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AN ESSAY, TOWARDS A DEFINITION OF ANIMAL VITALITY; READ AT THE THEATRE, GUY's HOSPITAL, January 26, 1793;

IN WHICH SEVERAL OF THE OPINIONS OF THE CELEBRATED JOHN HUNTER ARE EXAMINED AND CONTROVERTED.

By JOHN THELWALL, MEMBER OF THE PHYSICAL SOCIETY, &c.

FELIX, QUI POTUIT RERUM COGNOSCERE CAUSAS.
VIRGIL.

LONDON: PRINTED BY T. RICKABY; AND SOLD BY G. G. J. AND J. ROBINSONS, PATERNOSTER-ROW; DEBRETT, PICCADILLY; AND COX, ST. THOMAS'S STREET, BOROUGH.

1793.

[Entered at Stationers-Hall.]

TO HENRY CLINE, ESQ. Lecturer on Anatomy and Surgery, and Surgeon to St. Thomas's Hoſpital.

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SIR,

IT is with no ſmall degree, of diffidence that I preſume to dedicate this firſt effort at Scientific Inveſtigation to you; nor could I ever ſo far have prevailed upon myſelf, had not my deſire to teſtify the gratitude I feel for the many obligations I owe to yourſelf and family, been conſiderably ſtronger than my hopes, that any thing contained in this Eſſay could be worthy of your attention.—I do not, Sir, approach you with the venal breath of panegyric; nor can I have the preſumption to hope, that any laurels can be added to your reputation by one who has yet all his own to gather; but as I am now haſtening, in a new character, to the bar of the public, I am actuated by a feeling natural enough to mankind—the deſire of appealing firſt to that deciſion which is likely to have the ſtrongeſt bias towards lenity and indulgence. You, Sir, need not be told the diſadvantages under which I have attempted to form an opinion upon an abſtruſe Phyſiological Queſtion, which has always, even to the moſt learned profeſſors, appeared to be involved in ſo much obſcurity and doubt; and you will, perhaps, be kind enough (if my Definition ſhould ever engage ſo much attention, as to be the object of converſation in thoſe reſpectable medical circles you frequent) to apologize for the imperfections of a young Theoriſt, whoſe information upon the ſubject has almoſt entirely been derived (in the few hours he could ſteal from other ſtudies and other purſuits) from the Lectures to which yourſelf, Mr. Haighton, and Mr. Aſhley Cooper, have been ſo kind as to invite me*. I am aware, [iv]Sir, that to this the ill-natured critic might reply: but why, then, intrude his puerile ſpeculations on the world? To this I muſt reply, for myſelf, that the reception of this little Eſſay in the Society,* where it had the honour to be read, was by far too flattering for a young man like myſelf to be inſenſible to; and the ſolicitations of ſome of the moſt reſpected and intelligent members appeared a ſufficient juſtification, in the eye of prudence, for hazarding its publication. I have, therefore, committed it to the Preſs, in the aſſurance, that, if theſe gentlemen have leaned too far on the ſide of partiality. I ſhall not fail to be ſet right again by the kind ſeverity of ſome, who will incline, with ſufficient force, the other way. Among theſe, however, will not, I am ſure, be enumerated the Gentleman, whoſe,

With the utmoſt gratitude and eſteem, I have the honour to remain, JOHN THELWALL, Maze Pond, Southwark.

AN ESSAY, &c. READ TO THE PHYSICAL SOCIETY.
INTRODUCTION.

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MR. PRESIDENT,

AS my ſole motive for becoming a member of this ſociety was the pleaſure I always derived from the enlightended converſation of gentlemen of the Medical Profeſſion, and as I have hitherto attended to the ſcience only as a matter of entertaining curioſity, and not as a purſuit to which I have any preſent intention of devoting myſelf, I might, perhaps, without encountering the cenſure of the candid and conſiderate, have endeavoured to excuſe myſelf from the execution of a talk to which the nature of my purſuits muſt neceſſarily render me ſo inadequate. But, as I am no friend to privileges, and would have every member of ſociety endure his proportion of the public burthens; and as, above all, I would wiſh to exclude the idle drone from the hive of ſcience, I felt myſelf called upon to perform the part allotted by our inſtitutions, and [2]to give every gentleman that opportunity of canvaſſing and controverting my opinions, which, with reſpect to theirs, I have occaſionally exerciſed myſelf.

I have diſcarded, therefore, as far as poſſible, the timidity naturally attendant upon the many diſadvantages under which I labour, and launching into a new and untried region, have brought my little tribute of phyſical knowledge, or rather ſpeculation, to the general fund; confident only in the hope, that the ſmallneſs of its value will in ſome degree be compenſated by the cheerfulneſs with which it is contributed.

My Theory will no doubt be found, in many reſpects, defective, from the want of more general information in the ſciences of Anatomy and Phyſiology; and may, perhaps, be erroneous in others, from the miſapprehenſion of ſcattered facts, imperfectly collected, without the concatenation of circumſtances by which they might be elucidated and explained. But ſuch as it is, I am ſure the ſociety would pardon its imperfections, if they knew the numerous avocations among which it has been digeſted, and the ſmall proportion of time I have been enabled to devote to its compoſition.

I make theſe obſervations, not to abate the ardour of controverſy, or reſtrain the keenneſs of inveſtigation. It is from that ardour, from that keenneſs, and not from any vague conjectures [3]in this eſſay, that edification is to be expected by the ſociety; and ſo far am I from wiſhing to ſhelter my hypotheſis behind the ſcreen of any perſonal conſideration, that I ſhould neither be diſpleaſed at being convinced that I am wrong, nor backward in acknowledging my conviction. Reputation is not to be expected from ſo tranſient an attention as I have been enabled to pay to this ſubject; nor can there be any diſgrace in the failure of an attempt, which is the reſult rather of neceſſity than of choice.

