with the finger so placed as to feel the convexity of the cornea through the upper eye- lid, and the open eye be shut, the cornea of the other eye will be found to be elevated. This change takes place during the most rapid winking motions of the eyelids; and is obviously inservient to the protection of the eye: to the clearing of the eyeball of every thing that could obscure vision, and perhaps, as Sir Charles Bell presumes, to procure the discharge from the ducts of the lachrymal gland. During sleep, when the closure of the eye is prolonged, the trans- parent cornea is, by this action, turned up under the upper eyelid, v*i?PiflCotat' P* 102' and Anatomyand Physiology, 5th Amer. Edit. ii. 213, New ACTION OF THE MUSCLES OF THE EYEBALL. 211 where it is securely lodged and kept moist by the secretions of the lachrymal gland and conjunctiva. The different distributions of the motor nerves of the eye have been described in the anatomical sketch. It was there stated, that the superior oblique muscle receives one whole pair of nerves:—the fourth. This nerve, then, it seemed to Sir Charles Bell, must be concerned in the functions we have described ; and, as the various involuntary motions of the eyeball are intimately concerned in ex- pression, as in bodily pain, and in mental agony,—in which the action of the direct muscles seems, for a time, to be suspended,—he was led to consider the fourth pair as a nerve of expression—a re- spiratory nerve; and, hence, intimately connected with the facial nerve of the seventh pair, which, as has already been remarked, is the great nervous agent in the twinkling of the eyelids. Anatomical examination confirmed this view;—the roots of the nerve being found to arise from the same column as the other respiratory nerves. The coincidence of this twinkling, and of the motion of the eyeball upwards was, therefore, easily understood. There is a difficulty, however, here, which has doubtless already suggested itself. The fourth pair of nerves is distributed to the su- perior oblique only; the lesser oblique receives none of its ramifica- tions. They cannot, therefore, be identically situate in this respect. Yet they are both considered by Sir Charles Bell as involuntary muscles. The action, indeed, of the lesser oblique would appear to be even more important than that of the greater oblique, as the func- tion of the former, wrhen acting singly, is to carry the eye upwards and inwards; and, when the action of its antagonist is abolished, this is more clearly manifested. Sir Charles found, that the effect of dividing the superior oblique was to cause the eye to roll more forcibly upwards;—in other words, it was given up, uncontrolled, to the action of the antagonist muscle. This difficulty, although it is not openly stated by Sir Charles, must have impressed him ; as, after having referred to the effect of the division of the superior oblique, he is constrained to suggest an influence to the fourth pair, which would, we think, be anomalous:— that it may, on certain occasions, cause a relaxation of the muscle to which it goes, and, in such case, the eyeball must be rolled up- wards ! In addition to this, too, as Mr. Mayoa has observed, the distribution of the muscular nerves of the eye is not such as to allow of our opposing the straight muscles to the oblique, and one cogent reason is, that the third pair of nerves supplies part of each class. We have still, therefore, much to learn regarding this subject, into which so much interest, and, at the same time, so much uncertainty has been infused.15 In some recent experiments on the fresh subject, with Professor Pan- coast, who carefully separated the different muscles, with the view a Outlines of Human Physiology, 4th edit. p. 299, Lond. 1837. b See, on this subject, Elliotson's Human Physiology, p. 585, Lond. 1840. 212 SENSE OF SIGHT. of discovering their precise action, it was clearly apparent, that the oblique muscles act in the manner before mentioned; the superior oblique directing the eye slightly inwards and downwards; and the inferior, rolling it upwards and inwards, when they acted singly; but when the two were brought into action simultaneously, they appeared to antagonize each other as rotators, but projected the eye forward. It would seem, indeed, that an important use of these muscles is to keep the eye prominent during the action of the straight muscles. These results harmonize greatly with the deduc- tions from experiments on living animals by Mr. Bransby Cooper.9 He divided the superior and oblique muscles on the eyes of several living rabbits; and inferred, that the oblique muscles, when acting together, suspend the eyeball in a central position in the orbitar cavity, moderate the retracting influence of the four straight mus- cles, and, when acting in succession, without being restricted by the influence of the straight muscles, they roll the eye on its own axis, drawing the globe forward, and at the same time tending, in a great degree, to extend the sphere of vision. The great use of the tears would seem to be to moisten the con- junctiva, and to remove extraneous bodies from its surface,—thus assisting the motions of the eyelids and eyeball, just referred to. The tears are secreted by the lachrymal gland; and, by means of its excretory ducts, they are poured upon the surface of the tunica conjunctiva, at the upper and outer part of the eye. Their farther course towards the puncta lachrymalia has been the subject of dif- ference of sentiment. The generality of physiologists consider, that, owing to the form of the tarsal cartilages, a canal must exist, when the eyelids are closed, of a triangular shape, formed anteriorly by the junction of the cartilages, and behind by the ball of the eye. Magendie,b on the other hand, denies the existence of this canal, and asserts that the tarsal cartilages do not touch by a rounded edge, but by an inner plane surface. If we were to grant the existence of this canal, it could only aid us in our explanation of the course of the tears during sleep. In the waking state, they are not ordinarily secreted in such quantity as to require that much should pass to the puncta;—the movements of nictation spreading them over the surface of the eye, whence they are partly absorbed, and the rest, perhaps, evaporated. Under extraordinary circumstances, however, the gland increases its secretion so much, that the tears not only pass freely through the lachrymal ducts into the nose, but flow over the lower eyelid. The epiphora or watery eye, caused by obstruction of these ducts, also proves that a certain quantity of the secretion must always be passing into the puncta. The physical arrangement of the eyelids and tunica conjunctiva is doubtless the cause of their course in this direction. It has been gratuitously supposed by some, that the humour of 1 Guy's Hospital Reports, vol. iii. April and October, 1838 b Precis, &c. edit. cit. i. 52. COURSE OF THE TEARS. 213 Meibomius prevents the tears from reaching the outer surface of the lower eyelid, by acting like a layer of oil on the margin of a vessel filled with water. A similar function has been assigned to the secre- tion of the caruncula lachrymalis. Both these fluids, however, are probably inservient to other ends. They are readily miscible with water; become consequently dissolved in the tears, and, with the assistance of the fluid secreted by the tunica conjunctiva, aid the movements of the eyelids over the ball of the eye, and keep the tarsal margins and their appendages in the condition requisite for the due performance of their functions. The action of the puncta themselves in admitting the tears has received different explanations. Adelona regards it as organic and vital. We ought, however, in all cases, to have recourse to this mode of accounting for phenomena as the ultima ratio, and the pre- sent appears to us to be a case in which it is singularly unnecessary. In many of the results of absorption we are compelled to suppose, that a vital operation must have been concerned in the process. Where, for example, as in the case of the lymphatic vessels, we find the same fluid circulating, whatever may have been the nature of the substances whence it was obtained, the evidence, that a vital action of selection and elaboration has been going on, is irresistible; but no such action can have occurred in the case in question. The tears in the lachrymal ducts and in the ductus ad nasum are iden- tical with those spread upon the surface of the eye; the only differ- ence being in their situation. This is one of the few cases in the human body, which admit of satisfactory explanation on the physi- cal principles of capillary attraction. In vegetables, the whole of the circulation of their juices has been thus accounted for. If we twist together several threads of yarn, moisten them, and put one extre- mity of the roll into a vessel of water, allowing the other to hang down on the outside of the vessel, and to dip into an empty vessel placed below it, we find, that the whole of the fluid, in the first vessel, is in a short time transferred to the second. If, again, we take a small tube, less than the twentieth part of an inch in dia- meter, which is called capillary, and place it so as to touch the surface of water, we find, that the water rises in it to a height, which is greater, the smaller the bore of the tube. If the diameter of the tube be the fiftieth part of an inch, the water will rise to the height of two inches and a half; if the one hundredth part of an inch, to five inches ; if the two hundredth part of an inch, to ten inches; and so on. Now, the punctum lachrymale is, in our view of the subject, the open extremity of a capillary tube, which receives the fluid of the lachrymal gland and conveys it to the nose, the punctum being properly directed towards the eyeball by the tensor tarsi muscle of Horner. Lastly,—the tunica conjunctiva is another part of the guardian 1 Physiologic, 2de edit. p. 421, Paris, 1829. See, also, Richerand, Elements de Physiologie, edit. Beige, p. 187, Bruxelles, 1837. 214 SENSE OF SIGHT. apparatus of the eye. It secretes a fluid, which readily mixes with the tears, and appears to have similar uses. Like the mucous membranes in general, it absorbs; and, in this way, a part of the lachrymal secretion is removed from its surface. An animal, for the same reason, can be readily poisoned by applying prussic acid to it. As the conjunctiva lines the eyelids, and is reflected over the globe, it supports the friction, when the eyeball or eyelids are moved; but, being highly polished and always moist, the whole of this is insignificant. The extreme sensibility of the outer part of the eye appertains entirely to the tunica conjunctiva, and is dependent on the ophthal- mic branch of the fifth pair. When this nerve was divided in a living animal, Magendie2 found, that the membrane became en- tirely insensible to every kind of contact, even of substances that destroyed it chemically. In his experiments on this subject, he arrived at some singular results, regarding the influence of the fifth pair on the nutrition of the eye. When the trunk of the nerve was divided within the cranium, a little after its passage over the petrous portion of the temporal bone, the cornea was found, about twenty- four hours afterwards, to become troubled, and a large spot to form upon it. In the course of from forty-eight to sixty hours, this part was completely opaque; and the conjunctiva, as well as the iris, was in a state of inflammation; a turbid fluid was thrown out into the inner chamber, and false membranes proceeded from the inte- rior surface of the iris. The crystalline and vitreous humours now began to lose their transparency; and, in the course of a few days, were entirely opaque. Eight days after the division of the nerve, the cornea separated from the sclerotica; and the portions of the humours that remained fluid escaped at the opening. The organ diminished in size, and ultimately became a kind of tubercle, filled with a substance of a caseous appearance. Magendie properly con- cludes from these experiments, that the nutrition of the eye is under the influence of the fifth pair; and he conceives, that the opacity of the cornea was directly owing to the section of this nerve, and not to a cessation of the lachrymal secretion, or to the prolonged con- tact of air, caused by the paralysis of the eyelids; inasmuch as when the branches of the nerve proceeding to the eyelids were simply divided, or when the lachrymal gland was taken away, the opacity did not supervene. 5. PHENOMENA OF VISION. It has been more than once remarked, that the retina—the expan- sion of the optic nerve—is the part of the eye which receives the impressions of luminous rays, whence they are conveyed by the optic nerve to the brain. Yet this has been contested. The Abbe Mariotteb discovered the singular fact, that when a * Precis Elementaire, ii. 494. b Philos. Transact, iii, 668, and Memoir, de 1'Academie Royale des Sciences, torn, i, pp, 68 and 102, EXPERIMENT OF MARIOTTE. 215 ray of light falls, as he conceived, upon the centre of the optic nerve, it excites no sensation. " Having often observed," he remarks, " on dissections of men as well as of brutes, that the optic nerve does never answer just to the middle of the bottom of the eye; that is, to the place where the picture of the object we look directly upon is made; and that in man it is somewhat higher, and on the side towards the nose; to make therefore the rays of an object to fall upon the optic nerve of my eye, and to find the conse- quence thereof, 1 made this experiment. I fastened on an obscure wall, about the height of my eye, a small round paper, to serve me for a fixed point of vision. I fastened such another on the side thereof towards my right hand, at the distance of about two feet, but somewhat lower than the first, to the end that I might strike the optic nerve of my right eye, while I kept my left shut. Then I placed myself over against the first paper, and drew back by little and little, keeping my right eye fixed and very steady on the same, and being about ten feet distant, the second paper totally disappeared." The experiment of Mariotte can be readily repeated on the mar- ginal representations of the fleur-de-lis and the anchor. If we close the left eye, and direct the axis of the right eye steadily to- ^ *^* wards the anchor, whilst the page is held at the distance of about ten inches from the eye, the fleur-de- lis will vanish. The distance of the object which disappears from the eye, must be about five times as great as its distance from the other object. In this case the fleur-de-lis and anchor are two inches asunder.* It is obvious from what has been said, regarding the axes of the orbits, and the part of the eyeball at which the optic nerve enters —that rays of light from an object can never fall, at the same time, upon the insensible point of each eye. The defect in vision is, con- sequently, never experienced except in such experiments as those performed by Mariotte. In one of these he succeeded in directing the rays to the insensible point of both eyes at once. He put two round papers at the height of the eye, and at the distance of three feet from each other. By then placing himself opposite them, at the distance of twelve or thirteen feet, and holding his thumb before his eyes, at the distance of about eight inches, so that it concealed from the right eye the paper on the left hand, and from the left eye the paper on the right, he looked at his thumb steadily with both eyes, and both the papers were lost sight of. These experiments certainly show, that there is a part of the retina or optic nerve which is, in each eye, insensible to light; and that this point is on the nasal side of the axis. No sooner, however, 1 J. Mailer's Elements of Physiology, by Baly, P. v. 1186, June, 1839. 216 SENSE OF SIGHT. had Mariotte published an account of his experiments than it was de- cided that this spot was the basis of the optic nerve; a conclusion was accordingly drawn, that the nerve is incapable of distinct vision, and this conclusion has been embraced, without examination, in almost all the books of optics to the present time. Although probable, however, it is by no means certain that the light, in these cases, falls upon the base of the nerve. The direction in which the ray proceeds is such that it is reasonable to suppose it does impinge there: the suggestion of M. Tillaye,a that it falls upon the yellow spot of Sommering, can only be explained by presuming him to have been in utter ignorance of its situation, which we have seen to be on the outer side of the nerve. But, granting, that the light falls on the base of the nerve, it by no means demonstrates, that the nerve is incapable of receiving the impression. It has been already shown, that the central artery of the retina penetrates the eye through the very centre of the nerve; and through the same opening, the central vein leaves the organ. It is probable, therefore, that in these experiments, the ray falls upon the blood-vessels, and not upon the medullary matter of the nerve ; and if so, we could not expect that there should be sensation. That the insensible spot is of small mag- nitude is proved by the fact, that if candles are substituted for the round papers or wafers, the candle does not disappear but becomes a cloudy mass of light. It is true, Daniel Bernouillib considered the part of the nerve insensible to distinct impressions to occupy about the seventh part of the diameter of the eye, or about the eighth of an inch ; but there must evidently have been some error in his cal- culations, for the optic nerve itself can rarely equal this proportion. The estimate of Le Cat,c who was himself a believer in the views of Mariotte, that its size is about one-third, or one-fourth of a line, is probably still wider from the truth in the opposite direction. Simple experiment, with two wafers placed upon a door at the height of the eye, will show clearly, that both the horizontal and vertical diameters of the spot must be larger than this. The fact, observed by Mariotte, was not suffered to remain in repose. A new hypothesis of vision was formed upon it; and, as he considered it demonstrated, that the optic nerve was insensible to light, he drew the inference, that the retina was so likewise; and as vision was effected in every part of the interior of the eye, except at the base of the optic nerve, where the choroid is alone absent, he inferred, that the choroid must be the true seat of vision. The controversy, at one time maintained on this subject, has died away, and it is not our intention to disturb its ashes, farther than to remark, that M. De La Hire,d who engaged in it, entertained the opinion, that the retina receives the impression of the light in a secondary way, and through the choroid coat as an intermediate a Adelon, Physiologie 2de 6dit. i. 448, Paris, 1829. b See Haller. Element. Physiolog. xvi. 4, 4. «= Traite des Sens, Paris, 1767; and English translation, Lond. 1750. d Mem. de l'Academie, torn. ix. CAUSE OF ERECT VISION. 217 organ; that by the light striking the choroid coat, the membrane is agitated, and the agitation communicated to the retina. The views of De La Hire are embraced by Brewster,a as well as by numerous other philosophers. The opinions of Mariotte have now few supporters. The remarks already made, regarding the optic nerve ; the effect of diseases of the retina, of the nerve itself, and of its thalami, compel us to regard its expansion as the seat of vision : and if we were even to admit, with Mariotte, that the insensible portion is really a part of the medullary matter of the nerve, and not a blood-vessel existing there, we could still satisfactorily account for the phenomenon by the anomalous circumstances in which the nervous part of the organ is there placed. The choroid coat, of great importance in the func- tion, is absent; as well as the pigmentum nigrum; and hence we ought not to be surprised, that the function is imperfectly executed ; we say imperfectly, for the experiment with the candles exhibits that the part is not really insensible to light; or is so in a very small portion of its surface only. It may seem at first sight, that the fact of this defect existing only in the centre of the optic nerve, or at the porus opticus, as it has been termed, where the central artery of the retina enters, and the corresponding vein leaves the organ, militates against the idea of its being caused by the rays impinging upon these vessels; as, if so, we ought to have similar defects in every part of the retina, where the ramifications of these vessels exist. Circumstances are not here, however, identical. When the ray falls upon the porus opticus, it strikes the vessels in the direction of their length; but, in the other cases, it falls transversely upon them, pierces them, and impresses the retina beneath; so that, under ordinary circumstances, little or no dif- ference is perceived between the parts of the retina over which the vessels creep, and the remainder of its extent. We can, however, by an experiment of Purkinje, described by J. G. Steinbuch,b exhi- bit, that under particular circumstances such difference really exists, and renders the blood-vessels of the organ perceptible to its own vision. If, without closing the eyelids, the left eye be covered with the hand, or some other body, and a candle or lamp be held in the right hand, within two or three inches of the right eye, but rather below it, (keeping the eye directed straight forward,) on moving the candle slowly from right to left, (or if the candle be held on the right side of the eye, it may be moved up and down,) a spectrum appears, after a short time, in which the blood-vessels of the retina, with their various ramifications are distinctly seen, projected, as it were, on a plane without the eye, and greatly mag- nified. They seem to proceed from the optic nerve, and to consist of two upper and two lower branches, which ramify towards the field of vision, where a dark spot is seen, corresponding to the a Treatise on Optics, Amer. Edit, by A. D. Bache, p. 243, Philad. 1833. b Beitrag zur Physiologie der Sinne, Niirnberg, 1811. VOL. I. 19 218 SENSE OF SIGHT. foramen centrale. The origin of the vessels is a dark oval spot, with an areola/ This phenomenon must be accounted for by the parts of the retina, covered by the blood-vessels, not being equally fatigued with those that are exposed. It is by no means uncommon for appearances of cobwebs, small tubes with lateral pores, &c. to present themselves before the eyes, without changing their position when the eyes are fixed upon an object. These appearances are not owing to any modification in the humours, but are apparently dependent upon the physical condi- tion of the retina. Some years ago, a tube of the kind mentioned, but apparently terminating in an open mouth, was the occasion of some uneasiness to the author. This is now no longer seen, but numerous opacities, somewhat resembling plexuses of vessels or nerves are still apparent.b It has been remarked, that the rays, proceeding from the upper part of an object, impinge upon the lower part of the retina; and those from the lower part on the upper portion of the retina; hence, the image of the object is reversed, as in Fig. 37. It has, accordingly, been asked;—how it is, that in these circum- stances, we see the object in its proper position, inasmuch as its image is inverted on the retina? Buffon,c Le Cat,d and others believed, that originally, we do see them so inverted; but that the sense of touch apprises us of our error, and enables us to correct it at so early a period, and so effectually, that we are afterwards not aware of the process. Berkeley,6 again, asserted, that the position of objects is always judged of, by comparing them with our own; and that, as we see ourselves inverted, external bodies are in the same relation to us as if they were erect. It is not necessary to reply, at length, to these phantasies, which are obviously founded in error. Cases enough have occurred, of the blind from birth having been restored to sight, to show, that no such inversion, as that de- scribed by Buffon, takes place ; whilst the boy, who stoops down, and looks at objects between his legs, although he may be, at first, a little confused, from the usual position of the images on the retina being reversed, soon sees as well in that way as in any other. The truth is, the great error with all these speculatists has been, that they have imagined a true picture to be formed on the retina, which is regarded by the mind, and therefore seen inverted. It need hardly be said, that there is no interior eye to take cognizance of this image; but that the mind accurately refers the impression, made a See, on the subject of rendering the blood-vessels of the observer's retina apparent to him, the work of Mrs. Griffiths, entitled Discoveries in Light and Vision, p. 86, New York, 1836. b See, Dr. Alexander, in Boston Med. and Surg. Journal, June 7,1837, and Jan. 23, 1839, p. 389; also, Dunglison's Amer. Med. Intelligencer, i. 145 and 186, Philad. 1838; W. Clay Wallace, Lond. Med.Gaz., Oct. 1838; and Treatise on the Eye, 2d edit, New York, 1839. c Memoires de l'Academie, 1743, p. 231. <* Op. citat. e Essay on Vision, 2d edit,, Dublin, 1709. CAUSE OF ERECT VISION. 219 upon the retina, to the object producing it; and if the lower part of the retina be impressed by a ray from the upper part of an object, this impression is conveyed by the retina to the brain as it receives it, and no error can be indulged. Professor Alisona offers an explanation, first suggested to him by Mr. Dick, veterinary surgeon, which turns on the alleged fact, that the course of the optic nerves and tractus optici is such, that im- pressions on the upper part of the retina are, in fact, impressions on the lower part of the optic lobes, that is of the sensorium,—and impressions on the outer part of the former are on the inner part of the latter, and conversely. When a cone of light proceeds from a radiant point, as from B, Fig. 37, the whole of the rays,—whatever may be their relative obliquity,—are, as we have seen, converged to a focus upon the retina at b, yet the point B is seen only in one direction, in that of the central ray or axis of the cone B b. If we look over the top of a card at the point B, till the edge of the card is just about to hide it; or if, in other words, wre obstruct all the rays that pass through the pupil, excepting the uppermost ray, the point is still seen in the same direction as when it was viewed by the whole cone of rays pro- ceeding from B. If we look, again, beneath the card, in a similar manner, so as to see the object by the lowest ray of the cone, the radiant point will be equally seen in the same direction. Hence, says Sir David Brewster,1' it is manifest that the line of visible direc- tion does not depend on the direction of the ray, but is always per- pendicular to the retina; and, as the surface of the retina is a portion of a sphere, those perpendiculars must all pass through one point, " which may be called the centre of visible direction; because every point of a visible object will be seen in the direction of a line drawn from this centre to the visible point." The point o, Fig. 37, is, in Sir David's view, this centre of visible direction. Where a luminous cone proceeds in the direction of the axis of the eye, the centre of visible direction will fall in that line, and a perpendicular, drawn from the point b, where the rays of the cone meet at a focus on the retina, will pass through this centre of visible direction o, and the same thing, he conceives, will apply to every other pencil of rays. Thus, the rays from D and E, which fall upon the cornea at t, will be refracted so as to impinge upon the retina at s and r respectively, and D and II will be seen in the direction of lines drawn from these points to the centre of visible direction, o. This "law of visible direction," laid down by Sir David Brewster, removes at once, he thinks, every difficulty that besets the subject we have been considering;—the cause of erect vision from an inverted image on the retina. The lines of visible direction neces- a On Single and Correct Vision, by means of double and inverted Images on the Retinae, in Transact, of the Royal Society of Edinburgh, vol. xiii. Edinb. 1836. b Op, citat. p, 246. 220 SENSE OF SIGHT. sarily cross each other at the centre of visible direction, so that those from -the lower part of the image go to the upper part of the object, and those from the upper part of the image to the lower part of the object. The views of Sir David are embraced by Mr. Mayo,a who con- siders them confirmed by the fact—to which reference has already been made—that any pressure, made upon the retina through the eyeball, causes a spectrum to be seen in a direction opposite to the point compressed, as well as by the following experiments of Scheiner, by whom this law of visual direction was first shown. If the head of a pin, strongly illuminated, be viewed with one eye at a distance of four inches, that is, within the common limit of dis- tinct vision, the object is seen large and imperfectly defined, the outermost cone of rays, which enter the pupil from each point, being too divergent to be collected to a focus on the retina. If a card, pierced with a pinhole, be now interposed between the eye and the object, the latter may be seen distinctly defined through the pin- hole, by means of rays that have entered the pupil nearly parallel, with a slightly divergent tendency. But the object may be seen by rays passing either through the upper or lower part, the right or left side, or the centre of the pupil. Upon shifting the card for this pur- pose the object appears to move in an opposite direction. Or, if three pinholes be made, one in the centre, and one at either side, the object appears tripled; and if one of the side holes be closed, the opposite of the three objects disappears: if, for example, the left hand pinhole be closed, the right object disappears. Again, if the head of a pin, strongly illuminated, be viewed at the distance of eighteen inches, its outline is distinct and clear: the rays passing from each point of the object, are brought to a point on the retina, but these rays reach the retina at different angles, and, by interposing a card perforated with a single pinhole, the object may be seen by rays, which enter the upper part, or the lower part, or the centre of the pupil. No change, however, in the visual place of the object occurs in this instance, as the card is shifted; nor is the image multiplied when seen through several pinholes in the card. The last experiment, says Mr. Mayo, proves, that the angle at which rays of light fall upon the retina, does not affect our notion of the place of objects, and, taken with the preceding, establishes as an inductive law, that the retina is so constituted, that, however exerted, each point of it sees in one direction only, that direction being a line vertical to it; or that in every instance of vision, each point of an object is seen in the direction of a line vertical, to the point of the , retina upon which the rays proceeding from it are collected. A certain intensity of light is necessary, in order that the retina may be duly impressed, and this varies in different animals; some of which, as we have seen, are capable of exercising the function * Outlines of Human Physiology, 3d edit. p. 277. ACCIDENTAL COLOURS. 221 of vision in the night, and have hence been termed nocturnal. In man, the degree of light, necessary for distinct vision, varies accord- ing to the previous state of the organ. A person, passing from a brilliantly illuminated room into the dark, is, for a time, incapable of seeing any thing, but this effect differs in individuals; some being much more able to see distinctly in the dark than others. This is owing to the retina, in some, being more sensible than in others; and, consequently, requiring a less degree of light to impress it. On the other hand, a very powerful light injures the retina, and deprives it, for a time, of its function; hence the unpleasant im- pression produced by the introduction of lights into a room, where the company have been previously sitting in comparative obscurity; or by looking at the sun. The effect upon the retina, thus induced, is called dazzling. If the light that falls upon the eye be extremely feeble, and we look long and intensely upon any minute object, the retina is fa- tigued ; the sensibility of its central portion becomes exhausted, or is painfully agitated; and the objects will appear and disappear, acording as the retina has recovered or lost its sensibility; a kind of remission seeming to take place in. the reception of the im- pressions. These affections are considered by Sir David Brewstera as the source of many optical deceptions, which have been ascribed to a supernatural origin. " In a dark night, where objects are feebly illuminated, their disappearance and reappearance must seem very extraordinary to a person whose fear or curiosity calls forth all his powers of observation. This defect of the eye must have been often noticed by the sportsman, in attempting to mark, upon the monotonous heaths, the particular spots where moorgame had alighted. Availing himself of the slightest difference of tint in the adjacent heaths, he endeavours to keep his eye steadily upon it as he advances; but whenever the contrast of illumination is feeble, he almost always loses sight of his mark, or if the retina does take it up a second time, it is only to lose it again." In all these cases, in which the eye has been so long directed to a minute object, that the retina has become fatigued, on turning the axis of the eye slightly away from the object, the light from it will fall upon a neighbouring part of the retina, and the object will be again perceived; and in the mean time the part, previously in action,, will have recovered from its fatigue. By this fact—of the retina becoming fatigued by regarding an object for a long time—we explain many interesting phenomena of vision. If the eye be directed, for a time, to a white wafer, laid upon a black ground, and afterwards to a sheet of white paper, it will seem to have a black spot, of the same size as the wafer upon it; the retina having become fatigued by looking at the white wafer. On the other hand, if the eye be turned to a black wafer, placed 1 Op. citat. p. 250. 19* 222 SENSE OF SIGHT. upon a sheet of white paper, and afterwards to another part of the sheet, a portion of the paper, of the size of the wafer, will appear strongly illuminated;—the ordinary degree of light appearing in- tense, when compared with the previous deficiency. It is on this, that the whole theory of accidental colours, as they are called, rests. When the eye has been, for some time, regarding a particular colour, the retina becomes insensible to this colour; and if, afterwards, it be turned to a sheet of white paper, the paper will not seem to be white, but will be of the colour, that arises from the union of all the rays of the solar spectrum, except the one to which the retina has become insensible. Thus, if the eye be directed for some time to a red wafer, the sheet of paper will seem to be of a bluish green, in a circular spot of the same dimensions as the wafer. This bluish-green image is called an ocular spectrum, because it is impressed upon the eye and may be retained for a short time; and the colour bluish-green is said to be the accidental colour of the red. If this experiment be made with wafers of different colours, other accidental colours will be observed, varying with the colour of the wafer employed, as in the following table:— Colour of the Wafer Accidental Colour, or Colour of the Ocular spectrum. Red, Orange, Yellow, Green, Bluish-green. - Blue. Indigo. Violet, with a little red Blue, Indigo, Violet, Black, - Orange-red. Orange-yellow. Yellow-green. - White. While, Black. If all the colours of the spectrum be ranged in a circle, in the proportions they hold in the spectruni itself, as in the accompany- ing figure,—the accidental co- lour of any particular colour will be found directly opposite. Hence the two colours have been termed opposite colours. It will follow, from what has been said, that if the primary colour, or that to which the eye has been first directed, be added to the accidental colour, the result must be the same im- pression as that produced by the union of all the rays of the spectrum—that of white light. The accidental colour, in other words, is what the primitive colour requires to make it white light. The primitive and accidental colours are, therefore complements of each other; and hence accidental colours have also been called Black •oSrpuj POINT OF DISTINCT VISION. 223 complementary colours. They have likewise been termed harmonic, because the primitive and its accidental colour harmonize with each other in painting/ It has been supposed, that the formation of these ocular spectra has frequently given rise to a belief in supernatural appearances; the retina, in certain diseased states of the nervous system, being more than usually disposed to retain the impressions, so that the spectrum will remain visible for a long time after the cause has been removed. Such appear to be the views of Drs. Ferriar,b Hibbert,0 and Alderson11—the chief writers, in modern times, on apparitions. This subject may be the theme of future discussion. It may be suf- ficient at present, to remark, that the great seat and origin of spec- tral illusions is, in our opinion, the brain, and that the retina is no farther concerned than it is in dreaming or in the hallucinations of insanity. The retina is able to receive visual impressions over its whole surface, but not with equal distinctness or accuracy. When we regard an extensive prospect, that part of it alone is seen sharply, which falls upon the central part of the retina, or in the direction of the axis of the eye: we always, therefore, in our examination of minute objects, endeavour to cause the rays from them to impress this part of the retina;—the distinctness of the impression diminish- ing directly as the distance from the central foramen increases. This central point, called the point of distinct vision, is readily dis- criminated on looking at a printed page. It will be found that although the whole page is represented on the retina, the letter to which the axis of the eye is directed is alone sharply and distinctly seen; and, accordingly, the axis of the eye is directed in succession to each letter as we read. In making some experiments on indistinctness of vision, at a dis- tance from the axis of the eye, Sir David Brewster" observed a singular peculiarity of oblique vision, namely,—that when we shut one eye and direct the other to any fixed point, such as the head of a pin, and hence see all other objects within the sphere of vision in- distinctly,—if one of these objects be a strip of white paper, or a pin lying upon a green cloth, after a short time, the strip of paper or the pin will altogether disappear, as if it were entirely removed— the impression of the green cloth upon the surrounding parts of the eye extending itself over the part of the retina, which the image of the pin occupied. In a short time, the vanished image will re- appear, and again vanish. When the object, seen obliquely, is lumi- nous, as a candle, it never vanishes entirely, unless its light is much weakened, by being placed at a great distance; but it swells, and contracts, and is encircled with a nebulous halo; the luminous im- » Brewster's Optics, edit, cit., and Bostock's Physiology, 3d edit. p. 699, Lond. 1836. b An Essay towards a Theory of Apparitions, Lond. 1813. c Sketches of the Philosophy of Apparitions, Edinb. 1825. i An Essay on Apparitions, &c, Lond. 1823. e Op. citat. p. 248. 224 SENSE OF SIGHT. pressions extending themselves to adjacent parts of the retina not directly influenced by the light itself. From these, and other experiments of a similar character, Sir David infers, that oblique or indirect vision is inferior to direct vision, not only in distinctness, but from its inability to preserve a sustained vision of objects. Yet it is a singular fact, that the indirect has a superiority over direct vision in the case of minute objects, such as small stars, which cannot, indeed, be seen by direct vision. It is a mode, frequently adopted by astronomers for obtaining a view of a star of the last degree of faintness, to direct the eye to another part of the field, and in this way, a faint star, in the neigh- bourhood of a large one, will often become very conspicuous, so as to bear a certain illumination, and yet it will entirely disappear, as if suddenly blotted out when the eye is turned full upon it; and, in this way, it can be made to appear and disappear as often as the observer pleases. Sir J. F. W. Herschel and Sir James South, who describe this method of observation, attempt to account for the phenomenon, by supposing, that the lateral portions of the retina, being less fatigued by strong light, and less exhausted by perpe- tual attention, are probably more sensible to faint impressions than the central ones; and the suggestion carries with it an air of veri- similitude. Sir David Brewster, however,—from the result developed by his experiments, that, " in the case of indirect vision, a luminous object does not vanish, but is seen indistinctly and produces an enlarged image on the retina, beside that which is produced by the defect of convergency in the pencils,"—concludes somewhat mystically, " that a star, seen indirectly, will affect a large portion of the retina from these two causes, and, losing its sharpness, will be more distinct."1 In order that the image of any object may impress the retina, and be perceived by the mind, it must, first of all, occupy a space on the retina, sufficiently large for its various parts to be appre- ciated : in the next place, the image must be distinct or sharp; in other words, the luminous rays, that form it, must converge accu- rately to a focus on the retina: lastly, the image must be sufficiently illuminated. Each of these conditions varies with the size of the body, and the distance at which it is situate from the eye; and there are cases, where they are all wanting, and where the object is consequently invisible. An object may be so small, that the eye cannot distinguish it; because the image, formed on the retina, is too minute. To remedy this inconvenience, the object must be brought near to the eye, which increases the divergence of the rays and the size of the image; but if we bring it too close to the eye, the rays are not all brought to a focus on the retina, and the image is indistinct. If, therefore, an object be so small, that, at the visual point, to be pre- 1 Op. citat. p. 249. DISTINCT VISION. 