r » .»/ <*<,. H-\ /£q/> &, ^ J * J(*fc * t*'< 4. y / AM INAUGURAL DISSERTATION ON THE PRINCIPLE of ANIMATION, READ AND DEFENDED AT A PUBLIC EXAMINATION, HELD BY THE MEDICAL PROFESSOR, BEFORE THC Hon. JOHN WHEELOCK, L. L. D. President, AND THE GOVERNORS of DARTMOUTH COLLEGE, FOR THE DEGREE OF BACHELOR IN MEDICINE, Jult 18, 1799. by DANIEL ADAMS, a. b. What can we rtafen but from what we know f—— p ope. HANOVER, New-Hampshire, Printed by MOSES DAVI$.—1799. -?r~ :nz va no.?.- .1 JgG NATHAN SMITH, A. M. PROFESSOR 01 MEDICINE at DARTMOUTH UNIVERSITY, AND CORRESPONDING MEMBER OF THE XONDON MEDICAL SOCIETY, THIS DISSERTATION IS RESPECTFULLY INSCRIBED, BY HIS MUCH OBLIGED AND GRATEFUL PUPIL, ?ai AUTHO& 0 A /L .M .A • ' t - -.il#*V\ AYS U" U01* > »s J *. AN INAUGURAL DISSERTATION. THE healing art prefents an extenfive field for fpeculation. No fcience embraces a greater variety of principles, or affords more fubjects of phi- Jofophical difquifition. lis inquiries extend to all the operations of nature ; its objects are fcartered far as the folar light. Notwithstanding the painful refearches and unwea- ried investigations, which have been made to improve thjs branch of knowledge, fo engaging in itfelf, and fo important to the interefts of fociety, ftill this art is yet incumbered with the fwaddhng clothes of infan- cy. Syftcms of medicine have changed with times, and the phenomena ot. difeafes have been explained on principles of the reigning philofophy ; the bufinefs of one age has been to refute the reafonings of a preced- ing, fo that what began to be called a fcience, in the days of Hypocrates, is yet eflabliihed on little better foundation than that of hypothefisand conjecture. The ftudy of nature has been too much neglected, arid thofe intimations of her defigns,v*'hich, in her op- erations, fhe is continually fuggeiling to every con- templative mind, have been too little regarded.— From this unpardonable neglect, much falfe theory has crept into medicine ; reafon and reflection have given way to fancy, while the pedantry of philofophy, and an ambition to eftablifh a favourite fyltem has often triumphed over plain truths, obvious facts, and A **•) and ckaf dtirr^ilradon. That has been do;\c in the ciofcr, vhich fhould have been done in the open field, and nhyficians have fought for that information on the theatre of the anatomifi, which is only to be found on the theatre of nature. Notwithstanding many falfe theories have been of- feree! to the public, which have ferved in fome degree to confound the inexperienced, and oftentimes to mis- guide the more UnderiUnding, yet one advantage has been realized ; for by giving a new prehVntation of fads, they have often fuggefted ufeftjl and impor- tant ideas in medicine. Every theoryjinoreover, how- ever extravagant, fcrves this important purpofe, that it exciies inquiry^ and the author, if he mail have conducted bis reasoning by experiments and cbferva- tions, will have fome claim to the candour of the world, although! it mould afterwards appear, he had been too hafty in his cqnclulions. In this field now open before us, the principle of ani- mation becomes a fubject of- curiofity and ufefui in- quiry.. There is nothing in nature, which exhibits to our fenfes fuch a variety of linking phenomena,as life. It has been the wonder.of ages.j phjlofophers have contemplated It with admiration, and naturalifts have acknowledged, that the utmoft refearches of human fagacity were inadequate to an underftanding of its myftcry. That mankind can ever arrive to fomuch informa- tion, and fuch an acquaintance with the operations of nature, as to be able to anfwer every inquiry on this important fubject, is quite improbable ; at prefent we are furp the flock of human knowledge is too fcanty for fo much underftanding. Still, however, we have grounds for fuppofing, that human genius is not bounded by thole narrow limits, which at prefent mark our knowledge on this fubject; we have the mean) t 7 > rncans of knowing the infiruments, by w-hich natare does her work, although we may nof,be capable of underftanding completely the particular mode cf her operations ; and it is hot unphifofophical to fuppofc, that the principle of animation may be deteded, al- though fome things in the ccconomy of life fhould ftill remain lafling exprefHons of the limited capacity ef man. Every one, in the exercife of his fenfes,feel3 himfelf capable to diftinguilh living "beings from thofe pof- fefling no life ; but to give an explicit definition of life has been attended with fome difficulty, even with philofophers. Dr. Pxpnk has defined life, the proper- ty of ahing from an intrinfic power. .This appears not fufhciently definite, as it does not diltinguim be- tween "vitalafiiont and that a£Iion> which takes place, by attradion and combination in various other bodies, deftitute of life. . Dr.