In ſhort, candour of judgment, and not indulgence in inveſtigation, is what I ſolicit from the ſociety; and for that I ſhall not ſolicit in vain.

It is neceſſary, however, before I proceed to my ſubject, to premiſe one remark. I do not here profeſs to delineate a perfect ſyſtem. I have entitled my paper an Eſſay, and as ſuch only I wiſh it to be conſidered. I ſhall not therefore be expected to demonſtrate every propoſition, or to draw out every part of my theory with amplitude and perſpicuity.

This, I believe, is what has never yet been done; nor, from the limits of our preſent knowledge, can it rationally be expected of any hypotheſis upon this ſubject. The Anatomical Phyſiologiſt himſelf is frequently left to wander in the regions of conjecture. The functions of almoſt every organ [4]may be traced farther than the exiſtence of ſuch organs can be detected by the minuteſt enquiry: Analogy, therefore, is often called upon to ſupply the place of Demonſtration; or the more eaſy expedient is appealed to, of paſſing over in ſilence what cannot be readily accounted for. Many of the conjectures, it is true, which the imperfection of the ſenſes, or the deficiency of obſervation, has rendered neceſſary to profeſſors, have gathered confidence from the great authorities by which they have been ſanctioned: yet let it not be forgotten, that it is not in the nature of authorities to change conjectures into proofs. Let us remember alſo, that reaſon is the greateſt authority of all; and that when ſyſtems claſh, and demonſtrations are not to be had, we ought not to conſider who is the author of this, or who of that opinion, but which it is that involves the feweſt abſurdities, or is beſt ſupported by analogy, and the correſpondence of the general laws of Nature.

AN ESSAY, TOWARDS A DEFINITION OF ANIMAL VITALITY.

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IT is an apparent paradox, but it is not therefore the leſs true, that thoſe ideas, or phenomena, that are moſt familiar to us, ſhould frequently be the moſt difficult to explain. This is particularly the caſe with the ſubject of the preſent Eſſay.

Life is a term ſo conſtantly recurring, and, indeed, as one would at firſt ſuppoſe, an image ſo perpetually preſenting itſelf to our ſenſes—and the difference is ſo ſtriking, between the pale inſenſate corpſe, and a living being, with all the expreſſions, actions, and attributes with which, in the higher ſcale of animals, he generally offers himſelf to our [6]eyes, or our imaginations, that a vulgar obſerver would ſneer at the philoſopher who ſhould ſuggeſt the difficulty of aſcertaining in what vitality conſiſts: yet where is the ſtudent, who, upon ſerious examination, has found himſelf ſatisfied with any thing that has been ſaid upon the ſubject?

Does not the greateſt anatomical philoſopher, even of the preſent enlightened age, tacitly confeſs the confuſion of his ideas in this reſpect, when he declares that, ‘"From an examination and ſurvey of animal matter when dead, only we gain an idea of living animal matter;" and that ‘"as from life only we gain an idea of death, ſo from death only we gain an idea of life?"

Before we can poſſibly derive any ſort of information from this antitheſis, it is neceſſary that we ſhould be inſtructed how life and death may be accurately diſcriminated; for how are we to make compariſons between objects which we are unable to ſeparate from each other? But even this has never ſucceſsfully been attempted; for though there are certain ſigns (as putrefaction, &c.) by which the death of the animal may be demonſtrated; yet, as it is not even pretended that putrefaction is the act of vital diſſolution,—or, in other words, that the body which is not putrid is neceſſarily alive—death muſt have taken place, independently of any ſuch change; and we are, therefore, juſt as much in the [7]dark as ever with reſpect to the ultimate teſt by which the preſence of life may be aſcertained.

Treatiſe after treatiſe has been written on the Vital Principle; theory has pulled down theory without end; and the groſs contradictions which have marked the opinions of the greateſt characters upon the ſubject, might induce one to think that, even with reſpect to the general idea, we are ſtill entirely at a loſs; that we are ſeeking for an imaginary ſomething—a phantom of the brain, which, perhaps, has no real exiſtence: and, indeed, if the term is to be literally underſtood—if this Vital Principle is to be conſidered as a diſtinct or independent eſſence, ſeparable from the effects and actions by which the ſtate of vitality is to be aſcertained, I am not ſure that this concluſion will be found to involve as much abſurdity as is included in the contrary opinion.

I am well aware that there are ſome, who, from the firſt bluſh of this obſervation, may be inclined to ſmile, and conſider it as the ne plus ultra of ſcepticiſm: but the philoſopher will do well to keep the diſtinction between a vital principle, and the ſtate of vitality, conſtantly in his mind: the former properly meaning a living CAUSE—the latter ſimply a modification or effect, to which the name of life is given, and which may be the reſult of a co-operation of other cauſes, neither [8]of which need, in themſelves, of neceſſity be alive.—In other words, to contend for the exiſtence of a Vital Principle, is to contend that there is ſuperadded to organized matter a diſtinct ſomething, in itſelf alive, by which the vital functions are carried on; while, on the other hand, the State of Vitality need not of neceſſity be conſtrued, as meaning any thing more than the condition of the animal body during the continuance of thoſe functions.