225 sently mentioned, the rays, proceeding from it, do not form an image of sufficient size on the retina, the object is not seen. To obviate this imperfection of the sense, minute bodies may be viewed through a small hole in a piece of paper or card, or with the instrument called a microscope. By looking through the small aperture in the paper or card, the object may be brought much nearer to the eye; the rays of greatest divergence are prevented by the smallness of the hole from impinging upon the retina; and the rest are converged to a focus upon that membrane, so that a sharp and distinct im- pression is received. The iris is, in this way, useful in effecting distinct vision; the most divergent rays being—by its contracting the pupil—prevented from falling upon the crystalline. Any object, that does not subtend an angle of the sixtieth of a degree, is invisible; but it is obvious that the visual power must differ greatly in individuals. Some eyes are much more capable of minute inspection than others; and a greater facility is acquired by practice. Again, there is a point of approximation to the eye beyond which objects cease to be distinctly seen, in consequence of the rays of light striking so divergently upon the eye, that the focus falls behind the retina. This point, too, varies according to the refractive power of the eye, and is therefore different in different individuals. In the myopic or short-sighted eye, it is much nearer the eye than com- mon ; in the presbyopic or long-sighted, more distant. The iris, here again, plays an important part, by its action in shutting off the most diverging rays, as above described. There is also a limit beyond which objects are no longer visible. This is owing to the light from the object becoming absorbed before it reaches the retina, or so feeble as not to make the necessaiy im- pression. The distance, consequently, at which an object may be seen, will depend upon the sensibility of the retina, and partly on the colour of the object;—a light colour being visible to a greater distance than a darker. A distant object may also be imperceptible, owing to the image, traced on the retina, being too minute to be appreciated, for the image diminishes as the distance of the object increases. The range of distinct vision varies, likewise, with the individual, and especially with the myopic and presbyopic; and in such cases the pupil dilates to admit as much light as possible into the interior of the eye, and to compensate in some measure for the defect. Between the ranges of distant and near vision, a thousand different distances occur, which are seen more or less distinctly. In all cases, however, the ocular cone must be brought to a focus on the retina, otherwise there cannot be perfect vision. It has been already observed, in the proem on light, that the distance, at which the ocular cone arrives at a focus behind the lens, is always in pro- portion to the length of the objective.cone ; or in other words, that the focus of a lens varies with the distance at which a radiant point is situate before it: where the radiant point is near the lens the focus will be more remote behind it, and the contrary. If this 226 SENSE OF SIGHT. occurs in the human eye it must necessarily follow;—either that it is not necessary an object should be impressed upon the retina; or that the eye is capable of accommodating* itself to distances; or if it does not occur, we must admit, that, owing to the particular con- stitution of the eye, the impressions are duly made on the retina, without any necessity for such adaptation. The whole bent of our observations on vision would preclude the admission of the first of these postulates. The second has been of almost universal reception, and has given rise to many ingenious speculations; and the third has been seriously urged of late years only. It would occupy too much space to dwell, at length, upon the various ingenious discussions, and the many interesting and curious experiments, that have resulted from a belief in the power possessed by the eye of accommodating itself to distances. It is a subject, however, which occupies so large a field in the history of physiolo- gical opinions, that it cannot be wholly passed over. The chief views, that have been entertained upon the subject, are:—First. That the cornea or lens must recede from, or approach the retina, according to the focal distance, precisely as we adapt our tele- scopes, by lengthening or shortening the tube. Secondly. If we sup- pose the retina to be stationary the lens must experience a change in its refractive powers, by an alteration of its shape or density; or, Thirdly. In viewing near objects, those rays only may be admitted, which are nearest to the axis of the eye, and which are consequently the least diverging. 1. The hypothesis, that the adjustment of the eye is dependent upon an alteration of the antero-posterior diameter of the organ, or on the relative position of the humours and retina, has been strongly supported by many able physiologists. Blumenbach1 was of opinion, and his views seem to have been embraced by Dr. Hosack,b that the four straight muscles of the eye, by compressing the eyeball, cause a protrusion of the cornea, and thus an increase in the length of the axis. Dr. Monro secundus0 believed, that the iris, recti muscles, the two oblique, and the orbicularis palpebrarum have all their share in the accommodation; and Hamberger, Briggs,d and others, that the oblique muscles, being thrown in opposite directions around it, may have the effect of elongating the axis of the eye. Kepler*5 thought, that the ciliary processes draw the crystalline forwards, and increase its distance from the retina. Descartes1" imagined the same contraction and elongation to be effected by a muscularity of the crystalline, of which he supposed the ciliary processes to be the tendons. Porterfield,» that the corpus ciliare is contractile, and a Instit. Physiolog. § 276, or Elliotson's translation. b Philosoph. Transact, for 1794, p. 196. c Three Treatises on the Brain, the Eye, the Ear, p. 137, Edinb. 1797. d Nova Visionis Theoria, Lond. 1685. 8 Haller, Element. Physiol, xvi. 4, 2. f Opera., Amstel. 1677. s A Treatise on the Eye, the Manner and Phenomena of Vision, Edinb. 1753. ADAPTATION OF THE EYE TO DISTANCES. 227 capable of producing the same effect. Jacobson," that the aqueous humour, by entering the canal of Petit, through the apertures in it, distends the canal, and pushes the crystalline forwards. Sir Eve- rard Home,b that the muscular fibre?, which he has described as existing between the ciliary processes, move the lens nearer to the retina, and that the lens is brought forward by other means, (which he leaves to conjecture,) when the distance of the object is such as to require its being so. Dr. Knox,c that the annulus albus, or the part which unites the choroid and sclerotic coats, is muscular, and the chief agent in this adjustment. Professor Mile,d of Warsaw, that the contraction of the iris changes the curvature of the cornea; whilst Sir David Brewstere thinks it " almost certain, that the lens is removed from the retina by the contraction of the pupil." Without examining these and other views in detail, it may be remarked, that the nicest and most ingenious examination by the late Dr. Youngf could not detect any change in the length of the axis of the eyeball. To determine this, he fixed his eye, and at the same time forced in upon the ball the ring of a key, so as to cause a very accurately defined phantom to extend within the field of per- fect vision; then looking to bodies at different distances, he expected, if the figure of the eye were modified, that the spot, caused by the pressure, would be altered in shape and dimensions; but no such effect occurred; the power of accommodation was as extensive as ever, and there was no perceptible change either in the size or figure of the oval spot. Sir Everard Home, agajn, asserts, that all the ingenuity of the distinguished mechanician, Ramsden, was unable to decide, whether, in the adjustment of the eye, there is any alteration produced in the curvature of the cornea. These facts would alone induce a doubt of the existence of this kind of adjustment, even if we had not the additional evidence, that many animals are incapable of altering the shape of the eyeball, by the muscles at least. The cetacea and the ray, amongst fishes,— and the lizard amongst reptiles, have the sclerotica so inflexible as to render any variation in it impossible. With regard to many of the particular views that have been mentioned, they are mere " cobwebs of the brain," and unworthy of serious argument. In the action of the orbicularis palpebrarum, as suggested by Dr. Monro, there is, however, something so plau- sible, that many persons have been misled by it. He made a set of experiments to show that this muscle, by com- pressing the eyeball, causes the cornea to protrude, and thus enables a Magendie's Precis, i. 78. b Philosoph. Transact, for 1794, 1795, 1796, and 1797; and Lectures on Compara- tive Anatomy, iii. 213, Lond. 1823. c Edinb. Philos. Transact, x. 56, d Magendie, Journal de Physiologie, vi. 166; and Elliotson's Human Physiology, p. 571, Lond. 1840. e Edinburgh Journal of Science, i. 77; and a Treatise on Optics, edit, citat. p, 253. f Philos. Transact, for 1795. 228' SENSE OF SIGHT. the eye to see near objects more distinctly. When he opened his eyelids wide, and endeavoured to read letters, which were so near the eye as to be indistinct, he failed; but when he kept the head in the same relation to the book, and brought the edges of the eyelids within a quarter of an inch of each other, and then made an exer- tion to read, he found he could see the letters distinctly. But, on this experiment Sir Charles Bell1 properly remarks, that if the eyelids have any effect upon the eyeball by their approximation, it must be to flatten the cornea; and that the improvement in near vision pro- duced by such approximation, is owing to the most divergent rays being shut off,—as in the experiment of the pin-hole through paper, —and distinct vision being thus effected. 2. The second hypothesis, which attributes the adaptation to a change of figure in the crystalline itself, has been embraced by all those who regard that body to be muscular: and therefore by Leeuwenhoek and Descartes,b and more lately by Dr. Young.c These muscular fibres, however, could never be excited by Dr. Young, so as to change the focal power; and their existence is more than doubtful. The increasing density of the lens towards the cen- tre indicates rather a cellular structure, the cells being filled with transparent matter of various degrees of concentration ; and an ex- amination into its intimate physical constituents affords no evidence of muscularity. It is somewhat singular, that on a subject where so many oppor- tunities have occurred for establishing the fact definitively, such dif- ference of opinion should exist regarding the question, whether an eye from which the crystalline has been removed, as in the operation for cataract, is capable of adjusting itself to near objects ? Amongst others, Hallerd and Knox decide the question affirmatively; Porter- field, Young, and Travers,e negatively. Magendie, as we have seen, considers the great use of the crys- talline to be,—to increase the brightness and sharpness of the image by diminishing its size. Mr. Travers again, regards adjustment as a change of figure in the lens; not, however, from a contractile power in the part itself, but in consequence of the lamellae, of which it is composed, sliding over each other, when acted upon by external pressure ; whilst upon the removal of this pressure, its elastic nature restores it to its former sphericity. The iris is conceived to be the agent in this process; the pupillary part of the organ being, in the opinion of Mr. Travers, a proper sphincter muscle, which, when it contracts and relaxes, will tend, by the intervention of the ciliary processes, to effect a change in the figure of the lens, which will produce a corresponding change in its refractive power. 3. One of the causes to which the faculty of seeing at different » Anat. and Physiology, Amer. Edit, by Dr. Godman, ii. 227, New York, 1827. b Boerhaav. Praelect. § 527, torn. iv. p. 92; and Haller, Element. Physiol, xvi. p. 2. c Op. citat. and Medical Literature, Lond. 1813. d Element. Physiol, xvi. 4. « A Synopsis of the Diseases of the Eye, London, 1824. ADAPTATION OF THE EVE TO DISTANCES. 229 distances has been ascribed, is the contraction and dilatation of the pupil. It has been already observed, that when we look at near objects, the pupil contracts, so that the most divergent rays do not penetrate the pupil, and the vision is distinct. Hence, it has been conceived probable—by De La Hire,1 Hallerb and others—that the adjustment of the eye to various distances, within the limits of dis- tinct vision, may be effected by this mechanism, in the same man- ner as it regulates the quantity of light admitted into the interior of the organ. Certain it is, that if we look at a row of minute ob- jects, extending from the visual point outwards, the pupil is seen to dilate gradually, as the axis of the eye recedes from the nearest object. An experiment made by the author, when a student of medicine, on his own eye,c has been quoted by Dr. Fleming,*1 as confirmatory of this view. The extract of belladonna has the power, when ap- plied to the eyelids, of dilating the pupil considerably. This was so applied, and in the space of about twenty minutes the pupil was so much dilated, that the iris was almost invisible. From the time that it became preternaturally dilated, objects, presented to this eye with the other closed, were seen as through a cloud. The focus was found to be at twice the distance of that of the sound organ; but, in proportion as the effects of the belladonna went off, and the pupil approached its natural size, vision became more and more distinct, and the focus nearer the natural. In the open air, all objects, except those near, were distinctly seen, but, on entering a room, all was enveloped in mist. There is, indeed, more evidence in favour of the utility of con- traction and dilatation of the pupil in distinct vision, within certain limits at least, than of either of the other supposed methods of adjust- ment ; and, accordingly, the majority of opticians of the present day embrace this view of the subject; but without being able to ex- plain satisfactorily the change in the interior of the eye effected by its movements. " It seems difficult," says Sir David Brewster*5—one of the latest writers on this subject—" to avoid the conclusion, that the power of adjustment depends on the mechanism, which contracts and dilates the pupil; and as this adjustment is independent of the variation of its aperture, it must be effected by the parts in imme- diate contact with the base of the iris. By considering the various ways, in which the mechanism at the base of the iris may produce the adjustment, it appears to be almost certain, that the lens is re- moved from the retina by the contraction of the pupil." The con- clusion, drawn by Sir David, does not, however, impress us with the same degree of certainty. Mullerf thinks it most probable, that the faculty of the eye, which enables it to adjust itself to different distances, depends on an organ, » Memoir, de l'Acad. des Sciences de Paris, torn. ix. b Element. Physiol, torn. v. lib. 16, 4. c Annals of Philosophy, x. 432. d Philosophy of Zoology, i. 187, Edinburgh, 1822. • Op. citat, p. 252. f Elements of Physiology, by Baly, P. v. p. 1150, June 1839. vol. i. 20 230 SENSE OF SIGHT. which has a tendency to act by consent with the iris, but yet is in a certain degree independent of it. Reasoning per exclusionem, he thinks it certainly most probable, that the ciliary body has this motor power, and this influence on the position of the lens; but admits, that we have no positive proof of its possessing contractility. Pouillet, in his lecture before the Faculte des Sciences of Paris,8 explains the matter with no little confidence, by the double effect of the crystalline being composed of different layers, and the mobility of the pupil. These layers being thinner towards the axis of the crystalline than near its edges, by detaching them successively, the curvature of the remainder becomes greater and greater, until the most central portion has the shape of a sphere. Hence, he remarks, such an apparatus will not have one focus only, but several,—as many, in fact, as there are superposed layers;—the foci being nearer and nearer as we approach the central spherical portion. This ar- rangement, he says, enables us to see at all distances, inasmuch as, " having an infinite number of foci at our disposal," we can use the focus that suits the object we are desirous of viewing." If, for example, it be a near object, the pupil contracts, so as to allow the rays to fall only on the central parts; if more distant, the pupil is dilated to permit the rays to pass through a part that has a more distant focus. It is obvious, however, that in such a case, the ordinary inconve- nience of the aberration of sphericity must result; as when the pupil is dilated, the rays must pass through the more marginal, as well as through the central part of the lens. Pouillet himself is aware of this difficulty, but he does not dispose of it philosophically. " It may be said," he remarks, " that in opening the pupil widely, the light is not precluded from passing by the centre, and that a kind of cur- tain would be required to cover the part of the lens, which is unem- ployed. To this I reply, that there is no necessity to prevent the rays from passing by the axis of the crystalline; for, what is the light, which passes through this small space compared with that which passes through the great zone of the crystalline ? It may be looked upon as null." The whole affair, it must be admitted, is enveloped in perplexity, and it is rendered not the less so by the fact, mentioned by Magen- die, that if we take the eye of an albino animal, and direct it towards a luminous object, we find a perfect image depicted on the retina, whatever may be the distance of the object;—the image, of course, being smaller and less luminous when remote, but always distinct. Yet, in this experiment, the eye being dead, there could be neither contraction nor dilatation of the pupil. This result has induced Magendieb—and not too hastily, we think —to draw the conclusion, that although theory may suggest, that there ought to be such adaptation, as has been presumed and attempted a See, also, his Elemens de Physique Expenmerrtale, Paris, 1832, t. iii. p. 331. b Precis Elementaire, i. 72. ADAPTATION OF THE EYE TO DISTANCES. 231 to be accounted for, observation proves, that this is not the fact; and, consequently, all the speculations on the subject, however in- genious they may be, must fall to the ground. Dr. Fletcher, too, after alluding to the various hypotheses on the subject, adds, "It appears absurd to attempt to explain a fact which has no real exis- tence, since it has never been proved that the eyeball has any capa- bility of adapting itself to different distances, or that any such adaptation is required."1 We are, indeed, not justified, perhaps, in admitting more than a slight accommodation from the contraction of the pupil in viewing near objects, effected in the mode already explained. If the accom- modation existed to any material extent, it is difficult to understand, why slight cases of short or long-sightedness should not be rectified. Sir Charles Bellb conceives, " that the mechanism of the eye has not so great a power of adapting the eye to various distances as is generally imagined, and that much of the effect, attributed to me- chanical powers, is the consequence of the motion of the pupil, the effect of light and of attention. An object looked upon, if not attended to, conveys no sensation to the mind. If one eye is weaker than the other, the object of the stronger eye alone is attended to, and the other is entirely neglected: if we look through a glass with one eye, the vision with the other is not attended to." " The mind," he adds, " not the eye, harmonizes with the state of sensation, brightening the objects to which we attend. In looking on a picture or panorama, we look to the figures, and neglect the background; or we look to the general landscape, and do not perceive the near objects. It cannot be an adaptation of the eye, but an accommodation, and asso- ciation of the mind with the state of the impression." The view, which we have expressed upon the subject, is strikingly confirmed by the calculations of M. De Simonoff,e a learned Russian astronomer, who asserts, that from a distance of four inches to in- finity, the changes in the angle of refraction are so small that the apices of luminous cones, in a properly formed eye, must always fall within the substance of the retina, and hence no variation in the shape of the eye, according to the distance of the object, can be necessary. Such facts amply justify the interrogatory of Biotd—whether the aberration of the focus for different distances may not be compen- sated, in the eye, by the intimate composition of the refractive bodies, as the aberration of sphericity probably is 1 Yet, if this be the case, how admirable must be the construction of such an instrument! how far surpassing any effort of human ingenuity! an instrument capable of not only correcting its own aberration of sphericity, and its aberration of refrangibility, but of seeing at all distances.6 a Rudiments of Physiology, Part. iii. p. 48, Edinburgh, 1837. b Anat. and Physiology, edit. cit. ii. 230. c Magendie's Journal de Physiologie, torn, iv, and Precis de Physiologie, i. 73. d Traite de Physiologie Experimental, Paris, 1816. R Letters of Euler, by Sir D. Brewster, Amer. Edit. i. 163, New York, 1833. 232 SENSE OF SIGHT. It has been before observed, that the visual point varies in dif- ferent individuals. As an average, it may be assumed at eight inches from the eye. There are many, however, who, either from original conformation of the organ, or from the progress of age, wander largely from this average; the two extremes constituting myopy or short-sightedness, and presbyopy or long-sightedness. In the myope or short-sighted, the visual point is so close, that objects cannot be seen, unless brought near the eye. This defect is owing to too great a refractive Fig. 39. power in the transparent parts of the organ; or to too great a depth of the humours; or it may be caused by unusual convexity of the cornea or crystalline; or from the retina being too distant from the crystalline. From any one or more of these causes, the rays of light, proceeding from distant objects, are brought to a focus before they reach the retina, and the objects consequently are not distinctly visible. (Fig. 39.) To see them distinctly, they must be placed close to the eye, in order that the rays may fall more diver- gently, and the focus be thrown farther back, so as to impinge upon the retina. The defect may be palliated by the use of concave glasses, which render the rays, proceeding from the object, more divergent. It is by no means unfrequent in youth ; and the myope has been consoled with the common belief, that, in the progress of life, and in the alterations, that take place in the eye from age, he is likely to see well without spectacles, when others of the same age may find them essential. It is probable, however, that this is, in many cases at least, a vulgar error; as we have known different myopic sexage- narians, who have not experienced the slightest improvement in the progress of age. The presbyope, presbytic or long-sighted labours under an opposite defect. The visual point is much more distant than the average; and he is unable to see an ob- Fig. 40. ject unless it is at some dis- ^—^ tance. This condition is owing f >l ______-sssss^n *° *°° ^eeD^e a refractive power V^^^^^S^^^^^^ " hi tne transparent parts of the "^v^^^^^^ eye' *° insufficient depth of the b \? y eye; to too close an approxi- mation between the retina and crystalline; or to too little con- vexity of the cornea or crystalline; so that the rays of light, pro- ceeding from a near object, are not rendered sufficiently conver- gent to impinge upon the retina, but fall behind it. (Fig. 40.) This defect, which is experienced more or less by most people, after middle age, is palliated by the use of convex glasses, which MYOPIC AND PRESBYOPIC EYE. 233 render the rays, proceeding from an object, more convergont, and enable the eye to refract them to a focus farther forward, or on the retina. Although the presbyopic eye is unusual in youth, it is sometimes met with. A young friend, at ten or twelve years of age, was compelled to employ spectacles, adapted to advanced life; and this was the case with several of the members of a family, to whom the arts have been largely indebted in this country. One of them, at twenty, was compelled to wear spectacles which were almost microscopes. Both the myopic and the presbyopic conditions exist in a thou- sand degrees, and hence it is impossible to say, a priori, what is the precise lens, that will suit any particular individual. This must be decided by trial. The opticians have their spectacles arbitrarily numbered to suit different periods of life, but each person should select for himself such as will enable him to read without effort at the usual distance. A degree of myopy may be brought on by long-protracted atten- tion to minute and near objects; as we observe occasionally in the watchmaker and engraver; and again, a person, who has been long in the habit of looking out for distant objects, as the sailor, or the watchman at the signal stations, is rendered less fitted for minute and near inspection. During the domination of Napoleon, when the conscript laws were so oppressive, the young men frequently induced a myopic state of the eye, by the constant use of glasses, of considerable concavity; this defect being esteemed a sufficient ground of exemption from military service. Another question, which has given rise to much disputation and experiment is, why, as we have two eyes, and the image of an object is impressed upon each of them, we do not see such object double V Smithb and Buffonc consider, that in infancy we do see it double; and that it is not until we have learned by experience,—by the sense of touch for example,—that one object only exists, that we acquire the power of single vision. After the mind has thus become in- structed of its error, a habit of rectification is attained, until it is ultimately effected unconsciously. The objections to this hypothesis are many and cogent. We are not aware of any instance on record, in which double vision has been observed to occur in those, who, having laboured under cata- ract from birth, have received their sight by an operation; and we are obviously precluded from knowing the state of vision in the infant, although the simultaneous and parallel motions of the eyes, which is manifestly instinctive, and not dependent upon habit, would induce us to presume, that the images of objects—as soon as the 1 W. Ch. Wells, Essay upon Single Vision with Two Eyes, Lond. 1798. b Optics, Cambridge, 1738. c Memoir, de 1'Academ. des Sciences, 1743. 20* 234 SENSE OF SIGHT. parts have attained the necessary degree of developement—are made to fall upon corresponding parts of the retina. It may, also, be remarked, in favour of the instinctive nature of this parallel motion of the eyes, that in the blind,—although we may find much irregu- larity in the motions of the eyeball, owing to no necessity existing for the eyes being directed to any particular point,—the eyeballs move together, unless some deranging influence be exerted. The truth is, as we have already observed, the encephalon is com- pelled to receive the impression as it is conveyed to it; and even in cases, in which we are aware of an illusion, the perception of the illusion still exists in spite of all experience. If the finger be pressed on one side of the eyeball, an object, seen in front, will appear double, and the perception of two objects wall be made in the brain; although we know from experience, that one only exists. This oc- curs in all the various optical illusions to be presently mentioned. The effect of intoxication has been adduced in favour of this hypothesis. It is said that, in these cases, the usual train of mental associations is broken in upon, and hence double vision results. The proper explanation, however, of this diplopia of the drunkard rests upon other grounds. The effects of inebriating substances on the brain are, to interfere with all the functions of that organ; and most sensibly with the voluntary motions, which become irregularly exe- cuted. The voluntary muscles of the eye partake of this vacillation, and do not move in harmony, so that the impressions are not made on corresponding points of the retina, and double vision necessarily results. Another hypothesis has been, that although a separate impression is made upon each retina,—in consequence of the union of the optic nerves, the impressions are amalgamated, and arrive at the ence- phalon, so as to produce but one perception. This was the opinion of Briggs,1 and Ackermann, and at one time it was generally re- ceived. Dr. Wollastonb supposed the consentaneous motion of the eyes to be connected with the partial union of the optic nerves. The anatomical and physiological facts, relating to the union and decus- sation of these nerves have already engaged us. By a reference to that subject it will be found, that a true decussation takes place between them, that each eye has, notwithstanding, its distinct nerve from origin to termination; and that no such semi-decussation, as that contended for by Dr. Wollaston, probably exists. These facts are unfavourable to this hypothesis of amalgamation of impressions; and besides, if we press slightly on the eye, we have a double im- pression, although the relation of the optic nerves to each other is the same; and, moreover, the same explanation ought to apply to audition, in which we have two distinct impressions, but only a single perception:—yet no one conceives that the auditory nerves decussate. 1 Nova Visionis Theoria, Lond. 1685. b Philos. Transact, for 1824, p. 222. SINGLE VISION. 235 Another opinion has been maintained;—that we do not actually receive the perception of two impressions at the same time, but that vision consists in a rapid alternation of the eyes, according as the attention is directed to one or other of them by accidental circum- stances. Such \iias the opinion of Dutours." A modification of this view was entertained by Le Cat,b who asserts, that, although the right eye is not always the most powerful, it is the most frequently employed; and Gall openly denies, that we use both eyes at the same time, except in the passive exercise of the function. In active vision, he asserts, we always employ one eye only,—sometimes the one and sometimes the other; and thus, as we receive but one im- pression, we necessarily see but one object. In support of this view, he remarks, that, in many animals, the eyes are situate at the sides of the head, so as not to be capable of being directed together to the same object. In them, consequently, one eye can alone be used; and he considers this a presumption that such is the case in man. He remarks farther, that in many cases we use one eye by preference, in order that we may see better; as in shooting or in taking the direction of objects in a straight line, &c.; and that although, in other cases, both eyes may be open, we still use but one. In proof of this, he says, if we place a small object between the eyes and a lighted body, and look at the latter, the shade does not fall between the eyes, on the root of the nose, as it ought to do if the body were regarded with both eyes, but on each eye alter- nately, according as the one or the other is directed to it; and, he adds, if, when we squint voluntarily, we see two objects, it is be- cause one eye sees passively, whilst the other is in activity.0 Amongst the numerous objections to this view of the subject, a few may be sufficient. Every one must have observed how much more vividly an object is seen with both eyes than with one only. The difference indeed according to Jurind is a constant quantity; and in sound eyes of the ordinary degree of power, amounts to one-thirteenth of the whole effect. But we have experiment to show that a distinct impression is made upon each eyef If a solar beam be admitted into a dark chamber, and be made to pass through two glasses of tolerable thickness, but of different colours, placed close alongside each other, provided the sight be good, and the eyes of equal power, the light, which is perceived, will not be of the colour of either of the glasses, but will be of an intermediate shade; and, when this does not happen, it will be found that the eyes are of unequal power. When such is the case, the light will be of the colour of the glass, that is placed before the stronger eye. These results were obtained in the Cabinet de Phy- a Memoir. Presentees a 1'Academie des Sciences, &c. t. iii. and iv. b Op, citat, c Adelon, Physiologie, 2de edit. i. 457, Paris, 1829. d Essay appended to Smith's Optics, Cambridge, 1738; and Haller, Element. Phy- siol, lib. xvi. 4. e Steinheim, in Hecker's Annalen, 1836; and Dublin Journal of Medical Sciences, Jan. 1837. 236 SENSE OF SIGHT. sique of the Faculte de Medecine of Paris, by M. Magendie,1 in the presence of M. Tillaye the younger. The existence of this double impression is proved in another way. If we place any tall, slender object a few feet before us, and examine its relative situation, compared with a spot on .a w#ll in the distance, we find, that if the spot be hidden by the stick, when both eyes are open, it will become visible to each eye, when used singly; and will be seen on the side of the stick corresponding to the eye that is employed. But Prof. Wheatstoneb has instituted experiments, which place this matter entirely at rest. He has shown, that in viewing an object having length, breadth and thickness, the perspective projections upon the two retina? differ according to the distance at which the object is placed before the eyes. If it be placed so distant, that to view it the optic axes must be parallel, the two projections are pre- cisely similar; but if it be placed so near, that to view it, the optic axes must converge, a different perspective projection is presented to each eye, and these perspectives become more dissimilar as the convergence of the optic axes becomes greater. Notwithstanding this dissimilarity between the two pictures, which is in some cases very great, the object is still seen single, although not exactly re- sembling either of the two pictures on the retinae. Having thus established, that the mind perceives an object of three dimensions by means of the two dissimilar pictures projected by it on the two retinae, Mr. Wheatstone inquired, what would be the visual effect of presenting simultaneously to each eye, instead of the object itself, its projection on a plane surface as it appears to that eye 1 For this purpose he invented an instrument, which he calls a stereoscope. It consists of two plane mirrors, with their backs in- clined to each other at an angle of 90°, near the faces of which two monocular pictures are so disposed, that their reflected images are seen by the two eyes, each looking into one of the mirrors on the same place. The experiment may, however, be sufficiently well made by the subjoined figures. \ / \ Fix the right eye on the right-hand figure, and the left eye on . \™6cis' &Cl *• 86> See aIso Dntours, in Mem. Presentees a 1'Academ. iii. 514, and iv. 499. b Philosophical Transactions, P. ii. Lond. 1838. SINGLE VISION. 237 the left-hand figure; hold between the eyes, in front of the nose, the board of an octavo book. The two figures will be seen to approxi- mate, and then run into one, representing the skeleton of a trun- cated four-sided figure in bold reliefs All these facts signally demonstrate, that two impressions are really made in all cases,—one on each eye ;—and yet the brain has perception of but one. If the law of visible direction, which Sir David Brewster has pointed out (see page 219) be adopted, the cause of single vision with two eyes must be admitted as a neces- sary consequence of it. If we are placed at one end of a room, and direct the axis of both eyes to a circular aperture in a window- shutter at the other end, although an image of this aperture may be formed in each eye, yet because the lines of visible direction from similar points of the one image meet the lines of visible direction from similar points of the other image, each pair of similar points will appear as one point, and the aperture seen by one eye will exactly coincide with the aperture seen by the other eye. But if, when an object is seen single with both eyes, we press one eye aside, the image formed by that eye will separate from the other image, and the object will appear double; or, if the axes of both , eyes are directed to a point either nearer or more remote than the aperture in the window-shutter, then, in both of these cases, the aperture will appear double, because the similar lines of visible direction no longer meet at the aperture.b In the course of the preceding remarks, it was said, that the eyes are not always of the same power. The difference is, indeed, some- times surprising. M. Adelon0 mentions the case of a person, one of whose eyes required a convex glass, with a focus of five inches; the other a concave glass with a focus of four inches. In these cases, it is important to use one unassisted eye only; as confusion must necessarily arise from directing both to an object. This is the cause why vVe close one eye in looking through a telescope. The instru- ment has the effect of rendering the focal distance of the two eyes unequal, and of placing them in the same situation as if they were, originally, of different powers. From what has been said it will be understood, that if from any cause, as from a tumour pressing upon one eyeball, from a morbid debility of the muscles, or from a want of correspondence in the sensibility of the two retinae, the eyes are not properly directed to an object, double vision will be the consequence. In almost all cases, however, of distortion of the eyeballs, the image will fall upon a part of one retina, which is more sensible than the portion of the other on which it impinges; the consequence will be, that the mind will a See, on the subject of a single visual perception from two retinal images, some in- teresting remarks, in the British and Foreign Medical Review, No. 19, for July, 1840, p. 16; and Wheatstone, On some remarkable and hitherto unobserved Phenomena of Binocular Vision, in op. cit, b Optics, p. 44, in Library of Useful Knowledge, Natural Philosophy, vol. i. London, 1829, and Treatise on Optics, edit. cit. c Physiologie, edit. cit. i. 459. 238 SENSE OF SIGHT. acquire the habit of attending to the impression on one eye only; and the other will be so neglected, that it will assume a position to interfere as little as possible with the vision of its fellow—so that, although at first, in squinting, there may be a double impression, vision is ultimately single. Buffon,8 who was of this opinion, affirms, that he examined the eyes of many squinters, and found that they were of unequal power; the weaker, in all cases, having turned away from its direction, and generally towards the nose, in order that fewer rays might reach it, and consequently vision be less in- terfered with. Yet, it is always found, if the sound eye be closed, that the other resumes its proper direction; a fact, which disproves the idea of De La Hireb and others, that the cause of strabismus or squinting is a difference of sensibility in the corresponding points of the retinas, and that the discordance in the movements of the organs occurs, in order that the images may still fall upon points of the retinae, that are equally sensible. According to this view, both eyes must of course act. The fact of the diverted eye resuming its proper direction, when the sound one is closed, is of important practical application. Many of the cases of squinting, which occur in infancy, have been induced by irregular action in the muscles of the eyeball; so that some having been, from accident or from imitation, used more frequently than others, the due equilibrium has not been maintained; double vision has resulted; and the affected eye has gradually attained its full obliquity. In these cases, we can, at times, remedy the defect, by placing a bright or conspicuous object in such a position as to exercise the enfeebled muscles; or, we can compel the whole labour of vision to be effected by one eye, and that the affected organ, which, under the stimulus, will be correctly exerted, and thus, by perseverance, the inequality may often be obviated. These indeed are the only cases in which we can expect to afford relief; for if the defect be in the interior of the eye, in a radical want of corre- spondence between the retinae, or in inequality of the foci, it is irre- mediable. It would appear, then, that in confirmed squinting, one eye is mainly, if not solely used, and that vision is single,—that the inclina- tion of one eye inwards may be so great as to deprive it of func- tion, or so slight as to allow the organ to receive rays from the same object as its fellow; but, in either case, it would seem, that they, wrho squint habitually, neglect the impressions on the distorted eye, and see with but one. We have said, that the eyeball of the imperfect eye is drawn towards the nose, in order that as few rays as possible may pene- trate the organ; and the vision of the sound eye be less liable to confusion. Sir Everard Home,c however, conceives that it takes 1 Mem. de l'Academie, 1743. b Ibid. torn. ix. 530; also, Jurin, in Essay appended to Smith's Optics, § 178-194. c Philos. Transact, 1797, and Lectures on Comparative Anatomy, iii. p. 238, Lond, 1823. MULTIPLE VISION WITH ONE EYE. 239 this direction in consequence of the adductor muscle being stronger, shorter, and its course more in a straight line than that of any of the other muscles of the eye; and Sir Charles Bell1 ingeniously applies his classification of the muscles of the eye to an explanation of the same fact. He asserts, that the recti muscles of the eyeball are in activity during attention to the impression on the retina,— but that when the attention is withdrawn, the straight muscles are relieved, and the eyeball is given up to the influence of the oblique muscles, the state of equilibrium between which exists, when the eyeball is turned, and the pupil presented upwards and inwards. Lastly, in persons who are in the habit of taking repeated celes- tial observations, or in those who make much use of the micro- scope, the attention is so entirely directed to one eye, that the other is neglected, and, in time, wanders about, so as to produce squinting at the pleasure of the individual. In these cases, the eyes become of unequal power, so that one only can be employed where distinct vision is required. So far our remarks have been directed to double vision, where both eyes are employed. We have now to mention a very singular fact connected with double and multiple vision with one eye only. If a hair, a needle, or any small object be held before one eye—the other being closed —and within the point of distinct vision, so that the bright light of a lamp or from a window shall fall upon the object, in its passage to the eye, or be reflected from it, we appear to see not one object but many. This fact, when it was first observed by the author, appeared to him to have entirely escaped the observation of opticians and phy- siologists, inasmuch as it has not been noticed in any of the works recently published on optics or physiology. On reference, how- ever, to the excellent " system," of Smith,b on the former subject, he found in the " Essay upon Distinct and Indistinct Vision," by Dr. Jurin, appended to that work, the whole phenomenon explained, and elucidated at considerable length. The elaborate character of the explanation is probably the cause, why the fact has not been noticed by subsequent writers. The best way of trying the experiment is that suggested by Jurin. Take a parallel ruler, and opening it slightly, hold it directly before the eye, so as to look at a window or lamp through the aperture. If the ruler be held at the visual point, the aperture will appear to form one luminous line; but if it be brought nearer to the eye, it will appear double, or as two luminous lines, with a dark line between them ; and according as the aperture is varied— or the distance from the eye—two, three, four, five or more lumi- nous and dark parallel lines will be perceptible. At first sight, it might seem, that this phenomenon should be referred to the diffraction or inflection, which the light experiences * Anat. and Physiol, edit. cit. ii. 235. b Optics, edit, citat 240 SENSE OF SIGHT. in passing by the edges of the small body,—as the hair or needle. Newton had long ago shown, that, when a beam of light shines upon a hair, the hair will cast several distinct shadows upon a screen, and will, of course, present several images to the eye. Dr. Rittenhouse,3 explains, on the same principle, a very curious optical appearance, noticed by Mr. Hopkinson, in which, by the inflection of light, caused by the threads of a silk handkerchief, a multiple image of a distant lamp was presented. The objections, however, to the explanation by inflection are,— that the image always appears single, if the object be not icithin the distance of distinct vision; and, secondly, the same multiple image is presented, when the object is seen by reflection, as when we look at a fine line, drawn upon paper; or at a fine needle held in a bright light. In this case, a considerable number of parallel images of the needle may be seen, all equally or nearly equally distinct, and not coloured. Dr. Jurin considers the phenomena to be caused by fits of easy refraction and reflection of light. Newton demonstrated, that the rays of light are not, in all parts of their progress, in the same disposition to be transmitted from one transparent medium into another; and that sometimes a ray, which is transmitted through the surface of the second medium, would be reflected back from that surface, if the ray had a little farther to go before it impinged upon it. This change of disposition in the rays,—to be either trans- mitted by refraction, or to be reflected by the surface of a transpa- rent medium,—he called their fits of easy refraction, and fits of easy reflection; and he showed, that these fits succeed each other alter- nately at very small intervals in the progress of the rays. Newton does not attempt to explain the origin of these fits, or the cause that produces them; but it has been suggested, that a tolerable idea of them may be formed by supposing, that each par- ticle of light, after its emanation from a luminous body, revolves round an axis perpendicular to the direction of its motion, and presents alternately to the line of its motion an attractive and a repulsive pole, in virtue of which it will be refracted, if the attrac- tive pole be nearest any refracting surface on which it falls, and reflected, if the repulsive pole be nearest the surface. A less scientific notion of the hypothesis has also been suggested; by supposing a body with a sharp and a blunt end passing through space, and successively presenting its sharp and blunt ends to the line of its motion. When the sharp end encounters any soft body it penetrates it: but when the blunt end encounters the same body, it will be reflected or driven back. In applying this to the phenomenon in question, Jurin presumes, that the light, in passing through the humours of the eye, expe- riences these fits of easy refraction and easy reflection. This will ■ Amer. PhiloF. Transact., vol. ii. MULTIPLE VISION WITH ONE EYE. 241 From the point A, be understood by the marginal figure, Fig. 41, suppose a num- ber of rays of JV. 4]. light to proceed and to impinge, with different de- grees of obliqui- ty, on the denser medium, B C; all the rays, which are in fits of easy refraction, will pass through the medium to the point D ; whilst those that are in fits of easy re- flection, will be thrown back into the medium ABC; so that we may presume, that all the rays, which fall upon the parts of the medium B C, corresponding to the bases of the dark cones will be reflected back, whilst those, that correspond to the bases of the light cones, will pass to a focus at D. Now, if all the bundles of rays, transmitted through the surface B C, be accurately collected into a focus, no other consequence will arise from the other bundles of rays having been reflected back, than that the focus will be less luminous, than it would have been had all the rays been transmitted through it. This explains why, at the distance of distinct vision, we have only a single im- pression made on the eye. But if we approach the object A, so that the focus is not thrown,—say upon the screen R T, which may be presumed to represent the retina—but behind it; the dark and light spaces will be repre- sented upon the screen, and, of course, in concentric circles. This happens to the eye, when the hair or needle or other object is brought nearer to it than the visual point. We can thus understand, why concentric circles, of the nature mentioned, should be formed upon the retina; but how is it, that the objects seen preserve their linear form ? Suppose a b, Fig. 42, to be a luminous cone, which in a fit of easy refraction has im- pinged upon the retina: and A B, b a, the concentric circles, corresponding to the rays, that have been reflected. It is vol. 1. 