- Brown has been lefs exception- able ; bur, in his definition/he does not tell us what are thofe phenomena peculiar, to the living ftatc, ,which characterize animate beings. > .' Obfervation teaches us, that all living exiftehces are organic ; that water, heat, air, arid various other fiib- fiances external to them, as well as thofe contained within their own veffels, do excite in them certain adions ; that by thofe actions they have a power of .receiving, by organs adapted for that purpofe, por- tions of thefe flimulating fubflances, and thereby cauf- ing them to undergo fuch changes, as (halt aitrmulate them to their own nature and fubltance. We, then, come to this underftanding of animate beings : they are organized bodies, excited to adion by fubflances external, thereby affimulating to their own conflitu- tion and nature, things of different and oppofite na- tures, in a way fo as to continue their exigence, pro- duce their growth, and perpetuate their fpecics. This ( * y< *f his ability, which organized bodies have, of being excited to perform thofe adions, which are charader- " iftic of life, is called irritability. This is the lame^ whether we confider the conrradion of fibres irritated By mechanical impreflions, or that adion, by which fluids are taken up by the veffels, the fecrenons per- formed, and excrementitious parts thrown off. I: is this irritability, which charaderizes life ; exifts where ihat exifts ; and, as foon as the former is destroyed, the latter becomes extind. But what that may be, whi£H gives to organized bodies the capacity of being excited, or on what their life^depends, has for a long time agitated the fchools of medicine ; phrlofophers have kindly afforded their aid in this important inquiry, flill the fubjed is cloud- ed with doubts', and 'perplexed with controverty.—• Both phyficians and philofophers have been pretty unanimoufly agreed, that a tctteinfom?thing does cori- itantjy pervade the- whole fyftem, arid give life and adivity to every fibre. Tt»e ancients early adopted this opinion. This fubtle fluid they called'the Pabu- lum Vila.- The fame is the dnima Mundi of Plato, the Archeus of.Helmpt, the Vis Mcdicatrix of Cuilenf the Excitability of B^ovvri, and the Spirit of Animation of Darwin. The firiking conttajlt, exhibited in the different appearances of living and dead anirrials, nat- urally inculcates this idea, in both we find the Tamp organization, the fame folids, and ihe fame fluids, with" this furprizing d»fference,hcwever, that fn the former there is a constant ability to adion, while the latter is utterly deprived of this power. This ability to adion mult depend on a caufc, this caufe muft.be fomething, but what this may be, to the operation of which, are to be attributed fo many phenomena in the oeconomy of life, it is not at prefent agreed, and hew it is introduc- ed into the fyflem, and there operates to produce its effeds, is a fubjed of ftill greater controvcrfy. Some have ( 9 ) have fuppofed it to be a pure aeiherial fpirit, equally pervading all fpace, and all bodies. Some have thought it might be fire, others that it might be elec-, tricity, while many have fuppofed it to be an ex- tremely fubtle fluid, fecreted in the brain, and thence tranfmittcd thro' the nerves to every part of the body. Thele theories, however ingenious they may be, do not explain to our fatisfadion the phenomena of life ; neither do they reconcile thole facts, which have been afcertained by obfervation and experiment; and, con- fequently, cannot be fuppofed to have arifen from de- monftrated truthsi and a careful attention to the cir- cumftances attending life. Our obfervations, in reply to prefent exifling theo- ries, will toe direded to fhow, Firft, the uncertainty, that the principle of animation is an aetherial fpirit of fuch extreme fubtlety, as to pervade indifferently all bodies. Secondly, the improbability of its being a fecrction of the brain. This firft hypothefis, which attributes life to an aetheriaI fpirit, pervading indifferently all fubflances^ is liable to many objedions. It does indeed feern quite fuperfluous to attempt any refutation of a theory, fo much the work of fancy, and wholly detached from experiment and obfervation. What appears to have led philofophers to adopt fuch an one, was the necef- fity of attributing the phenomena of life to fomething^ Still there was nothing in the fyflem of nature, with whofc properties and qualities they were acquainted* to which, with fairnefs, they could attribute fuch mar- vellous efteds. The alternative, then, was to acknow- ledge their incapacity to underftand fo deep a myftery, or elfe to attribute animation to the agency of ibme-^ thing yet unknown. They did the latter, and, confe- quently, taught mankind to believe their powers of life and activity depended on fomething, whofe exiflence they have neither proved, nor rendered probable to be B any ( to-) Hhy where but in the imagination of its projedors.—- Examine the writings on medicine, from the dayR'of 'Hypocrates to the prefent time, not one fad is adduc- ed to fubftantiate this hypothefis, which may not be more rationally accounted for on other principles.