Now—that there is a ſtate of animal exiſtence, that may properly be called the State of Life, and be put in direct contradiſtinction to that of Death, and that upon the previous induction of this ſtate depend all the higher functions of the ſenſitive being, are certainly among the moſt ſelf-evident of all ſimple propoſitions. Nor is it leſs certain, that there muſt be an exact and preciſe moment (nay, fraction, or, if I may ſo expreſs myſelf, mathematical point of a moment), in which this ſtate of life ceaſes, and that of death begins; though whether that moment can ever be aſcertained by any ſenſible and poſitive mark of diſcrimination, is matter of conſiderable doubt: but if this Vitality is to be conſidered, ab origine, as a Principle, (by which, phyſically or philoſophically ſpeaking, I conceive is always to be underſtood, a ſimple, elementary, and firſt natural cauſe), and not, as itſelf, an effect of the co-operation of other principles, or natural and pre-exiſting cauſes, [9]I own, for my own part, I muſt be rather ſlow in yielding my aſſent; and, while I bow with reſpect to ſuperior judgments, muſt claim the prerogative of exerciſing my own.

Egypt, Greece and Rome are, it is true, againſt me:—the ancients and the moderns—Ariſtotle and Plato, Plutarch, Moſes, and John Hunter; and yet againſt this hoſt of Giants I preſume to lift my pigmy lance, and brave the unequal combat.

The moſt ancient of the opinions tranſmitted to us upon this ſubject, I believe, is that of the Egyptians, which conſiders the Soul (or living Principle) as a kind of ſhadow, or aerial ſubſtance, diffuſed through every part of the body, animating every limb, and partaking of all its proportions.

Man, according to them, conſiſts of three parts—a groſs periſhable body—an intellectual principle, or intelligent mind, by which he is elevated above the brute creation—and an image, or ſoul, exactly reſembling the body in ſhape, in magnitude and feature, upon which animation, and all the functions of the animal frame depend; and in which, alſo, they conceive the intellectual principle to be enſhrined.

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That theſe were conſidered, in the proper meaning of the word, as diſtinct principles, is evident, ſince they are treated as being capable of independent exiſtence—the ſoul, or vital principle, continuing many of its functions after its ſeparation from the body; and the mind, or intellectual power, after the final ſeparation, being ſometimes conſigned to a different reſidence from the ſoul.

This opinion (which ſtill, with ſome ſlight variations, continues to be popular among Divines and Moraliſts, and has been mangled and metamorphoſed even by our philoſophers themſelves) was adopted by the Greeks, was infuſed into the ſubtile and intricate philoſophy of Ariſtotle, dilated upon by the divine genius of Plato, beautified by the ſublime invention of that moſt ancient of their poets and philoſophers, the immortal Homer; and, at length, was taught by Plutarch to the Roman World, in the following manner:

‘"Man,"’ ſays he, ‘"is a compound ſubject, but not of two parts, as is commonly believed, becauſe the underſtanding is generally accounted a part of the ſoul; whereas it as far exceeds the ſoul, as the ſoul is diviner than the body. Now the ſoul, when compounded with the underſtanding, makes REASON, and, when compounded with the body, makes PASSION; whereof one is the ſource or principle of [11]pleaſure or pain—the other of vice or virtue. Man, therefore, properly dies two deaths; the firſt makes him two of three, and the ſecond makes him one of two."’

This hypotheſis has certainly beauty and ingenuity to recommend it to our imaginations; and is alſo, to my conceptions at leaſt, ſomewhat more comprehenſible than thoſe ſyſtems which refer the operations of groſs matter to immaterial agency. It is, however, like all the ſpeculations of the ancients upon theſe ſubjects, unfounded in experimental enquiry, and unſupported by facts or obſervation: yet St. Paul, (who derived much of his inſpiration from the ancient poets and philoſophers) has given it the ſanction of his authority, by dividing, in diſtinct terms, the triune man into Body, Soul, and Spirit.

This being the caſe, it is not at all ſurpriſing that modern philoſophy ſhould have been more anxious to frame ſuch ſyſtems as were reconcileable with this tripartite diviſion, than ſuch as might be conſiſtent with known facts, or maintainable on the grounds of reaſon; and that we ſhould accordingly find this theory ſo ſtoutly defended to the preſent hour, with the ſlight alteration only of tranſpoſing the ſoul into the place of mind or ſpirit, and ſubſtituting Vital Principle in the place of ſoul. Some philoſophers, however, by conſidering [12]the immaterial eſſence as the animating principle, and others, by conſidering the animating principle as the only medium of intelligence, have reduced human exiſtence to a two-fold nature: I, for my part, ſhall ſimplify the ſubject ſtill farther—and, regarding man as differing from other animals rather in the extent than in the nature of his powers, ſhall conſider him, together with the inferior tenants of creation, in an individual point of view only; as conſiſting of a ſimple organized frame, from the ſuſceptibility and preſence, or the non-ſuſceptibility, or abſence of ſtimuli in which ariſes the whole diſtinction between the living body and the dead. Wherever there is a perfect organization of the animal ſubſtance, there, I conceive, we have the ſuſceptibility (or, as it may, perhaps not improperly, be called, the PRE-DISPOSING CAUSE) of Life: whatever may be that ſpecific ſtimulus, by which ſuch ſuſceptibility may be diſpoſed to be excited, that, I conceive, muſt be admitted to be the REMOTE CAUSE, or agent by which Life is to be produced: from the intimate combination of theſe reſults, that meliorated or altered ſtate of the organized frame, which may be conſidered as the PROXIMATE CAUSE; and the Vital Action, as it may properly be called, or the power by which the vital functions are performed, being the ultimate effect of theſe co-operating cauſes, is, in reality, as I humbly preſume, to be conſidered as that Life, or Animal Vitality, for which, under ſo [13]many denominations and imaginary forms, the Philoſopher and the Medical Profeſſor have ſo long been ſeeking.