21 Fig. 42. 242 SENSE OF SIGHT. obvious, that every point of the object, will be the centre of so many concentric circles'on the retina; and if we imagine the fits of easy reflection and refraction to be the same around those points, we shall have the dark and lucid lines represented by the tangents to these circles; and hence we can comprehend why, instead of having one lucid line e f, we have three, separated by dark lines parallel to them ; and if the light from the luminous point be strong enough to form more lucid rings than are represented in Fig. 42, and the breadth of those rings be not too minute to be perceived, we may have the appearance of five, seven, or more lucid lines, separated by parallel dark lines. We proceed now to consider the advantages, which the mind derives from the possession of this sense, so pre-eminently entitled to the epithet intellectual. Its immediate function is to give us the sensation of light and colour. In this it cannot be supplied by any of the other senses. The action is, therefore, the result of organization; or is a "law of the constitution;" requires no education; but is exercised as soon as the organ has acquired the proper developement. Yet, occa- sionally, we meet with singular cases, in which the eye appears to be totally insensible to certain colours, although capable of per- forming the most delicate functions of vision. Sir David Brewster1 has collected several of these cases from various sources. A shoe- maker, of the name of Harris, at Allonby, in Cumberland, could only distinguish black and while; and, whilst a child, could not discri-^ minate the cherries on a tree from the leaves, except by their shape and size. Two of his brothers were almost equally defective. One of them constantly mistook orange for grass green, and light green for yellow. A Mr. Scott, who describes his own case,b mistook pink for a pale blue, and a full red for a full green. His father, his ma- ternal uncle, one of his sisters, and her two sons, had all the same defect. A Mr. R. Tucker, son of Dr. Tucker, of Ashburton, mis- takes orange for green, like one of the Harrises; and cannot dis- tinguish blue from pink, but almost always knows yellow. He mistakes red for brown, orange for green, and indigo and violet for purple. A tailor at Plymouth, whose case is described by Mr. Harvey,6 of Plymouth, regarded the solar spectrum as consisting only of yellow and light blue; and he could distinguish, with cer- tainty, only yellow, white and gray. He regarded indigo and Prus- sian blue as black, and purple as a modification of blue. Green puzzled him exceedingly; the darker kinds appearing to him brown, and the lighter kinds a pale orange. On one occasion he repaired an article of dress with crimson instead of black silk; and on another occasion, patched the elbow of a blue coat with a piece of crimson cloth. A still more striking case is given by Dr. Nichollsd of a * Optics, edit. cit.; Letters on Natural Magic; and art. Optics, in Library of Useful Knowledge. b Philos. Trans, for 1778. e Edinb. Phil. Transact, x. 253. d Medico-Chirurgical Trans, vii. 477, ix. 359. INSENSIBILITY OF THE EYE TO COLOURS. 243 person in the British navy, who purchased a blue uniform coat and waistcoat, with red breeches to match. Sir David Brewster refers to a case that fell under his own observation, where the gentleman saw only the yellow and the blue colours of the spectrum. This defect was experienced by Mr. Dugald Stewart,1 who was unable to perceive any difference between the colour of the scarlet fruit of the Siberian crab and that of its leaves. Dr. Dalton,b the chemist and philosopher, could not distinguish blue from pink by daylight; and, in the solar spectrum, the red was scarcely visible; the rest of it appearing to consist of two colours, yellow and blue. Mr. Troughton, the optician, was fully capable of appreciating only blue and yellow; and when he named colours, the terms blue and yellow corresponded to the more or less refrangible rays;—all those that belong to the former, exciting the sensation of blueness; and those that belong to the latter, that of yellowness. Dr. Hays,c who has collected the history of numerous cases of achromatopsia,—as this defect has been termed,—and has added the history of one which fell under his own care,d was led to infer, from all his researches; 1, that entire inability of distinguishing colours may co-exist, with perfect ability to perceive the forms of objects ; 2, that the defect may extend to all but one colour, and in such case the colour recognised is always yellow; and, 3, that the defect may extend to all but two colours, and in such case the colours recognised are always yellow and blue. The opinions of philosophers have varied regarding the cause of this singular defect in eyes otherwise sound, and capable of perform- ing every other function of vision in the most delicate and accurate manner. By some, it has been presumed to arise from a deficiency in the visual organ ; and by such as consider the ear to be defective in function, in those that are incapable of appreciating musical tones, this deficiency in the eye is conceived to be of an analogous nature. " In the sense of vision," says Dr. Brown,e " there is a species of defect very analogous to the want of musical ear,—a defect which consists in the difficulty, or rather the incapacity, of distinguishing some colours from each other—and colours which, to general ob- servers, seem of a very opposite kind. As the want of musical ear implies no general defect of mere quickness of hearing, this visual defect, in like manner, is to be found in persons who are yet capable of distinguishing, with perfect accuracy, the form, and the greater or less brilliancy of the coloured object; and I may remark, too, in confirmation of the opinion, that the want of musical tone depends a Elements of the Philosophy of the Human Mind, ch. iii. b Manchester Memoirs, v. 28. c Proceedings of the American Philosophical Society for August 21, 1840. ■i Amer. Journal of the Medical Sciences, August, 1840, p. 277. See, also, Seebeck, in Puggenilorf's Annalen., 42; and Midler's Physiology, by Baly, p. 1213, Part v. Lond. ] 839; also, some elaborate communications on the subject by Victor Szokalski, in Bullet. Med. Beige, Fevrier, 1840, p. 35, Mars, 1840, p. 64, Avril, 1840, p. 98, and Mai, 1840, p. 129. e Lectures on the Philosophy of the Human Mind, vol. i., Boston, 1826. 244 SENSE OF SIGHT. on causes not mental but organic, that in this analogous case some attempts, not absolutely unsuccessful, have been made to explain the apparent confusion of colours by certain peculiarities of the external organ of sight." Dr. Dalton, who believed the affection to be seated in the physical part of the organ, has endeavoured to explain his own case, by supposing that the vitreous humour is blue, and therefore absorbs a great portion of the red and other least refrangible rays, and Sir David Brewster, in the Library of Useful Knowledge? appears to think, that it may depend upon a want of sensibility in the retina, similar to that observed in the ears of those who are incapable of hearing notes above a certain pitch; but as this view is not con- tained in his more recent Treatise on Optics, it is probably no longer considered by him to be satisfactory. The defect in question—difficult as it is to comprehend5—has always appeared to us entirely cerebral, and to strikingly resemble, as Dr. Brown has suggested, the " want of musical ear." As we have already endeavoured to establish that the latter is dependent upon a defective mental appreciation, the parity of the two cases will, of course, compel us to refer the visual defect, or the want of the " faculty of colouring," to the same cause. It has been re- marked, that the eye in these cases exercises its function perfectly, as regards the form and position of objects, and the degree of illumi- nation of their different portions. The only defect is in the imperfect conception of colour. The nerve of sight is probably accurately impressed, and the deficiency is in the part of the brain whither the impression is conveyed, and where perception is effected, which is incapable of accurately appreciating those differences between rays, on which their colour rests ;c and this we are glad to find is the view taken of it by one of the most eminent philosophers of the present day, Sir J. F. W. Herschel.d The mediate or auxiliary functions of vision are numerous; and hence, the elevated rank that has been assigned to this sense. By it, we are capable of judging, to a certain extent, of the direction, position, magnitude, distance, surface, and motion of bodies. Meta- physicians have differed greatly in their views on this subject; the majority believing, that, without the sense of touch, the eye is inca- pable of forming any accurate judgment on these points; others, that the sense of touch is no farther necessary than as an auxiliary; and that a correct appreciation could be formed by sight alone. The a Natural Philosophy, vol. i.—Optics, p. 50, Lond. 1829. b Purkinje, art. Achromatopsia in Encyclopadisch. Worterbuch der Medicinischen Wissenschaften, u. s. w. Band i. S. 261, Berlin, 1828 ; and Brewster's Optics, edit. cit. p. 261. c Elliotson, Lancet, July 14, 1838; and Human Physiology, p. 582, Lond. 1840; and Victor Szokalski, Bulletin Medical Beige, Fevrier, 1840, p. 43, and Mai, 1840, p. 136. d Encyclopaedia Metropolitana, art. Light. APPRECIATION OF DISTANCES. 245 few remarks that may be necessary on this subject, will be deferred until the physical and other circumstances, which enable us to judge of distance, &c, have been canvassed. The direction or position of objects has already been considered, so far as regards the inverted image, formed by them on the retina. The errors that arise on this point are by no means numerous, and seldom give rise to much inconvenience. The direction of the light that impinges on the retina, is always referred, as we have attempted to demonstrate, in the direction of a line, drawn from the luminous point through the centre of visible direction. Whenever, therefore, the luminous cone meets with reflection or refraction, before reach- ing the eye, the retina conveys erroneous information to the senso- rium, and we experience an optical illusion. To ascertain the magnitude, distance, and surface of bodies, we are obliged to take into consideration several circumstances con- nected with the appearance of the object—such as its apparent size, the intensity of light, shade, and colour, the convergence of the axes of the eyes, the size or position of intervening objects, &c. Porterfield1 enumerates six methods, which are employed in ap- preciating the distance of objects—1. Their apparent magnitude; 2. The vivacity of their colours ; 3. The distinction of their smaller parts; 4. The necessary conformation of the eye for seeing dis- tinctly at different distances; 5. The direction of their axes; and 6. The interposition of objects. Dr. Brownb reduces them to three—1. The difference of the affec- tions of the optic nerve; 2. The different affections of the muscles, employed in varying the refracting power of each eye, according to the distance of objects, and in producing that particular inclina- tion of the axes of the two eyes, which directs them both equally on the particular object; and 3. The previous knowledge of the dis- tance of other objects, " which form, with that we are considering, a part of one compound perception." Lastlv, Dr. Arnottc enumerates four modes by which this is ef- fected—1. The space and place, Fig. 43. occupied by ob- jects in the field of view, measured by what is termed the visual angle. 2. The intensity of light, shade, and colour. ' 3. The divergence of the rays of light—and 4. The convergence of the axes of the eyes. This enumeration may be adopted with some * A Treatise on the Eye, ii. 409, Lond. 1759. b Lectures on the Philosophy of the Human Mind, vol. i. Boston, 1826. c Elements of Physics, 2d Amer. Edit. vol. ii. P. i. p. 175, Philad. 1836. 21* 246 SENSE OF SIGHT. slight modifications. The circumstances, in our opinion, to be con- sidered, are:— 1. The visual angle, or that formed by two lines, which shave the extremities of an object and cross at the centre of the crystalline; so that the visual angle, subtended by the object, as a d, Fig. 43, is exactly equal to that subtended by its image i u on the retina. It is obvious, from this figure, that if all objects w^ere equidistant from the1 eye, and of the same magnitude, they would subtend the same angle; and, if not of the same magnitude, the difference would be accurately indicated by the difference in the visual angle subtended by them; thus, the comparative size of the two crosses a d and b d is represented by that of the images i u and i o. The cross c e, however, which is twice the size of b d, subtends the same visual angle, and is alike represented on the retina by the image i o. It is clear, then, that the visual angle does not, under such circumstances, give us a correct idea of the relative magnitudes of bodies, unless we are acquainted with their respective distances from the eye; and, conversely, we cannot judge accurately of their distances, without being aware of their magnitudes. A man on horseback, when near us, subtends a certain visual angle, but, as he recedes from us, the angle becomes less and less; yet we always judge accurately of his size, because aware of it by experience; but if objects are at a great distance, so as not to admit of their being compared with nearer objects by simple vision, we are in a constant state of illusion—irresistibly believing, that they are much smaller than they really are. This is the case with the heavenly bodies. The head of a pin held close to the eye will sub- tend as large a visual angle as the planet Jupiter, which is one thou- sand two hundred and eighty-one times bigger than this earth, and is eighty-six thousand miles in diameter. In like manner, a five-cent piece, held at some distance from the eye, will shut off the sun, although its diameter is eight hundred and eighty-eight thousand miles. The sun and moon, again, by subtending nearly the same visual angle, appear to us of nearly the same size; and the illusion persists in spite of our being aware of the mathematical accuracy, with which it has been determined, that the former is ninety-six millions of miles from us, and the latter only two hundred and forty thousand. The visual angle, again, subtended by an object, differs greatly according to the position of the object. A sphere has the same appearance or bulk, when held at a certain distance from the eye, whatever may be the position in which it is viewed; and, accord- ingly, the visual angle, subtended by it, is always identical. Not so, however, with an oval. If held, so that the rays from one of its ends shall impress the eye, it will occasion a circular image, and subtend a much smaller angle than if viewed sideways, when the image will be elliptical, or oval. The same thing must occur with every object, whose longitudinal and transverse diameters differ. It is obvious, that if any such object be held in a sloping position to- APPRECIATION OF DISTANCES. 247 wards the eye, it will appear more or less shortened; precisely in the same manner as the slope of a mountain or inclined plane would appear much greater, if placed perpendicularly before the eye. This appearance is what is called foreshortening; and it may be eluci- dated by the following figure. Suppose a man to be standing on a level plain, with his eye at c, looking down on the plain. The por- tion of the surface a d, which is next to him, will be seen without any foreshortening; but if we suppose him to regard successively the portions d f, f g, and g b of the plain, the angle, subtended by each portion, will di- minish ; so that if the an- gle a c d be 45°, d c f will be 18°; f c g 8°, and so on; until, at length, the obliquity will be so great, that the angle becomes inappreciable. This is the cause why, if we look obliquely upon a long avenue of trees, we are unable to see the intervals between the farthest in the series; although that between the nearest to us may be readily distin- guished. In all paintings, of animals especially, the principle of foreshorten- ing has to be rigidly attended to: and it is owing to a neglect of this, that we see such numerous distorted representations—of the human figure particularly. It has been already stated, that objects appear smaller according to their distance; hence, the houses of a street, or the trees of an avenue, that are nearest Fig. 45. are to us, or in the fore- ground, will form the lar- gest images on the retina, and there will be a gra- dual diminution, so that, if we could imagine lines to be drawn along the tops and bottoms of the objects, and to be suffi- ciently prolonged, they would appear to meet in a point, as in Fig. 45. The art which traces ob- jects, with their various degrees of apparent diminution on account of distance, and of fore- shortening on account of obliquity of position, is called perspective. 2. The intensity of light, shade, and colour.—It has been shown, that the intensity of light diminishes rapidly, according to the dis- tance of the body, from which it emanates; so that it is only one- fourth as powerful when doubly distant, one-sixteenth when quad- ruply distant, and so on. This fact is early recognised; and the 248 SENSE OF SIGHT. mind avails itself of it to judge, with much accuracy, of relative distances. It is, however, a pregnant source of optical illusions. In a bright sunshine, the mountains appear much nearer to us than when seen through the haze of our Indian summer? In a row of lamps along a street, if one be more luminous than the rest, it will seem to be the nearest; and, in the night, we incur the strangest errors, in judging of the distance of any luminous body. The sky appears nearer to the earth directly above, than it does towards the horizon ; because the light from above having to pass only through the atmosphere, is but slightly obstructed, whilst a por- tion only of that, which has to pass through the dense heterogeneous air, near the surface of the earth, arrives at the eye. The upper part of the sky being, therefore, more luminous, seems nearer; and, in the same manner, we explain, in part, why the sun and moon appear larger at rising and setting. The shade of bodies keeps pace with their intensity of light; and accordingly, the shadows of objects near us, are strongly defined;— whilst in the distance they become confused, and the light altogether so faint, that the eye at last sees an extent of distant blue mountain or plain; " appearing bluish," says Dr. Arnott,b " because the trans- parent air, through which the light must pass, has a blue tinge, and because the quantity of light arriving through the great extent of air is insufficient to exhibit the detail." " The ridge called Blue Mountains," he adds, " in Australia, and another of the same name in America, and many others elsewhere, are not really blue, for they possess all the diversity of scenery, which the finest climates can give; but to the discoverer's eye, bent on them from a distance, they all at first appeared blue, and they have ever since retained the name." As regards the Blue Ridge of America, Dr. Arnott probably labours under misapprehension. Within a very few miles from the whole of this extensive chain, as well as from a distance, the blue tinge is perceptible, especially when the air is dense and clear, soon after the sun has descended behind it; so that the name is as appro- priate in the vicinity as it was when " the discoverer's eye was bent on it from a distance." It is obvious, that without the alternation of light and shade we should be unable to judge, by the eye, of the shape of bodies; to dis- tinguish a flat circle from a globe; or any of the prominences and depressions, that are every where observable. The universe would a A delightful season, in the southern and western parts of North America more especially, generally occurring in October or November; and having nothing similar to it, so far as we are aware, in any other part of the globe. It is dependent upon some meteorological condition of the atmosphere, and occurs only when the wind is southerly, or from the warmer regions; disappearing immediately as soon as it veers to the north. By some, this phenomenon has been supposed to be caused by the large fires in the western prairies; but the warmth that attends the haze cannot be explained on this hypothesis, independently of other sufficient objections to it. b Op. cit. vol. ii. P. i. p. 203. APPRECIATION OF DISTANCES. 249 appear a flat surface, the outlines of which would not even be per- ceptible ; and the only means of discriminating objects would be by their difference of colour. It is partly by attending to the varying intensity of light and shade, that the painter succeeds in representing the near as well as the distant objects in an extensive landscape: those in the foreground are made bold and distinct; whilst the remote prospect is made to become gradually less and less distinct, until it fades away in the distance. This part of his art is called aerial perspective. 3. Convergence of the axes.—When objects are situate at a mode- rate distance from us, we so direct the eyes, that if the axes were prolonged they would meet at the object. This angle will, of course, vary inversely as the distance; so that if the axes be turned to a nearer object, the angle will be greater; if to one more distant, less. By this change in the direction of the axes the mind is capable of judging, to a certain extent, of near distances. A definite mus- cular effort is required for each particular case; and the difference in the volition necessary to effect it enables the brain to discrimi- nate, precisely in the same manner as it judges of the height of a body, by the muscular action., required to carry the axis from one extremity of the object to the other.1 We have the most satisfactory evidence, that-such convergence of the axes is indispensable for judging accurately of distance, in near vision. If we fix a ring to a thread suspended from a beam, or attach it to a stand, and endeavour, with one eye closed, to pass a hook, fixed to the extremity of a rod four or five feet long, into the ring, we shall find it impracticable unless by accident or by touching the ring with the rod. The hook will generally be passed on the far or near side of the ring; but if we use both eyes, we can readily succeed. They, however, whose eyes are of unequal power, cannot succeed with both eyes. The fact is strikingly corroborated by the difficulty experienced by those who have lost an eye. Magendie6 says it sometimes takes a year, before they can form an accurate judgment of the distance of objects placed near the eye. We know, however, one or two interesting examples, in which the power was never regained; not- withstanding every endeavour to train the remaining organ. It need scarcely be said, that the convergence of the axes is no guide to us in estimating objects, which are at such a distance, that the axes are nearly parallel,—as the sun and moon, or any of the celestial luminaries. 4. The interposition of known objects.—Another mode of esti- mating the magnitude or distance of objects is, by a previous knowledge of the magnitude or distance of interposed or neigh- bouring objects; and if no such objects intervene, the judgment we form is extremely inaccurate. This is the reason, why we are so deceived in the extent of an unvaried plain or in the distance at » Sir C. Bell, in Philos. Transact, for 1833. b Precis, &c. i. 88. 250 SENSE OF SIGHT. which a ship, on the ocean, may be from us: it is also another cause, why the sky appears to us to be nearer at the zenith than it is at the horizon. The artist avails himself of this means of judging of magnitude in his representations of colossal species of the animal or vegetable kingdom, or of the works of human labour and ingenuity; by placing a well known object alongside of them as a standard of comparison. Thus, the representation of an elephant or a giraffe might convey but imperfect notions to the mind, without that of his keeper being added as a corrective. It is in consequence of the interposition of numerous objects, that we are able to judge more accurately of the size and distance of those that are on the same level with us, than when they are either much above or much below us. The size and distance of a man on horseback are easily recog- nised by the methods already mentioned, when he is riding before us on a dreary plain; the man and horse appearing more dimi- nutive, but, being seen in their usual position, they serve as mutual sources of comparison. When, however, the same individual is viewed from an elevated height, his apparent magnitude, like that of the objects around him, is strikingly less than the reality.1 The apparent diminution in the size of objects seen from a height is not to be wholly explained by the foreshortening, which deprives us of our usual methods of judging. It is partly owing to the ab- sence of intervening bodies; and still more perhaps to our not being accustomed to view objects so circumstanced. Similar remarks apply to our estimates of the size and distance of objects placed considerably above us. A cross, at the summit of a lofty steeple, will not appear more than one-fourth of its real size, making allowance for the probable distance; yet a singular ano- maly occurs here:—the steeple itself seems taller than it really is, and every one supposes that it would extend much farther along the ground, if prostrated, than it would in reality. The truth, however, is, that if the steeple were laid along the ground, unsurrounded by objects to enable us to form an accurate judgment, it would appear to be much shorter than when erect, on the principles of foreshorten- ing, already explained. The cause of this small apparent magni- tude of the cross and upper part of the steeple is, that they are viewed without any surrounding objects to compare with them: 1 Beautifully and accurately is this effect depicted by the great dramatist:—. " How fearful And dizzy 'tis to cast one's eyes so low! The crows and choughs, that wing the midway air, Show scarce so gross as beetles. Halfway down Hangs one that gathers samphire; dreadful trade! Methinks he seems no bigger than his head. The fishermen, that walk upon the beach, Appear like mice; and yon tall anchoring bark, Diminish'd to her cock; her cock a buoy Almost too small for sight," King Lear. APPRECIATION OF THE MOTION, ETC. OF BODIES. 251 they, therefore, seem to be smaller than they are; and, being smaller, the mind irresistibly refers them to a greater distance. For these reasons, then, it becomes necessary, that figures, placed on lofty columns, should be of colossal magnitude. It is owing partly to the intervention of bodies, that the sun and moon appear to us of greater dimensions, when rising or setting, although the visual angle, subtended by them, may be the same. "The sun and moon," says Dr. Arnott,1 "in appearance from this earth are nearly of the same size, viz:—each occupying in the field of view about the half of a degree, or as much as is occupied by a circle of a foot in diameter, when held one hundred and twenty- five feet from the eye—which circle, therefore, at that distance, and at any time, would just hide either of them. Now, when a man sees the rising moon apparently filling up the end of a street, which he knows to be one hundred feet wide, he very naturally believes, that the moon then subtends a greater angle than usual, until the reflection occurs to him, that he is using, as a measure, a street known, indeed, to be one hundred feet wide, but of which the part concerned, owing to its distance, occupies in his eye a very small space. The width of the street near him may occupy sixty degrees in his field of view, and he might see from between the houses many broad constellations instead of the moon only; but. the width of the street afar off may not occupy, in the same field of view, the twentieth part of a degree, and the moon, which always occupies half a degree, will there appear comparatively large. The kind of illusion, now spoken of, is yet more remarkable, when the moon is seen rising near still larger known objects,—for instance, beyond a town or a hill which then appears within a luminous circle." Such are the chief methods by which we form our judgment of the distance and magnitude of bodies;—1st, by the visual angle— 2dly, by the intensity of light, shade, and colour—3dly, by the con- vergence of the axes of the eyes—and 4thly, by the interposition of known objects. The eye also enables us to appreciate the motion of bodies. This it does by the movement of their images upon the retina ; by the variation in the size of the image; and by the altered direction of the'light in reaching the eye. If a body be projected with great force and rapidity, we are inca- pable of perceiving it;—as in the case of a shot fired from a gun, especially when near us. But if it be projected from a distance, as the field of view is very extensive, it is more easy to perceive it. The bombs, sent from an enemy's encampment, can be seen far in the air for some time before they fall, in the darkness of night; and affords objects for interesting speculation regarding their probable destination. To form an accurate estimation of the motion of a body, we must a Op. cit. vol. ii. p. 196. 252 SENSE OF SIGHT. be ourselves still. When sailing on a river, the objects, that are stationary on the banks, appear to be moving, whilst the boat, which is in motion, seems to be at rest. Bodies, that are moving in a straight line to or from us, scarcely appear to be in motion. In such cases, the only mode we have of detecting their motion is by the gradual increase in their size and illumination, when they approach us; and the converse, when they are receding from us. If at a distance, and the visual angle between the extreme points of observation be very small, the motion of an object will likewise appear extremely slow; hence the difference between a carriage dashing past us in the street, and the same object viewed from a lofty column. A balloon may be moving along at the rate of nearly one hundred miles per hour; yet, except for its gradual diminution in size and in intensity of light, it may appear to be a't rest; and, when bodies are extremely remote from us, however astonishing may be their velocity, it can scarcely be detected. Thus, the moon revolves round the earth at the rate of between thirty and forty miles a minute—above forty times swifter than the fleetest horse; yet her motion, during any one moment, completely escapes detec- tion; and the remark applies still more forcibly to those luminaries, which are at a yet greater distance from the earth. These are cases in which the body moves with excessive velocity, yet the image on the eye is almost stationary; but there are others, in which the real motion is extremely slow, and cannot be at all observed, as that of the hour-hand of a clock or watch. It will be obvious, from all the remarks that have been made, regarding the information derived by the mind from the sense of sight, that a strictly intellectual process has to be executed, without which no judgment can be formed; and that nothing can be more erroneous than the notion,—at one time prevalent,—that the method by which we judge of distance, figure, &c, is instinctive or dependent upon an original " law of the constitution," and totally independent of any knowledge gained through the medium of the external senses. It has already been remarked, that metaphysicians may be considered as divided into those, who believe that, without the sense of touch, the eye would be incapable of forming any accurate judgment on these points; and those, who think, that the sense of touch is no farther necessary than as an auxiliary, and that a correct appreciation can be formed by sight alone. Molyneux,1 Berkeley,b Condillac,0 &c, support the former view; Gall,d Adelon,6 &c, the latter. Of the precise condition of the visual perception, during early infancy, we are of course entirely ignorant. So far as our own re- collections would carry us back, we have always been able to form a Locke's Essay on the Human Understanding, book ii. chap. 9. b Essay on Vision, 2d edit., Dublin, 1709. c Traite des Sensations, Part i. d Sur les Fonctions du Cerveau, i. 80, Paris, 1825. e Physiologie de I'Homme, edit. cit. i. 466. APPRECIATION OF MAGNITUDE, ETC. 253 a correct judgment of magnitude, distance, and figure. Observa- tion, however, of the habitudes of infants would seem to show, that their appreciation of these points—especially of distance—is singularly imprecise, but whether this be owing to the sense not yet having received a sufficient degree of assistance from touch, or from want of the necessary developement in the structure or func- tions of the eyeball or its accessory parts, we are precluded from judging. The only succedaneum is the information to be obtained, regard- ing their visual sensations, from those who have been blind from birth, and have been restored to sight by a surgical operation. Although in the numerous operations of this kind, which have been performed, it might seem, that cases must have frequently occurred for examining into this question, such is not the fact; and metaphysicians and physiologists have generally founded their observations on the celebrated case described by Cheselden.1 The subject of this was a young gentleman, who was born blind, or lost his sight so early, that he had no remembrance of ever having seen, and was " couched," so says Cheselden, " between thirteen and fourteen years of age." Magendieb affirms, that there is every reason to believe that the operation was not that for cata- ract, but consisted in the incision of the pupillary membrane. It need hardly be remarked, that Cheselden must be the best possible authority on this subject. " When he first saw," says Cheselden, " he was so far from making any judgment about distances, that he thought all objects whatever touched his eyes, (as he expressed it,) as what he felt did his skin, and thought no objects so agreeable as those which were smooth and regular, though he could form no judgment of their shape, or guess what it was in any object that was pleasing to him. He knew not the shape of any thing, nor any one thing from another, however different in shape or magnitude; but upon being told what things were, whose form he before knew from feeling, he would carefully observe, that he might know them again; but having too many objects to learn at once, he forgot many of them; and, (as he said,) at first he learned to know, and again forgot a thousand things in a day. At first he could bear but very little light, and the things he saw he thought extremely large; but, upon seeing things larger, those first seen he conceived less, never being able to imagine any lines beyond the bounds he saw; the room he was in, he said, he knew to be but part of the house, yet he could not conceive that the whole house could look bigger." A much more interesting case, in many respects, than this of Cheselden's, which has always appeared to us too poetical, was laid before the Royal Society of London, in 1826, by Dr. Wardrop.0 It was that of a lady born blind, who received sight at the age of a The Anatomy of the Human Body, 13th edit., Lond. 1792. b Precis, &c. i. 95. c Philos. Transact. 1826, p. 529. vol.i. 22 254 SENSE OF SIGHT. forty-six, by the formation of an artificial pupil. During the first months of her infancy, this lady was observed to have something peculiar in the appearance of her eyes; and, when about six months old, a Parisian oculist operated on both eyes, with the effect of complete destruction of the one, and not the slightest improve- ment to the other. From this time, she continued totally blind, being merely able to distinguish a very light from a very dark room, but without the power of perceiving even the situation of the window through which the light entered, though, in sunshine or bright moonlight, she knew its direction; she was, therefore, in greater darkness than the boy in Cheselden's case, who knew black, white, and scarlet, apart from each other; and, when in a good light, had that degree of sight, which usually exists in an eye affected with cataract; whilst in this lady the pupil was completely shut up, so that no light could reach the retina, except such rays as could pass through the substance of the iris. After a third operation had been performed, for the formation of an artificial pupil, she returned from Dr. Wardrop's house in a carriage, with her eyes covered with only a loose piece of silk. The first thing she noticed was a hackney-coach passing by, when she exclaimed, " What is that large thing that has passed by us ?" In the course of the evening she requested her brother to show her his watch, and she looked at it a considerable time, holding it close to her eye. " She was asked what she saw, and she said there was a dark and a bright side; she pointed to the hour of twelve and smiled. Her brother asked her if she saw any thing more; she replied yes, and pointed to the hour of six, and to the hands of the watch. She then looked at.the chain and seals, and observed that one of the seals was bright, which was the case, being a solid piece of rock crystal." On the third day she observed the doors on the opposite side of the street, and asked if they were red. They were of an oak colour. In the evening, she looked at her brother's face, and said she saw his nose; he asked her to touch it, which she did; he then slipped a handkerchief over his face, and asked her to look again, when she playfully pulled it off, and asked, " What is that ?" On the thirteenth day, she walked out with her brother in the streets of London when she distinctly distinguished the street from the foot pavement, and stepped from one to the other, like a person accustomed to the use of her eyes. " Eighteen days after the last operation," says Dr. Wardrop, " I attempted to ascertain, by a few experiments, her precise notions of the colour, size, and forms, posi- tion, motions and distances of external objects. As she could only see with one eye, nothing could be ascertained respecting the ques- tion of double vision. She evidently saw the difference of colours ; that is, she received and was sensible of different impressions from different colours. When pieces of paper, one and a half inch square, differently coloured, were presented to her, she not only distinguished them at once from one another, but gave a decided preference to some colours, liking yellow most, and then pale pink. APPRECIATION OF MAGNITUDE, ETC. 255 It may be here mentioned, that, when desirous of examining an object, she had considerable difficulty in directing her eye to it, and finding out its position, moving her hand as well as her eye in various directions, as a person, when blindfolded or in the dark, gropes with his hand for what he wishes to touch. She also dis- tinguished a large from a small object, when they were both held up before her for comparison. She said she saw different forms in various objects, which were shown to her. On asking what she meant by different forms, such as long, round, and square, and desiring her to draw with her finger those forms on her other hand, and then presenting to her eye the respective forms, she pointed to them exactly ; she not only distinguished small from large objects, but knew what was meant by above and below; to prove which, a figure drawn with ink was placed before her eye, having one end broad, and the other narrow, and she saw the positions as they really were, and not inverted.