— Nor indeed do they plead as an excufe, for their opin- ion, that it is fupported by obfervation, or experiment; in their ignorance, only, can we find an apology. So far from affording any light on the fubjed, this does but involve us in deeper obfcurity, and rivets on our minds the chains of perpetual ignorance, by adigning that to be the caufe of animation, of which it is not pofliblc we fhould have any knowledge. Difgufled with a theory fo unfatisfadory, others have afTumed another hypothefis, now become more genera!, although, perhaps, no lefs falfe, which is, that the principle of animation is a fluid fecreted in the brain, and thence tranfmitted by the nerves to every part of the body. That this fuppofition is premature and erroneous,I think will be obvious to every one, who refleds with fobernefs, judges with candour, and rea- fons with attention. There are abundance of circumftances to convince us, that the brain is an organ of vaft importance in the animal oeconomy. The diforders produced in the fyflem, by affedions of this part, are fuch as might well be thought, would have led many to fuppofe this to be the feat of life. But fuch is the reciprocal rela- tion and dependence fubfifting between each organ of our bodies, that it is oftentimes extremely difficult, if not impofiible, to diftinguifh the appropriate fundion of each, and to know its juft agency in the fyflem.— Thcbrain cannot perform its fundions without the adion of the heart, and the confequent circulation of the blood ; and without the myfierious influence of the former, the latter would foon ceaie to move : Nor can either of thefe continue their operations without the ( II ) the act of refpiration ; and were it not for the wonder- ful procefsofdigeflion and affimilation.all other powers would be in vain to maintain life. It requires, there-* fore, a particular attention to the different parts, or- ganization, faculties, and power?, of different animals, to iearn the importance of each, and its jufl agency in the fyflem. We have the fulleft conviction, that the brain and its appendages, the nerves, are the feat of fenfibility ; and that, thefe are the medium of all our fenfations and volition?. It exercifes, therefore, one of the moft1 confpicuous fundions in the animal cecor.omy ; con- founding this with irritability, a thing before defcrib- ed, and very different, has led to many miflakes in phyfiology. Was it fo that irritability depended on the fame caufe, as fenfibility, we fhould exped to find thofe parts moll irritable, to which were diflributed the greatefl proportion of nerves. This, however, is not the cafe ; the heart is the moft irritable part of the body, notwithftanding its nerves are not numerous. It is always fo in animals, that thofe paits, or mufclcs, defigned for fenfation, or voluntary motion, are rhoft abundantly fupplied with nerves ; while thofe parts, which receive the great eft number of blood veffels, as the heart and inteflines, polTefs the greateit irritability. Further to illuftrate this idea, we know, that by palling a ligature round a nerve, or by dividing it with a knife, we deftroy all fenfation and voluntary motion in that parr, which has its communication with the brain thus interrupted ; ftill, however, it does not lofe its irritability. Indeed, fo tenacious are parts of this power, and fo independently of the brain do they exercife it, that this organ may be com- pletely deftroyed, and they ftill continue to exhibit evident contradions. The heart and interlines, after being ( 12 ) being removed from the body, will have their motions excited by mechanical irritations. There have been many inflances of the nerves of one part having been destroyed, or their fundions fuf- pended, while yet that part has been able to exercife thofe fundions, which were neceffary to the continu- ance of life. This has often been the cafe in paralytic limbs. That the fundions of the nerves are com- pletely fufpended, we are certain ; for the patient can exert no voluntary motion, nor is he fenfible to any impreflion of external bodies ; and that the part is polTeiTed of irritability and life, we are equally certain ; becaufe there are often involuntary contradions of the fibres, the blood circulates, and abforption and fecre- lion regularly take place. ^ What makes this, if poffiblc, more certain is, that no putrefadion occurs, which in all cafes commences fo foon as the animal, or a part is dead. Dr. Munro, that indefatigable anatomifl, affords iis a very conclufive argument, in his experiments on the nerves, one of which I beg leave to relate in his own words. " In feveral frogs after cutting off the back part of the fix undermoft true vertebrae, I took out all that part of the fpinal marrow with the cauda equina, which they cover. The lower extremities were ren- dered in fenfible to common injuries, and lay motion- Jefs, yet the frogs lived feveral months thereafter, and the wounded parts on their backs cicatrized, and the bones of their legs which I fradured united, the blood circulating freely in their veffels." In thefe animals the fundions of life appear not to have been impaired, when all the nerves of the lower extremities were deflroycd. Not only did the parts, deftitute > ( *3 ) deftitute of nervous influence, retain their vital affini- ties, but exercifed th moty vigorous fundions of life, that of uniting fradured Lanes and forming new gra- fulations. But to underftand a thing we mutt corvfrder it in all the circumftances of its exiflence ; and to gain a knowledge of our fubjed, we muft contemplate life, not only, as pertaining to animals, but likewife to the whole vegetable creation, and obferve what things con- ftantly