Such is the general idea, which, upon the ſimple principles of materialiſm, I have formed of life; and ſo to define this idea as to account for the phenomena, without appealing to the fanciful creations of the viſionary brain, or abſtruſe and unmeaning terms of pretended ſcience, is the taſk I have undertaken.

But before I enter more particularly into the ſubject, it will be neceſſary to beſtow ſome conſideration on another theory that has lately very much amuſed, and, according to my judgment, miſled the ſcientific world—The theory, I mean, of the Vital Principle being reſident in the blood.

This doctrine, in all probability, had its origin in the remoteſt antiquity; ſince the fatal conſequences that reſult to the animal frame, from the ſpilling of this important fluid, muſt have been frequently obſerved, eſpecially in the ages of barbariſm and violence, long before the faculties of man were ſufficiently improved for refined ſpeculations, or philoſophical reſearches into nature: but the prejudices of ignorance have ſometimes been aſcertained, and more frequently adopted, by the luminaries of ſcience and the world; and this haſty opinion [14](for ſuch to me at leaſt it appears) has not wanted ſupporters among thoſe who will long continue to claim the applauſe and admiration of mankind.

And firſt, I muſt particularize, that this doctrine has received the direct ſanction of the great Jewiſh Law-giver (or whoever was the author of the Five Books of Sacred Hiſtory generally aſcribed to him) in the following, among a variety of texts of a ſimilar nature—"For it is the life of all fleſh; the blood of it is the life thereof: therefore I ſaid unto the children of Iſrael, Ye ſhall eat of the blood of no manner of fleſh: for the life of all fleſh is the blood thereof; whoſoever eateth it ſhall be cut off."

I am very well aware, that the ſublime language of Revelation is not always to be interpreted with philoſophical preciſion—the enthuſiaſm of divine inſpiration frequently elevating the ſtyle of the holy penman to a degree of poetical hyperbole, which would be perfectly unintelligible to the cold perceptions of reaſon and enquiry, if it were not for the friendly appeals of the commentator to myſtical allegory, and metaphorical elucidation: but as the doctrine here quoted is merely illuſtrative of the ſimple mandate, that the Jews ſhould not eat of the blood of animals ſlain for their ſuſtenance, there can be no doubt of its being intended to be literally [15]underſtood as the opinion of Moſes, that the blood is abſolutely the Vital Principle.

For this opinion, I am very much inclined to ſuſpect, that no better foundation will be diſcovered than the acknowledged fact, that when the blood, or any very conſiderable portion of it, is drawn away, the vital functions of the animal will ceaſe: but, unfortunately for this theory, theſe functions will alſo ceaſe, without the proportion of this fluid being at all diminiſhed: and as there are alſo ſeveral other parts entering into the compoſition of the animal, which, if ſubtracted, even in part, reſign the body to inevitable deſtruction, we might as well ſay, that the ſtomach thereof, or the kidneys, or the liver thereof, is the life thereof, as that the blood is to be ſo conſidered. Nay, from what we are now acquainted with concerning the nervous ſyſtem, there would be much better reaſon to ſuppoſe, with ſome later philoſophers, that the life of the animal is in the brain, rather than in the blood, ſince ſo much of the latter may be loſt without eſſential injury, while the former cannot receive the ſlighteſt wound without bringing on immediate diſſolution; and though, upon ſerious reflection, there is every reaſon to believe, that the fatal cataſtrophe is produced as much, at leaſt, by the conſequent extravaſation of the blood, as by any immediate ſuſceptibility of injury in the ſubſtance of the brain; [16]yet this does not weaken the argument, ſince it is evident, that it is not the loſs of blood from the veſſels which is the real cauſe of the miſchief (for much larger quantities may be drawn from the ſame part by mere external wounds, without any alarming conſequences); but that the injury produced by the extravaſation reſults from the conſequent oppreſſion on the organ, by which its active energy is reſtrained and benumbed, and, of courſe, its vital functions will be ſtopped.

From this, and a variety of other conſiderations, it is evident that the brain is, at leaſt, more vital than the blood, ſince the compreſſion of the former is more dangerous than even a very conſiderable deduction of the latter.

But it might, perhaps, be objected to the whole of this reaſoning, that many animals have life, which have neither brain, nor kidneys, nor liver, nor, ſtrictly ſpeaking, even ſtomachs; for I know not how the ſimple cavities of the leech or polipus can, in ſtrict propriety, be conſidered as ſtomachs.

This objection being founded in truth, it is neceſſary that we ſhould give it its utmoſt force, and admit it as a demonſtration, that animal life neither conſiſts in, nor is abſolutely [17]dependant upon any one of theſe particular organs: but as it will be admitted, that though they have not theſe, they have ſome other organs, which, as far as is neceſſary for the performance of their functions, ſupply the place of theſe, the caſes will ſtill be found to be in ſome degree parallel—for, ſtrictly ſpeaking, many of the moſt imperfect animals have no blood (at leaſt, according to the general idea which is given of it in the deſcriptions of anatomiſts), there being, perhaps, as much difference between the ichor, which ſupplies its place in ſeveral claſſes of inſects and reptiles, and the compound fluid, which, in the more perfect animals, we call by the name of blood, as between this ichor and the ſap of vegetables, and a variety of other ſimple juices of animal or vegetable ſubſtances. If, therefore, the Vital Principle is to be ſought in the circulating fluids, we ought rather to ſay, that the SERUM thereof is the life thereof, than the BLOOD.