(!!) She could also perceive motions; for when a glass of water was placed on the table before her, on approaching her hand near it, it was moved quickly to a greater distance, upon which she immediately said, ' you move it; you take it away.' She seemed to have the greatest difficulty in finding out the distance of any object; for, when an object was held close to her eye, she would search for it by stretching her hand far beyond its position, while on other occasions she groped close to her own face for a thing far remote from her." We have given the particulars of this case at some length, inas- much as they are regarded by Dr. Bostock3—and apparently by Dr. Wardrop himself—as strikingly confirmatory of those of Che- selden, than which we cannot imagine any thing more dissimilar. It will have been noticed, that, from the very first after the recep- tion of sight, she formed an imperfect judgment of objects, and even of distances, although she was devoid of the elements necessary for arriving at an accurate estimate of the latter—the sight of both eyes. This was, doubtless, the chief cause of that groping for objects, which is described by Dr. Wardrop. Of forms, too, she must have had at least an imperfect notion, for we find, that, on the thirteenth day after the operation, she stepped from the elevated foot-pavement to the street, " like a person accustomed to the use of her eyes." The case is, we think, greatly in favour of the view, that the sight does not require much education to judge with tolerable accu- racy of the position, magnitude, distance, surface, and motion of bodies; and that, by a combination of the methods we have already pointed out, or of some of them, this imperfect knowledge is ob- tained, without the aid of any of the other senses; but is of course acquired more easily and accurately with their assistance, espe- cially with that of touch. What other than visual impressions could have communicated to the mind of Miss Biffin—whose case was referred to under another head—the accurate and minute informa- 11 Physiology, 3d edit. p. 703, Lond. 1836. 256 SENSE OF SIGHT. tion, which she possessed regarding the bodies surrounding her, at all distances? Or how does the animal, immediately after birth, acquire its knowledge of distance? We observe the young of some animals immediately after they are extruded from the uterus, turn round and embrace the maternal teat; whilst others, as the partridge, follow the mother immediately after they have burst the shell. The experience required for obtaining an imperfect knowledge of distance, shape, &c. must, therefore, be trifling; although an accu- rate acquaintance may demand numerous, and careful comparisons. This first degree of knowledge is probably obtained, by comparing the visual angle with the intensity of light, shade, and colour—the more accurate appreciation following the use of the other methods already described. That the convergence of the axes requires education is demonstrated in the case of the infant. It has been remarked, that the eyeballs harmonize instinctively in their parallel motions; but the convergence requires an effort of volition, and it is some time before it can be effected, which is probably the great cause of the mal-appreciation of near distances, which we notice in the infant; whilst it seems to exhibit its capability of judging more correctly of objects, that are somewhat more remote, and where less convergence, and, consequently less muscular effort is necessary. The numerous optical illusions, which, we have been compelled to describe, in the progress of the preceding remarks, will render it necessary to refer to but few under this head. It has already been said, that we lay it down as a rule, that the progress of light to the eye is always in a straight line from the luminous object; and, accordingly, if the course of the rays be modified before they reach the organ, we fall into an optical illu- sion. Such modifications arise either from the reflection or refrac- tion of the rays proceeding from the object that causes the sensa- tion. By reflection of the rays, we experience the illusion caused by mirrors. A ray of light, K C, Fig. 22, falling upon a plane mirror, I J, is reflected back in the same line; but, as we have seen, the object will not appear to be at K, but at E. Again, a ray of light, proceeding obliquely from B, and impinging on a plane mirror at C, will be reflected in the direc- Fig. 46. tion of C A; but to the eye at A, the object B will appear to cj... '"*".....-.... ^ be at H, in the prolongation of the ray that reaches the eye. If the mirror be concave, the object will appear magni- Dj.....- fied, provided the light from the upper part of the object, as A B, Fig. 46, be reflected to an eye at F, and that from the lower part of the object meet the other at this point. To an eye so placed, the object will appear magni- OPTICAL ILLUSIONS. 257 fied and seem to be at C D, or in the prolongation of the rays which fall upon the cornea. If the mirror, as in Fig. 47, be convex, for like reasons, the cross will seem to be smaller. The cornea constitutes a mirror of this class, in which we have an accurate miniature representation of objects. Rays, that are refracted in passing Fig. 47. through different media, also give rise to visual illusions. We have seen, that the ray from an object at F, Fig. 23, in the ..[.*.'..........._ pool of water, I J, does not proceed into j the air in the direction of F C O, but in ; ....- that of the line F C A; and if we suppose ":" the eye to be placed at A, the object will not be seen at F, but will appear to be at /; the pool will, consequently, appear shallower than it really is, by the space at which/is situate above the bottom. We can now understand why rivers should appear shallower than they really are, when viewed obliquely; and why the lower end of a pole, immersed in water, should, when seen obliquely, appear to be bent towards the surface. In shooting fish in the water, or'in attempting to harpoon them, this source of error has to be cor- rected. Those birds, too, that live upon the inhabitants of the water, will have to learn, from experience, to obviate the optical illusion; or to descend perpendicularly upon their prey, in which direction, as we have seen, no refraction takes place. Similar remarks apply to the fish that leap out of the streams to catch objects in the air. The Chcetodon rostratus, about six or eight inches long, frequents the sea-shores in the East Indies: when it observes a fly, sitting on the plants that grow in shallow water, it swims to the distance of five or six feet, and then, with surprising dexterity, ejects out of its tubular mouth a single drop of water, which never fails to strike the fly into the sea, where it soon becomes its prey.1 Hommel—a Dutch governor—put some of these fish into a tub of water, and then pinned a fly on a stick within their reach. He daily saw the fish shoot at the fly, and, with such dexterity, that they never failed to hit their mark.b Pallas describes the Sicena jaculatrix as securing flies by a similar contrivance.0 If the light, before reaching the eye, passes through bodies of a lenticular shape, it undergoes modifications, which have given occa- sion to the formation of the useful instruments, that have been devised for modifying the sphere of vision. If the lens be double convex, the body, seen through it, appears larger than it is, from the illusion, so often referred to, that we always refer the object in the direction of the line, that impinges upon the retina. The object, a Fleming's Philos. of Zoology, i. 195. b Philos. Trans, liv. 89. c Ibid. Ivi. 186; also, Mr. Sharon Turner's Sacred History of the World, Amer. Edit. i. 205, New York, 1832. 22* *&~ 258 SENSE OF SIGHT. consequently, appears to be greatly augmented. (See Fig. 29.) For the same reasons an object seems smaller to the eye at A, Fig. 26, when viewed through a double concave lens. Again, if the light, before reaching the cornea, is made to pass through a diaphanous body, which is itself coloured, and conse- quently allows only the rays of its own colour to traverse it, the object is not seen of its proper colour, but of that of the transparent body. An impression of light continues to affect the retina for the sixth part (M. D'Arcy says the seventh part,) of a second. If, therefore, a live coal be whirled round a circle, six or seven times in a second, it will seem to be a continuous circle of fire. It is owing to this circumstance, that meteors seem to form a line of light,—as in the case of the falling star,—and that the same impression is conveyed by a sky-rocket in its course through the air. We have an elucida- tion of this fact in the instrument or toy—called, by Dr. Paris, the thaumatrope—which consists of a circle, cut out of a card, and having two silken strings attached to opposite points of its diameter: by twisting these with the finger and thumb the card may be twirled round with considerable velocity. On one side of the card an object is drawn—as a chariot—and on the other, the charioteer. If the card be twirled round six or seven times in a second, the cha- rioteer will be seen in the chariot, the duration of the impressions on the retina being such as to cause the figures, drawn on both sides of the card, to be seen at the same time. The phantasmascope and anorthoscope act upon similar principles. Lastly,—it is by accurate attention to various optical illusions, and to the laws of the animal economy on which they are founded, that many of them can be produced in the arts at pleasure. Paint- ing is, in truth, little more than depicting on canvass the various optical errors, which we are habitually incurring. To conclude,—the sense of sight differs materially in the scale of animals: in few is the organization more perfect or the function better executed than in man. Situate at the upper and anterior part of the body, it is capable of directing its regards over a large extent of surface; of converging the axes of the two organs upon" objects in various situations, which cannot be effected by many animals; and it is very movable, and under the domination of a muscular apparatus of admirable arrangement. Still, it is not as delicately organized as in some animals, which are capable of seeing objects at a distance, that would be totally beyond the reach of the visual powers of man. Like the other senses, sight can be exerted actively and passively; hence the difference between simply seeing and looking. In the latter, the eye is directed to the object by the proper muscles; and it is not improbable but that the nerve may be aroused to a more accurate and delicate reception of impressions, as we have some reason for believing it to be in the case of the other senses. Like them, it admits of great improvement by education. The painter, ADDITIONAL SENSES. 259 and the worker in colours are capable of great discrimination, and detect the minutest shades of difference with the greatest facility. In savage life, where the tracks or marks through the almost interminable forests, or over the pathless wilds, are the only guides, the greatest acuteness of vision is necessary; and, accordingly, we find the North American Indian, in this respect, eminently dis- tinguished. The mariner, too, accustomed to look out for land, or for a hos- tile sail, will detect it in the distant horizon long before it can be perceived by the landsman, and will appreciate its distance and course with signal accuracy,—education, in this case, not only com- municating to his eye facility in being impressed, but improving the intellectual process, by which he arrives at the estimation of distances. ADDITIONAL SENSES. The five senses, which have been considered, constitute so many special nervous systems, each concerned in its appropriate function; and, although conveying ideas of the external world to the brain, and connected with that organ, to a certain extent independent of it. The generality of physiologists admit only these five; but some have suggested others, differing, in general, however, from the five, in having no organ at the surface of the body exclusively concerned in the function. Buffon regarded as a sixth sense, the intense sen- sation experienced during the venereal act; but this can only be esteemed a peculiar variety of tact in the mucous membrane of the genital organs ;—differing from ordinary tact in those parts, by requiring in both sexes a special condition of the membrane; and, in the male, one such, that the sperm, when excreted, shall make the necessary impression upon it; and, consequently, appertaining to both the external and internal sensations;—the state of the mem- brane being referable to the latter, and the effect of the contact of the sperm to the former. Some have spoken of a sense of heat and cold:—this we have described under the head of tact;—others of a muscular sense, by which we acquire a knowledge of the motions to which muscular contractions give rise, and thus learn to apportion the effort to the degree of effect to be produced. The animal magnetizers, again, have suggested a sixth sense, to which man owes the capability of being acted upon by them : but this is entirely supposititious, and the facts admit of a more ready and satisfactory explanation. A sense of hunger has been described as situate at the upper orifice of the stomach:—a sense of thirst in the oesophagus, and a pneumatic sense in the lungs; but all these are more properly internal sensations. The German physiologists have suggested another sense, which they term ccencesthesis.* This is not seated in any particular part of 1 Gemeingefuhl, gemeinsinn, kor per gefuh'I, lebenssinn, individual itatssinn, and s e lb stgef ah 1 ("common feeling, common sensation; bodily feeling, feeling of life, sense of life,'sense of individuality, and self- feeling.")' 260 ADDITIONAL SENSES. the body, but over the whole system, and hence termed " common." It is indicated by the lightness and buoyancy, which we occasion- ally experience, apparently without any adequate cause; as well as by a sense of lassitude and fatigue, unconnected with muscular action or disease. To it likewise, belongs the involuntary shudder- ing, glow, or chillness, experienced under similar circumstances. It is manifestly one of the numerous internal sensations felt by the frame, and every portion of it, according as they are in a perfect state of health, or labouring under some cause of irritation or op- pression ; but can scarcely be regarded as an additional or sixth sense." Again; it has been supposed, that certain animals may possess other senses than the five we have mentioned. Of this we can have no positive evidence. We are devoid of all means of judging of their sensations; and if we meet with an additional organ, which seems adapted for such a purpose, we have nothing but conjec- ture to guide us. Under the sense of touch it was said, that Spallanzani found the bat capable of avoiding obstacles, placed in its way intentionally, when the eyes, nostrils, and ears had been closed up; and it readily returns to the holes in the caverns to which it is habituated. Spallanzani supposed, that this was owing to its being possessed of a sixth sense. We have seen, that the circum- stance is explicable by these animals being possessed of unusual delicacy of touch. Again; the accuracy with which migratory animals return to their accustomed haunts has given rise to the notion of a sense of locality, which is presumed to preside over this faculty. This is, doubtless, however, a cerebral faculty. Quadrupeds, the ape not excepted, have two bones in the face, in addition to those found in man. These contain the roots of the dentes incisores, when such are present; but they exist in animals also that are destitute of teeth. They are termed ossa intermaxil- laria, ossa incisoria, and ossa labialia, and are situate, as their names import, at the anterior part of the jaw, and between the ossa maxillaria or jaw bones. Jacobsonb considers them to be an organ of sense, as they communicate with the exterior, and are largely supplied with vessels and nerves. Accordingly, this has been es- teemed a sensitive apparatus, connected with the season of love in animals; and, by other naturalists, as a sense, intermediate between those of taste and smell, and intended to guide the animal in the proper selection of food. It need hardly be said, that this is all imaginary.0 a Dissert, praes. J. Chr. Reil. resp. Fr. Chr. Hubner. Hal. 1794; Greiner, art. Gemein- gefilhl, in Pierer's Anat. Phys. Worterb. iii. 489, Leipz. 1819; Purkinje, art. Ccenses- thesis, in Encyclopad. Worterb. der Medicinischen Wissenschaften, viii. 116, Berlin, 1832; Hempel's Einleitung in die Physiologie und Pathologie, &c. s. 459, Gotting. 1828; and Puchelt, System der Medicin, Th. i. s. 173; Heidelb. 1835; Mailer's Ele- ments of Physiology, by Baly, P. v. p. 1087, Lond. 1839. b Annales du Musee, xviii. 412. c Magendie, Precis Elementaire, i. 158; Richerand, Etemens de Physiologie, 6dit. 13eme par M. Berard aine; edit. Beige, p. 213; Bruxelles, 1837; Roget's Animal and INTERNAL SENSATIONS. 261 Adelon,a it was remarked, makes two divisions of the external sensations:—these that convey information to the mind; and those that do not. The former have engaged attention; the latter will not occupy us long. They comprise but two—itching and tickling. Both of these occur in the skin and mucous membranes, and near the communication of the latter with the skin; or, in other words, near the termination of the outlets which they line. Itching, however, is not always an external sensation,—that is, not always caused by the contact of a body external to it. It frequently arises from an altered condition of the organic actions of the part in which it is experienced, as in cutaneous affections; in itching at the nose produced by irritation in the intestinal canal; itching at the glans penis in cases of calculi of the urinary bladder, &c, but com- monly the sensation is caused by an extraneous body; and we are irresistibly led to scratch, no matter how it may be produced. When it arises extraneously, it can generally be readily allayed; but, when dependent upon a morbid condition of the texture of the part, it becomes a true disease, and the source of much suffering. If the itching be accompanied with a feeling of motion, or of purring in the part, it is called tingling. This kind of purring often occurs without itching. Tickling or titillation is always caused by the contact of some extraneous substance, and is therefore a true external sensation. Although occurring in the skin, and in the commencement or ter- mination of the mucous membranes, all parts are not equally suscep- tible of it: and some,—as the lining membrane of the genital organs, —are only, or chiefly so, under particular circumstances. The sides, palms of the hands, and soles of the feet, are the most sensitive in this respect; not, perhaps, because the nerves are more numerous in those parts, but because, owing to thinness or supple- ness of skin, or to other inappreciable circumstances, they are more susceptible of this kind of excitation. We find, too, that individuals differ as much as the parts of the body do in this respect: some being not ticklish, or incapable of being thrown into the spasm, which the act, nay, even a threatening of the act, produces in others. Cases are on record, in which prolonged titillation has produced general convulsions, and even death. Le Catb terms it an herma- phroditic sensation, inasmuch as, on the one hand, it excites laughter; and, on the other, is insupportable; and, consequently, appears to be intermediate between pleasure and pain, b. Internal Sensations. The external sensations make us acquainted with the universe surrounding us; and convey to the mind a knowledge of every thing Vegetable Physiology, Amer. Edit. ii. 399, Philad. 1836; and Bostock's Physiology, 3d edit. p. 734, Lond. 1836. a Physiologie de I'Homme, 2de edit. i. 481, Paris, 1829. b Traite des Sens, Paris, 1767. 262 INTERNAL SENSATIONS. that can be, in any manner, inservient to our necessities. Such necessities have, however, to be suggested to the mind, before it reacts through the aid of the organs of prehension or otherwise on external bodies, and this is accomplished by the agency of the internal or organic sensations. Without the intervention of any external cause, every organ of the body is capable of transmitting to the brain a number of different impressions, many of which impel the organ to acts that are neces- sary not only for the preservation of the individual and of the spe- cies, but also for the perfect developement of the faculties. Such are the sensations of hunger and thirst; the impulse that leads to the union of the sexes; and the feeling we have of the necessity for intermission in the exercise of the muscles and of the intellect. They have been divided into three species by some physiologists: the first arousing, or giving impulse to, the action of organs ; and warning the brain of the different necessities of the system. They have been called wants or instinctive desires.* Such are, hunger, thirst, the desire to evacuate the urine and faeces; that of respiration, the venereal appetite, accouchement, &c. They belong to those that arise, when it is necessary the organs should act. The second species occur during the action of organs. They are often obscure, but sometimes very acute. Amongst these are the impressions accompanying the different excretions,—as that of the sperm, urine, &c. (although, as we have seen, these partly belong to the external sensations); the impressions that warn us of our partial or general movements, of the progress of digestion, and of the intellectual labours. The last species succeed to the action of organs, especially when such action has been too long continued; hence the inward feeling of fatigue, after too long exertion of the functions of the senses, of the intellectual and moral faculties, and of the organs of muscular motion ; the necessity of repose after prolonged muscular exertion ; and of sleep, to recruit the nervous system, and to fit it for the exer- tions it has to make during the waking condition. The mode in which these sensations are effected is analogous to that of the external sensations. There is an impression on the part to which the sensation is referred; an action of perception, accom- plished by the brain, and one of transmission, executed by a nerve passing between the two parts. The two last actions are probably executed in the same manner as they are in the external sensations. The first, or the mode in which the impression is effected, and the character of the impression itself, are much more obscure. In the external sensations, we can refer the impression to a known irritant, —special in some of the senses:—more general in others. We know, that light impresses the retina:—aerial undulations the acoustic nerve, &c.: but, in the internal sensations or sentiments, as some of 8 Adelon, art. Besoins, in Diet, de Medecine, i. 367, Paris, 1821; and Physiologie. de I'Homme, i. 482, MORBID SENSATIONS. 263 the French writers term them, the source of the irritation is in some modified action of the part itself, in the very tissue of the organ, and hence the result 'is said to be organic. In the internal sensation of hunger, for example, the impression is engendered in the organ,— how, we know not,—is thence conveyed to the brain; and the sen- sation is not effected until the latter has acted. The same may be said of all the other internal sensations. They differ, in other respects, from the external sensations. Whilst the latter may be entirely passive, or be rendered active by volition, without either action being the cause of particular pleasure or inconvenience, the former are but little influenced by volition. Constituting the wants—the instinctive desires—which impel to acts, that are necessary for the preservation and full developement of the individual and of the species, such independence is of course essen- tial. On many of them, however, habit or accustomed volition has a certain degree of influence: and they can unquestionably be aug- mented or moderated by licentious indulgence or restraint. The influence of habit is exemplified by the regularity with which the appetite returns at stated intervals; and by the difference between that of the gourmand and of the temperate individual. It is most strikingly evidenced, however, in its influence over the moral wants; which may even spring up from social indulgence, and hence are not instinctive or organic: we are every day, indeed, compelled to notice the striking difference between the individual, who practises restraint upon his wants, and the libertine, who, like the animals surrounding him, gives unbridled sway to his natural and acquired appetites. All the internal sensations, when satisfied or responded to in moderation, communicate a feeling of pleasure; but if resisted, pain results. If hunger be prolonged, there is a general feeling of uneasiness, which rapidly abates after food is received into the stomach in due proportion; but if satiety be produced, uneasiness follows; and this applies to all the appetites or wants. The particular internal sensations will engage us, when the func- tions to which they belong fall under consideration. Like the external sensations they must, of course, administer to the intellect; to an extent which will be seen hereafter. Their influence and nature were entirely neglected, until of comparatively late years: but attention has been directed to them chiefly through the labours of Cabanis" and of Destutt-Tracy,b and they now form subjects for interesting speculation with the metaphysician. The morbid sensations belong more particularly to pathology: a brief notice of them will consequently be all that is necessary here. They are comprised under the term pain. In its enlarged significa- tion, this word, as is well known, means every uneasy or disagree- able sensation or moral affection;—thus including sadness, anger, terror, as well as the painful impressions felt in the extremities or a Rapport du Physique et du Morale de I'Homme, torn, ii., Paris, 1802. b Elemens d'Ideologie, 2de edit., Paris, 1804. 264 MENTAL FACULTIES. trunks of the nerves. It is the latter only—or physical pain—that concerns us at present. Like every other sensation, although it may be referred exclu- sively to the part impressed, pain requires the intervention of the brain: for if the nerves, proceeding from a part to that organ, be cut, tied, compressed, or stupified by narcotics; or if the action of the brain itself be blunted from any cause, as by the use of opium, or by any compression, accidental or other, the sensation is no longer experienced. We can thus undersand why pain is less felt during sleep; and the astonishing cases of resistance to pain, which we witness in the lunatic, and in religious or other enthusiasts, who have been subjected to bodily torture. An opposite condition of the nervous system is the cause of the great sensibility to impressions, which we witness in the nervous and hysterical. It is obvious, that pain may be either an external or internal sen- sation, according as the cause of irritation is extraneous, or seated in the tissue of organs; and that it must vary considerably, both as regards the precise irritant, and the part affected; hence the difference between the pain caused by a burn, and that by a cutting instrument; and the immense variety of pains to which the human frame is subject, and the attentive study of which is so indispensa- ble to the pathologist. So much for the sensations.* These, we have seen, are innume- rable, for each sense is capable of myriads of different impressions. We now pass to the consideration of those functions which enable man—although worse provided with means of defence and offence than the beasts surrounding him, and possessing no covering, to protect him from the solar heat or the winter's cold—to provide himself means of defence; to render, the animals around him sub- servient to his use; to cover his nakedness and protect himself against atmospheric changes; to devise every mechanical art; to fathom the laws, that govern the bodies by which he is surrounded, and to establish himself undisputed master of the earth. II. OF THE MENTAL FACULTIES. The external senses convey to the brain the different impressions, made upon them by surrounding bodies; but, of themselves, they would be unable to instruct the mind regarding the universe. It is necessary, that the brain should act before any perception, any idea of them, can exist. The mental faculties, in other words, convert the impressions into such ideas. The internal sensations, on the other hand, consist, as we have seen, of the numerous wants and appetites, necessary for the preservation of the individual and of the species. In addition to these, man possesses another series of faculties, which influence his character and disposition, and direct a See, on the Sensations in General, Gerdy, Archives Gen6rales de M^decine, Oct. MENTAL FACULTIES. 265 his social existence: these are the affective or emotive faculties, or the faculties of the heart. The study of these different mental and moral phenomena em- braces, what has been called, psychology, from a notion that they are exclusively dependent upon the mind. This notion was, at one time, universal, and hence the appellation metaphysician, applied to such as were considered to proceed in their investigations of those subjects beyond what was physical, material, or corporeal. There is no subject, which has given occasion to so much excite- ment and controversy, as that of the connexion of the mental facul- ties with the encephalon. " It has unfortunately happened," says Dr. Bostock," " that this subject, which is one of great interest and curiosity, has seldom been viewed with that philosophical spirit which should always direct our investigations, and by which alone we can expect to arrive at truth. It is admitted, that certain errors may be so interwoven with our accustomed associations, on topics connected with morals and religion, as to render it doubtful, on some occasions, how far we ought to attempt their removal: but if this concession be made on the one hand, it is incumbent upon us, on the other, not to inflame the prejudices, which may exist on these topics, but to use our endeavours to correct all undue excitement, and thus to bring the mind into that tranquil state, which may enable it to receive truth without fear of injury." In such a spirit ought every discussion on this interesting subject to be conducted; and in such a spirit will the few remarks, which we have to make, be offered. The chief opinions, which have been indulged on this subject, are, —1st. That all the mental phenomena are immaterial and the exclu- sive product of the mind. 2dly. That the sentient principle, within us, requires the intervention of an organ, through which it acts; in other words, that mind is a principle superadded to organization ; and 3dly. That where there is no organization there is no percep- tion:—that wherever an organized structure, like the brain, exists, perception exists; that where the organization is imperfect, percep- tion is imperfect; where the organization is sound and vigorous, perception is clear and vigorous; where it is impaired, perception" is impaired; and that, when the organization ceases, perception ceases also. This last view is materialism. It supposes that a cer- tain condition of matter is capable of thinking, reasoning, and understanding. The doctrine,—that our intellectual and moral acts are superadded to organization, during life, and that there is an organ of the body concerned in their manifestation,—is the one embraced by the gene- rality of physiologists, and is most consistent with reason and analogy; it is but justice, however, to admit that the views of those, who consider that a certain organization produces thought, are not deserving of the anathemas which have been directed against Ihem • Physiology, 3d edit. p. 744, Lond. 1836. vol. i. 23 266 MENTAL FACULTIES. on the score of irreligion. The charge would rather apply to those who could doubt the power of Omnipotence to endow matter with such attributes.* Were the mental and moral phenomena the exclusive products of the immaterial principle within us, they would hardly form subjects for physiological inquiry. That they are allied to organization is in- ferred for the following reasons. As they constitute so many func- tions, were they not provided with an organ or organs, they would form so many exceptions;—each of the sensations requiring an organ for its accomplishment. Again, our inward feeling induces us to refer them to a particular part of the frame; whilst thought appears to us to be effected within the head, the chief effects of the passions are felt in the region of the heart or stomach. The faculties, more- over, are not the same in every individual. One man is a poet, an- other a mathematician; or one is benevolent, another cruel. If these faculties were the exclusive product of the mind, and of course not to be ascribed to diversity of organization, we should have to admit, that each individual has a different immaterial principle, and of course, that there must be as many kinds as there are individuals. Lastly. The faculties vary in the same individual according to circumstances. They are not the same in the child as in the adult; in the adult as in one advanced in life; in health as in disease; in waking as in sleep. During an attack of fever they become tem- porarily deranged, and permanently so in all the varieties of insanity. These facts are inexplicable under the doctrine, that they are the exclusive product of the mind or immaterial principle. An immate- rial or spiritual principle ought to be immutable; yet we should have to suppose it capable of alteration; of growing with the growth of the body, and of becoming old with it; of being awake or asleep; sound or diseased. All these modifications are impressed by vary- ing organization—of the brain in particular. We may conclude, then, that the intellectual and moral faculties are not the exclusive product of the mind, but that they require the intervention of an organ. That this organ is the encephalon, or a part of it—the brain—is announced by many circumstances. In the first place, they are phenomena of sensibility, and hence we should be disposed to refer them to a nervous organ; and being the most elevated phenomena of the kind, to the highest of the ner- vous organs. In the second place, inward feeling induces us to refer them thither. We not only feel the process there, during meditation, but the sense of fatigue, which succeeds to hard study, is experienced there likewise. The brain, again, must be in a state of integrity, otherwise the faculties are deranged; or, for the time, abolished. In fever, the brain becomes affected directly or indirectly, and the consequence * Elliotson's Human Physiology, chap. xix. p. 360, Lond. 1840. MENTAL FACULTIES. 267 is—perversion of the intellect, in the form of delirium. If the organ be more permanently disordered, as by the pressure of an exostosis or of a tumour, or by some alteration in its structure or functions —less appreciable in its nature—insanity, in some of its forms, may be the result. In serious accidents to the encephalon, we observe the importance of the cerebral organ to the proper exercise of the mental faculties most clearly evinced. A man falls from a height, and fractures his skull. The consequence of this is depression of a portion of bone, which exerts a degree of compression upon the brain; or extravasa- tion of blood from some of the encephalic vessels, attended with similar results. From the moment of the infliction of the injury, the whole of the mental and moral manifestations are suspended, and do not return until the compressing cause is removed, by the operation of the trephine. Richerand cites the case of a female, who had a portion of the brain accidentally exposed, and in whom it was found, that pressure upon the brain completely deprived her of all conscious- ness, which was not restored until the pressure was removed. A similar case occurred to Professor Wislar; and another is related by Lepelletier.* A patient of a Dr. Pierquien had an extensive caries of the os frontis, with a perforation of the bone, which exposed the brain covered by its membranes. When she slept soundly the organ sank down; when she dreamed, or spoke with feeling, a tur- gescence and marked oscillations were perceptible; when the brain was pressed upon she stopped in the middle of a sentence or of a word, and when the pressure was removed, she resumed the con- versation, without any recollection of the experiment to which she had been subjected. We notice, however, an important difference in the effect, accord- ing to the suddenness or tardiness with which the pressure is pro- duced. Whilst a sudden compression suspends the intellectual and moral manifestations for a time, slow pressure, produced by the gradual formation of a tumour, may exist without exhibiting, in any manner, the evidences of its presence. Accordingly, the anatomist is sometimes surprised to discover such morbid formations in the brains of those who have never laboured under any mental aberra- tion. A negative argument in favour of this function of the brain has been deduced from the fact, that disease of other portions of the bod)', even of the principal portions, may exist and pass on to a fatal termination, leaving these faculties almost wholly unimpaired. Such is proverbially the case with phthisis pulmonalis, the subject of which may be flattering himself with hopes never to be realized, and devising schemes of future aggrandizement and pleasure, until within a few hours of his dissolution. The intellectual faculties differ in each individual, and vary ma- terially with the sex. The brain is, in all these cases, equally dif- » Physiologic Medicale, &c. iii. 242, Paris, 1832. 268 MENTAL FACULTIES. ferent. Much may depend upon education; but it may, we think, be laid down as an incontrovertible position, that there is an original difference in the cerebral organization of the man of genius and of him who is less gifted; and that, as a general principle, in the for- mer the brain is much more developed than in the latter. Whilst the brain of the man of intellect may measure from nineteen to twenty-two inches in circumference, that of the idiot frequently does not exceed thirteen, or is not greater than in the child one year old. It was an ancient observation, that a large developement of the anterior and superior parts of the head is a characteristic of genius; and, accordingly, we find, that all the statues of the sages and heroes of antiquity are represented with high and prominent foreheads. In the older poets, we meet with many evidences, that the height of the forehead was regarded as an index of the intellectual or moral cha- racter of the individual." The relation between the size of the head and the mental mani- festations has, indeed, interwoven itself into our ordinary modes of speech. Perhaps, as a general observation, it may be found true, that the menial capacity is in a ratio with the size of the brain, compared to that of the rest of the body. " Let it not be believed," says a distin- guished writer,b " an affair of accident, that a head of considerable dimensions is found, from time to time, to coincide with a distin- guished genius. Although the amour propre may object, the law is general. I have neither met in antiquity, nor in modern times, a man of vast genius, whose head ought not to be ranged in the latter class, which 1 have just established, especially if attention be paid to the great developement of the forehead. Look at the busts and en- gravings of Homer, Socrates, Plato, Demosthenes, Pliny, Bacon, Sully, Galileo, Montaigne, Corneille, Racine, Bossuet, Newton, Leibnitz, Locke, Pascal, Boerhaave, Haller, Montesquieu, Voltaire, J. J. Rousseau, Franklin, Diderot, Stoll, Kant, Schiller, &c." Yet we are not always accurate in estimating the size of the brain from the developement of the head. Dr. Sewallc has clearly shown, that skulls of the same dimensions, as measured by the craniometer, differ largely as to the quantity of cerebral substance which they are capable of containing. With the assistance of Dr. Thomas P. * Thus Shakspeare: " We shall lose our time, And all be turn'd to barnacles, or to apes, With foreheads villanous low." Caliban, in " Tempest."—Act iv. And again:— " Ay, but her forehead's low, and mine's as high." Julia, in the " Two Gentlemen of Verona."—Act iv.* b Gall, Sur les Fonctions du Cerveau, ii. 342, Paris, 1825. c An Examination of Phrenology, in two Lectures, 2d edit. p. 66, Boston, 1839. * Kidd, on the Adaptation of External Nature to the Physical Condition of Man, p. 61, Amer. Edit. Philad. 1833. MENTAL FACULTIES. 269 Volume of Skull, Brain included. Volume of Brain, II. . 70 oz. - 56.22 oz. IV. . do. 46.21 VII. - do. - . 25.33 Jones, of Washington, and of Professor Ruggles, of the Columbian College, he insttuted various experiments. In the first series, he ascertained the volume of each skull, brain included; in the second series, the volume of the brain alone, or the capacity of the cerebral cavity, and in order to render the difference in capacity more ob- vious, the voiume of each skull, brain included, was reduced to the dimensions of 70 fluid ounces. The results of the experiments on five skulls, delineated in the plates of Dr. Sewall's work, were as follows: Plate In two of ihese skulls, consequently, of the same external dimen- sions, there was a difference in the volume of brain of 31.89 oz. Dr. Sewall infers from his observations, that no phrenologist, however experienced, can, by any inspection of the living head, ascertain whether a person has a skull,of one inch or one-eighth of an inch in thickness; or whether he has 56.22 ounces of brain in volume, or only 25.33 ounces. To the view, that the mental capacity is in a ratio with the size of the brain there must, indeed, be numerous exceptions ; for, inde- pendently of bulk there may obviously be an organization, produc- tive of the same results; and in which the largely developed organ may be greatly deficient. Size is only one of the elements of the activity of an organ. The difference between the moral of the male and female is signal; and there is no less in the shape of the encephalon in the two sexes. Observation, not only by anatomists but by sculptors and painters, shows, that the superior and anterior parts of the brain are less developed in the female, whose forehead is, therefore, as a general rule, smaller; whilst the posterior parts are larger than in the male. In the system of Gall, the anterior and superior parts are considered to be connected with the intellectual manifestations, which are more active in man; whilst the posterior are concerned in the softer feelings, which predominate in the character of the female. The mental and moral faculties vary in the same individual according to age, health and disease; and in the waking and sleep- ing state. In all these conditions, we have reason to believe, that the state of the encephalon is as various. The anatomist notices a manifest difference between its organization in the infant and in the adult or the aged. Like the other organs of the body, it is gradually developed until the middle period of life; after which it decays along with the rest of the frame. Our acquaintance with the minute or- ganization of the body does not enable us to say on what changes these differences are dependent. We see them only in their results. By the minutest examination of the special nerves of the senses we 23* 270 MENTAL FACULTIES. are incapable of saying, why one should be able to appreciate the contact of sapid bodies—another that of light, &c. During sleep, again, in which the functions of the brain are more or less suspended, the condition of the organ is modified ; and mania or delirium probably never occurs, without the physical condition of the brain having undergone some change, directly or indirectly. It is true, that, on careful examination of the brains of the insane, it has often happened that no morbid appearance has presented itself; but the same thing has been observed on inspecting those, who have died of apoplexy or paralysis, in which cases, not a doubt is enter- tained that the cause is seated in the encephalon, and that it consists in a physical alteration of its tissue. These are a few of the cases, which make us sensible of the limited nature of our powers of ob- servation. They by no means encourage, in the most sceptical, the belief, that the tissue of the organ is not implicated. The investiga- tions of the morbid anatomist consequently afford us but few data, on which to form our opinions on this subject. The effect of intoxicating substances must be mainly exerted on the brain. When taken in moderation, we find all the faculties ex- cited; but, if pushed too far, the intellectual and moral manifesta- tions become perverted. This can only be through the action of those substances upon the cerebral organ. We can thus understand, how regimen may cause important modifications in the brain. Cli- mate has probably a similar influence: hence, the difference between the characters of different nations and races. The skull of the Mongol is strikingly different from that of the Kelto-Goth or of the Ethiopian; and the brain, as well as its functions, exhibits equal diversity. Again, it has been argued, that the facts we notice in the animal kingdom are in favour of the brain being the organ concerned in the manifestations of the mind ; that, if each animal species has its own psychology, in each the encephalon has a particular organiza- tion ; and that, in all those which exhibit superior powers, the brain is found large and more complicated. To a great extent this is doubt- less true. Nothing, indeed, seems more erroneous than the notion, that even sensibility to pain is equal in every variety of the animal creation. As we descend in the scale, we find the nervous system becoming less and less complicated, until ultimately it assumes the simple original character, which has laid the foundation for one of the divisions of Sir Charles Bell's system; and although it is im- possible to change places with the animal, we have the strongest reasons for believing, that their sensibility diminishes as we descend; and that the feeling, expressed by the poet, that the beetle, which we tread upon— " In corporal sufferance finds a pang as great As when a giant dies"— however humane it may be, is physiologically untrue/ The frog » Good's Book of Nature, i. 426, Lond. 1826. MENTAL FACULTIES. 