attend it, and are infeperable from it, in all the modes of its exiflence. The life of vegetables i$ analogous to that of ani- mals; they pofTefs many fundions in common ; and certain circumftances.are indifpenfible to its exiflence, in both. Like^animai* they are excited to the proper difcharge of their fundions by ftimulating fubflances; they elaborate and prepare their food in a way fimilar to animal?, and like them they perform a variety of fecretions,: produce their growth, and perpetuate their fpecies. They have glands, they have vefTels, they have refpiratOQ7 organs, and do exercife the fundions of life, as perfectly, as animals. Notwithftanding this, they poflefs neither brain nor nerves, nor do they ex- hibit any marks of fenfation. Neither the Senfitive Plant, fo,much celebrated by Naturalifts, nor the Di- concea Mufcipula, or Venus' Fiy Trap, the Angularity of which is, that it clafps infects in its leaves with fuch power, as to deftroy them, exhibit any other marks, than thofe of irritability, common to mufcular fibres. Seeing, then, there are living exiflences pofleffing no brain, and parts having their communication with the brain destroyed in beings pofTefiing it, do ftill retain their life, the unavoidable conclufion is, that life does not depend on the brain, but that the fundions of this organ are entirely of a different nature. But flill, to fhow the abfurdity, as well as the utter impoflibility ( 14 ) impoffrbility that the principle of animation mould be afforded by the brain, I wjould beg leave to fuggefl one confideration further. It is not fufficient for our purpofe to confider how life is prolonged, but we muff likewifc inquire how the firft viral motions are produced, and what are the cir- cumftances attending their production. Animate beings are capable of producing their fpe- cies. The different ways, in which they produce them, have laid the foundation for a divifion of animals into viviparous^ and oviparous. Vegetables produce their fpecies by feeds, which are in fome degree analogous to the eggs of animals. Notwithstanding this variety of ways, the changes which take place, and the delinea- tion of the embryo of each fpecies are governed by much ihe fame laws. What thefe may be, the egg affords us the bed opportunity for infpedion. After incubation, what firft appears is the heart and* umbilical blood-veffe's. In eggs, which I have ex- amined, the heart was feen to beat diftindly two days before any traces of the brain could be difcovered.— The fame we learn, from good authorities, of vivipa- rous animals. In all fpecies of animals, the heart is the part firft formed : it is here that vital adion does firft commence, and this is the organ which firft cx- crcifes its fundion in the fyflem. By the adion of the heart and its appendages, the arteries, the other parts become diltended and evolved. Now the firft pulfa- tion of the heart is as much dependent on the principle of animation, as the fame adion is at a time when the animal has arrived to that Mate, which is the ilandard of its fpecies ; and by the fame laws, the firft particle Y7t7£T of matter becomes aflimilated to this organ, it is, that the body receives its growth and nourifhment. All this, however, as we have feen, takes place before there are any veftiges of the brain, and fome time before this organ f IS ) organ tan be fuppofed to exercifc its fundions. Here, then, is the fulleft demonflration, that the principle of animation is not afforded by the brain, as the fundions of this organ are fubfcquent to the exiftence of life.-— As we have noticed this phenomenon in the egg, thofe difpofed to quibble, cannot efcape its conviction, by faying, that the embryo is dependent on its parent for its firft vital adions, as the egg is detached from the animal, which bears it. It is indeed wonderful, that any men fhould have fuppofed life to depend on a flu- id fecreted in the fy ft em, when the very pkodudion of this fluid mult of neceffity require life and vital adion, in the fyflem, in order to produce it. The fuppofition plainly carries this afTertion, that a thing can at the fame time ad and not exift, than v.hicrrthere can be no greater abfurdity. This confideration mail be fuf- ficient to filence every murmur, and demonffratc to the fatisfadion of every one, that the principle of ani- mation cannot be afforded by the brain. Thus, I have confidered thofe theories, on which the phenomenon of life has been moft: ufually explained: I have, to my apprehenfion, found them infufficient and unfatisfadory. Not becaufe they leave fome points hard, and difficult to be explained, but becaufe they are contradided by experiment, and do not cor- refpond with fads and obfervation. v It now remains to point out what this principle may be, and the fource from whence it is derived. In the firft place, it may be ufeful to notice fome confiderations, which may ferve to throw us into a . proper channel of inveftigation. We have confidered life, and pointed out itscharac- teriilics. From the obfervations then made, we are , led to confider thofe produds of animate beings, de- figned by nature for the propagation of their fpecies, as f ■ 16 ) as void of life. This is evident, when we confider that life confifts in certain adions before defined ;— that adion implies change, and that feeds are kept for years without fullering any change, of alteration.