But as I am informed, that the immortal Harvey upheld a doctrine ſimilar to that I am combating; and as ſo great an authority as John Hunter has thought proper, in ſome degree, to ſanction the opinion, it is neceſſary to treat it more at large, and to abandon the curſory obſervation of the Jewiſh Law-giver, for the more elaborate and practical reſearches of the Britiſh Anatomical Philoſopher.

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I have ſaid, that John Hunter's Theory ſanctions, in ſome degree, the opinion of Moſes; for I think it very doubtful, whether he means to carry it to the full extent, and to aſſert, that the Vital Principle is peculiarly, or originally, in the blood. The Editors of the Encyc. Brit. it is true, (title BLOOD, vol. iii. p. 313), evidently underſtood him in this manner, as will appear from the following quotation: ‘"The uſes of this fluid are ſo various, and of ſuch an important nature, that ſome have not ſcrupled to affirm the blood to be actually poſſeſſed of a living principle, and that the LIFE of the whole body is derived from IT. This opinion was firſt broached by the celebrated Harvey,"’ (this I have already ſhewn to be a miſtake *), ‘"the diſcoverer of the circulation: but in this he was never much followed; and the hypotheſis itſelf, indeed, has been pretty much laid aſide and neglected, till of late that it was revived by Mr. J. Hunter." After which are quoted the ſix arguments, (which I ſhall preſently endeavour to examine) as advanced by that great profeſſor, to ſupport this broad and unqualified opinion: but, in the manuſcript copy of his Lectures, which I have principally made uſe of, he begins the ſubject with the ſimple aſſertion only, that the blood ‘"is endowed with a principle of life, in itſelf, equally with the ſolid parts."

[19]

Now, whether all or any, either of the particular fluid or ſolid parts,* poſſeſs in themſelves (that is to ſay, either ſeparately, or abſolutely) a principle of life, I do not at preſent enquire, becauſe it ſeems to involve the general queſtion, (which muſt be referred to its proper place in my Eſſay); namely—Whether life itſelf is to be conſidered as a diſtinct and poſitive eſſence, or, ſimply, as the reſult of a particular harmony and correſpondence of the whole, or aggregate combination, preſerved and acted upon by a particular ſtimulus? On this ſubject, indeed, it is ſufficiently evident that I have the misfortune to differ from the illuſtrious authority before me; but as I am now examining the doctrine only of the Vitality of the Blood, it is but neceſſary for me juſt to obſerve, that as nothing more is directly aſſerted in the propoſition, than that the blood of the living body is equally alive with the bones and ligaments, and muſcular fibres, &c. of which ſuch living body is compoſed, it does not ſeem to lie conſiderably in the way of my theory; becauſe, if in other reſpects I can but ſubſtantiate my opinion, the difference will not be very great, whether we admit the blood as participating in the Vitality, produced as I ſhall endeavour [20]to ſhew, or conſider it as nothing more than a ſpecific fluid, giving nouriſhment to the various ſubſtances, and conveying to the different organized parts the neceſſary ſtimuli, by which Life or the Vital Action is to be produced or ſuſtained. Nay, when he afterwards proceeds to aſſert, that ‘"Blood is not only alive itſelf, but alſo, by circulation through every part of the body, becomes the means of, and carries Life to, the other parts;"’ I do not yet perceive the abſolute neceſſity of entering the liſts upon this part of the ſubject, becauſe he does not palpably aſſert, that the Life to be conveyed is, ſui generis, or originally in the blood; but only that this fluid is the agent by which the Vitality is communicated to the reſpective parts; and it is my intention to admit that the blood, in the more perfect, and the ſerous fluid, ſubſtituted in its place, in the leſs perfect animals, is the appropriate medium, by which alone the ſtimuli neceſſary for the production and ſuſtainment of Life can be abſorbed and properly diffuſed through the organized frame: and, indeed, ſeveral paſſages might be produced to countenance the ſuſpicion, that this juſtly admired Lecturer ſo far agrees with the Theory I mean to enforce, as to admit that the Vital Principle is, at leaſt, ſuſtained and re-invigorated (if not abſolutely generated), not independently by the blood itſelf, but from ſomething imbibed in its paſſage through the lungs; for he acknowledges, that ‘"Before blood is capable of giving [21]life," (in other words, according to his own theory, before it is alive), ‘"it muſt have circulated through the lungs, where it undergoes ſome eſſential change. Perhaps,"’ continues he, ‘"it is then in its ſecond ſtate, or vivification."’

It is obvious to remark, that if the blood is not ‘"in its ſtate of vivification"’ till it has paſſed through the lungs, Vitality cannot be the property of the blood itſelf, but only a conſequence of ſome action, or ſuperaddition, acquired in its paſſage through that organ; and, conſequently, that the Vital Principle (to uſe the language of thoſe philoſophers who conſider Life as a ſeparate eſſence) is to be ſought, not in the blood, but in that ſubtile element, or whatever it is, which is imbibed by means of the reſpitory ſyſtem.

But (if it is not preſumption for me to ſay ſo) there ſeems to be ſome degree of obſcurity—perhaps, if I were ſpeaking of any man but John Hunter, I ſhould venture to ſay contradiction, in the doctrines of the Lecturer, upon this ſubject; for he immediately afterwards denies that the blood derives its Vitality from its paſſage through the lungs, in the following words: ‘"Perhaps it might be thought that Life is given to the Blood in the Lungs in conſequence of the heat applied there, as heat is ſuppoſed to act upon the Egg; but it muſt be remembered, that Life is not given to [22] the Egg by heat, only action produced by it." By which it ſhould ſeem that he means to be underſtood as conſidering the Vital Principle to be a property of the blood itſelf (ſo long as it continues in its perfect ſtate) independent of reſpiration; and that this action of the Lungs is only neceſſary for the purpoſes of circulation, and the production of action in the other parts of the frame, by the diſtribution of this principle.