271 will continue sitting, apparently unconcerned, for hours after it has been eviscerated; the tortoise walks about after losing its head; and the polypus, when divided by the knife, forms so many separate animals. Redi removed the whole of the brain from a common land tortoise: the eyes closed to open no more, the animal walked as before, but, as it were, groping its way for want of vision. It lived nearly six months after. All have noticed the independence of the parts of a wasp, when the head has been severed from the body. The head will try to bite, and, for a considerable period, the abdomen will attempt to sting. An illustrative instance of this kind occurred to Dr. Harlan.1 He cut off the head of a rattle- snake, and grasping the part of the neck, attached to the head, with his finger and thumb, the head twisted itself violently, endeavour- ing to strike him with its fangs. A live rabbit was afterwards presented to the head, which immediately plunged its fangs deep into the rabbit; and when the tail was laid hold of, the headless neck bent itself quickly round as if to strike him. The instances of a similar kind, which occur to the naturalist, are numerous and interesting; and afford signal evidence of crea- tive wisdom, in endowing the frames of those beings of the animal kingdom, that are most exposed to injury and to torture, with a less sensible organization. On all the above accounts, then, we may conclude,—that the brain is the organ, through which the mind acts, in the production of the different mental and moral manifestations.1" Yet, amongst those who admit the accuracy of this conclusion, a difference of sentiment exists; some conceiving that other organs participate in the function. Some have ascribed to each of the known temperaments as many intellectual and moral dispositions. Others have affirmed, that, if the brain be manifestly the organ of the intellect, the passions must be referred to the organs of internal or organic life; whilst others, again, have considered the brain as a great central apparatus, for the reception and elaboration of the different impressions, made upon the external senses; thus conceiv- ing the latter to be direct agents in the execution of the function, as well as the brain. The influence of the temperaments upon the mental and bodily powers is much less invoked at the present day than it was of old. The ancients regarded organized bodies as an assemblage of ele- ments, endowed with different qualities, but associated and com- bined so as to moderate and temper each other. Modern physiolo- gists mean, by the term, the reaction of the different organs of the body upon each other, consistent with health; so that if one set or apparatus of organs predominates, the effect of such predominance may be exerted on the whole economy. In the description of the * Medical and Physical Researches, p. 503, Philad. 1835. b Haller. Element. Physiolog. torn. iv. sect. 16; Sommering, Lehre vom Gehirn, u. s. w. S. 373, § 308; Gall, Sur les Fonctionsdu Cerveau, ii. 69, Paris, 1825; Adelon, art. Encephale, Diet, de Medec. vii. 517 ; and Physiologie de I'Homme, ed. cit. i. 496. 272 MENTAL FACULTIES. temperaments, in different authors, we find a particular character of intellectual and moral faculties assigned to each. The man of the sanguine temperament is described as of ready conception, retentive memory, and lively imagination, inclined to pleasure, and generally of a good disposition, but inconstant and restless. He of the bilious, on the other hand, is said to be hasty, violent, ambi- tious, and self-willed; whilst the lymphatic bestows feeble passions, cold imagination, tendency to idleness; and the melancholic disposes to dulness of conception, and to sadness and moroseness of disposi- tion. Galla has animadverted on this assignment of any intellectual or moral faculty to temperament. If we look abroad, he affirms, we find the exceptions more numerous than the rule itself; so numerous, indeed, as to preclude us from establishing any law on the subject; and, moreover, the idiot, who possesses a temperament like other persons, has no intellectual faculties. The temperament doubtless influences the brain within certain limits, as it does other functions: this, he suggests, it does probably by impressing them with a character of energy or of languor, but without, in any respect, regulating the intellectual sphere of the individual; and it may be regarded as one of the media of connexion between the mind and the body. Bichat,b again, maintained, that whilst the encephalon is evidently the seat of the intellectual functions, the organic nervous system, and, consequently, the different organs of nutrition, which are sup- plied from this system, are the seat of the emotions or passions. That distinguished physiologist, than whom, as Corvisart wrote to the First Consul, in announcing his death, " personne en si peu de temps n'a fait tant de choses et aussi bien,,,c rests his views upon the three following considerations:—1st. That whilst inward feeling induces us to refer the intellectual acts to the brain, the passions are felt in the viscera of the thorax or abdomen. 2dly. That the effects of intellectual labour are referred to the encephalon, as indicated by the redness and heat of the face and the beating of the temporal arteries, in violent mental contentions, &c.; whilst the passions affect the organic functions, the heart is oppressed, and its pulsa- tions are retarded or suspended; the respiration becomes hurried and interrupted; the digestion impeded or deranged, &c.; and, Sdly. That whilst our gestures and language refer the intellect to the encephalon, they refer the emotions to the nutritive organs. If we wish to express any action of the mind, or if we are desirous of recalling something that has escaped the memory, the hand is carried to the head, and we are in a constant habit of desig- nating a strong or weak intellect by the terms a " strong or weak head;" and we say, that the possessor has " much or little brain." On the other hand, if we are desirous of depicting the passions, the a Op. citat. ii. 140. * Sur la Vie et la Mort, Part i., Paris, 1806. c Eloge de Xavier Bichat, par Miquel, p. 58, Paris, 1823. ORGAN OF INTELLECT. 273 hand is carried to the region of the stomach or heart; and the pos- sessor of benevolent or uncharitable sentiments is said to have a good or a bad heart. Bichat properly adds, that this idea is not novel, inasmuch as the ancients conceived the seat of the passions to be in the epigastric centre; that is, in the nervous plexuses situate in that region: he remarks, that, amidst the varieties presented by the passions, according to age, sex, temperament, idiosyncrasy, regimen, climate, and disease, they are always in a ratio with the degree of predominance of the different nutritive apparatuses; and he concludes with a deduction, which ought not to have been hazarded without full reflection—that as the functions of the nutritive organs, in which he ranges the passions, are in- voluntary, and consequently uninfluenced by education, education can have no influence over the passions, and the disposition is con- sequently incapable of modification. The answer of Gall3 and Adelonb to the views of Bichat appears to us irrefragable. How can we conceive that viscera, whose functions are known, and which differ so much from each other, are the agents of moral acts ? The passions are sensorial pheno- mena, and like all phenomena of the kind must be presumed to be seated in essentially nervous organs. Again, when an injury befalls the brain, and the intellectual facul- ties are perverted or suspended by it, the same thing happens to the affective faculties; and if the viscera fulfil the high office assigned to them, why are not the passions manifested from the earliest infancy, a period when the viscera are in existence and very active? The argument of Bichat—that the phenomena which attend and succeed to the passions, are referable to the organs of internal life— is not absolute. The functions of animal life are frequently dis- turbed by the passions, as well as those of organic life. It is not uncommon for them to induce convulsions, mania, epilepsy, and other affections of the encephalon. The effect here, as Adelon remarks, is mistaken for the cause. The heart certainly beats more forcibly in anger, but the legs fail us in fear; and if we refer anger to the heart, we must, by parity of reasoning, refer fear to the legs.c By reasoning of this kind, the passions might be referred to the whole system, as there is no part which does not suffer more or less during their violence. The error arises from our being im- pressed with the most prominent effect of the passion—the feeling accompanying it—and this is the cause of the gesture and the de- scriptive language, to which Bichat has given unnecessary weight in his argument. If, then, the views of Bichat, regarding the seat of the passions, be unfounded, the mischievous doctrine deduced from them—that they are irresistible, and cannot be modified by education, falls to * Op. citat. i. 94. b Art. Enceph. (Physiol) in Diet de Med. vii. 521, and Physiologie de I'Homme, edit cit. i. 510. c See, also, Elliotson's Human Physiology, p. 22, Lond. 1840. 274 MENTAL FACULTIES. the ground. His notion was, that the nutritive organs are the source of irritative irradiations, which compel the brain to form the determinations that constitute the passion, and to command the movements by which it is appeased or satisfied. A similar view is embraced by Broussais,a who, however, conceives, that the passions can be fomented and increased by attention, until they become predominant. Daily experience, indeed, shows us the powerful effect produced on the passions by a well-directed moral restraint. How many gratifying instances have we of persons, whose habitual indulgence of the lowest passions and propensities had rendered them outcasts from society, having become restored to their proper place in the community by exerting the due control over their vicious inclinations and habits! We can not only curb the expres- sion of the passions, as we are constantly compelled to do in social intercourse; but we can even modify the internal susceptibility, by well-directed habits of repression. Lastly. Many physiologists, we have seen, have considered the brain as a great nervous centre for the reception and elaboration of the different impressions, conveyed thither by the external senses; and absolutely requiring such impression for the mental manifesta- tions. They consequently rank, amongst the conditions necessary for such manifestations, not only the brain which elaborates them, but the parts that convey to it the impressions or materials on which it has to act; and they conceive, that a necessary connexion exists between these two orders of parts. The supporters of these opinions ascribe the differences, observed in the intellectual and moral faculties of different individuals, as much to diversity in the number and character of the impressions, as to differences in the encephalon itself. They do not all, how- ever, agree as to the source of the impressions, which they con- ceive to be the raw material for the intellectual and moral mani- festations. Condillacb and his school admit only one kind ;—those proceeding from the external senses; and which they term external impressions. Cabanis,0 on the other hand, in addition to these, admits others proceeding from every organ in the body, which he terms internal impressions, in contradistinction to the first. The school of Condillac set out with the maxim ascribed to Aristotle, "nihil est in intellectu quod non prius fuerit in sensu;" and they adopt, as an elucidation of their doctrine, the ingenious idea of Condillac—of a statue, devoid of all sensation, which is made to receive each of the five senses in succession; and which, he attempts to show, from the received impressions, can gradually develope the different intellectual and moral faculties. All these, he affirms, are derived from the impressions made on the external * Examen des Doctrines Medicales, ii. 388, and Physiology applied to Pathology, Drs. Bell and La Roche's translation, p. 136, Philadelphia, 1832. b Traite des Sensations, torn. i. 119. c Rapport du Physique et du Moral de I'Homme, 4eme edit, par G. Pariset, Paris, INTELLECTUAL SPHERE. 275 senses; and he considers, that the whole of human consciousness is mere sensation variously transformed. The views of Condillac have been largely embraced, with more or less modification ; and, at the present day, many metaphysicians believe, that the impressions of the senses are the necessary and exclusive materials for all the intellectual acts. Condillac's case of the statue seems, however, to be by no means conclusive. It must, of course, be possessed of a centre for the re- ception of the impressions made upon the different senses, otherwise no perception could occur; and if we can suppose it possible for such a monstrous formation, as a being totally devoid of the exter- nal senses, to exist, such a being must not only be defective in the nerves which, in the perfect animal, are destined to convey the im- pressions to the brain, but probably in the cerebral or percipient part likewise. From defective cerebral conformation, therefore, the different mental phenomena might not be elicited.1 If, however, we admit the possibility of the cerebral structure,— particularly those portions that are especially concerned in the func- tion of thought,—being properly organized, it appears to us, that certain mental or moral manifestations ought to exist. Of course, all knowledge of the universe would be precluded, because deprived of the instruments for obtaining such knowledge; but the brain would still act, as regarded the internal sensations. In order that such a being may live, he must be supplied with the necessary nourishment; he must possess all those internal sensations or wants that are inseparably allied to organization; he must consequently feel the desires of hunger and thirst; but. we have seen that these sensations require the intervention of the brain as much as the external sensations. Supposing him, again, to survive the period of puberty, he must experience the instinctive changes, that occur at this period, and which are doubtless dependent upon encephalic organization. In this assumed case, then, a certain degree of men- tal action might exist; and, under the supposition of a properly organized brain, ideas—limited, it is true, in consequence of the privation of the ordinary inlets of knowledge—might be formed; and memory, imagination, and judgment, be compatible within cer- tain limits. The objections to the idea, that the intellectual and moral sphere of man and animals is proportionate to the number and perfection of the external senses are overwhelming.'' Many animals have the same number of senses as man, and frequently have them more perfect; yet, in none is the mental sphere co-extensive. The idiot, too, has the external senses as delicate as the man of genius, and often much more so; many of those of the greatest talents having the senses extremely obtuse. It has been already remarked, that the superiority of the human intellect has been referred entirely to the sense of touch, and to the happy organization of the human » Adelon, Op. citat. i. 519. b Helvetius, De I'Homme, &.c, torn. i. 276 MENTAL FACULTIES. hand; but the case of Miss Biffin, and others, and that of the young artist cited by Magendie,* completely negative this presumption. The senses are important secondary instruments, indispensably necessary for accomplishing certain faculties of the mind; but, in no way, determining its power. The example of the deaf and dumb is illustrative of this matter.b If a child be born deaf, he is necessarily dumb, inasmuch as he is unable to hear those sounds which, by their combination, constitute language, and he cannot therefore imitate them ; yet this connexion between the functions of hearing and speech was not well known to the ancients. For a length of time, these objects of compassionate interest were esteemed to be beyond the powers of any kind of intel- lectual culture, and were permitted to remain in a state of the most profound ignorance. The ingenuity of the scientific philanthropist has, however, devised modes of instruction, by which their mental manifestations have been exhibited in the most gratifying manner, and in one which proves that the sense of hearing is not absolutely necessary for mental developement; but that its place may be sup- pi ied, to a great extent, by the proper exercise of others. The deaf and dumb, being deprived of the advantages of spoken language, are compelled to have recourse to the only kind available to them—that addressed to the eye. In this typical way, by a well- devised system of instruction, they can be taught to preserve their ideas, and to multiply them, as we do, by two combined methods— the spoken and the written language—without one or the other of which the human mind would have remained in perpetual infancy. Thus, the deaf and dumb have not only our ideas, but the same words to convey them to others. Yet the deaf and dumb are not so much the objects of our commi- seration as those who have been deprived, from birth or from early infancy, of both the senses of sight and hearing, and who have thus been devoid of two of the most important inlets for the entrance of impressions from the surrounding world. In such case, it is obvious, they are shut out from all instruction, except what can be afforded by the senses of touch, smell, and taste; yet even here we have the strongest evidence of independent intellect. One of the most striking cases of this kind is that of the Scottish boy Mitchell, the object of much interest to Spurzheim and to Dugald Stewart,6 both of whom have described his case in their writings. It is matter of uncertainty, whether either his deafness or blindness was total. The evidences 'of the sensation of hearing were, in a high degree, vague and unsatisfactory, but he gave more convincing proofs of the possession of partial vision. He could, for example, distinguish day from night; and, when quite young, amused himself with looking at the sun through crevices in the door, and by kindling » See page 106 of this volume. b Gall, op. cit. i. 119. c Elements of the Philosophy of the Human Mind, &c; Transactions of the Royal Society of Edinburgh, vol. vii.; and Dr. Gordon, ibid. vol. vi.; also, History of James Mitchell, a boy born blind and deaf, by James Wardrop, London, 1813. MENTAL SPHERE OF THE DEAF AND DUMB. 277 a fire. At the age of twelve, the tympanum of both ears was per- forated, but without any advantage. In his fourteenth year, the operation for cataract was performed on the right eye, after which he recognised more readily the presence of external objects, but never made use of his sight to become acquainted with the qualities of bodies. Before and after this period, red, white, and yellow par- ticularly attracted his attention. The senses, by which he judged of external bodies, were those of touch and smell. His desire to become acquainted with objects was signal. He examined every thing he met with, and every action indicated reflection. In his infancy, he smelt at every one who approached him, and their odour determined his affection or aversion. He always recognised his own clothes by their smell, and refused to wear those which he found to belong to others. Bodily exercises, such as rolling down . a small hill, turning topsy-turvy, floating wood or other objects on the river that passed his father's house, gathering round, smooth stones, laying them in a circle, and placing himself in the middle, or building houses with pieces of turf, &c, were always a source of amusement to him. After the operation on his right eye, he could better distinguish objects. His countenance was very expressive, and his natural language was not that of an idiot, but of an intelligent being. When hungry, he carried his hand to his mouth, and then pointed to the cupboard, where the provisions were kept; and, when he wished to lie down, he reclined his head on one side upon his hand, as if he wished to lay it upon the pillow. He easily recol- lected the signification of signs that had been taught him, all of which were of course of the tactile kind. To make him compre- hend the number of days before an event would happen, they bent his head as a sign that he would have to go to bed so many times. Satisfaction was expressed by patting him on the shoulder or arm, and discontent by a sharp blow. He was sensible to the caresses of his parents, and susceptible of different emotions—of hatred, passion, malice, and the kindlier feelings. He was fond of dress, and had great fears of death, of the nature of which he had mani- festly correct notions. Mitchell's case has been pregnant with interest to the metaphysi- cian, but it is not so elucidative as it would have been had the pri- vation of the senses in question been total. There is, at present, in the American Asylum at Hartford in Con- necticut, a being, not less deserving of attention, than the one to whom allusion has just been made.1 Her name is Julia Brace. She is the daughter of John and Rachael Brace, natives of Hartford, and was born in that town in June, 1807; so that she is now. (1838,) thirty-one years old. At four years of age, she was seized with typhus fever; was taken sick on the evening of Monday, November 29, 1811, and, on the Saturday morning following, became both a Twenty-first Report of the Directors of the American Asylum at Hartford, for the Education and Instruction of the Deaf and Dumb, p. 15, Hartford, 1837. vol. i. 24 278 MENTAL FACULTIES. blind and deaf. Prior to her illness, she had not only learned to speak, but to repeat her letters, and to spell words of three or four syllables ; and, for some time after the loss of her sight and hearing, she was fond of taking a book, and spelling words and the names of her acquaintances. She retained her speech pretty well for about a year, but gradually lost it, and appears to be now condemned to per- petual silence. For three years she could still utter a few words, one of the last of which was " mother." At first she was unconscious of her misfortune, appearing to think, that a long night had come upon the world; and often said, " It will never be day." She would call upon the family to " light the lamp," and was impatient at iheir seeming neglect, in not even answering her. At length, in passing a window, she felt the sun shining warm upon her hand, and pointed with delight to indicate that the sun shone. From the January after her illness, until the following August, she would sleep during the day, and be awake through the night; and it was not until autumn, by taking great pains to keep her awake during the day, that she was set right. At present, she is as regular in this respect as other persons. From the period of her recovery, she seemed to perceive the return of Sabbath; and, on Sunday morning, would get her own clean clothes, and those of the other children. If her mother was reading, she would find a book, and endeavour to do so likewise. The intervention of a day of fasting or thanksgiving confused her reckoning, and some time elapsed before she got right. During the first winter after her recovery, she was irritable almost to mad- ness; would exhibit the most violent passion, and use the most profane language. The next summer she became calmer; and her mother could govern her, to some extent, by shaking her, in sign of disapprobation; and stroking or patting her head, when she conducted herself well. She is now habitually mild, obedient, and affectionate. During the first summer after her illness, she was very unwilling to wear clothes, and would pull them off violently. At length, her mother took one of her frocks and tried it on her sister, with a view of altering it for her. Julia had ever been re- marked for her sense of justice in regard to property. This seemed to be awakened, and she took the frock and put it on herself. After this, she was willing to wear clothes, and even cried for new ones. She has ever since been fond of dress. At nine years of age, she was taught to sew; and, since that time, has learned to knit. She has been resident for several years in the American Asylum at Hart- ford, where she is supported in part, by the voluntary contributions of visiters; and, in part, by her own labours in sewing and knitting. A language of palpable signs was early established, as a means of communication with her friends; and this has been so improved as to be sufficient for all necessary purposes. Her countenance, as she sits at work, is said to exhibit the strongest evidence of an active mind, and a feeling heart: " thoughts and feelings," says a writer who describes her case, " seem to flit across it like the clouds in a summer sky: a shade of pensiveness will be followed by a cloud of MENTAL SPHERE OF THE DEAF, DUMB AND BLIND. 279 anxiety or gloom; a peaceful look will perhaps succeed; and, not unfrequently, a smile lights up her countenance, which seems to make one forget her misfortunes. But no one has yet penetrated the darkness of her prison house, or been able to find an avenue for intellectual or moral light. Her mind seems, thus far, inaccessible to all but her Maker." A still more interesting example is cited by Dr. Abercrombie," from the Medical Journals of the time. A gentleman in France is asserted to have lost every sense except the feeling of one side of his face; yet his family acquired a method of holding communica- tion with him, by tracing characters lapon the part which retained its sensation. x These cases are not, perhaps, so unfrequent as has been supposed. Dr. Howe, the superintendent of the Perkins Institution and Mas- sachusetts Asylum for the Blind, states, that four cases in New England, beside that of Julia Brace, have come within his own observation. One of these has been now (1841) upwards of three years under his care ; and the results of his diligence and judgment in this instance have furnished more gratifying results to the psycho- logist and philanthropist than any other, perhaps, on record. Laura Bridgman, the subject of the case, was born in December, 1829 : at two years of age, her eyes and ears inflamed, suppurated, and their contents were discharged. At the expiration of two more years of suffering, it was discovered, that her sense of smell was 'almost wholly destroyed, and, consequently, that her taste was much blunted. She had, therefore, but one sense remaining—that of touch—by which she could become acquainted with the external world. Whilst at home, before her reception into the Asylum, she would explore the house, become familiar with the form, density, weight, and temperature of every article she could lay her hands upon: followed her mother, felt her hands and arms, and endeavoured to repeat every thing herself. She even learned to sew a little, and to knit. She exhibited warm affection towards the members of her family; but the means of communicating with her were limited. When it was desired, that she should go to a place, she was pushed; or, that she should approach, she was drawn towards the person. Gently patting on the head signified approbation ; on the back, dis- approbation. She had made, however, a natural language of her own, and had a sign to express her idea of each member of the family,—such as drawing her finger down each side of her face, to allude to the whiskers of one ; twirling her hand and arm around, in imitation of the motion of the spinning-wheel, for another, &c. In October, 1837, she was received into the Institution for the Blind, in Boston. The first experiments made with her consisted in taking articles in common use, such as knives, forks, spoons, keys, a Inquiries concerning the Intellectual Powers, &c, Amer. Edit. p. 56, New York, 1832. 280 MENTAL FACULTIES. &c, and pasting labels upon them with their names printed in raised letters. These she felt very carefully, and speedily found, that the crooked lines spoon differed as much from the crooked lines k e y, as the spoon differed from the key in form. Then small detached labels, with the same words printed upon them, were put into her hands, and she soon observed, that they were similar to the ones pasted on the articles. She showed her perception of this similarity by laying the label key upon the key, and the label spoon upon the spoon. In this manner she proceeded to acquire a knowledge of language; and now she uses the manual alphabet of the deaf mutes with great facility and rapidity ; she has increased her vocabulary so as to comprehend the names of all common objects. She can count to high numbers; she can add and substract small numbers. But the most gratifying acquirement which she has made, and the one which has given her the most delight, is the power of writing a legible hand, and expressing her thoughts upon paper. She writes with a pencil in a grooved line, and makes her letters clear and distinct. She is very expert with her needle; knits very easily, and can make twine bags and various fancy articles very prettily; is very docile; has a quick sense of propriety; dresses herself with great neatness, and is always correct in her deportment. No definite course of instruction can be marked out; for her in- quisitiveness is so great, that she is very much disconcerted if any question, which occurred to her, is deferred until the lesson is over. It is deemed best to gratify her, if her inquiry has any bearing on the lesson; and often she leads her teacher far away from the objects with which he commenced. With regard to the sense of touch it is very acute, even for a blind person. It is shown remarkably in the readiness with which she distinguishes persons. There are forty inmates in the female wing, with all of whom, of course, she is acquainted ; whenever she is walking through the passage-way, she perceives by the jar of the floor, or the agitation of the air, that some one is near her, and it is exceedingly difficult to pass her without being recognised. Her arms are stretched out, and the instant she grasps a hand, a sleeve, or even part of the dress, she knows the person and lets them pass on with some sign of recognition. The details concerning this interesting being, and her gradual progress in moral and intellectual culture, can be learned from the annual reports of the Institution which Dr. Howe superintends.1 How strongly do these cases demonstrate the independence of the organ of intellect; requiring, indeed, the external senses for its perfect developement, but still capable of manifesting itself with- out the presence of many, and probably of any of them ; and how a Annual Reports of the Trustees of the Perkins Institution, and Massachusetts Asylum for the Blind to the Corporation, for the years 1837, 1838, 1839, and 1840. VIEWS OF CABANIS. 281 inaptly, although humanely, does the law regard such beings. " A person," says Blackstone,1 " born deaf, dumb, and blind, is looked upon by the law as in the same state with an idiot, he being supposed incapable of any understanding, as wanting all those senses which furnish the human mind with ideas." But if he grow deaf, dumb, and blind, not being born so, he is deemed non compos mentis, and the same rules apply to him as to other persons supposed to be lunatics. With regard to the deaf and dumb, they are properly held to be competent as witnesses, provided they evince sufficient understand- ing, and to be liable to punishment for a breach of the criminal laws. Cabanisb embraces the views of Condillac regarding the external senses; but he thinks, that the impressions from these are insufficient to constitute the materiel of the mental and moral manifestations. In confirmation of this opinion, he observes, that the young infant, and animals at the very moment of birth, frequently afford evi- dences of complicated intellectual processes; and yet the external senses can have been scarcely at all impressed. How can we, he asks, refer to the operation of the external senses the motions of the foetus in utero, which are perceptible to the mother, for the latter half of utero-gestation; or the act of sucking executed from the first day of existence '! Can we refer to this cause the fact of the chick, as soon as it is hatched, pecking the grain that has to nourish it ? or that, so frequently quoted from Galen, of the young kid, scarcely extruded from the maternal womb, which was able to select a branch of the cytisus from other vegetables presented to it? Man and animals, continues Cabanis, during the course of their existence, experience mental changes as remarkable as they are frequent; yet nothing in the condition of the senses can account for such difference. For example, at the period of puberty, a new appetite is added ; and this, even, when the being is kept in a com- plete state of isolation. This he argues, it is impossible to refer to any change in the external senses; which, if they furnished the materials at all, must have been doing so from early infancy; and he concludes, that the difference observable in the mental manifesta- tions, according to sex, temperament, climate, state of health or disease, regimen, &c. cannot be referable to the senses, as they remain the same; and that, consequently, we must look elsewhere for the causes of such difference. These, Cabanis conceives to be, the movements by which the organs of internal life execute their functions. Such movements, he says, although deep-seated and imperceptible, are transmitted to the brain, and furnish that organ with a fresh set of materials. At,puberty, for example, when the testicles become developed, and their function is established by the secretion of sperm, the organic movements in the process of this secretion are the materials of the new desires, which appear at that ao-e. These impressions Cabanis calls internal, in contradis- * Commentaries on the Laws of England, i. 304. b Rapport du Physique et du Moral, edit. cit. 24* 2g2 MENTAL FACULTIES. tinction to the external, or those furnished by the senses; and he considers, that, whilst the external senses serve as the base of all that we include under the term intellect, the internal impressions are the materials of what are called instincts; and, as the organs of internal life, whence the internal impressions proceed, vary more than the senses, according to age, sex, temperament, climate, regimen, &c, it is more easy, he thinks, to find in them organic modifications, which coincide with those exhibited by the mind under these various circumstances. In proof of these opinions, Cabanis adduces, besides others, the following specious affirmations. First. As the venereal appetite appears in man and animals synchronously with the developement of the testicles, and is never exhibited when the testicles are removed in infancy, we have reason to believe, that the impressions, which constitute the materials for this new catenation of ideas, must pro- ceed from the testicles. Secondly. Numerous facts demonstrate, that the condition of the uterus has much influence on the mental and moral manifestations of the female. For example, the period of the developement of that organ is the one at which new feelings arise, and when the whole of those manifestations assume more activity; and there is generally a ratio between their activity and that of the uterus. If the state of the uterus be modified, as it is at the menstrual period, or during pregnancy, or after delivery, the mind is so likewise. All these facts ought to induce a belief, he thinks, that impressions are continually emanating from this organ, which, by their variety, occasion the diversity in the state of mental and moral faculties, observed in these different cases. Thirdly. It is impossible in the hypochondriac and melancholic constitutions, to mistake the influence exerted upon the mind by the abdominal organs; according as these organs execute their functions more or less perfectly, the thinking faculty is more or less languid or brilliant; and the affections are more or less vivid and benevolent, or the con- trary; hence the expressions melancholy* and hypochondriasis? assigned to the state of mind characterizing these constitutions, and which denote that the cause must be referred to the organs of the abdomen. The origin of the alternations of inactivity and energy in the intellect, of benevolent and irascible fits of humour, as well as of insanity, are also referable, he says, to the abdominal viscera. Hence, Cabanis concludes, it is evident, that the abdominal organs are to the brain the source of fortuitous and abnormous impressions, which excite it to irregular acts; and is it not, he asks, probable, that what takes place in excess, in these morbid movements, may happen to a less and more appropriate extent in a state of health; and that thus impressions may emanate, in a continuous manner, from every organ of the body, which may be indispensable to the production of the mental and moral faculties? Cabanis, therefore, considers that the axiom of Aristotle should be * From (At\*t, " black," and ^oxx, *' bile." b Disease of the hypochondres. VIEWS OF CABANIS. 283 extended; and that the statue of Condillac is incomplete, in not having internal organs for the emanation of the internal impressions, which are the materials of the instincts. In this way he accounts for the instincts, which, by some metaphysicians, have been looked upon as ordinary judgments, so rapidly executed, that the process has ceased from habit to be perceptible. Finally, he remarks, there is a ratio between the duration and intensity of the intellectual results and the kind of impressions, which have constituted the materials of them. All the mental and moral acts, for instance, that are derived from impressions engendered in the very bosom of the nervous system or in the brain,—such as those of the maniac,—are the strongest and most durable. After these come the instincts, of which the internal impressions are the materials. They are powerful and constant. Lastly; the acts of the intellect are more transient, because they emanate from the external impressions, which are themselves fickle, and somewhat superficial. According to the views, then, of Cabanis and his followers, amongst the organic conditions of the mental and moral manifestations must be placed, not only the encephalon and the external senses, but the different organs of the body, which fur- nish the different internal impressions. The influence of the external senses on the intellectual and moral developement has already been canvassed: we have seen, that they are only secondary instruments for making us acquainted with external bodies, but in nowise regu- lating the intellectual or moral sphere. The notion of internal im- pressions is ingenious, and has led to important improvements in the mode of investigating the different mental and moral pheno- mena. It was suggested, as we have seen, by Cabanis, in conse- quence of the external senses appearing to him insufficient to explain all the phenomena. By Gall, Adelon,a and others, however, all these cases are considered explicable by the varying condition of the brain itself. In the foetus in utero, in the new-born animal, there are already parts of the brain, they say, sufficiently developed and capable of action; and, accordingly, we witness the actions to which reference has been made by Cabanis; and if the intellectual and moral manifestations vary according to sex, temperament, climate, regimen, state of health, &c. it is because the encephalon is, under these circumstances, in different conditions. The chief facts, on which Cabanis rests his doctrine, are,—the coincidence between the developement of the testicle and the appearance of the venereal appetite; and the suppression of this appetite after castration. It must be recollected, however, that these are not the only changes, that happen simultaneously at puberty. The voice also assumes a very different character; but the change in the voice is not a cerebral phenomenon. It is dependent upon the developement of its organ, the larynx. Yet castration, prior to puberty, has a decided effect upon it; preventing it from becoming raucous and unmelodious. All these developements are synchronous, but not directly consequent a Physiologie de I'Homme, 2de edit. i. 251. 284 MENTAL FACULTIES. upon each other. The generative function has two organs,—one encephalic, the other external; and it is not surprising, that both of these should undergo their developement at the same period. We shall see hereafter, that Gall offers us reasons for believing, that the instinct of propagation has its seat in the cerebellum; and as the most intimate connexion and dependence must exist between the encephalic and the external apparatus, it is not surprising, that the removal of the latter should prevent the developement of the former, and of the instinct of which it is the organ. If, however, the opera- tion of castration be performed after puberty, the instinct is not suppressed, because the necessary developement has already taken place, and the cerebellum is in a condition for fulfilling the function. The continuance of the instinct, however, under such circum- stances, Adelon conceives to be strong evidence against the exist- ence of such internal impressions; whilst the influence which Cabanis has ascribed to the uterus in females, and to the abdominal organs in the melancholic and hypochondriac, are esteemed to belong to that excited by the temperament, or by the different organs of the body on the brain; a subject which has already fallen under dis- cussion. On the whole, then, we are perhaps justified in concluding, that the encephalon alone is the organ of the intellectual and moral faculties. The interesting topic of the various instinctive operations of the frame will be considered in another part of this work. We shall there find, that instinct cannot well be defined, in the language of Broussais,1 to consist in sensations originating in the internal and external sensitive surfaces, which solicit the cerebral centre to acts necessary for the exercise of the functions—such acts being frequently executed without the participation of the mind, and even in its absence—inasmuch as it is not confined to beings possessed of brain, but exists also in the vegetable. Having now decided upon the organ of the mental and moral faculties, according to the system adopted in this work, it would be necessary to describe its anatomy. But this has been done else- where. 