— This obfervation applies to eggs, and is equally true, £0 far as it rcfpeds any vital change, in every fpecies of animals. Another confideration, leading to the fame conclu- fion, is, that all living beings have a power of refifting putrefadion. Thole affinities and combinations of matter, which, take place in animate exiflences, are diametrically oppofite to thofe, which take place in the fame fubflances after death. The former may with propriety be called vital, and are thofe, by which the principles of the body become combined, its fize increafed, and its waftes repaired. The latter are call- ed chemical, and are thofe, by which thefe principles become difunited, fet at liberty, and the whole body diforganized. Thefe different affinities, therefore, cannot fubfift, and be going on in the fame body, at the fame time. Seeds of plants, and thofe produds of animate exiflences, of which we are fpeaking, and by which their fpecies are propagated, as they are firft afforded, have neither of thefe adions going on within themfclves. But there is a certain balance of affinities among their conftituent principles, by which they con- tinue the fame without any change. As circumftances may favour, however, one or the other of thefe kinds of adion now delcribed, is liable to commence in their fubftance ,- either a vital adion, by which is produced another of the fpecies fimular to that which afforded the feed or egg, or elfe a chemical one, called putre- fadion, by which its principles are uncombincd and fet at liberty. When the feed or egg is not attended with thofe circumftances, favorable for its receiving vital adion, it poflefles no power of refifting putrefac- tion, any more than the ftock of the plant, or carcafe of the animal, which gave it exiflence. We C X7 ) We have now a view of what is to be underftood by the principle of animation ; it is that, which is the caufe of the jirft vital att ion in thofe different kinds of mat- ter, by which the various fpecies of animate beings are propagated ; and, which, continuing to be fup- plied, does maintain and fupport the fhrne of life, through all the varying ftages of its exiftence. We muft, therefore, look for fomething,' which is as extcn- five as life itfelf, and which is prefent, with living be- ings, and confumed by them, not only when arrived to the ftandard of their perfedion, but likewife, which is afforded the embryo, and the germ in their moft rude and imperfed flate, and, which being withdrawn, leaves all animated exiflences to die 1 Led by thefe different inquiries to the confideration of life in the various circumftances of its exiftence, I am induced to believe, that Oxygen is the principle of animation, that it is received into the fyftem from trie atmofphere by the refpiratory organs. So far as it can be proved by obfervation and experiment, that oxygen is received by every living exiftence, that it is of indifpenfible neceflity, in order to the firft excite- ment of vital adion in the eggs of animals, and the feeds of plants, and on its being withheld; thar life does immediately become extind, fo far, I conceive, this opinion will gain belief, and efcape the cenfure of te- merity, and the reproach of folly. It is now generally known, that the atmofphere is a heterogenius fluid confifting of two different kinds of gas ; one maintaining combuftion and animal life, exifting in the proportion of about 27 ; the other con- tributing to neither, the proportion of which in the atmofphere is eftimated at 73. The former is called oxygen, vital air, highlv refpirable air, depblogifticated, or empyreal air ; the latter has obtained the name of nitro- gene,fepton, azote» or phhgijlicated air. That oxygen is ' C the ( I* ) the principle of combuftion, has been proved by the experiments of M. Lavoisier, and others ; the foun- dation of our belief for fuppofing it the fame of ani- mation, I proceed now to fhow in the order before in- timated. Every one knows that refpifing animals take air in- to their lungs, and that air, which, has once been breathed, is then unfit for refpiration. But on what this phenomenon depended was not known till Dr. Priestly difcovercd, that in the ad of refpiration, oxygen was abforbed from the atmofphere, through the thin membrane, which feparates between the bronchia and blood veffels ; and, that deprived of this, in fome way or other, animals do immediately die.