And yet, if the Egg be alive (which, let it be remembered, I do not poſitively admit), how can this be? ſince (previous to the alteration taking place, from the application of heat, during the period of incubation), it contains no blood whatever; and, conſequently, if the Vital Principle be in the blood, muſt be alive without the principle of life—a paradox, which, perhaps, it would be a little entertaining to hear the advocates of this doctrine explain.

Not, however, to dwell upon ſo ambiguous a paſſage, there are, in the Lectures of this truly great man, ſufficient foundations for the opinion apparently entertained by the Editors of the work above quoted, as well as by ſeveral of his pupils and admirers—namely, That he means to repreſent Vitality, or, according to his own expreſſion, the Vital Principle, as reſiding originally, and in an emphatic ſenſe, in the [23] blood, and derived from it to the other parts of the ſyſtem. He even, in the cleareſt manner, affirms its ſuperior vivification over the nerves in particular: for while theſe, according to one of his aphoriſms on the Vitality of the Blood, are not concerned in ‘"conveying life to parts, but only direct the motions of the parts,"’ the blood is explicitly affirmed not only to ‘"convey life to the other parts,"’ but to be abſolutely ‘"the living ſupport of the nerves themſelves:"’ by which it is evident, that we muſt underſtand not only that the nouriſhment of theſe ſenſitive organs, but even their Vitality, is derived, not from their organization and the ſtimuli (of which they are, perhaps, the important repoſitories, or reſervoirs), but from the Vital Principle peculiarly reſident in the blood, and depoſited there for the purpoſe of being communicated and diffuſed to other parts.

Theſe other parts then being dependant (according to this theory) upon the blood, not only for their ſupport and enlargement, but, alſo, in an immediate view, for their Vitality, it is clear that if the ſyſtem of the Lecturer does not go the whole length with Moſes, of ſaying that the blood of the animal is the life thereof, at leaſt that he ſuppoſes Life, of itſelf, and independent of any particular action or ſtimulus to belong to, or be a property of, the blood; while to the reſt of the animal ſubſtance, it only belongs in a ſecondary [24]ſignification, as being imparted by the blood. And this, perhaps, we are the more bound to conſider as his real meaning, as he maintains the doctrine of its vitality even after coagulation; and even delivers it as his opinion that this phenomenon ‘"is owing to an action of ſelf-preſervation in the blood, or to an effort for its continuance."’ So that, according to this poſition, and the arguments that follow upon the circumſtance of coagula becoming vaſcular under particular circumſtances, we are not to conſider the vitality of the blood as the conſequence of its ſtate, condition, and harmony, with the other parts * of the body, but to look upon it as a principle inherent in it, and equally a property of it, whether in one ſtate and ſituation, or another—whether in its veſſels, or in a ſtate of extravaſation—whether in a fluid or a ſolid form—a circumſtance attributed to no other of the component parts of the animal frame: theſe being conſidered as having no other principle of life, but what they immediately derive either from the blood, or from their harmony with the ſyſtem in general; whoſe reſources muſt ceaſe before any material change in their nature and ſubſtance can take place. And yet, if this argument is properly ſifted, I queſtion whether it will make much for the Vitality of the blood, in any point of view whatever. For as no ſimilar change in any other fluid was ever brought forward as an evidence of a Vital Principle in ſuch fluid, I cannot [25]ſee that any phenomenon, that would not be conſidered as a proof of Vitality, or of an effort of ſelf-preſervation, in any other inſtance, ſhould have ſuch ſtreſs laid upon it, for ſuch purpoſes in the caſe before us.

With reſpect to the generality, probably to all, of the fluids capable of congelation, it might, perhaps, be objected, that they afford no parallel example of permanent change of ſtructure; as they are capable of reſolution to their original form, which blood is not. But petrified ſubſtances, in which the change is permanent and entire, might at leaſt be ſaid, in this reſpect, to have as good a claim to the attributes of a vital principle and action of ſelf-preſervation, as the blood, which is here ſaid to metamorphoſe itſelf into ſomething elſe, in order to continue its exiſtence. Beſides, if the coagulation of the blood be an action of its Vitality, and an effort of its Vital Principle for its preſervation, how comes it that it will coagulate after having been frozen; for John Hunter admits, that what he calls the Vital Principle of the Egg, is deſtroyed by freezing; and, indeed, nothing is more injurious to vitality of every kind, than the frigorific proceſs: and yet Mr. Hewſon informs us, that blood may be completely frozen, and preſerved in that condition (as other dead animal ſubſtances may) for a conſiderable time; and yet, after it is again reduced, by an increaſe of temperature, to its fluid form, it will coagulate juſt as uſual.

[26]

Having thus examined the general ſtate of the queſtion, I ſhall preceed to review the ſix arguments brought forward upon the authority of the lecturer, in the Encyclopedia, in ſupport of the opinion previouſly quoted—(vide page 18 of this Eſſay.) For the more ample ſtatement of theſe, however, (not to ſwell my Eſſay to an unneceſſary length, by quotations from a book, which is in the hands of every body) I ſhall refer to the work itſelf.