1. PHYSIOLOGY OF THE INTELLECTUAL AND MORAL FACULTIES. When the organ of the intellect is exposed by accident, and we regard it during the reception of a sensation, the exercise of volition, or during any intellectual or moral operation, the action is found to be too molecular to admit of detection. At times, during violent mental contention, a redness has been apparent, as if the blood were forced more violently into the vessels; but no light has been thrown by such examinations on the wonderful action, which constitutes thought. We ought not, however, to be surprised at this, when we reflect, that the most careful examination of a nerve does not con- *■ Physiol, appliquee a la Pathologie, ch. vii.; and Bell and La Roche's translation, Philad., 1832. PHYSIOLOGY OF THE MENTAL FACULTIES. 285 vey to us the slightest notion how an impression is received by it from an external body; and how such impression is conveyed to the brain. All that we witness in these cases is the result; and we are thus compelled to study the intellectual and moral acts by themselves, without considering the cerebral movements concerned in their pro- duction. Such study is the basis of a particular science—meta- physics, ideology or philosophy. Apart from organization, this subject does not belong to physiology; but as some of the points of classi- fication, &c, are concerned in questions that will fall under consi- deration, it may be well to give a short sketch of the chief objects of metaphysical inquiry ; which are, indeed, intimately connected in many of their bearings,—as commonly treated of by the metaphysi- cian,—with our subject. Broussais has considered, that metaphysics and physiology should be kept distinct; and that all the investiga- tions of the metaphysician should be confined to the ideal. " I wish metaphysicians, since they so style themselves," he remarks, some- what splenetically, " would never treat of physiology; that they would only occupy themselves with ideas as ideas, and not as modi- fications of our organs; that they would never speak either of the brain, the nerves, the temperaments, or of the influence of climates, of localities, or of regimen; that they would never inquire whether there are innate ideas, or whether they come through the medium of the senses; that they would not undertake to follow their develope- ments according to age or state of health ; for I am convinced that they cannot reason justly on these points. Such questions belong to physiologists, who can unite a knowledge of the moral nature with that of the structure of the human body." " It is possible," he adds, " that particular circumstances may oblige them to introduce physiological considerations into their calculations; as when it is necessary to estimate the influence of certain laws or customs in relation to temperature, to the nature of the soil, the prevailing diseases, &c, but then they should avail themselves of the experience of physiologists and physicians."3 A more appropriate recommenda- tion would have been, that the metaphysician should make a point of becoming acquainted with physiological facts and reasoning; and, conversely, that metaphysics should, form a part of the study of every physiologist. The cerebral manifestations comprise two very different kinds of acts ;—the intellectual and the moral: the former being the source of all the knowledge we possess regarding ourselves and the bodies surrounding us: the latter comprising our internal feelings, our appe- tites, desires, and affections, by which we are excited to establish a relation with the beings around us:—the two sets of acts respectively embracing the qualities of the mind and of the heart? If we attend to the different modes in which the intellectual mani- 1 Dc l'Irritation et de la Folie, Paris, 1828; or Dr. Cooper's translation, Columbia, S. C, 1831. *> Adelon, Facultes de l'Esprit et de l'Ame, in Diet, de Med. viii. 469, Paris, 1823; and Physiologie de I'Homme, edit. cit. i. 527. 286 MENTAL FACULTIES. festations are evinced in our own persons, we shall find that there are several operations, which differ essentially from each other. We are conscious of the difference between perceiving an impression made upon one of the external senses, which constitutes perception, and the recalling of such impression to the mind,—which is the act of memory; as well as the distinction between feeling the relations, which connect one thing to another, constituting judgment; and the tendency to act in any direction, which we call will. The con- sciousness of these various mental acts has induced philosophers to admit the plurality of the intellectual acts, and to endeavour to reduce them all to certain primary faculties; in other words, to faculties, which are fundamental or elementary; and which, by their combination, give rise to other and more complex manifestations. To this analytical method they have been led by the fact, that these different acts, which they have esteemed elementary, exhibit great variety in their degrees of activity; that one, for example, may be impressed with a character of great energy—as the memory— whilst another, as the judgment, may be singularly feeble,—and con- versely. Broussais, indeed, conceives, that without the memory we cannot exercise a single act of judgment; since it is always neces- sary, in order to judge, that we should experience two successive perceptions; that is, that we should feel them alternately, which we could not do, unless possessed of the faculty of renewing that, which we felt an instant before ; or, in other words, unless wre possessed memory. Hence the loss of this faculty, he says, necessarily occa- sions that of judgment, and reduces man to a state of imbecility. To a certain extent this is doubtless true. Total privation of memory must be attended with the results described; that is, if the individual retains no consciousness of that which has impressed him previously; for it is obvious, that in such a case, there can be no comparison. A man, however, may have an unusual memory for certain things, and not for others; he may astonish us by the extreme accuracy of his recollection of numbers, places, or persons, and yet he may be singularly deficient in judging of ordinary matters;—his memory suggesting only one train of objects for comparison. In enumerating the faculties, which, by their union, constitute the intellect, we observe the greatest discrepancy amongst metaphysi- cians; some admitting will, imagination, understanding, and sensi- bility ; others sensibility, imagination, memory, and reason; others will, intelligence, and memory; others, again, imagination, reflection, and memory. The views of Condillac1 on this subject have perhaps excited more attention than those of any other individual. Professing, as we have seen, that all our ideas are derived from the successive operations of the senses and the mind, he admits the following constituent faculties of the intellect:—sensation, attention, comparison, judgment, reflec- tion, imagination and reason. Sensation he defines—the faculty of » Op. citat PHYSIOLOGY OF THE MENTAL FACULTIES. 287 the mind, which affords the perception of any sensitive impression. Mention, the faculty of sensation, applied exclusively to a deter- minate object; being, as the word imports, the tension of the mind upon a particular object. Comparison, the faculty of sensation ap- plied to two objects at once. Judgment, the faculty by which the mind perceives the connexions, that exist between the objects com- pared. Reason, the faculty of running through a succession of judg- ments, which are connected with, and deduced from each other. Reflection, as the word indicates, the faculty by which the mind re- turns upon itself, upon its owrn products, to prove their correctness, and to subject them again to its power; and imagination, to which Condillac attaches memory,—the faculty possessed by the mind of reproducing at will the different impressions, and all the products of its own operations. With regard to the order of catenation of these different faculties, he considers sensation to be first put in play; and if, amongst the perceptions, there is one, of which we have a more lively consciousness, and which attracts the mind to it alone, it is the product of attention ; then comes comparison, which is nothing more than a double attention ; comparison is irresistibly succeeded by judgment; if, from one judgment, we pass to another deduced from it, we reason; if the mind turns back on its own products, we reflect; and lastly, if the mind spontaneously awakens its different perceptions, imagination is in action. All these faculties are thus made to be deduced from each other; to originate in the first, or in sensation; and all are this first sensation successively transformed. The doctrine of Condillac, abstractly considered, has already engaged attention. The division of the faculties, which, he con- ceives, by their aggregation, form the intellect, is simple and inge- nious, and appears to be more easily referable to physiological prin- ciples than that of other metaphysicians; accordingly, it has been embraced, with more or less modification, by certain physiological writers. The power of reflection, according to Broussais, is the character- istic of the human intellect; and to reflect is to feel. Man not only feels the stimulation produced by external organs, and by the move- ments of his own organs, which constitutes sensation or perception, but he is conscious that he has felt these stimulations; or, in other words, he feels that he has felt; he has consequently a perception of his actual perception. Tnis, he says, constitutes mental reflection. This process man can repeat as often as he thinks fit, and can ob- serve all his sensations, and the different modes in which he felt, whilst occupied with his feelings. From this study he derives an idea of his own existence. " He distinguishes himself in the midst of creation, and paying regard only to his own existence, compared with all that is not himself, he pronounces the word I, (moi,) and says, I am ; and viewing himself in action, says, I act, I do," &c. Perception of himself and of other bodies procures him what are denominated ideas. This is therefore, another result of reflection ; or, in other words, of the faculty he possesses of feeling himself 288 MENTAL FACULTIES. feel. But man feels, besides, that he has already felt—this constitutes memory. In comparing two perceptions with each other, which are felt in succession, a third perception results, which is judgment. Consequently, to judge is only to feel. Hence, he concludes, " sensa- tion, reflection, and judgment, are absolutely synonymous, and pre- sent to the physiologist nothing more than the same phenomenon. The will, or that faculty by virtue of which man manifests his liberty by choosing, among different perceptions, the one he must obey— that faculty, which gives him the power of resisting, to a certain extent, the suggestions of instinct, is founded on reflection. Conse- quently, when we consider it in a physiological point of view, we can only discover in it the faculty of feeling ourselves, and of per- ceiving that we feel ourselves." Some of the later French metaphysicians have proposed certain modifications of the system of Condillac. M. De La Romiguiere," for instance, denies that sensation is the original faculty, and he derives all from attention. The mind, he remarks, is passive during the reception of sensation, and does not commence action until directed to some object, or until it attends. According to him, the intellect consists of only three faculties—attention; comparison or double attention ; and reason or double comparison. Judgment, imagination, and memory, are not primary faculties : judgment is the irresistible product of comparison; memory is but the trace, which every perception necessarily leaves behind it; and imagina- tion is but a dependence on reason. M. Destutt-Tracy,b again, re- duces the number of primary faculties to four—perception, memory, judgment, and will or desire. According to him, attention is not an elementary faculty. It is but the active exercise of the intellectual faculties. The same applies to reflection and reason, which are only a judiciously combined employment of those faculties ; and to com- parison and imagination, both of which enter into the judgment. This division is embraced by Magendie.c Stewart's6 classification is into, 1. Intellectual powers, and, 2, Active and moral powers; including in the former, perception, attention, conception, abstraction, the associating principle, memory, imagination, and reason. Brown' reduces all the intellectual states to simple suggestion and relative suggestion, comprising in the former, conception, memory, and ima- gination,—in the latter, judgment, reason, abstraction, and taste. Abercrombief considers the mental operations to be chiefly referable to four heads,—memory, abstraction, imagination, and reason, or judgment; whilst Kant has twenty-five primary faculties or forms; pure conceptions or ideas a priori. * Lecons de Philosophic, i. 4eme lecon. b Elemens d'Ideologie, 2de edit. Paris, 1804, and Gall, Sur les Fonctions du Cer- veau, i. 39, Paris, 1825. c Precis Elementaire, i. 196. d Elements of the Philosophy of the Human Mind, 3d edit. Lond. 1808; and Amer. edit., Brattleborough, Vt. 1813. e Lectures on the Philosophy of the Human Mind, Amer. edit. Boston 1826. 1 Inquiries concerning the Intellectual Powers, Amer. edit. p. 91, New York, 1832. CLASSIFICATION OF THE AFFECTIVE FACULTIES 059 These are a few only of the discrepant divisions of psychologists. The list might have been extended by the classifications of Aris- totle, Bacon, Hobbes, Locke, Bonnet, Hume. Vauvenargues, Dide- rot, Reid, and others. Perhaps the most prevalent opinion at present is, that the original faculties are—perception, memory, judgment, and imagination. It is impossible for us, were it even our province, to reconcile these discrepancies. They are too considerable for lis to hope, that this will ever be effected by metaphysical inquiry. We must, therefore, look to physiological investigation, if not with well- founded—with the only—hopes, we can entertain, for the elucida- tion of the subject: and we shall find presently, that the minds of metaphysical physiologists have been turned in this direction, and that many interesting facts and speculations have been the result. A second topic of metaphysical inquiry regards the formation of the intellectual notions we possess. On this, there have been two principal opinions; some, as Plato, Descartes, the Kantists. Kanto- Platonists, &c. believing in the existence of innate ideas of things;— others, as Bacon, Locke, and Condillac, denying the existence of such innate ideas, and asserting that the human intellect, at birth, is a tabula rasa, and that the mind has to acquire and form all the ideas it possesses from impressions made on the senses. The truth includes probably both these propositions—the action of the senses and of the intellectual faculties being alike necessary; the former receiving the external and internal impressions, and transmitting them to the mind, which, through the cerebral organ, produces the different intellectual acts. Under the terms ajfective faculties, affections, and passions, are comprehended all those active and moral powers, which connect us with the beings that surround us, and are the incentives to our social and moral conduct. To this class belong the feeling, which attaches the parent to the child; that which draws the sexes toge- ther ; and the feeling of compassion, by which we are led to assist a suffering fellowr-creature. They are, in truth, internal sensations, but of a higher cast than those of hunger and thirst; the latter being purely physical and announcing physical necessities, the former sug- gesting social and moral relations. Such affective faculties are the foundation of what are called moral wants, and, like the internal sensations in general, are the source of pleasure, when satisfied,—of pain, when resisted; and it is only when they are extreme and opposed, that they acquire the name of passions? The analysis of these is attended with the same difficulties as that of the intellectual faculties. Their plurality is universally admitted, but still greater discrepancy exists as to their precise number and connexion.b Many moralists have united the moral faculties under a From patior, I suffer. b Adelon, art. Affection, in Dictionnaire de Medecine, lere edit.; and Physiologie de I'Homme, edit. cit. i. 537. VOL. I. 25 290 MENTAL FACULTIES. the head of will or desires. Condillac8 is one of those. Every sensa- tion, he observes, has the character of pleasure or pain, none being indifferent; as soon, therefore, as a sensation is experienced, the mind is excited to act. This tendency is at first but slightly marked, and is only an uneasiness (malaise): but it soon increases, becomes restlessness or inquietude ; in other words, a difficulty experienced by the mind of remaining in the same situation. This gradually becomes desire, torment, passion, and finally ivill, excited to the exe- cution of some act. Some have endeavoured, by ultimate analysis, to derive all the affective faculties of the mind, from one principal faculty—that of self-love,— the inward feeling, which induces all men to attend to themselves, their own preservation, and welfare. All the faculties, they assert, are returns of this self-love upon itself; and, as in the case of the intellectual faculties, attempts have been made to classify them; but no two scarcely agree. Some have divided them into the agreeable and the distressing; others into those of love and hatred; many—regarding their effects upon society— into the virtuous, vicious, and mixed;—the first comprising those that are useful to society,—as filial, parental, and conjugal love, which form the foundation of families; goodness, pity, and generosity, which, by inducing men to assist each other,facilitate the social condition; and the love of labour, honour, and justice, which have the same result, by constituting so many social guarantees. The vicious pas- sions, on the contrary, are such as injure man individually and society in general, as pride, anger, hatred and malice. Lastly, the mixed passions are such as are useful or injurious, according to their use or abuse; such as ambition, which may be a laudable emu- lation, or an insatiable passion, according to its extent and direction. Again, the passions have been divided into the animal or such as belong to physical man, and the social or such as appertain to man in society. The first are guides to him for his own preservation as well as for that of the species. To them belong fear, anger, sad- ness, hatred, excessive hunger, the venereal desires when vehement, jealousy, &c. In the second are included all the social wants, when inordinately experienced. These vary according to the state of civilization of the individual and the community. Ambition, for in- stance, it is said, may be regarded, when inordinate, as excessive love of power:—avarice, as an exaggeration of the desire for for- tune:—hatred and vengeance, as the natural and impetuous desire of injuring those that injure us, &c. Stewart'sb division of the active and moral powers embraces, 1. Instinctive principles, and 2. Rational principles: the former in- cluding appetites, desires, and affections, the latter self-love and the moral faculty; all of which Brown0 comprises under emotions, im- mediate, retrospective, or prospective;—and lastly, Abercrombied a Op. citat.; and Dzondi, art. Affect, in Pierer's Anat. Phys. Real Worterb. i. 106, Leipz, und Altenb. 1816. b Op citat. c Op. citat. d Philosophy of the Moral Feelings, Amer. Edit. p. 35, New York, 1833. MENTAL SPHERE HOW REGULATED. 291 refers all the principles, which constitute the moral feelings, to the following head: 1. The desires, the affections, and self-love; 2. The will; 3. The moral principle, and 4. The moral relation of man towards the Deity. It is obvious that the analysis of the moral faculties has been still less satisfactorily executed than that of the intellectual; and that little or no attempt has been made to specify those that are primary or fundamental, from those that are more complex. The remarks, consequently, which were made regarding the only quarter we have to look to, for any improvement in our knowledge of the intellectual acts, apply a fortiori to the moral; although it must be admitted, that the difficulties attendant upon the investigation of the latter are so great as to appear to be almost, if not wholly, insuperable. As the brain, then, is admitted to be the organ of the intellectual and moral faculties, its structure probably varies according to the number and character of those; and if there be primary or funda- mental faculties, each may be conceived to have a special organ concerned in their production, as each of the external senses has an organ concerned in its production. According to this view, the cere- bral organization of animals ought to differ according to their psycho- logy: where one is simple the other should be so likewise. This seems, so far as we can observe, to be essentially the fact. " In the series of animals," says Adelon,1 " we observe the brain more complicated as the mental sphere is more extensive; and in this double respect a scale of gradation may be formed from the lowest animals up to man. If he has the most extensive moral sphere, if he alone possesses elevated notions of religion and morality, he has also the largest brain, and one composed of more parts; so that if the physiology of the brain were more advanced, we might be able, by comparing the brains of animals with his, to detect the material condition, which constitutes humanity. If the brain were not con- structed, a priori, for a certain psychology, as the digestive appa- ratus is for a certain alimentation, if the mental and moral facul- ties were not as much innate as the other faculties, there would be nothing absolute in legislation or morals. The brain and its faculties are, however, in each animal species, in a ratio with the role, which such species is called upon to fulfil in the universe. If man is, in this respect, in the first rank; if he converts into the delicate affec- tions of father, son, husband, and country, those brute instincts, by which the animal is attached to its young, its female, or its kennel; if, in short, he possesses faculties which animals do not,—religious and moral feelings, with all those that constitute humanity,—it is owing to his having a more elevated vocation; to his being not only the king of the universe, but destined also for a future exist- ence, and specially intended to live in society. Hence it was neces- a Art. Enceph. in Diet, de Med. vii. 526; and Physiologie de I'Homme, edit, cit, i. 542. 292 MENTAL FACULTIES. sary that he should not only have an intellect sufficiently extensive to make all nature more or less subject to him, but also a psycho- logy such, that he might establish social relations with his fellows. It was necessary that he should have notions of the just and the un- just, and be able to elevate himself to the knowledge of God;—to those sublime feelings, which cause him so to regulate his conduct as to maintain with facility his mortal connexions, and to deserve the future life to which he is called." But if the intellectual sphere be regulated by the cerebral deve- lopement, can we not, it has been asked, estimate the connexion between them? And if there be different primary cerebral faculties, each of which must have an organ concerned in its production, can we not point out such organ in the brain 1 Several investigations of this character have been attempted, with more or less success: generally, however, they have added but little to our positive knowledge, and this, principally, from the intricacy of the subject. Until of late years, attention was chiefly paid to the mass and size of the encephalon; and it was, at one time, asserted, that the larger this organ, in any species or individual, the greater the intellect. Man, however, has not absolutely the largest encephalon although he is unquestionably the most intelligent of beings. The weight of the encephalon of a child six years of age is given by Haller at two pounds three ounces and a half; whilst that of the adult is estimated by Sommering at from two pounds three ounces, to three pounds three ounces and three quarters ;a by Tiedemannb_ at from three pounds three ounces, to four pounds eleven ounces troy—the brain of the female weighing, on an average, from four to eight ounces less than that of the male. The average weight, after the meninges have been stripped off, is, in the healthy adult male, according to Lelutc about 1346 grammes, or three pounds and a half avoirdu- pois; of which the cerebrum weighs 1170, the cerebellum 176 grammes. In the female, the weight of the encephalon he found to be about J^th less than in the male. The encephalon of the elephant, according to Haller, weighs from seven to ten pounds. This, con- sequently, overthrows the proposition; and, besides, in certain in- sects with very minute brains, as the bee and the ant, we meet with evidences of singular intelligence. The proposition was therefore modified, and it was laid down, that the larger the encephalon, compared with the rest of the body, the greater the mental sphere. When the subject was first investigated in this way, the result, in the case of the more common and domestic animals, was considered so satisfactory, that, without farther comparison, the proposition was considered to be established. More modern researches have a Weber's Hildebrandt's Handbuch der Anatomie, Band iii. 423; Rudolphi, Grund- riss, u. s. w. ii. 11. b Proceedings of the Royal Society for 1836, and Dunglison's American Medical Intelligencer, i. 368, Philad., 1838; also, Das Him des Negers, mit des Europaers und Orang-outangs verglichen, Hcidelb. 1837, cited in Brit, and For. Med. Rev., for Oct. 1839, p. 374. c Gazette Medicale; and Medico-Chirurgical Review for Oct. 1837, p. 507. SIZE OF THE BRAIN. 293 shown, that it admits of numerous exceptions, and that several of the mammalia, and many diminutive and insignificant animals have the advantage over man in this respect. It has, indeed, been pro- perly observedvby Mr. Lawrence/ that it cannot be a very satisfac- tory mode of proceeding to compare the body, of which the weight varies so considerably, according to illness, emaciation, or embon- point, with the brain, which is affected by none of these circum- stances, and appears to remain constantly the same. This is the cause, why, in the cat, the weight of the encephalon, compared with that of the body, has been stated as 1 to 156 by one compara- tive anatomist, and as 1 to 82 by another; that of the dog as 1 to 305 by one, and as 1 to 47 by another, &c. The following table, taken chiefly from Hallerb and Cuvier,c ex- hibits the proportion which the encephalon bears to the rest of the body, in man and certain animals. 1 • • %s -'- to -1- 4 1 2 2 t02^ -i_ to -1 4~8~ ■54 L to Child; 6 years old Adult .... Gibbon .... Sapajous, from Apes .... Baboons . . . Lemurs . . . Bat (vespertilio).....-^ Mole........3-L- Bear........^ Hedgehog,.......T-»F Fox.........^ Wolf........jfa Beaver........jig- Hare .... Rabbit .... Rat..... Mouse .... Wild boar . . . Domestic do. . . 14-0*0 228 1_ "15" 2 4? 1 6T2 Elephant . . . Stag . . . . Roebuck (young) Sheep .... Ox..... Calf .... Horse .... Ass .... Dolphin . . . Eagle .... Goose .... Cock .... Canary bird . Humming bird . Turtle .... Tortoise . Frog .... Shark .... Pike .... Carp .... To"0 . _i_ 290 . _!_ 94 TTTT t0 XT* 1 *~ Tso 1 2~19 * T0"0" lU 4 0 0 1 ' ~\~5% ' 1 J l_ 25' T6> 6 0' 10" 2 1 • ¥6 0 1 ' 35 0 1 2240 1 TT2 1__ 2496 1 T70 5 _1_ 5 6~o It has been the general belief, that the brain of the negro is inferior to that of the white varieties of the species; but recent observations of M. Tiedemann lead him to the belief, that there is no perceptible dif- ference either in the average weight or average size of the brain in the two varieties, and that the nerves compared with the size of the brain are not larger in the former than in the latter. In the external form of the brain of the negro a very slight difference only can be traced; but, according to M. Tiedemann, there is absolutely no difference in its external structure, nor does the negro brain exhibit a Lectures on Physiology, Zoology, &c, p. 191, Lond. 1819; and Buffon, Hist. Nat. ix. b Element. Physiol, x. sect. 1. c Lecons d'Anat. Comp. ix. art. 5. a On the authority of Ex-President Madison. 25* 294 MENTAL FACULTIES. any greater resemblance to that of the ourang-outang than the brain of the European, excepting, perhaps, in the more symmetrical dis- position of its convolutions. Tiedemann's observations were made, however, upon very few subjects; and his own facts do not bear out all his deductions. He admits, that the anterior part of the hemisphere was something narrower than is usually the case in Europeans, " which," says Dr. Combe,a " as the anterior portion is the seat of intellect, is really equivalent to conceding that the negro is naturally inferior in intellectual capacity to the European!" M. Tiedemann established the fact, that the average capacity of the Ethiopian skull is somewhat less than that of the European, and that a large size is considerably less common among them than among any other races of mankind.b Wrisberg and Sommering0 proposed another point of comparison, —the ratio of the mass of the encephalon to that of the rest of the nervous system ;a and they asserted, that, in proportion as any animal possesses a larger share of the former; or, in other words, in pro- portion as the percipient and intellectual organ exceeds the other or the organ of the external senses—the mental sphere may be expected to be more diversified and developed. But although man is, in general, pre-eminent in this respect, he is not absolutely so. It would be still more important to know the ratio, that the cerebrum or brain proper bears to the cerebellum and medulla oblongata. The first is essentially the organ of intellect; and the most striking character of the human brain is the large developement of the cere- bral hemispheres, of which we have no parallel in the animal king- dom. The last is the encephalic part in which all the nerves of the senses arise or terminate. The assertion, that man has the largest cerebrum in proportion to the cerebellum, is not accurate. The Wenzels6 found the ratio, in man, to be as 6 ,f;\ or 8T\2T to 1; in the horse, 4| to 1; in the cow, b\\~ to 1; in the dog, 6^ to 1 ; in the cat, 474j to 1; in the mole, 3-| to 1 ; and in the mouse, 6f to 1. Nor is it true that man has the largest cerebrum in proportion to the medulla oblongataf and medulla spinalis; although to this position there are perhaps fewer objections than to any of the others. None of them, it is obvious, are distinctive between man and animals, or assist us in solving the great problem of the source and seat of the numerous psychological differences we observe in different animals and men. Various plans have been devised for appreciating the comparative size of the cranium,—which is in a direct ratio with that of the brain—and of the bones of the face. As the former contains the a Phrenological Journal, No. liv. Dec, 1837. b Brit, and For. Med. Rev. for Oct. 1839, p. 379. c Corpor. Human. Fabric, iv. § 92; and Blumenbach's Comp. Anat. by Lawrence, p. 292, Lond. 1807. d Mojon's Leggi Fisiologiche, &c., translated by Skene, p. 24, Lond. 1827. e De Penitiori Structur. Cerebr. Hominis et Brutorum, tab. iv. f Cuvier, Lecons d'Anat. Compar. ii. 512. CAMPER'S FACIAL LINE AND ANGLE. 295 organ of the intellect, and the latter those of the external senses and of mastication; it has been presumed, that the excess of the former would indicate the predominance of thought over sense ; and, con- versely, that the greater developement of the face would place the animal lower in the scale. One of these methods, which was first proposed by Camper," is by taking the course of the facial line, and the amount of the facial angle. The facial line is a line drawn from the projecting part of the forehead to the alveoli of the incisor teeth of the upper jaw; and the facial angle is that formed between this line and another drawn horizontally backwards from the upper jaw. The course of the horizontal line and its point of union with the facial line are not uniform in all the figures given by Camper: sometimes it is made to pass through the meatus auditorius externus, but it often falls far below it; yet Dr. Bostock thinksb " we cannot hesitate to admit the correctness of Camper's observations, and we can scarcely refuse our assent to the conclusion that he deduces from them." In man, whose face is situate perpen- dicularly under the cranium, Fig. 48. the facial angle is very large. In animals, the face is placed in front of the cranium; and, as we descend from man the angle becomes less and less, until it is finally lost; the cranium and face being, in most reptiles and fish, completely on a level. The marginal figure exhibits the difference between the facial angle of those of European descent, and that of the negro. By covering with the finger the parts below the nose alternately, we have the countenance of the white or of the negro, in which the facial angle dif- fers as much as 10°, or 15°. Fig. 49 exhibits the facial line and angle of the ourang- outang. Those animals that have the snout long, and the facial angle consequently small, have been proverbially esteemed foolish,0—such as the snipe, stork, crane, &c.; whilst superior a Dissertation Physique de M. Camper, sur les Differences Reelles que Presentent les Traites du Visage, &c, traduit du Hollandois, par D. B. Q. Disjonval, Autrecht, 1791; Gall, Sur les Fonctions, &c, ii. 301. b Physiology, 3d edit. p. 804, Lond. 1836. c Lawrence, op. citat. p. 168. 296 MENTAL FACULTIES Fig. 49. 58° intelligence is ascribed to those in which the angle is more largely developed—as the elephant and the owl; although in them, the large facial angle is caused by the size of the frontal sinuses, or by the wide separation between the two tables of the skull, and is necessarily no index of the size of the brain. Yet, from this cause, perhaps, the owl was chosen as an em- blem of the goddess of wisdom; and the elephant has received a name in the Ma- //^a> i\l m^i ^ language' indicating an opinion, that /L.............^:C/L^6^...jL„ he is possessed of reason. The following table exhibits the facial angle in man and certain animals, taken by a line drawn parallel to the floor of the nostrils, and meeting another, drawn from the great- est prominence of the alveoli of the upper jaw to the prominence of the forehead : Man . . . . . 65° to 85° and more. Sapajou..........65° Ourang-outang .... 56° or 58° Guenon..........57° Mandril....... 30° to 42s Coati...........28° Polecat .........31° Pug dog.........35°, Mastiff..........41° Hare ..........30° Ram ..........30° Horse..........23° The facial angle may, then, exhibit the difference between man and animals; and, to a certain extent, between the species or in- dividuals of the latter; but, farther, it is of little or no use.a In man it may be 'considered to vary from 70° to 85° in the adult, but in children it reaches as high as 90°;—a sufficient proof that it cannot be regarded as a measure of the intellect. In the European, it is, on the average perhaps, 80°, in the Mongol, 75°, and in the negro, 70°, not many degrees above the ourang-outang.b It is found, how- ever, that the skulls of different nations, and of individuals of the same nation, may agree in the facial angle, whilst there may be striking distinctions in the shape of the cranium and face, in the air and character of the whole head, as well as in the particular fea- tures,—the inclination of the facial line being obviously more de- pendent on the prominence of the upper jaw and frontal sinuses than on the general form of the head. The ancients had been impressed with the intellectual air exhibited by the open facial angle ; for we find in all their statues of legislators, sages, and poets, an angle of at least 90°, and in those of heroes and of superhuman natures it is carried as high as 100°. This angle, according to Camper, never existed in nature ; and yet he conceives it to be the beau ideal of the 1 Dr. S. G. Morton, Crania Americana, p. 250, Philad. 1839. Dr. Morton, in his splendid work, describes a " Facial Goniometer," originally suggested by Dr. Turn- penny, of Philadelphia, which is admirably adapted for measuring the facial angle. b Prichard's Physical History of Mankind, i. 288, 3d edit. Lond. 1836. COMPARATIVE SIZE OF THE CRANIUM AND FACE. 297 human countenance, and to have been the ancient model of beauty. It was, more probably, the model of superior intellectual endowment, although ideas of beauty might have been connected with it. Every nation forms its notions of beauty, derived from this source, chiefly from the facial angle to which it is accustomed. With the Greeks it was large, and therefore the vertical facial line was highly estimated. For the same reason, it is pleasing to us; but such would not be the universal impression. Savage tribes on our own continent, have preferred the pyramidal shape of the head, and made use of every endeavour, by unnatural compression in early infancy, to produce it; whilst others, not satisfied with the natural shape of the frontal bone, have forced back the forehead, either by applying a flat piece of board to it, like the Indians of our own con- tinent, or by iron plates, like the inhabitants of Arracan. By this practice, the Caraibs are said to be able to see over their heads. Daubenton,a again, endeavoured, by taking the occipital line and angle, to measure the differences between the skulls of man and ani- mals. One line is drawn from the posterior margin of the foramen magnum of the occipital bone to the inferior margin of the. orbit, and the other from the top of the head to the space between the occipital condyles. In man, these condyles, as well as the foramen magnum, are so situate, that a line drawn perpendicular to them would be a continuation of the spine; but in animals they are placed more or less obliquely; the perpendicular would necessarily be thrown farther forward, and the angle be thus rendered much more acute.b Blumenbach says, that Daubenton's method may be adapted to measure the degrees of comparison betwixt man and brutes, but not the varieties of national character ; for he found it different in the skulls of two Turks, and of three Ethiopians. The methods of both Camper and Uaubenton he discovered to be insufficient to in- dicate the varieties in the national and individual character. He accordingly, describes a new method,—which he calls the norma verticalis." It consists in selecting two bones, the frontal from those of the cranium, and the superior maxillary from those of the face, and comparing these with each other,—by regarding them verti- cally,—placing the great convexity of the cranium directly before him, and marking the relative projections of the maxillary bone beyond the arch of the forehead. The Georgian is thus found to be characterized by the great expanse of the upper and outer part of the cranium, which hides the face. In the Ethiopian, the nafrow, slanting forehead allows the face to appear, whilst the cheeks and jaws are compressed laterally and elongated in front; and in the a Memoires de l'Academie des Sciences de Paris, 568, Paris, 1764. b By some writers, Daubenton's method is said to consist of " a line drawn from the posterior margin of the occipital foramen to the inferior margin of the orbit; and, another drawn horizontally through the condyles of the occipital bone." It is obvious, that little or no comparative judgment of the cranium and face could be formed from this. c Decad. Collection is sues Craniorum diversarum Gentium; and De Gener. Human. Var. Nativ., edit. 3a, Gotting. 1795. 298 MENTAL FACULTIES. Tungoose, the maxillary, malar, and nasal bones are widely ex- panded on each side; and the two last rise to the same horizontal level with the space between the frontal sinuses—the glabella. Blumenbach's method, however, only affords us the comparative dimensions of the two bones in one- direction. It does not indicate the depth of the maxillary bone or of the os frontis, or their compa- rative areas. The view thus obtained is therefore partial. Finding the inapplicability of other methods to the greater part of the animal creation,—to birds, reptiles, and fishes, for example,— Cuvier* suggested a comparison between the areas of the face and cranium under the vertical section of the head. The result of his observations is,—that, in the European, the area of the cranium is four times that of the face,—excluding the lower jaw. In the Cal- muck, the area of the face is one-tenth greater than in the European; in the negro, one-fifth, and in the sapajou, one-half. In the mandril, the two areas are equal; and, in proportion as we descend in the scale of animals, the area of the face gains over that of the cranium; in the hare, it is one-third greater; in the ruminant animals double; in the horse, quadruple, &c.; so that the intelligence of the animal is said to be greater or less, as the preponderance of the area of the face over that of the skull diminishes or increases. The truth, according to Sir Charles Bell,b is, that the great dif- ference between the bones of the cranium and face in the European and negro is in the size of the jaw bones. In the negro, these were found to bear a much greater proportion to the head and to the other bones of the face than those of the European skull; and the ap- parent size of the bones of the negro face was discovered to proceed solely from the size and shape of the jaw bones, whilst the upper bones of the face, and, indeed, all that had no relation to the teeth and to mastication, were less than those of the European skull. Other methods, of a similar kind, have been proposed by natu- ralists, as by Spigel,c Herder,d Mulder/5 Walther/ Doornik,s Spix,h and Oken,' but they are all insufficient to enable us to arrive at an accurate comparison. Blumenbach asserts, that he found the facial and occipital angles nearly alike in three-fourths of known animals. Moreover, it by no means follows, that, in the same species, there should be a correspondence between the size of the a Lecons d'Anatomie Compar., No. viii. art. i. torn. ii. p. 1. b Anatomy of Expression, 2d edit., Lond. 1824. c Lineae Cephalometricae Spigelii, in Spigel. de Human. Corpor. Fabric, i. 8. d Nackenlinien (Linear nuchales Herderi) in Herder's Ideen zur Philosophic der Geschichte der Menschheit, Th. iii. s. 186, Tubing. 1806. e Vorderhauptwinkel (Angulus sincipitalis Mulderi,) in Art. Kopflinien, in Pierer's Anat. Physiol. Real Worterb. iv. 524, Leipz. 1821. f Schadelwinkel (Angulus Cranioscopicus Waltheri,) in Walther's Kritische Dar- stellung der Gallschen Anat. Physiol. Untersuch. des Gehirn und Schadelbaues, s. 108, Zurich, 1802. g Wijsgeerig Natuurkundig Onderzoek aangande den Oorsprongliken Mensch en de Oorspronglike Stammen van Deszelfs Geslacht, Amsterd. 1808. h Cephalogenesis, Monach. 1815. 