— It is further proved, likewife, that the blood having thus received the oxygen, acquires an additional de- gree of hear, and a florid colour. Thefe propositions having been already fufficiently eftablifhed by various writers, I proceed to take notice that fomething fimilar to this takes place in all living exiflences. M. Lavoisier has demonstrated that oxygen is one of the conftituent parts of water, and* likewife, that water contains air in its pores. Times, therefore, are not excluded from this vital fluid. Notwithstanding 3?he fymptoms of uneafinefs, diftrefs, a,jd even (death, which happen to them, when removed into the atmof- phere, yet they can no more live without air, than thofe animals, which inhabit the land. Fifties are provided with gills, which ferve for them the place of lungs. Thefe are compofed of a vaft number ot red fibrilU, fubjed to perpetual motion from the water. Through thefe the blood circulates, coming from the heart; it is here again colleded by fmall veins, which uniting, form an aorta, by which the blood is carried to all parts of their bodies. That the blood is here oxyginated, as in the lungs of other animals, is very certain wrc- { I? ) certain from analogy. The blood, in both, undergoes the fame changes ; that in the gills of fifties appearing extremely florid, like that in the lungs of animals. In either cafe, that portion of the element refpired has no longer the power of fupporting life, confequently, a renovation is continually required. Fifties exhibit the fame fyrnptoms, when deprived of oxygen, that other animals do—.violent convulsions, and immediate death. In fevere winters, when much of the communication of the air with water is intercepted, by meaivs of ice, many of thefe animals die ; by opening the ice, and admitting the air, they rufh violently to the furface of the water, with fuch eagernefs for air, that they often- times fuffer themfelves to be taken by the hands of the fifhermen. Infeds, likewife, are provided with organs for re- ceiving air, called tracheae ; thefe being befmeared with oil, they foon die. Oxygen is not only neceffary to the life of all ani- mals, but, likewife, to that of all the vegetable crea- tion. That the fap of plants circulates through their leaves, has been ascertained by experiment. On the upper furfaces of them, the fap is expofed to the adion of the atmofphere, beneath a thin pellicle. Here it undergoes a change, and is carried back by veffels on the under fide of the leaf. A flaik having been plac- ed, feveral days, in a decodion of madder, on the up- per furface were feen many red arteries going to the extremities of the leaves, which were not vifible on the under fide. On cutting acrofs a leaf, by the help of a lens, the returning veffels, on the under fide, were {zqw to difcharge a milky fluid, but none of the red fluid, contained in the veffels, on the other fide of the leaf. The upper furfaces of leaves, likewife, being covered with oil, they foon die. The leaves of plants, there- fore, have an office fimilar to the lungs in animals,, trachea ( 29 ) trachea in infeds, and gills in fifh. Excluded iiom the air, they decay and die, as has been proved by the experiments of Schekle, and others. Thus it appears that all living existences doconfume oxygen. This, however, is not on'y neceffary to the continuance of vitality, but without it, neither the em- bryo of animals, nor the feeds of plants can be ufhereo' into life. The.firft attention of nature, in the produc- tion of all the myriads of her exiflences, appears to be to make provifion for a fupply of this oxygen gas.—- While as yet there are neither veffels, nor organs for receiving it, this vital principle is neceffary to excite the first motions of life ; at this early period therefore, there is a mechariifm peculiarly fitted for that pur- pofe. This, in viviparous animals, is the placenta j its fundion is analogous to that of the lungs, after the foetus is delivered from its parent. It appears from the opinions and experiments of rcfpcdable wrkers, that there is no circulation of blood between the pa- rent and the foetus j but that the blood of the foetus is carried to the placenta by an artery, and is there dis- tributed to its extremities, and again brought back by veins. This appears, from this circumftance, that the placental veffels do not bleed when torn from the utc* rus, while thofe of the uterus diichafgc a large quantity of florid blood. This is accounted for by Mr. J. Hunter. " That ingenious philofopher," fays Dr. Darwin, " has ffiown that there are numerous cavi- ties, or lacunas formed on that fide of the placenta, which is in contad with the uterus; thefe cavities or cells are filled with blood from the maternal arteries, Which open into them, which blood is again taken up by the maternal veins, and is thus perpetually changed; while the terminations of the placental arteries and veins are fprcad in fine reticulation on the fides of thefe ( 21 ) f.hefe cells." From this relation it appears evident, that the placenta receives the blood for the purpofe of bxygination ; the fame is further confirmed by ihe changes the blood there undergoes, which are the fame as thofe it fuffers in the lungs of animals. In oviperous animals producing their young from eggs detached from the parent, .this procefs of oxyg- inating the blood is not poflib!e. Thinking, however, that oxvgtn mult fome way be communicated, I made the following experiments. Experiment ift. In the large end of the egg it is well Known there is included a fmall t?ag of air. Having procured a num- ber of eggs, I colleded a quantity-of this air in a glafs tube, in contad.with whi6h I put a folution of ful- iphure of potafh, a property of which is to abforb ox- ygen. Part of the air thus cnclofed was foon abforb- ed, after which there remained a portion of azote. Experiment 2d. Having ascertained that eggs do.contain oxygen "within their fnells, I