With reſpect to the firſt of theſe, derived from ‘"the power which the blood poſſeſſes, of uniting living parts,"’ it is to be remembered, that this is only the caſe in thoſe inſtances where blood is immediately ſupplied by the parts to be united, and where, conſequently, from its temperature, its aſſimilitude to the parts with which it is to enter into combination, its glutinous texture, and a variety of obvious reaſons, it may naturally be ſuppoſed to form the beſt cementing medium; and the healing of wounds, by other applications, which have evidently no Vital Principle, appears to me ſufficient to ſhew, that this is no proof of Vitality. All that is requiſite, in either inſtance, being to keep the living parts in contact, and exclude the air, and other injurious, extraneous particles, till Nature has a ſufficient opportunity of exerting her reſtoring powers.

[27]

The blood, yet warm, and fluid from the wound, may naturally enough be expected to enter intimately into the different portions of the ſevered parts; and all further injuries being thus prevented, it is neither ſingular nor ſtrange, that the ſeparated veſſels ſhould again unite, from the attraction of ſimilar particles ſo frequently obſerved, when circumſtances are favourable to the experiment; and that the ſtream of blood, driving towards its uſual courſe, ſhould at laſt find its way again through the coagulum formed by the blood thus bound up with the injured parts, and complete their reſtoration.—2 and 6. Exactly upon the ſame principle I account for the phenomenon from which the ſecond argument is drawn; namely—That ‘"coagula of extravaſated blood will become vaſcular:"’ for this, I believe, is never the caſe, except when the coagula come in contact, or nearly in contact, with arteries previouſly formed. This, therefore, ſeems to prove nothing more than that coagulated blood, when preſerving a proper degree of temperature, from its ſituation, is the proper medium, or ſoil, into which the arteries may ſtrike and ramify—all living parts, perhaps, having a tendency to grow and enlarge, ſo long as ſufficient ſtimuli are ſupplied, and the proper medium is preſented. For my own part, I cannot but obſerve, that all the preparations I have ſeen, intended to ſupport this argument, have only ſuggeſted a proceſs ſimilar to that obſervable in vegetation, where the moiſt earth, in contact [28]with the roots of plants or trees, ſupplies the proper medium into which the fibres are ſtimulated to extend their growth. And hence it is, that I find no difficulty in accounting for the junction of the teſticle of the cock, to the liver of the hen, into whoſe abdomen it had been introduced, as mentioned in illuſtration of the firſt argument; or, for the vaſcular appearance of the coagulum, found between the ſeparated parts of the fractured os humeri, upon which the ſixth, or rather the reiteration of the ſecond argument, is founded.—3. As for the third argument, drawn from the power of the blood, to preſerve an equal degree of temperature in the living body, during the prevalence of different temperatures of the atmoſphere—I ſhall at preſent make no other anſwer to this, than by obſerving, that if the Theory I am about to ſuggeſt is well founded, that will be ſufficient to account for this phenomenon, without appeal to any other hypotheſis: for if the air may be admitted to be ſufficiently impregnated with the ſame ſpecific ſtimuli in the coldeſt, as well as in the hotteſt day, there can be no reaſon why the blood ſhould be expected to have a lower degree of temperature on the former than on the latter—whether it be admitted to be poſſeſſed of a Vital Principle independent of ſuch ſtimuli, or not.—4. As for the ‘"Blood being capable of being acted upon by a ſtimulus,"’—this is ſaying no more than may be proved of a variety of things that have confeſſedly no pretenſions to life [29]whatever: and as the only particular effect which is inſtanced as produced by the ſtimulating influence on the blood, (namely coagulation), would never be admitted as a proof of life in any other fluid whatever, it cannot, as far as I am able to diſcover, be made any uſe of in illuſtration of the point in queſtion. 5. The fifth argument, that ‘"the blood preſerves life in different parts of the body,"’ is equally applicacable to the Theory of the Lecturer, and to my own; for, whether it be conſidered as retaining in itſelf the Vital Principle, or being the ſole medium through which Vitality can be produced, we muſt equally admit its importance, not only in preſerving, but in diffuſing life: I ſhall therefore only obſerve, that the collateral part of the argument, which aſſerts, that ‘"when the nerves, going to a part, are tied, the part becomes paralytic,"’ is, I believe, overthrown by later experiments; and that ſenſation only, and not the power of acting the muſcles, is interrupted by the ligature of nerves. Upon this, however, (as I certainly do not mean to rob the blood of its vital honours, to beſtow them on the Brain and Nerves), I ſhall not at preſent enlarge; but ſhall conclude what I have to ſay upon this ſubject, by obſerving that, perhaps, the whole doctrine of the Vitality of the Blood (in whatever point of view it may be taken) originated in the mind of the Lecturer, from obſerving the important offices it performs in the fuſtainment and reproduction of parts confeſſedly [30]and palpably alive. Now, that the nerves (for example), as well as every other part of the animal body, are nouriſhed by the blood, is ſufficiently evident, and that, but for ſuch nouriſhment, theſe parts muſt, by exhauſtion, loſe their Vitality, is equally obvious; but that the fluid, nouriſhing and ſuſtaining a living part, muſt of neceſſity be itſelf alive, is what I cannot readily admit, becauſe it ſeems to contradict the known laws and phenomena of nature. Air and water are the proper and neceſſary nouriſhment of plants, without which vegetation muſt quickly be exhauſted and expire; but no one will, therefore, contend, that air and water are alive: nor will the difficulty be removed, by objecting, that air and water are only the food of plants, and that the nouriſhment of the vegetable is immediately derived from the circulating ſap, as that of the animal from the blood; for as no digeſtive proceſs can be aſſigned to the plant, air and water muſt be the immediate nouriſhers of the ſap; and, conſequently, the concluſion muſt either be, that the living ſap is nouriſhed by air and water, which are not alive, or that the ſap, which is not alive, nouriſhes the living plant; which, with reſpect to the argument before us, is juſt the ſame: in ſhort, it might as well be maintained, that whatever ſupports a ſenſitive part muſt itſelf be ſenſitive; or that nothing but nerve ſhould nouriſh a nerve, or muſcle but muſcle, &c. which would drive us back to the obſolete opinion of thoſe philoſophers, [31]who maintained, that all things contain the component parts of all things; and, in ſhort, would even compel us to appeal to the doctrine of an ancient ſect of Atheiſts, who, to get rid of the neceſſity of a Deity, inſiſted upon the original and eternal Vitality of matter, and accounted for the growth and nouriſhment of living things, by arguing, that the particles that nouriſhed them were themſelves poſſeſſed of a living principle. If, however, we abide by the mode of reaſoning ſuggeſted by the known phenomena of nature, a much more ſimple theory will preſent itſelf, in the evident tendency of ſmall accumulations of matter (when placed under favourable circumſtances) to aſſimilate, and even identify themſelves with the larger maſſes to which they adhere, or with which they enter into combination; which will ſufficiently account for the nouriſhment and growth of the living body, without attributing Vitality to the blood, by which it is ſuſtained.