1 Lchrbuch der Zoologie, Abth. ii. s. 660. A description of all these methods is given by Choulant, in Picrer, loc, cit. VIEWS OF DESMOULINS AND GALL. 299 cranium and face. In the European, the face may be unusually large; and yet the mental endowments may be brilliant. Leo X. and Montaigne and Leibnitz, Racine, Haller, Mirabeau and Franklin, had all large features.* All the methods, again, are confined to the estimation of the size of the whole encephalon ; whereas we have seen, that the brain alone is concerned in the intellectual and moral manifestations; although Gall includes, also, the cerebellum. It has already been remarked, that no animal equals man in the develope- ment of the cerebral hemispheres. In the ape, they are less pro- minent; and below it in the scale of creation, they become less and less; the middle lobes are less arched downwards; and the posterior lobes are ultimately wanting, leaving the cerebellum uncovered; the convolutions are less and less numerous and deep, and the brain at length is found entirely smooth. The experiments of Rolando of Turin, and of Flourensb of Paris, are likewise confirmatory of this function of the brain proper. These gentlemen experimented upon different portions of the encephalon, with the view of detecting their functions; endeavouring, as much as possible, not to implicate any part except the one which was the subject of investigation; and they found, that if the cerebral hemispheres were alone removed, the animal was thrown into a state of stupor or lethargy ; was in- sensible to all impressions ; was to every appearance asleep, and evidently devoid of all intellectual and affective faculties. On the other hand, when other parts of the encephalon were mutilated,— the cerebellum, for example,—leaving the cerebral hemispheres uninjured, the animal was deprived of some other faculties,—that of moving, for instance,—but retained its consciousness, and the exercise of all its senses.. M. Desmoulins,c in his observations on the nervous system of vertebrated animals, is in favour of a view, originally suggested by M. Magendie,d that the intellectual sphere of man and animals depends exclusively on the cerebral convolutions; and that eximina- tion of the convolutions will point out the intellectual differences, not only between different species, but between individuals of the same species. According to him, the cerebral convolutions are numerous in animals in proportion to their intelligence; and, in animals of similar habitudes, have a similar arrangement. In the same species, they differ sensibly, according to the degree in which the individuals possess the qualities of their nature:—for example, they vary in the foetus and in the adult; are manifestly less numerous and smaller in the idiot, and become effaced in protracted cases of insanity. He farther remarks, that the morbid conditions of the encephalon, which occasion mental aberration, are especially such as act upon the con- volutions ; and that, whilst apoplectic extravasation into the centre a Gall, Sur les Fonctions du Cerveau, ii. 296. b Recherches E.vperimentalcs sur le Systeme Nerveux, Paris, 1824. c Anatomie des Systemes Nerveux des Animaux a Vertdbres, Paris, 1825. d Precis Elementaire, edit. cit. i.185. 300 MENTAL FACULTIES. of the organ induces paralysis of sensation and motion, the least inflammation of the arachnoid membrane causes delirium. Hence, he deduces the general principle, that the number and perfection of the intellectual faculties are in proportion to the extent of the cerebral surfaces. This view of M. Desmoulins, so far as regards the seat of the intellectual and moral faculties, accords with one to which attention must now be directed, and which has given rise to more philoso- phical inquiry, laborious investigation, and, it must be admitted, to more idle enthusiasm and intolerant opposition, than any of the psychological doctrines advanced in modern times:—we allude to the views of Dr. Gall on the functions of the brain.a These are, 1st, That the intellectual and moral faculties are innate. 2dly, That their exercise or manifestation is dependent upon organization. Sdly, That the brain is the organ of all the appetites, feelings and facul- ties ; and, 4thly, That the brain is composed of as many particular organs as there are appetites, feelings, and faculties, differing essen- tially from each other. The importance of Gall's propositions; the strictly physiological direction which they have taken,—the only one, as we have said, which appears likely to aid us in our farther acquaintance with the psychology of man,—require that the physiological student should have them placed before him as they emanated from the author. The work of Gall, however, on the functions of the brain, com- prises six octavo volumes, not distinguished for unusual method or clearness of exposition. Fortunately, the distinguished physiologist, Adelon, to whom we have so frequently referred, has spared us the necessity of a tedious and difficult analysis, by the excellent and im- partial view which he has given in the Dictionnaire de Medecine? which has been since transferred to his Physiologie de VHomme; both being abridgments of the Analyse d'un Cours du Dr. Gall, published by him in 1808. The foundation of this doctrine is, that the brain is not a single organ, but is composed of as many nervous systems as there are primary and original faculties of the mind. In the view of Gall, the brain is a group of several organs, each of which is concerned in the production of a special moral act: and, according as the brain of an animal contains a greater or less number of these organs, and of a greater or less degree of developement, the animal has, in its moral sphere, a greater or less number of, or more or less active, faculties. In like manner, as there are as many sensorial nervous systems and organs of sense as there are external senses, so there are, it is maintained, as many cerebral nervous systems as there are special moral faculties or internal senses. Each moral faculty has, a Sur les Fonctions du Cerveau, Paris, 1825. b Art. Encephale (Physiologie) Paris, 1823, and art. Facultes de l'Esprit et de l'Ame, &c. viii. 469, Paris, 1823. See, also, Roget, in art. Craniology, Suppl. to Encyclop. Brittanica; and Purkinje, art. Cranioscopie, in Encylcopad Worterb. der Medic. Wis- sensch. viii. 590, Berlin, 1832. VIEWS OF GALL. 301 in the brain, a nervous part, concerned in its production, as each sense has its special nervous system; the sole difference being, that the nervous systems of the senses are separate and distinct, whilst those of the brain are crowded together in the small cavity of the cranium, and appear to form but one mass. The proofs adduced by Galla in favour of his proposition, are the following:—1st. It has been established as a principle, that the dif- ferences in the psychology of man and animals correspond to varie- ties in the structure of the encephalon, and that the latter are de- pendent on the former. Now, the differences of the brain consist less in changes of the general form of the organ than in parts, which are present in some and not in others; and if the presence or absence of such parts is the cause why certain animals have a greater or less number of faculties than others, they ought certainly to be esteemed the special organs of such faculties. 2dly. The intellec- tual and moral faculties are multiple. This every one admits. Each, consequently, ought to have its special organ; and the admission of a plurality of intellectual and moral faculties must induce that of a plurality of cerebral organs, in the same manner as each external sense has its proper nervous system. 3dly. In different individuals of the same species,—in different men,—much psychological variety is observable. The cause of this is doubtless in the brain; but we can hardly ascribe it to a difference in the general shape of the organ, the form of which is sensibly the same. It is owing rather to diffe- rences in the separate parts of the brain. Are not such parts, there- fore, he asks, distinct nervous systems ? 4thly. In the same individual —in the same man—the intellectual and affective faculties have never the same degree of activity; whilst one predominates, another may be feeble. Now, this fact, which is inexplicable under the hypo- thesis, that the brain is a single organ, is readily intelligible under the theory of the plurality of organs. Whilst the cerebral part, which is the agent of the one faculty, is proportionably more voluminous or more active, that which presides over the other is less so. Why, he asks, may not this happen with the cerebral organs, as with the other organs of the body—the senses, for example ? Cannot one of these be feeble and the other energetic 1 5thly. In the same indivi- dual, all the faculties do not appear, nor are they all lost at the same periods. Each age has its own psychology. How can we, then, explain these intellectual and moral varieties according to age, under the hypothesis, that the brain is a single organ ? Under the doctrine of the plurality of cerebral organs, the explanation is simple. Each cerebral system has its special period of developement and decay. 6thly. It is a common observation, that when we are fatigued by one kind of mental occupation, we have recourse to another; yet it often happens, that the new labour, instead of adding to the fatigue experienced by the former, is a relaxation. This, Gall remarks, would not be the case, if the brain was a single organ and acted as such, 1 Op. cit. ii. 394. vol. i. 26 302 MENTAL FACULTIES. but it is readily explicable under the doctrine of plurality of organs. It is owing fo a fresh cerebral organ having been put in action. 7thly. Insanity is frequently confined to one single train of ideas, as in the variety, called monomania, which is often caused by the constancy and tenacity of an original exclusive idea. This is frequently re- moved by exciting another idea opposed to the first, and which dis- tracts the attention from it. Is it possible, Gall asks, to compre- hend these facts under the hypothesis of the unity of the brain ? 8thly. Idiocy and dementia are often only partial; and it is not easy to conceive,* under the idea of the unity of the brain, how one faculty remains amidst the abolition of all the others. 9thly. A wound or a physical injury of the brain will frequently modify but one faculty, paralysing or augmenting it, and leaving every other uninjured. lOthly, and lastly. Gall invokes the analogy of other nervous parts ; and, as the great sympathetic, the medulla oblongata, and medulla spinalis are—in his view at least—groups of special nervous sys- tems, it is probably, he says, the same with the brain. Such are the arguments employed by Gall for proving, that the brain consists of a plurality of organs, each of which is concerned in the production of a special intellectual or moral faculty, and should they not carry conviction, it must be admitted, that many of them are ingenious and forcible, and all merit attention. It is a prevalent idea, that this notion of a plurality of organs is a phantasy, which originated with Gall. Nothing is more erroneous : he has adduced the opinions of numerous writers who preceded him, some of whom have given figures of the cranium, with the seat of the different organs and faculties marked upon it.a To this list we might add numerous others. Aristotle, in whose works we find the germs of many discoveries and speculations, thought that the first or anterior ventricle of the brain was the ventricle of common sense; because from it, according to him, the nerves of the five senses branched off. The second ventricle connected by a minute opening with the first, he fixed upon as the seat of imagination, judgment, and reflection; and the third ventricle, as a storehouse into which the conceptions of the mind, digested in the second ventricle, were transmitted for retention and accumulation; in other words, he regarded it as the seat of memory. Bernard Gordon, in a work writ- ten in 1296, gives nearly the same account of the brain. It contains, he says, three cells or ventricles. In the anterior part of the first ventricle lies common sense; the function of which is to take cogni- zance of the various forms and images, received by the several senses. In the posterior part of the first ventricle he places phan- tasia: and in the anterior part of the second, imaginativa: in the posterior part of the middle ventricle lies estimativa. It would be a waste of time and space, to adduce the absurd notions entertained by Gordon on this subject. He thinks there are three faculties or virtues,—imaginatio, cogilatio, and memoria,—each of which has a a Op. citat. ii. 353, and Broussais's Lecons de Phrenologie, Brussels edit. p. 21,1836. VIEWS OF GALL. 303 special organ engaged in its produc- Fig. 50. tion. For many centuries it was be- lieved, that the cerebrum was the or- gan of perception, and the cerebellum that of memory. Albert the Great, in the thirteenth century, sketched a head on which he represented the seat of the different intellectual facul- ties. In the forehead and first ventri- cle he placed common sense and ima- gination ; in the second, intelligence and judgment; and in the third, me- mory and the motive force. The head in the margin (Fig. 50) is from an old sketch contained in the Book Rarities, of the University of Cam- bridge. Servetus conceived that the two anterior cerebral cavities are for the reception of the images of exter- nal objects; the third is the seat of thought; the aqueduct of Sylvius, the seat of the soul, and the fourth ven- - -T„ tricle that of memory. In 1491, Peter Montagnana published an engraving, in which were represented the seat of the sensus com. munis, a cellula imaginativa, cellula estimativa seu cogitativa, a cellula memorativa and a cellula rationalis. A head by Ludovico Dolci exhibits a similar arrangement. (Fig. 51.)a The celebrated Dr. Thomas Wil- lis, in 1681, asserted, that the cor- pora striata are the seat of percep- tion ; the medullary part of the brain that of memory and imagination: the corpus callosum that of reflec- tion : and the cerebellum, according to him, furnished the vital spirits necessary for the involuntary mo- tions.11 It would appear, too, that Swe- denborg, half a century before the promulgation of Gall's theory, maintained the doctrine, that every man is born with a disposition to all sorts of evil, which must be checked by education, and as far as possible rooted out, and that the degree of success or of failure in this respect would be indi- Olfactus. Gustus Head by Dolei, A. D. 1562. a Burton's Anatomy of Melancholy, 11th edit. i. 32, Lond. 1813. See, also, Marga- rita Philosophica, lib. ix. cap. 40, Basil. 1508, cited by Dr. John Redman Coxe, in Dunglison's American Medical Intelligencer, i. 58, Philad. 1838. b Gall, Sur les Fonctions du Cerveau, ii. 350, Paris, 1835, 304 MENTAL FACULTIES. cated by the shape of the skull. " The peculiar distinctions of man," he argued, " will and the understanding, have their seats in the brain, which is excited by the fleeting desires of the will, and the ideas of the intellect. Near the various spots where these irritations produce their effects, this or that part of the brain is called into a greater or less degree of activity, and forms along with itself corresponding parts of the skull."a The view, that exercise of the cerebral organs occasions their developement in bulk, and want of due exercise their decrease, is now maintained by many phrenologists, but denied by others. The above examples are sufficient to show, that the attempt to assign faculties to different parts of the brain, and, consequently, the belief, that the brain consists of a plurality of organs, had been long indulged by anatomists and philosophers. The views of Gall are resuscitations of the old; but resembling them little more than in idea. Those of the older philosophers were the merest phantasies, unsupported by the slightest observation: the speculations of the modern physiologist have certainly been the result of long and careful investigation, and of the deepest meditation. Whilst, there- fore, we may justly discard the former, the latter are worthy of rigid and unprejudiced examination. Admitting, with Gall, the idea of the plurality of organs in the brain, the inquiry would next be,—how many special nervous sys- tems are there in the human brain, and what are the primary intel- lectual and moral faculties over which they preside? This Gall has attempted. To attain this double object, he had two courses to adopt; either, first of all, to indicate anatomically the nervous systems that constitute the brain, and then to trace the faculties of which they are the agents; or, on the contrary, to point out first the primary faculties, and afterwards to assign to each an organ or particular seat in the brain. The first course was impracticable. The cere- bral organs are not distinct, isolated in the brain: and if they were, simple inspection could not indicate the faculty over which they pre- side; any more than the appearance of a nerve of sense could indi- cate the kind of sensation for which it is destined. It was, only, therefore, by observing the faculties, that he could arrive at a speci- fication of the cerebral organs. But here, again, a source of diffi- culty arose. How many primary intellectual and moral faculties are there in man? and what are they? The classifications of the mental philosophers, differing, as we have seen they do, so intrinsically and essentially from each other, could lead him to no conclusion. He first, however, followed the notions on which they appeared to be in accordance; and endeavoured to find particular organs for the facul- ties of memory, judgment, imagination, &c. But his researches in this direction were fruitless. He, therefore, took for his guidance the common notions of mankind; and having regard to the favourite occupations, and the different vocations of individuals, to those a Dr. Sewall, Examination of Phrenology, 2d edit., p. 14, Boston, 1839. PHRENOLOGY. 305 marked dispositions, which give occasion to the remark, that a man is born a poet, musician, or mathematician, he carefully examined the heads of such as presented these predominant qualities, and endeavoured to discover in them such parts of the brain as were more prominent than usual, and which might be considered as spe- cial nervous systems,—the organs of these faculties. After multi- tudinous empirical researches on living individuals, on a collection of crania, and on casts made for the purpose, attending particularly to the heads of such as had one of their faculties predominant, and who were, as he remarks, geniuses on one point,—to the maniac, and the monomaniac;—after a sedulous study, likewise, of the heads of animals, comparing especially those, that have a particular faculty, with such as have it not—in order to see if there did not exist in the brain of the former some part which was wanting in that of the latter; by this entirely experimental method, he ventured to specify, in the brains of animals and man, a certain number of organs; and, in their psychology, as many faculties, truly primary in their character. But, in order that such a mode of investigation be applicable it must be admitted, 1st. That one of the elements of the activity of a function is the developement of its organ. 2dly. That the cerebral organs end, and are distinct, at the surface of the brain. 3dly. That the cranium is moulded to the brain, and is a faithful index of its shape; for it is, of course, through the skull and the integuments covering it, that Gall attempts, in the living subject, to appreciate the state of the brain. Within certain limits, these positions are true. In the first place, we judge of the activity of a function, by the size of the organ that executes it: the greater the olfactory nerve, the more acute we expect to find the sense of smell. In the second place, according to the anatomical theory of Gall, the cerebral con- volutions are the final expansions of the cerebrum: if we trace back the original fasciculi, which, by their expansions, form the hemi- spheres of the brain, they are observed to increase gradually in size in their progress towards the circumference of the organ, and to terminate in the convolutions. Lastly, to a certain extent the cra- nium is moulded to the brain; and participates in all the changes, which the latter undergoes, at different periods of life, and in disease. For example, during the first days after the formation of the brain in the fcetus, the cranium is membranous, and has exactly the shape of that viscus. On this membrane, ossific points are deposited, so that, when the membrane has become bone, the cranium has still the shape of the brain. In short, nature having made the skull to contain the brain, has fitted the one to the other, and this so accu- rately, that its internal surface exhibits sinuosities, corresponding to the vessels that creep on the surface; and digitations, corresponding to the cerebral convolutions. The brain, in fact, rigidly regulates the ossification of the cranium ; and when, in the progress of life, the brain augments, the capacity of the cranium is augmented like- wise ; not by the effect of mechanical pressure, but owing to the 306 MENTAL FACULTIES. two parts being catenated in their increase and nutrition. This remark applies not only to the skull and brain, regarded as a whole, but to their separate parts. Certain portions of the brain are not developed simultaneously with the rest of the organ; and the same thing happens to the portions of the skull that invest them. The forehead, for example, begins to be developed after the age of four months : but the inferior occipital fossae do not increase in propor- tion until the period of puberty. Again ; when the brain fades and wastes in advanced life, the cavity of the cranium contracts, and its ossification takes place on a less and less outline. In advanced life, however, according to Gall, the correspondence between the brain and the inner table of the skull is alone maintained; the outer table appearing to be a stranger to all nutritive movement, and preserving its dimensions. Lastly, the cranium partakes of all the variations experienced by the brain in disease. If the brain be wanting, as in the acephalous monster, the cranium is wanting also. If a portion of the brain exist, the corresponding portion of the cranium exists. If the brain be smaller than natural, as in the idiot, the cranium is so likewise. If the brain, on the contrary, be distended by hydroce- phalus, the cranium has a considerable capacity; and this, not owing to a separation, at the sutures, of the bones composing it, but owing to ossification taking place on a larger outline. If the brain be much developed in any one part, and not in another, the cranium is protuberant in the former; restricted in the latter. Lastly, in cases of mania, the cranium is often affected; seeming, for example, to be unusually thick, dense, and heavy. These reasons, adduced by Gall, may justify the admission, that, within certain limits, the skull is moulded to the brain; and, if we admit this, the method followed by him, of specifying the organs of the mental faculties, may be conceived practicable. Such is the basis of the system of craniology, proposed by Gall. It also bears the name cranology, organology, phrenology, and cra- nioscopy: though, strictly speaking, it is by cranioscopy that we acquire a knowledge of craniology, or the art of prejudging the intel- lectual and moral aptitudes of man and animals, from an examina- tion of the cranium. It is, of course, limited in its application. Gall admits, that it is not available in old age—owing to the physiological fact before stated;—that the external table of the skull is no longer modified by the changes, that happen to the brain; and he acknow- ledges, that its employment is always difficult, and liable to nu- merous errors. We cannot, in fact, touch the cranium directly, for it is covered by hair and integument. The skull is, likewise, made rough,1 in particular parts, by muscular impressions, which must not be confounded with what are termed protuberances;—in other words, with the prominences, that are formed by a corresponding deve- lopement of the brain. In this respect, craniology presents more difficulties in animals, from their heads being more covered with muscles, and from the inner table of the skull being, alone, in a ratio with the brain beneath. Other errors again may be incurred from the existence of the frontal sinuses, of the superior longitudinal sinus, J CRANIOl.OGIC'AL DIVISIOTNT of UALI. T(hK Soft Ml » 7 /'^^f^J !?Jp- k mm1 5 mk %i V CEREBRAL ORGANS ENUMERATED BY GALL. 307 and from the possible separation of the hemispheres at the median line. The difficulty is, of course, extremely great in appreciating the parts of the brain, that are situate behind the eyes; and cranio- logy must be entirely inapplicable to those organs of the brain, that do not terminate at its base. Gall has taken especial pains to remark, that by craniology we can only prejudge the dispositions of men, not their actions; and that we can appreciate but one of the elements of the activity of organs—their size—not what belongs to their intrinsic activity, and to the impulse or spring they may receive from the temperament, or general formation. Setting out, however, from the principle, that the predominance of a faculty is in a great measure dependent on the developement of the portion of the brain which is its organ, he goes so far as to particularize, in this developement, what is owing to the length of the cerebral fibres, and what to their breadth; referring the activity of the faculty to the former circumstance, and its intensity to the latter. In applying cranioscopy to animals, he observes, that the same cerebral organ frequently occupies parts of the head, which seem to be very different, on account of the differ- ence between station in animals and man, and of the greater or less number of systems, that compose their brain. The cerebral organs, enumerated by Gall, with the corresponding faculties, are as follows:—the numbers corresponding with those of the accompanying engravings. 1. Instinct of generation, of reproduc- f tion; amativeness. Instinct of pro- \ Seated in the cerebellum. It is manifested pagation; venereal instinct. J at the surface of the cranium by two round {German.) Zeugungstrieb, S protuberances, one on each side of the nape Fortpflanzungstrieb, / of the neck. Geschlechtstrieb. f 2. Love of progeny; philoprogenitive- / ness. \ Indicated at the external occipital protube- (G.) Jungenliebe, Kinder- \ ranee. 1 i e b e. ( 3. Attachment, friendship. 5 About the middle of the posterior margin of (G.) Freundschaftsinn. ^ the parietal bone; anterior to the last. 4. Instinct of defending self and pro- f~ perty; love of strife and combat; \ Seated a little above the ears; in front of the combativeness; courage. J last, and towards the mastoid angle of the (G.) Muth, Raufsinn, ) parietal bone. Zanksinn. Q_ - „ . . .. . . 7. .. ( Greatly developed in all the carnivorous ani- 5. Carnivorous instinct; inclination \ -,J r r . , ., , • ' , , . .. ' i. j mals; forms a prominence at the posterior tomarder.-dertructije.fieM; cruelly, j and superior part of the squamous surface of (G). Wurgsinn, Mordsmn. ( the temporal bone, above the mastoid process. 6. Cunning; finesse; address ; secre- t tiveness. ) Above the meatus auditorius externus, upon (G.) List, Schlauheit, K lug- ) the sphenoidal angle of the parietal bones. h e i t. V. 7. Desire of property; provident in- r ^^ ^ of cunni of which it geems stmct; cupidity; inclination to rob. \ ^ fce a j ti an|'above that of me_ bery; acquisitiveness. 7 chani with which it contributes to wi(kn (G). Eigen thumssmn Hang ) fte crani b the projectionj whioh they z u s t e h 1 e n, E i n s a m m 1 u n g s- / form at ^ ^ of ^ ^^ > * sinn, Diebsinn. ^ 308 MENTAL FACULTIES. 8. Pride; haughtiness; love of au- thority; elevation. (G.) Stolz, Hochmuth, Ho. hen sin n, Herrschsucht. 9. Vanity; ambition; love of glory. (G.) Eitelkeit, Ruhmsucht, Ehrgeitz. 10. Circumspection; foresight. (G.) Behutsamkeit, Vorsicht, Vorsichtigkeit. 11. Memory of things; memory oft facts; sense of things ; educability; perfectibility ; docility. (G.) Sachgedachtniss, Er- ziehungsfahigkeit, Sach- s i nn. 12. Sense of locality; sense of the re- lation of space; memory of places. (G.) Ortsinn, Raumsinn. 13. Memory of persons ; sense of per- sons. (G.) Personensinn. 14. Sense of words; sense of names; verbal memory. (G.) Wortgedachtniss, Na- me n s i n n. 15. Sense of spoken language; talent of philology; study of languages. (G.) Sprachforschungssinn, Wortsinn, Sprachsinn. 16. Sense of the relations of colour; talent of painting. (G.) Farbensinn. 17. (Sense of the relations of tones; musical talent. (G.) Tons inn. 18. Sense of the relations of numbers; mathematics. (G.) Zahlensinn. 19. Sense of mechanics; sense of con- struction ; talent of architecture; industry. (G.) Kunstsinn, Bausinn. 20. Comparative sagacity. (G.) Vergleichender Scharf- sinn. 21. Metaphysical penetration; depth of mind. (G.) Metaphysischer Tief- s inn. 22. Wit. (G.) W i t z. 23. Poetical talent. (G.) Dichtergeist. 24. Goodness ; benevolence; mild-1 ness ; compassion ; sensibility;' moral sense; conscience; bonhom- mie. (G.) Gutmiithigkeit, Mitlei- den, moralischer Sinn,, Gewissen. Behind the top of the head, at the extremity of the sagittal suture, and on the parietal bones. Situate at the side of the last, near the poste- rior internal angle of the parietal bones. Corresponds to the parietal protuberances. I Situate at the root of the nose, between the two eyebrows, and a little above them. Answers to the frontal sinuses, and is indi- cated externally by two prominences at the inner edge of the eyebrows, near the root of the nose, and outside the organ of memory of things. At the inner angle of the orbit. Situate at the posterior part of the base of the two anterior lobes of the brain, on the frontal part of the bottom of the orbit, so as to make the eye prominent. Also at the top of the orbit, between the pre- ceding and that of the knowledge of colour. The middle part of the eyebrows; encroach- ing a little on the forehead. A little above and to one side of the last; above the outer third of the orbitar arch. On the outside of the organ of the sense of the relations of colour, and below the last. A round protuberance at the lateral base of the frontal bone, towards the temple, and behind the organs of music and numbers. At the middle and anterior part of the frontal bone, above that of the memory of things. In part, confounded with the preceding. In- dicated, at the outer side of this last, by two protuberances, which give to the fore- head a peculiar hemispherical shape. At the lateral and outer part of the last; and giving greater width to the frontal promi- nences. 1 On the outer side of the last; divided into two halves by the coronal suture. I Indicated by an oblong prominence above the organ of comparative sagacity; almost at the frontal suture. CEREBRAL ORGANS ACCORDING TO SPURZHEIM. 309 25. Imitation; mimicry. (G.) Nachahmungssinn. 26. God and religion; theosophy. (G.) Theosophisches Sinn. 27. Firmness; constancy; perseve- rance; obstinacy. (G.) Stretigkeit, fester Sinn. Fig. 52. At the outerside of the last. At the top of the frontal bone and at the supe- rior angles of the parietal bones. The top of the head; at the anterior and most elevated part of the parietal bones. Fig. 53. Fig. 54 ORGANS ACCORDING TO SPURZHEIM. 1. Amativeness. 2. Phi loprogen i t i veness. 3. Inhabiliveness. 4. Adhesiveness or At- tachment. 5. Combativeness. 6. Destructiveness. 7. Construcliveness. 8. Acquisitiveness. 9. Secreti veness. 10. Self-esteem. 11. Love of Approbation. 12. Cautiousness. 13. Benevolence. 14. Veneration. 15. Firmness. 16. Conscientiousness or Justice. 17 Hope. 18. Marvellousnes3. 19. Wit. 20. Ideality. 21. Imitation. 22. Individuality. 23. Form. 24. Size. 25. Weight and Resist- ance. 26. Colour. 27. Locality. 28. Numeration. 29. Order. 30. Eventuality. 31. Time. 32. Melody or Tune. 33. Language. 34. Comparison. 35. Causality. The first nineteen of these, according to Gall, are common to man and animals : the remaining eight, man possesses exclusively. They are, consequently, the attributes of humanity. Spurzheim,a a fellow-labourer with Gall, who accompanied him Phrenology, Amer. Edit., Boston, 1833. 310 MENTAL FACULTIES. in his travels, and was associated with him in many of his publica- tions, has added some other faculties, so as to make the whole num- ber thirty-five; but they have not been embraced by Gall in his most recent publication, whence many of these details are taken; and, indeed, many of the positions of Spurzheim are repudiated by several of Gall's followers.3 The organs admitted by Spurzheim are given on the opposite page: the numbers corresponding with those of the accompanying figures. On the situation of the different cerebral organs, Gall remarks,— 1st. That those which are common to man and animals are seated in parts of the brain that are common to both:—at the posterior in- ferior, and anterior inferior, portions. On the contrary, those, that are exclusive to man, are situate in parts of the brain, which exist only in him;—in the anterior superior parts, which form the fore- head. 2dly. The more indispensable a faculty, and the more im- portant to the animal economy, the nearer is its organ to the median line and to the base of the brain. 3dly, and lastly. The organs of the faculties, that aid, or are similar to each other, are generally situate in proximity. In his exposition of each of these organs, and of the reasons that induce him to assign it as the seat of a special faculty, he sets out by demonstrating the necessity of the faculty, which he regards to be fundamental and primary, and to which he assigns a special nervous system or organ in the brain. 2dly. He endeavours to show, that this faculty is really primary. He considers it to be such, whenever psychological facts show, that it has its exclusive source in organization; for example, when it is not common to all animals and sexes ; when, in the individual pos- sessing it, it does not exhibit itself in a ratio with the other faculties with which he is endowed; when it has its distinct periods of deve- lopement and decrease, and does not in this respect, coincide with the other faculties; when it can be exerted alone, be diseased alone, continue sound alone, or be transmitted alone from parent to child, &c. Lastly, he points out the part of the brain, which he considers to be its organ, founding his decision on numerous empirical obser- vations of the brains of men and animals, that have possessed, or been devoid of, the faculty and organ in question; or have had them in unequal degrees of developement. It is impossible for us, in a work of this kind, to exhibit all the views of Gall, and the arguments he has adduced in favour of the existence of his twenty-seven faculties. The selection of one—the instinct of generation—will be sufficient to show how he treats of the whole. Gall's instinct of generation is that, which in each ani- mal species impels the individuals of different sexes towards each other for the purpose of effecting the work of reproduction. The necessity for such an inclination for the general preservation of ani- mals is manifest. It is to the preservation of the species what the sensation of hunger is to that of the individual. Again, it is cer- a Elliotson, Human Physiology, p. 384, and 1147, London, 1840, SITUATION OF THE CEREBRAL ORGANS. 3J] tainly primary and fundamental, for it is independent of all external influence. It does not make its appearance until puberty, and it disappears long before other faculties. In many animals it returns periodically. In each animal species, and in each individual, it has a special and different degree of energy ; although external circum- stances may be much the same in all, or at least may not present differences, in any manner proportionate to those of the instinct. It may be either alone active, amidst the languor of other faculties, or it may be alone languishing. Lastly, it cannot be referred to the genital organs, for it has been observed in children, whose organs have not been developed; it has frequently continued to be felt in eunuchs; and has been experienced by females who, owing to original monstrosity, have had neither ovary nor uterus.(?) The part of the brain which is the organ of this instinct, is, according to Gall, the cerebellum. His reasons for this belief are the follow- ing. 1st. In the series of animals a cerebellum exists only in those, which are reproduced by copulation, and which, consequently, must have the instinct in question. 2dly. There is a perfect coin- cidence between the periods at which the cerebellum becomes developed, and the appetite appears. In infancy, it does not exist, and the organ is therefore small. 3dly. In every species of animal and in every individual, there is a ratio between the size of the cerebellum and the energy of the inclination. In males, in whom it is generally more imperious, the cerebellum is always larger. 4thly. A ratio exists between the structure of the cerebellum and the kind of generation. In oviparous animals, for instance, the cerebellum is smaller at its median part; and it is only in the vivi- parous, that the hemispheres exist. 5thly. A similar ratio exists between the cerebellum and the external genital organs. If the latter are extirpated at an early age, the developement of the cere- bellum is arrested, and it continues small for the remainder of life. Neighbouring parts, too, which are attributes of the male sex, as the horns of the stag, and the crest of the cock, are often similarly stunted. On the other hand, the cerebellum, in its turn, exerts an intimate influence on the venereal appetite, and modifies the external genital organs. Injuries of the cerebellum either render the indi- vidual impotent, or excite erotic mania. In nymphomania, the patient often complains of acute pain in the nape of the neck ; and this part is more tumid and hot in animals at the rutting season. Gall asserts, that he had noticed in birds, that the cerebellum differs both in size and excitation, during the season of love, from what it is at other times; and he affirms, that if erection is observed in those who are hanged, or in consequence of the application of a blister or a seton to the nape of the neck, or of the use of opium, or, who are threatened with apoplexy, especially when the apoplexy is cerebellous,1 or, during sleep, the effect is, in all these cases, owing a See a case of Arachnitis Cerebelli—in which there was genital excitement—by the author, in Lond. Med. Rep. for Oct. 1822; also, Abercrombie on Diseases of the Brain, 312 MENTAL FACULTIES. to congestion of blood in the brain in general, and in the cerebellum in particular. From these data, Gall concludes, that the cerebellum is the organ of the instinct of reproduction; and he remarks, that as this organ presides over one of the most important faculties, it is situate on the median line; and at the base of the skull. In this manner, he proceeds, with more or less success, in his investigation of other cerebral organs and faculties. But Gall does not restrict himself to the physiological applications of his system. He endeavours, likewise, to explain the differences, that exist between him and other philosophers. He altogether rejects the primary faculties of instinct, intelligence, will, liberty, reason, perception, memory, judgment, &c. of the metaphysician as mere generalizations of the mind, or common attributes of the true primary faculties. Whilst, in the study of physics, the general and special qualities of matter have been carefully distinguished, and the latter have been regarded as alone founding the particular nature of bodies, the metaphysician, says Gall, has restricted him- self to general qualities. For example, it is asserted, that " to think is to feel.'" Thought is doubtless a phenomenon of sensibility; but it is a sensitive act of a certain kind. To adhere rigidly to this expression, says Gall, is but to express a generality, which leaves us in as much ignorance as to what thought is, as we should be of a quadruped or bird, by saying that it is an animal; and as, to become acquainted with such animals, their qualities must be specified, so to understand thought, the kind of sensation must be specified, that constitutes it. Instinct, according to him, is a general expression, denoting every kind of internal impulse; and consequently there must be as many instincts as there are fundamental faculties. Intel- ligence is likewise a general expression, designating the faculty of knowledge; and, as there are many instincts, so there are many kinds of intelligence. Philosophers, he thinks, have erroneously ascribed instinct to animals, and intelligence to man. All animals have, to a certain extent, intelligence; and in man many faculties are instincts. Neither is the will a fundamental faculty. It is only a judgment, formed amongst several motives, and the result of the concourse of actions of several faculties. There are as many desires as faculties; but there is only one will, which is the product of the simultaneous action of the intellectual forces. So that the will is frequently in opposition to the desires. The same thing applies to liberty and reason; the former merges into what has been said of the will, and the latter is only the judgment formed by the superior intellectual faculties. In this respect, however, he remarks, it must not be confounded with intelligence: many animals are intelligent, but man alone is rational. 3d edit. p. 60, Lond. 1836; and Stokes's Lectures on the Theory and Practice of Phy- sic, Amer. Med. Lib. Edit. p. 214, Philad. 