wifhed to know its importance in the incubated egg.. For this purpofe, i took a number of eggs, and having broken the fhell into the air bag, 1 completely filled .the. cavity with a dolil of lint, fop- ped in glue ; over this 1 fpread a varnifh, fo as totally to exclude the air. Thefe eggs I put under a fetting hen, together with other eniire eggs." On the fourth day of incubation, I'examined them ; in thofe which were put under dnt?re, was diftindiy feen the heart of the future chick beating, together with the umbilical blood-veffels, beautifully ramified, and appearing ex- % ceedi*igly florid. At this time, in the place of the head, was feen a dark fpeck, which did not appear two days before, notwithstanding the heart and blood-vef- fels were evident, as on this day. In thofe eggs, whofe {hells ( 22 ; ihells had been broken, and the air, they contained, excluded, no xyiral adion had been excited ; on the contrary, putrefadion had evidently commenced. Experiment 3d. In another parcel of eggs, having opened into the cavity, or air bag, I introdoced fulphureof potafh,and fealed it clofe with varnifh,as in the other experiment. This abforbed the oxygen, only, leaving the azote ftill to occupy the cavity. Thefe eggs being fubjeded to incubation, the refult was the fame as in the preced- ing experiment; not one of them hatched. From fome difappoiniments, and the inconveniency in my prefent situation, of making thefe experiments, I have not purfued this inquiry fo far as I had intend- ed ; but that oxygen is contained within the fheli of the egg, to be of ufeat the time of incubation, I think is evident from the experiments I have related. For without the prefence of this, the cicatricula of eggs is not animated, no part evolved, nor does it affutne any adion of life. At the time of making thefe experi- ments, a woman of more than common obfervation in- formed me, fhe had a hen among her poultry, in whofe eggs this portion of air was always wanting, ard that not one of thefe eggs had ever hatched, although trial of them had been repeatedly made. We are, therefore, led to this conclusion, that in eonlequence of the heat, which the eggs acquire by incubation, the oxygen becomes adive, and that in this way the firft vital motions are produced ; that it continues to oxyginate the blood till the time the chick is extricated from its fhell. This will be evident to any one by infpedion, who will take the trouble to examine an egg, fome days after incubation. Then may be feen an almoft infinite number of blood veflels fpread on the membrane, which confines the air in one end ( 23 ) end of the (hell; thefe veffels are colleded, arid form the umbilical artery, which leads to the heart. That the blood is carried here, for the purpofe of oxygina- tion, we have no caufe to doubt ; the appearance makes it almoft certain. Thefe veffels appear ex- tremely Jlorid, and of a bright red colour, whereas, the vein, which is fpread on the albumen, appeats of a dark modena. We have next to examine, what part oxygen has in the germination of feeds. Seeds, when fown, are in fuch a situation thar the air communicates with them freely. That provision, therefore, which is made to fupply animals with oxygen, at an early period of their exiftence, is not neceffary for plants ; ftill, to deter- mine what office oxygen might have in their vegeta- tion, I made the following experiment. I put into a glafs globe a handful of beans, a little water, and flopped it clofe, it being filled with atmof- pheric air. In this situation, it flood a week, in which time the feeds fprouted, and grew half an inch. I then unstopped the veffel, having immerfed it in water.— On withdrawing the ftopper, the water rufhed in, and the air remaining was found to have loft every parti- cle of its oxygen. The feeds had begun to putrefy, which I fuppofe to be in confequence of the oxygen having been confumed, before the globe was unftop- ped ; the vital principle, then, not being afforded, the adions of life could no longer be continued—chemical affinities were therefore fuffered immediately to take place; Such are the fads we have been able to colled, to fhow, that at the firft dawning of life, vital adion is excited and kept up by oxygen. We know it, becaufe eggs and feeds are not animated without it, becaufe nature has invariably made provision for its fupply, and becaufe in all inftances of life it is confumed. The U f *4 )' The necessity of refpiration to animals, through the varying ftages of their exiftence, could not efcape the attention or man. The obfervation has been made from time immemorial, hut its ufe in the oeconomy of life was not till lately known, rror even yet has its full importance been acknowledged. By this way oxygen is (implied to the fvftem, which in fome way or other, z;> we have ken, is afforded to all living «xiftences. Mr. Cruikshpank, in his experiments on the re- produdion of the nerves, relates one, from which, I rhink, he might have drawn more important inferenc- es than he has. It fhews in a ftriking manner the im- portance of refpiration, and how, independently of the brain, the fundions of life are excrcifed. Mr. Cruiksurank took a dog, and by detaching the fcapuia from the fpine, divided all the nerves of the axillary plexus on each fide. He then divided the fpinal marrow between the laft vertebrae of the neck, and the firft of the back, and likewife the parvagum and intercostal nerves. In this experiment, all com- munication of the heart, lungs, diaphram, and thorax with the brain, was cut oft. The whole animal took the alarm ; all the flexor mufcles feemed to contrad, and inftantly to relax again ; all appearances of life were gone. Hejthen opened the cheft, and found the heart had ceafed its motion. Then he introduced a hrge blow-pipe into the trachea, below the cricoid rartilagc, and inflating the lungs, imitated refpiration. The heart began to move again, and in about three minutes was beating 70 times in a minute. After fome intermiflion, this was again repeated, and continued for half an hour, the heart and arteries beating regu- larly all that time. This experiment fhews that refpiration is the prime mover of the machine j and that the nervous influence, whatever ( :> J whatever it may-he, ferves mcrc'y as a ftimulus to excite the adion of the mufcles and din ph ram, thereby to enlarge the-thorax and favour the admiftion of a.r into,thc lungs.i Further, it explains, what at firft: thought, might feern difficult to be accounted for, that the chick, before the formation of the brain, v/:H have its heart beating, whereas after incomplete formation, and it has efcaped from its cenfincment; the nervous influence is neceffary in order to the continucncc of this adion. By this experiment, it appears, that noth- ing but a fufficiency of oxygen is rieccfiary to the ac- tion of the heart, and that the brain does contribute to this adion by opening the way fpr this fupply. Animals fubjeded to inhale the fame air, without renovation, foon die ; that death in this cafe is in con- fequence of a deficiency, or want of oxygen, and not from noxious vapour thrown off from the lungs, wc know for this reafon; that animals confined in any other, gas, however pure, or in the exhaufted receiver' die with the fame train of fymptoms. When the ufual proportion of oxygen in the atmofphere is diminiftied, life languilnes \ but the moment this proportion is increafed, the powers of life become invigorated, the fundions are performed with alacrity, and the whole fyftem feems to have acquired a new degree of anima-* tion. From a review of thefe obfervations, we may learn what advances have been made in favour of our fub- jed. Irritability we confidered as the charaderiftic of life ; and in thofe adions, by wliich the fundions of living beings are performed, does life confift. Seeds of plants and thofe prbduds'of animated exiflences, by which their fpecies are propagated, we confidered as void of life, not poffeffihg thofe adions in which D life « ( 26 ) life confifts. In thefe, likewife, we have proved by obfervation and experiment, that vital adion does not lake place without the prefence of oxygen, that the embryo of viviparous animals receives it from its pa- rent ; in oviparous animals it is afforded the young in the fhell ; that feeds in the time of germination do abforb it from the atmofphere. That a constant Cup- ply of this is ncceflary to every living being, for the fupport of life, through the varying flages of its exist- ence—nor an infed moves, nor a plant fhoots its branches, but by the instrumentality of this univerfal diffufer of animation. Thefe confiderations arc fuffictent to justify us, in our opinion, refpeding its importance, in animation;; and fhould any doubts remain, perhaps further expeii- ments and obfervations, may remove them, and finally enthrone fcience in thofe regions, which too long have been occupied by fancy and conjedure. Let it not be thought an objedion to this theory, that oxygen is fomething, whofe exiftence is made cer- tain, ?;nd many of whdfe properties have been ascer- tained by experiment; and becaufe the chemist, in his laboratory, has not been able to excite life in thofe fubflances, with which he has combined oxygen, thar, therefore, nature is incapable of the operation. It has been common, with philofophers, in attempt- ing to dcvelope the myfteries of nature, when, from the concunence of known caufes, an efled has been pioduced out of the way of their common courfe of operation, in other circumftances, to fuppofc that an unknown caufe cooperated to produce this effed. But till the relation^of things are all pcrfedly understood, and every combination of matter known, we may exped continually to be afcertaining new properties, qualities, and effeds, of thofe things, which are the objects of our fenfes. , fV ( 27 ) in things, which men do not understand, they are always prone to run into great prolixity, and vain im- agination. Nature is uniformlyvmore fimple, in her operations, than the bigotted opinion of man is wont to conceive. She proceeds to her objed by dired fteps, but man wanders a devious way, and thinks to purfue her, like the wily fox, through mazy windings and intricate paths. When philofophy fhall have withdrawn the veil, from the eyes of mortals, and difclofed to human view, her operations, then will be feen the uniformity that fo constantly marks her fteps, and that fimplicity0 which pervades all her works. \J Q /si