1837. For some cases of cerebellous dis- ease, without genital excitement, see Duplay, in Archives Generates de Medecine, Nov. 1836; also, Mailer's Elements of Physiology, by Baly, 1st edit. p. 833, London, 18?8. VIEWS OF GALL. 313 On the other hand, what are termed, in the intellect, perception, memory, judgment, imagination, &c. are attributes common to all the intellectual faculties, and cannot, consequently, be considered primary faculties. Each faculty has its perception, memory, judg- ment and imagination ; and, therefore, there are as many kinds of perception, memory, judgment, and imagination, as there are pri- mary intellectual faculties. This is so true, Gall remarks, that we may have the memory and the judgment perfect upon one point, and totally defective upon another. The memory of tones, for instance, is not the same as that of language; and he, who pos- sesses the one, may not have the other. The imaginations, again, of the poet, musician, and philosopher, differ essentially from each other. These faculties are, therefore, according to him, nothing more than different modes of the activity of all the faculties. Each faculty perceives the notion to which it has been attracted, or has perception; each preserves and renews the recollection of this no- tion, or has memory. All are disposed to act without being excited to action from without, when the organs are largely developed or have considerable intrinsic activity, which gives rise to imagination: and, lastly, every faculty exerts its function with more or less per- fection, whence results judgment. Attention, in his view, is only the active mode of exercise of the fundamental faculties of the intellect; and, being an attribute of all, it cannot be called a primary faculty. As regards the affective faculties, or what have been called the passions and affections, Gall, in the first place, asserts, that the term passion is faulty, when used to indicate a primary faculty. It ought only to designate the highest degree of activity of any faculty. Every faculty requires to be put into action, and, according to the degree of activity which it possesses, it is a desire, a taste, an incli- nation, a want, a passion. If it be only of the medium energy it is a taste. If, on the other hand, it be extremely active, it is a passion. There may, consequently, be as many passions as there are facul- ties. We speak of a passion for study, or a passion for music, as we do of the passion of love, or that of ambition. Gall objects, also, to the word affection, which, according to him, expresses only the modifications the primary faculties may present, according to the mode in which the external and internal influences affect them. Some of these modes are common to all the faculties, as those of pleasure and pain. Every faculty may be the occasion of the one or the other. Other affections are special to some faculties; as pretension, which, he says, is an affection of pride: and repentance an affection of the moral sense. Finally, these affections are simple or compound: simple when they only bear upon one faculty, as anger, which is a simple affection of the faculty of self-defence;—com- pound, when several faculties are affected at the same time, as shame, which is an affection of the primary faculties of the moral sense and of vanity. Gall reproaches the moralists with having multiplied too much the number of the primary affective faculties:—in his view, the modifi- vol. i. 27 314 MENTAL FACULTIES. cations of a single faculty, and the combination of several, give rise to many sentiments, that are apparently different. For instance, the primary faculty of vanity begets coquetry, emulation, and love of glory. That of self-defence gives rise to temerity, courage, a quar- relling spirit, and fear. Contempt is the product of a combination of the faculties of pride and of the moral sense, &c. Lastly, as regards their psychological differences, Gall divides all men into five classes. First. Those in whom all the faculties of humanity predominate; and in whom, consequently, organization renders the developement of the mind and the practice of virtue easy. Secondly. Those in whom the organs of the animal faculties predominate; and who, being less disposed to goodness, will need the aid of education and legislation. Thirdly. Those in whom all the faculties are equally energetic, and who may be either excellent individuals, or great criminals, according to the direction they may take. Fourthly. Those who, with the rest of the faculties nearly equal and mediocre, may have one predominant. Fifthly, and lastly. Those who have the faculties alike mediocre:—this is the most numerous class. It is rare, however, he remarks, that the charac- ters and actions of men proceed from a single faculty. Most com- monly, they are dependent upon the combination of several; and, as the possible combinations of so many faculties are almost innu- merable, the psychological varieties of mankind may be extremely various. Again, as each of the many organs of the brain may have, in different men, a particular degree of developement and activity, seeing that each of the faculties, which are their products, has, most commonly, a special shade in every individual; as these organs can establish between each other a considerable number of combinations; and as men, independently of the differences in their cerebral orga- nization, which gives rise to their dispositions, never cultivate and exert their faculties in an equal and similar manner, it may be con- ceived, that nothing ought to be more variable than the intellectual and moral characters of men; and wre may thus explain, why there are not two men alike in this respect. Such is an imperfect sketch of the physiological doctrine of Gall, which we may sum up in the language of the author, in his Revue Sommaire, appended to his great work.1 " I have established, by a great number of proofs, as well negative as positive, and by the refutation of the most important objections, that the brain alone has the immense advantage of being the organ of the mind. Farther researches on the measure of the degree of intelligence of man and animals have shown, that the brains of animals are more simple or more complex, as their instincts, desires, and faculties are more simple or more compound; that the different regions of the brain are concerned in different categories of function; and, finally, that the brain of every species of animal, and, consequently, that of man, constitutes an aggregation of as many special organs, as there are » Sur les Fonctions du Cerveau, vi. 500, Paris, 1825. VIEWS OF GALL. 315 essentially different moral qualities and intellectual faculties in the man or animal. The moral and intellectual dispositions are innate. Their manifestation is dependent upon organization. The brain is the exclusive organ of the mind. Such are four incontestable prin- ciples, forming the whole physiology of the brain;" and he adds, " the detailed developement of the physiology of the brain has un- veiled the deficiencies of the hypotheses* of philosophers regarding the moral and intellectual powers of man ; and has been the means of bringing to light a philosophy of man, founded on his organiza- tion, and, consequently, the only one in harmony with nature." It is impossible for us to enter, at length, into the various facts and hypotheses developed in the preceding exposition. The great points of doctrine in the system of Gall, are:—First. That the brain consists of a plurality of organs, each engaged in a separate, distinct office,—the production of a special intellectual or moral faculty. Secondly. That each of these organs ends at the periphery of the brain, and is indicated by more or less developement of the part; and Thirdly. That, by observation of the skull, we maybe enabled to detect the protuberance, produced by such cerebral de- velopement, and thus to indicate the seat of the cerebral organs of the different faculties. It has been shown, in the preceding history, that the notion of the plurality of organs has extensively prevailed in all ages; and what- ever may be the merit of the arguments adduced by Gall on this subject, it is difficult not to conceive, that different primary faculties may have their corresponding organs. Simple inspection of the brain indicates that it consists of numerous parts, differing essen- tially in structure and appearance from each other; and it is but philosophical to presume, that these are adapted to equally different functions, although our acquaintance with the physiology of the organs may not be sufficiently extensive to enable us to designate them. Of the innate character of several of the faculties, described by Gall, it is scarcely possible for us to admit a doubt. Take, for instance, the instincts of generation and of love of progeny. With- out the existence of these instincts, every animal species would soon be extinct. It seems fair, then, to presume, that these instincts or innate faculties may have encephalic organs, specially concerned in their ma- nifestation. Gall places them in the posterior part of the head,—the instinct of generation in the cerebellum; and his causes for so doing have been cited ; yet, striking as his reasoning on this topic seems to be, it has been contested by many physiologists ; by Broussais, Foville and Pinel-Grandchamp, Rolando, Flourens, Desmoulins, and others; and, not only by argument, but by that which must ulti- mately test the validity of the doctrines of the phrenologist—direct experiment. It is affirmed, indeed, that the genital excitement which is supposed by the followers of Gall to be seated in the cerebellum, can be equally produced by irritating the posterior column of the spinal marrow, and it would seem, that coincidence of disease of the spinal cord, with affection of the genital organs is much more 316 MENTAL FACULTIES. frequent.* The views of the gentlemen, cited above, regarding the influence of the cerebellum, will be given under the head of Muscu- lar Motion. One of the greatest objections that has been brought against the system of Gall is the independence in it of the different faculties of each other. Each is made to form a separate and independent state, with no federative jurisdiction to produce harmony in their actions, or to regulate the numerous independent movements and complicated associations, which must inevitably occur in the various intellectual and moral operations. Gall appears indeed to have lost sight of the important doctrine of association, which applies not only to the ideas, but to every function of the frame; and with which it is so important, for the pathologist particularly, to be acquainted. The second point of doctrine,—that each of the cerebral organs ends at the periphery of the brain, and is indicated by more or less developement of the part,—is attended with equal difficulties. It is admitted, as we have seen, by the most eminent physiologists, that the exterior part of the brain is probably chiefly concerned in the mental and moral manifestations. Almost all believe, that this func- tion is restricted to the brain proper. Gall and his followers include the cerebellum. Yet we meet with cases, which appear to militate strongly against this notion. Hernia of the brain is one of these : in this, owing to a wound of the cranium and dura mater, a portion of the cerebral substance may protrude and be removed; yet the individual may do well; and to all appearance retain his faculties unimpaired. This is explained by the craniologist, by presuming, that as the fibres of the brain are vertical, their extremities have alone been removed, and a sufficient amount of fibres has remained for the execution of the function; and he farther entrenches him- self in the difficulty of observing accurately, in these cases, whether the faculties be really in their pristine integrity. He asserts, that it is frequently extremely difficult to prove the existence of mental aberration; that the precise line of demarcation between reason and unsoundness of mind is not easily fixed; and that commonly, in these cases, attention is paid only to the most general qualities, and if the patient is seen to take food and medicine when offered to him, to reply to questions put to him, and to have consciousness, the moral sense is esteemed to be free, and in a state of integrity. It must, however, be admitted, that the explanation of the craniologist on these topics is feeble and unsatisfactory. It is, of course, gratu- itously assuming, that observation in such cases has been insuffi- cient; and if he finds, that the fact in question militates against the faith he has embraced, he is too apt to deny its authenticity alto- gether. With all the candour which Gall possessed, this failing is too perceptible in his writings. Again, in many of the cases of severe injury of the brain, which 1 Midler's Elements of Physiology, by Baly, p. 833, Lond. 1838. EXAMINATION OF THE VIEWS OF GALL. 317 are on record, but one hemisphere was implicated; and accordingly, the impunity of the intellectual and moral manifestations has been ascribed to the cerebrum being a double organ; so that, although one hemisphere may have been injured; the other, containing similar organs, may have been capable of carrying on the function; as one eye can still execute the function of vision, when the other is diseased or lost. Cases, however, have occurred in which the faculty has been lost, when only one hemisphere was implicated. Such cases are given by Mr. Combe. One interesting example, the author heard Mr. Combe relate. A gentleman suddenly forgot all words but yes and no, and after death a lesion was found in the left hemisphere of the brain, involving the phrenological organ of language. The explanation by Mr. Combe of this phenomenon is plausible but not probable. It appears to me, he observed, " that the lesion's being on one side only acounts for his power of under- standing words, while he had not the power of employing them."a Many cases, again, are recorded, in which injury was sus- tained by both hemispheres, and in corresponding parts; yet the faculties persisted;15 whence Miiller has concluded, that the his- tories of injuries of the head are directly opposed to the existence of special regions of the brain, destined for particular mental faculties. Cases of hydrocephalic patients are likewise cited, who have preserved their faculties entire. These Gallc explains, by affirming, that the brain is not dissolved in the fluid of the dropsy; that it is only deployed, and distended by the presence of the fluid; and as the distension takes place slowly, and the pressure is moderate, the organ may be so habituated to it as to be able to continue its functions. Lastly, some experiments of Duver- neyd have been adduced as objections to the view of Gall. These consisted in removing the whole of the brains of pigeons ; yet no change seemed to be produced in their faculties; but, in reply to this, it is asserted, that Duverney could only have removed some of the superficial parts of the organ; for, whenever the experiment has been repeated, so as to implicate the deeper seated portions, opposite results have been obtained. The truth is, that under any view of the subject these facts are equally mysterious. We cannot understand why, in particular cases, such serious effects should result from severe injury done to the brain ; and, in others, the comparative immunity attendant upon a Combe's Lectures, by Boardman, p. 261, New York. b See a fatal case of disorganization of the brain, without corresponding derangement of the intellectual and moral acts, by Dr. G. W. Boerstler, of Lancaster, Ohio, in Dun- glison's American Medical Intelligencer, No. 1, for April 1,1837. Mr. Combe, in his re- cent work,—Notes on the United States of North America, during a phrenological visit in 1838-9—40 ; Phila. 1841—refers to a case of injury of both hemispheres, which he thinks, from examining the case, was confined almost entirely to the organs of Eventu- ality. The man recovered, and was exhibited to Mr. Combe with a history of his case by Drs. Knight and Hooker, of New Haven. In the opinion of the latter, the intel- lectual faculties were not impaired—vol. ii. p. 276. c Op. citat. ii. 263. Male's Epitome of Forensic Medicine, in Cowper's Tracts on Medical Jurispru- dence, Philad. 1819; Beck's Medical Jurisprudence, 5th edit. ii. 164; also Devergie, in Annales d'Hygiene Publique, 1829. 28* 330 MUSCULAR MOTION. 3. OF THE BONES. The bones are the hardest parts of the animal frame: and, con- sequently, serve as a base of support and attachment to the soft parts. They constitute the framework of the body, and determine its general shape. The principal functions they fulfil are,—to form defensive cavities for the most important organs of the body —the encephalon, spinal marrow, &c.—and to act as so many levers for transmitting the weight of the body to the soil, and for the different locomotive and partial movements. To them are attached ihe different muscles, concerned in those functions. In man and the higher classes of animals, the bones are, as a general rule, within the body; his skeleton is, consequently, said to be inter- nal. In the Crustacea, the testaceous mollusca, and in certain insects, the skeleton is external, the whole of the soft parts being contained within it. The lobster and crab are familiar instances of this arrangement. The stature of the human skeleton is various, and may be taken, on the average, perhaps,—in those of European descent,—at about five feet eight or nine inches." We find, however, examples of con- siderable variation from this average. A skeleton of an Irish giant, in the museum of the Royal College of Surgeons of London, mea- sures eight feet four inches. On the other hand, Bebe, the dwarf of Stanislaus, king of Poland, was only thirty-three inches high; and a Polish nobleman, Borwlaski, measured twenty-eight French inches. He had a sister, whose height was twenty-one inches.11 The bones may be divided into the short, broad or flat, and long. The short bones are met with in parts of the body, which require to be both solid and movable:—in the hands and feet, for example, and in the spine. The flat or broad bones form the parietes of cavities, and they aid materially in the movements and attitudes, by affording an extensive surface for the attachment of muscle. The long bones are chiefly intended for locomotion, and are met with only in the extremities. The shape of the body or shaft, and of the extremities merits attention. The shaft or middle portion, is the smallest in diameter, and is usually cylindrical. The extremities, on the other hand, are expanded; a circumstance, which not only adds to the solidity of the articulations, but diminishes the obliquity of the in- sertion of the tendons, passing over them, into the bones. In their interior is a medullary canal or cavity, which contains the medulla, marrow or pith:—a secretion, whose office will be a theme for after inquiry. One great advantage of this canal is, that it makes the a See Quetelet, Sur I'Homme, &c, Paris, 1835; and Prof. Forbes's Experiments on the weight, height, and strength of above eight hundred persons,—English, Scotch, Irish, and Belgian, in Lond. and Edinb. Philos. Magaz., March, 1837, p. 197, and Dunglison's Amer. Med. Intelligencer, p. 74, May 15, 1837. b Lectures on Physiology, Zoology. &c, by W. Lawrence, p. 434, Lond. 1819. BONES. 331 bone a hollow cylinder, and thus diminishes its weight. On many of the bones, prominences and cavities are perceptible. The emi- nences bear the generic name of apophyses or processes. Their great use is, to cause the tendons of muscles to be inserted at a much greater angle into the bones they have to move.- It may be seen hereafter, that the nearer such insertion is to the perpendicular to the lever, the greater will be the effect produced. The cavities are of various kinds. Some are articular: others for the insertion, reception, or transmission of parts. Those of insertion and reception afford space for the attachment of muscles; those of transmission, &c. are frequently incrusted with cartilage, converted into canals by means of ligament, and furnished with a synovial membrane, which lubricates them, and facilitates the play of the tendons, for the passage of which they are destined. The mechanical structure of the bone is a laminated framework, incrusted by an earthy substance, and penetrated by exhalant and absorbent vessels, arteries, veins, and nerves. Herissant,a appears to have been one of the first who stated, that bone is essentially composed of two substances:—the one a cartilaginous basis or parenchyma, giving form to the part,—the other a peculiar earthy matter deposited in this basis, and communicating to it its hardness. These two constituents can be readily demonstrated ; the first, by digesting the bone in dilute muriatic acid, which dissolves the earthy part, without acting on the animal matter; and the second, by burn- ing the bone, until all the animal matter is consumed, whilst the earthy part is left untouched. If we take a long bone and divide it longitudinally, we find, that it is composed of three different substances, all of which may, how- ever, be regarded as the same osseous tissue, in various degrees of condensation. These are,—the hard or compact substance, the spongy or areolar, and the reticulated. The first is in the most con- densed form; it exists at the exterior of the bone, and constitutes almost the whole of the shaft. The second is seen towards the extremities of the long bone, and in almost the whole of the short bones. In it, the lamina? are less close, and have a cancellated appearance,—the cellules bearing the name of cancelli. The reticu- lated substance is a still looser formation; the laminae being situate at a considerable distance, and the space between filled up with a series of membranous cells, which lodge the marrow. The marginal figures represent a longitudinal section of the os femoris, and os humeri, in which this arrangement is well exhibited. We have seen the advantages of the expanded extremities of long bones, as regards the insertion of muscles; but it is obvious, that if these portions of the bone had consisted of the heavy com- pact tissue, the increased weight of the limbs would have destroyed the advantages, which would otherwise have accrued; whilst, if a Memoir, de 1'Academ. des Sciences de Paris, p. 322, pour 1758. 332 MUSCULAR MOTION, the shaft of the bone, exposed, as it is, to external violence, had consisted of the spongy tissue only, it would not have beemable to offer the necessary resistance. It is, therefore, formed almost entirely of the compact tissue; so that a section of one inch in height, taken from the body of the bone, will not differ essentially in weight from an inch taken from the ex- Fig. 58. tremity. Nor does the cavity, within the bones, diminish their strength as might be at first sight presumed. By enlarging the circum- ference, the contrary effect is produced; for we shall see, in the mechanical proem to the particular movements, that of two hollow co- lumns, formed of an equal quantity of matter and of the same height, that, which has the larger cavity, is actually the stronger. A very important use of the cancellated or spongy texture of the bones was suggested by a dis- tinguished individual of this country, to whom surgical science, in particular, has been so largely indebted. Dr. Physick1 asserts, that it serves to diminish, and, in many cases, to pre- vent, concussion of the brain, and of the other viscera, in falls and blows. The demonstra- tion, which he gives of this, is simple and satis- factory. If we suspend a series of six ivory balls by threads; raise the ball at one extremity, and allow it to fall on the next to it, we find, that the farthest ball in the series is impelled to a distance, which corresponds with the mo- mentum communicated by the first ball to the second. But if we substitute, for the middle ball of the series, a ball made of the cellular structure of bone, we find that almost the whole of the momentum is lost in this osseous structure; especially, if it be previously filled with tallow or well soaked in water, so as to bring it to a closer approximation to the natural, living condition. Bones consist of earthy salts and animal matter intimately blended. The latter is chiefly cartilage, gelatine, and the peculiar fatty matter—the marrow. On reducing bones to powder and di- gesting them in water, the fat rises and swims upon its surface, and the gelatine is dissolved. According to the analysis of Berzelius, 102 parts of dry human bones consist of animal matter, 33.3; phosphate of lime, 51.04; carbonate of lime, 11.30; fluate of lime, 2 ; phosphate of magnesia, 1.16; soda, muriate of soda, and water, 1.2. Fourcroy and Vau- quelin did not detect any fluoric acid, but they found oxides of iron a Horner's Special and General Anatomy, 4th edit., Philad. 1836. ANALYSIS OF BONES. 333 and manganese, silica, and albumen. Hatchett detected, also, a small quantity of sulphate of lime.a Schregerb gives the following as the proportions of the animal and earthy parts of bone : INFANTS. ADULTS. AGED. Animal matter,.....47.20 20.18 12.20 Earthy matter, .... - 48.48 74.84 84.10 95.68 95.02 ,96.30 The bones are enveloped by a dense fibrous membrane, termed, in the abstract, periosteum: but assuming different names according to the part it covers. On the skull, it is called pericranium: and its extensions over the cartilages of prolongation, are called peri- chondrium. The chief uses of this expansion are, to support the vessels in their passage to and from the bone, and to assist in its formation; for we find, that if the periosteum be removed from a bone, it becomes dead at the surface previously covered by the mem- brane, and exfoliates. In the foetus, it adds materially to the strength of the bone, prior to the completion of ossification. In the long bones, ossification commences at particular points; one generally in the shaft, and others at the different articular and other processes. These ossified portions are, for some time, separated from each other by the animal matter, which alone composes the intermediate por- tions of the bone; and, without this fibrous envelope, they would be too feeble perhaps to resist the strains to which they are exposed. The periosteum, moreover, affords a convenient insertion for the muscles destined to act upon the bones; and enables them to slide more readily when in action; hence friction is avoided. The cavity of long bones is lined by a membrane—called the medullary membrane or internal periosteum—which is supplied with numerous vessels, adheres to the interior surface of the bone, and is not only concerned in its nutrition, but also in the secretion of the marrow,—and likewise of a kind of oily matter, which differs from marrow merely in being more fluid, and is contained in the cells, formed by the spongy substance, and in the areolae of the compact substance. This is called the oil of bones. The marrow is considered to be lodged in membranous cells, formed by an extension of the internal periosteum ; whilst, accord- ing to Howship,c the oil of bones is probably deposited in longitu- a Turner's Elements of Chemistry, 4th Amer. Edit. p. 576, Philad. 1832. See, also,' Dr. Davy, in Monro's Outlines of Anatomy, i. 36, and Meckel's Handbuch der Anato- mie, i. 358 ; Rudolphi, Grundriss der Physiologie, i. 160, Berlin, 1821; and Multer's Handbuch, Baly's translation, P. i. p. 370. b (Isteochemice Specimen. Vitcberg. 1810 ; Miescher De Ossium Genesi, Structura et Vita, Dissert. Anat. Phys. Inaugural, p. 47, Berol. 1836; and American Med. Intelligencer for June 15,1837, p. 115; Weber's Hildebrandt's Handbuch der Anato- mie, i. 316, Braunschweig, 1830 ; and Purkinje and Deutsch, De Penitiori Ossium Structura, Vratisl. 1834 ; and Dublin Journal of Med. Science, Sept. 1836, c Medico. Chirurg. Transact, vii. 393. 334 TABLE OF THE BONES. dinal canals, which pass through the solid substance of the bone, and through which its vessels are transmitted. The nature and fancied uses of the marrow and of the oil of bones will be considered in another part. The bones, periosteum, and marrow are, in the sound state, amongst the insensible parts of the frame. They are certainly not sensible to ordinary irritants; but, when morbid, they exhibit intense sensibility. This, at least, applies to the bones and periosteum; the sensibility, which has been ascribed to the marrow, in disease, being probably owing to* that of the prolongations of the membrane, in which it is contained. The number of the bones in the body is usually estimated at two hundred and forty, exclusive of the sesamoid bones, which are always found in pairs at the roots of the thumb, and great toe, between the tendons of the flexor muscles and joints, and, occasion- ally, at the roots of the fingers and small toes. In the following Table of the Bones, the numbers on the left hand correspond with those of the accompanying plates of the skeleton. TABLE OF THE BONES. ''Bones of the Cranium or Skull, < Bones op the C Head | Bones of the Face, . Dentes or Teeth, Bone of the Tongue, Bones of the Ear, . ' Vertebra, }Sacrum, Bones of the/Os Coccygis, Trunk. jThe Thorax, wThe Pelvis, 1. Frontal, 2. Parietal, - 5. Occipital, - 3. Temporal, - Ethmoid, - 4. Sphenoid, - 7. Superior Maxillary, 6. Malar or cheek, - Nasal, Lachrymal, Palatine, - Inferior Spongy, Vomer, 8. Inferior Maxillary, Incisors, Cuspidati, . Molares, . Hyoid, Malleus, . Incus, Orbiculare, HOW many. 1 2 1 2 1 1 2 2 2 2 2 2 1 1 8 4 20 1 2 2 2 1 12. Dorsal, . . . .12 1,13. Lumbar, .... 5 .......1 1 S14. Sternum, .... 1 C 28, Innomlnatum, comprising 1 25..? 29. Ilium, 30. Ischium, and > 2 / 31, Pubis, S TABLE OF THE BONES. 335 Bones of the UrrER Extremity. rThe Shoulder, - The Arm, iThe Forearm, - /Carpus or [ Wrist, JTheHand,) 22., Bones of the Lower Extremity. The Thigh, kThe Leg, The Foot, 38. 23. Metacarpus, 24. Phalanges, < 17. Clavicle, - £18. Scapula, 19. Humerus, - J 21. Ulna, I 20. Radius, - Os Naviculare, Lunare, Cuneiforme, Orbiculare, Trapezium, Trapezoides, Magnum, - Unciforme, Tarsus or ^ Ankle or /Instep, 36 '39. Metatarsus, £0. Phalanges, - 32. Femur, C 33. Patella, 1 34. Tibia, f 35. Fibula, 37. Os Calcis, - Astragalus, Cuboides, - Naviculare, Cuneiforme, 2 2 2 2 2 2 2 2 2 2 2 2 2 10 28 2 2 2 2 2 2 2 2 6 10 28 Total, - 240 The bones are connected by means of articulations or joints, which differ materially from each other. To all the varieties, names are appropriated, which form a difficult task for the memory of the anatomical student. Technically, every part at which two bones meet and are connected, is called an articulation, whether any degree of motion is permissible or not. This, indeed, is the foundation of the division that prevails at the present day, the arti- culations being separable into two classes: the immovable or synar- throses : and the movable or diarthroses. The synarthroses are variously termed, according to their shape. When the articular surfaces are dovetailed into each other, the joint is called a suture. This is the articulation that prevails be- tween the bones of the skull. Harmony is when the edges of the bones are even, and merely touch, as in the bones of the head in quadrupeds and birds. When a pit in one bone receives the pro- jecting extremity of another, we have a case of gomphosis. It is exhibited in the union between the teeth and their sockets. Lastly, schindylesis is when the lamina of one bone is received into a groove of another; as in the articulation of the vomer, which separates the nasal fossae from each other. The movable articulations comprise two orders:—the amphiar- throses, in which the two bones are intimately united by an inter- mediate substance, of a soft and flexible character, as in the junc- tion of the vertebrae with each other; and the diarthroses, properly so called. The last admit of three subdivisions—the enarthroses or ball and socket joints; the condyloid, in which, owing to the head being oval, the movements are not as easy in all directions as where 336 MUSCULAR MOTION. the head is spherical; and the ginglymoid or ginglymus, in which the motion can occur in only one direction as in a hinge. The farther subdivision of the joints belongs more to anatomy than physiology. The articular surfaces of the bones never come into immediate contact. They are tipped with a firm, highly elastic substance, called cartilage; which, by its smoothness enables the bones to move easily upon each other, and may have some influence in deadening shocks, and defending the bones, which it covers. The arrangement of the cartilage varies according to the shape of the extremity of the bone. If it be spherical, the cartilage is thick at the centre, and gradually diminishes towards the circumference. In a cavity the reverse is the case; the cartilage is thin at the centre, and becomes thicker towards the circumference ; and on a trochlea or pulley, its thickness is nearly every where alike. An admirable provision against displacement of the bones at the articulations exists in the ligaments. These, by the French anato- mists, are distinguished into two kinds—the fibrous capsules, and the ligaments properly so called. The former are a kind of cylindrical sac, formed of a firm, fibrous membrane; open at each extremity, by which they closely embrace the articular end of the bones; and loose, when the joint admits of much motion. In this way, the arti- culation is completely enclosed : they generally bear the name of capsular ligaments. The ligaments, properly so called, are bands of the same kind of tissue, which extend from one bone to another; by their resistance preserving the bones in situ; and by their suppleness admitting of the necessary motion. The interior of all these articulations is lubricated by a viscid fluid, called the synovia. This is secreted by a peculiar membrane of a serous nature; and its use is to diminish friction, and, at the same time, to favour adhesion. The mode in which it is secreted, and its chief properties and uses, will be the subject of future inquiry. In certain of the movable articulations, fibro-cartilaginous sub- stances, frequently called inter articular cartilages, are found be- tween the articular surfaces, and not adherent to either of them. These have been supposed to form a kind of cushion, which, by yielding to pressure, and returning upon themselves, may thus pro- tect the joints to which they belong ; and, accordingly it is asserted, that they are met with in the joints, which have to sustain the greatest pressure; but Magendiea properly remarks, that they do not exist in the hip-joint, or in the ankle-joint, which have constantly to support the strongest pressure. The use, which he suggests, is more specious;—that they may favour the extent of motion, and prevent displacement. The stability of the joints is likewise aided by the manner in which the muscles or tendons pass over them. These are contained in an a Precis Elementaire, 2de edit. i. 292, Paris, 1823. Plate I. Prawn Pi/ J Perry Engraved by JDrwit.m PlaU U,. /Mini/ byJ.Pmy. EHgravfit In/ J.ZH'auton PHYSIOLOGY OF MUSCULAR MOTION. 337 aponeurotic sheath, to prevent their displacement; and thus the whole limb becomes well protected, and dislocation infrequent, even in those joints, as that of the shoulder, which, as regards their osseous arrangement, ought to be very liable to displacement. It has been suggested by Weber, that the head of the thighbone is retained in situ, not by the power of the muscles or ligaments, but by the pressure of the surrounding atmosphere; and Lauer," who repeated Weber's experiments under the directions of Fricke, of Hamburg, considers, that the pressure of the atmosphere must be classed among the means by which the lower extremity is kept in apposition with the trunk of the body. 4. PHYSIOLOGY OF MUSCULAR MOTION. By voluntary motion we mean a contraction of the muscles under the influence of volition or the will. This influence is propagated along the nerves to the muscles, which are excited by it to contrac- tion. The encephalon, spinal marrow, nerves, and muscles are, therefore, the organs of voluntary contraction. Volition is one of the functions of the encephalon, and might have been, with much propriety, included under the physiology of the intellectual and moral acts ; but as it is so intimately concerned with muscular motion, it was judged advisable to defer its consideration until the present occasion. That volition is a product of encephalic action is proved by many facts. If the brain be injured in any manner;—by fracture of the skull, for example, or by effusion of blood, producing apoplectic pressure on some part of it;—or if it be deprived of its functions by the use of a strong dose of any narcotic substance ;—or if, again, it be in a state of rest, as in sleep:—volition is no longer exerted, and voluntary motion is impracticable. This is the cause why the erect attitude cannot be maintained during sleep; and why the head falls forward upon the chest, when the somnolency is to such an extent as to deprive the extensor muscles of the back and head of their stimulus to activity.b That an emanation from the encephalon is necessary is likewise proved by the effect of tying, cutting, compressing, or stupifying the nerve proceeding to a muscle; it matters not, that the will may act; the muscle does not receive the excitant, and no motion is pro- duced ; a fact which proves, that the nerves are the channels of communication between the brain and the muscles. If, again, we destroy the medulla oblongata and medulla spinalis, we abolish all muscular motion, notwithstanding the brain may will, and the muscles be in a state of physical integrity; because we have destroyed the parts whence the nerves proceed. In like manner, by successively slicing away the medulla spinalis from its base to the * Zeitschrift fur die gesammte Medicin, Band ii. Heft 3. b Adelon, art. Encephale (Physiol.) in Diet de Med. vii. 516, Paris, 1823; and Physiol, de I'Homme, L 25, 2de 6dit. Paris, 1829. vol. i. 29 338 MUSCULAR MOTION. occiput, we paralyse, in succession, every muscle of the body, which receives its nerves from the spinal marrow. Experiments of different physiologists have confirmed the view, that the encephalon is the chief seat of volition. When it has been sliced away to a certain extent, the animal has been thrown into a state of stupor, attended with the loss of sensibility, of the power of locomotion, and especially of spontaneous motion ; and in writing, dancing, speaking, singing, &c, we have indisputable evidence of its direction by the intellect. It is not so clear, that the seat of volition is entirely restricted to the encephalon. There are many actions of the yet living trunk, which appear to show, that an obscure volition may be exerted, even after the brain has been separated from the rest of the body; and acephalous children have not only moved perceptibly when in utero, but at birth. Without referring to the lower classes of animals, which, as we have already had occasion to remark, execute voluntary motions for a long time after they have been bisected, every one must have noticed the motions of decapitated fowls, which will continue for a time, to run and leap, and, appa- rently, to suffer uneasiness in the incised part. The feats of the Emperor Commodus are elucidative of this mat- ter. Herodian relates, that he was in the habit of shooting at the ostrich, as it ran across the circus, with an arrow having a cutting edge; and, even when the shaft was true to its destination, and the head was severed from the body, the ostrich usually ran several yards before it dropped. Kaauw Boerhaave—nephew of the cele- brated Hermann, and himself an eminent medical teacher at St. Petersburg—asserts, that he saw a cock, thus decapitated, run for a distance of twenty-three feet afterwards. Some cases are also recorded of men walking a few steps after decapitation, striking their breasts, &c; but they can scarcely be regarded as authentic* In those countries where judicial execution consists in decapitation by the sword, sufficient opportunities must have presented them- selves for testing this question; but no zealous Naturforscher appears to have been present to record them. Similar opportunities have likewise occurred under the operations of the guillotine. Legallois,b in some experiments, which he instituted, for the pur- pose of determining the nervous influence on the heart, &c, found, that rabbits, which he had decapitated and deprived of their hinder extremities, but still kept alive by artificial respiration, moved their fore paws whenever he stimulated them by plucking some of their hairs.c With regard to complete acephali, or those foetuses which are totally devoid of encephalon,—although they may vegetate in utero, a Adelon, op. citat. ii. 28 ; and Dr. J. R. Coxe, in Dunglison's Amer. Med. Intelli- gencer for May 15, 1837. b CEuvres, Paris, 1824. c See, also, Sir Gilbert Blane, in Select Dissertations on several subjects of Medical Science, Lond. 1822, p, 262; and Berard, Rapports du Physique et du Moral, p. 97, Paris, 1823. VOLITION SEATED IN THE ENCEPHALON. 339 they quickly expire after birth, owing to their being devoid of the organs of the animal functions, and to the consequent impossibility of respiring. Some monsters have, however, been born without the brain, but with part of the encephalon. These have been called, by way of distinction, anencephali or hemicephali. Where the medulla oblongata exists, they possess the nervous system of the senses, and are, consequently, able to live for some time after birth, and to exert certain muscular movements, such as sucking, moving the limbs, evacuating the excretions, &c. Professor Adelon asserts, that none of these facts ought to shake the proposition, which he embraces; that in the superior animals, and consequently in man, the medulla spinalis and the nerves are merely the conductors of volition, or of the locomotive will; and that, in the encephalon alone, volition is produced. His arguments on this point, however, are not characterized by that ingenuousness and freedom from sophism, for which his physiological disquisitions are generally distinguished. " First of all," he observes, " the fact of the progression and motions of men and quadrupeds, after de- capitation, is manifestly apocryphal; and even if we must admit, that certain animals still execute some movements after decapita- tion, are such movements evidently regular and ordained? And, supposing them to be so, may not this have arisen from the confor- mation of the parts, or from habits contracted by the organs? This last appears to us most probable; for if, from any cause whatever, the muscles of a part contract, they will cause the part to execute such motions as the joints, entering into its composition, require; and which may, therefore, be similar to those that the will pro- duces." He farther attempts to deny the facts related of the lower classes of animals, and asserts, that " they are not evinced in the experiments instituted in our day." The cases, which are adduced to prove the defective sensibility of the lower tribes of animated nature, are, however, incontestable; —the trunk of the wasp will attempt to sting after the head is re- moved ; and the experiment, which was made by Dr. Harlan,a in the presence of Capt. Basil Hall, certainly demonstrates something like design in the headless trunk. Our conclusion ought probably to be, from all these cases,—that volition is chiefly seated in the encephalon, but that an obscure voli- tion may, perhaps, extend over the whole of the cerebro-spinal axis. This conclusion, of course, applies only to the higher classes of ani- mals; for we have seen, that the polypus is capable of division into several portions, so as to constitute as many distinct beings; and it is probable that the principal seat of volition may extend much lower down in the inferior tribes. Attempts, and of a successful nature, have been made to discover, whether the whole brain is concerned in volition, or only a part. 1 Medical and Physical Researches, Philad. 1835. See, also, Richerand's Elemens de Physiologie, 13eme edit, par M. Berard, aine: edit, de Bruxelles, p. 252, Bruxelles, 1837. 340 MUSCULAR MOTION. Portions of the brain have been disorganized by disease, and yet the individual has not been deprived of motion; at other times, as in paralysis, the faculty has been impaired; and again, considerable quantities of brain have been lost, owing to accidents, (in one case the author knew nineteen tea-spoonfuls,) with equal immunity, as regards the function in question. The experiments, executed on this subject, go still farther to con- firm the idea, that volition is not seated exclusively in the encepha- lon. Rolando and Flourens* performed several, with the view of detecting the seat of the locomotive will; or of that which presides over the general movements of station and progression; and they fixed upon the cerebral lobes. Animals, from which these were removed, were thrown into a sleepy, lethargic condition; were de- void of sensation and spontaneous motion, and moved only when provoked. On the other hand, Magendieb affirms, that the cerebral hemispheres may be cut deeply in different parts of their upper sur- face, without any evident alteration in the movements. Even their total removal, if it did not implicate the corpora striata, he found to produce no greater effect; or, at least, none but what might be easily referred to the suffering induced by such an experiment. The results, however, are not alike in all the classes of vertebrated ani- mals. Those detailed, were observed on quadrupeds, and particu- larly on dogs, cats, rabbits, Guinea-pigs, hedgehogs, and squirrels. In birds, the removal or destruction of the hemispheres—the optic tubercles remaining untouched—was often followed by the state of stupor and immobility, described by Rolando and Flourens; but, in numerous cases, the birds ran, leaped, and swam, after the hemi- spheres had been removed, the sight alone appearing to be destroyed. In reptiles and fish, the removal of the hemispheres seemed to exert but little effect upon their motions. Carps swam with agility; frogs leaped and swam as if uninjured, and the sight did not appear to be affected. Magendie0 properly concludes, from these experiments, that the spontaneity of the movements does not belong exclusively to the hemispheres; that in certain birds, as the pigeon, the adult rook, &c. this seems to be the