Having thus taken as brief a ſurvey as the nature of the ſubject would permit, of ſome of the principal opinions, that have, at different times, commanded the attention of the ſcientific world, I ſhall proceed to the profeſſed object of my Eſſay; namely—to conſider of the Definition. Of this undertaking the difficulty muſt be readily admitted; or, ſhould pride or petulance be inclined to deny it, the ſubterfuges to [32]which the moſt ingenious ornaments of medical ſcience have been driven, would furniſh a ſufficient reply. Some have given it up entirely, and ſatisfied themſelves with a negative teſt, inſtead of a poſitive definition; aſſerting, that the only criterion of its abſence is putrefaction: but theſe cautious maxims, though they may be adopted, for ſecurity, by the practitioner employed in the benevolent labour of ſnatching from premature diſſolution the pale victims of accident or deſpair, will not ſatisfy the ſpirit of the philoſophical enquirer: he, indeed, may frequently be compelled to wander in the gloom of doubt and negation; but his active mind will ſcorn ſuch ſullen darkneſs, and pant for the glorious proſpects of truth and certitude; to which, however, I have not the arrogance to profeſs that I ſhall conduct him.

By ſome it has been contended, that life conſiſts in action, or excited irritability; by others, ſimply in organization: but both of theſe would admit a variety of inſtances, that can lay no claim to any ſort of Vitality, much leſs to that ſort of Vitality which is the ſubject of the preſent paper: with reſpect to the former, I need only inſtance, that parchmen, leather, thread, &c. may be excited to conſiderable action by either heat or moiſture, as may alſo a variety of light bodies, by the application of electricity: and, as for organization, this I conſider to be no other than that arrangement [33]of diſſimilar parts, by which a harmony and communication of the whole is produced, ſo as to enable it to preſerve itſelf in a given ſtate, and reſiſt its own diſſolution. This, therefore, is very inadequate to our idea of life; for matter will continue to be organized when LIFE has ceaſed; as it alſo, I conceive, muſt be organized before LIFE begins; in illuſtration of which, I ſhould rather be inclined to quote the inſtance of the Egg, which (with all the deference due to the high authority of John Hunter) appears to me to be organized, though not alive, previous to incubation: I conceive alſo, that many bodies may be conſidered as organized, that were never intended to live at all. To thoſe, however, who wiſh to conſider life as entirely dependant on Organization, I ſubmit the following Definition: That perfect harmony of organized parts, by which the animal frame is rendered ſo far ſuſceptible of the proper ſtimuli, as to have its functions, or any of them, induced upon ſuch ſtimuli being applied: and this the Society will be kind enough to keep in their minds, as what I mean, when I come hereafter to ſpeak of Specific Organization.— Others have conſidered Animal Life as conſiſting in the performance of the Animal functions: but this definition would exclude, from all pretenſions to Vitality, many beings, which common ſenſe muſt admit to be alive; for an animal may certainly live, when it neither does, nor can perform, all its functions; and, as for aſcertaining which may be diſpenſed [34]with, and which may not, this, I believe, has never been ſucceſsfully attempted.

The definition of John Hunter appears to me particularly vague and unſatisfactory. "Life," ſays he, "does not conſiſt in any modification of matter: it either is ſomething ſuperadded to matter, or elſe it conſiſts in a peculiar arrangement of certain fine particles of matter, which, being thus diſpoſed, acquire the properties of Life."’ The Diſciples of this juſtly celebrated man muſt pardon me, if I am inclined to ſmile at this definition, or rather indefinite deſcription of Life, and to declare, that I never in my life met with any thing more completely incomprehenſible. ‘"Life does not conſiſt in any modification of matter;"’ and yet, perhaps, ‘"it conſiſts in a peculiar arrangement of certain fine particles of matter, which, being thus diſpoſed, acquire the properties of Life!"’ What is the fineneſs of theſe particles of matter, but a modification of matter?—What is the peculiar arrangement— what the diſpoſition of theſe particles, but a modification of matter? In ſhort, is not this telling us, in other words, that Life poſitively is not a modification of matter, but that yet, perhaps, it is a modification of matter? As for the other poſition, that Life conſiſts in ſomething ſuperadded to matter, I had once occaſion to controvert this incomprehenſible axiom at the Lyceum, when, all of a ſudden, a ſneer went [35]round the Theatre, and a hundred mouths were filled with fury againſt me, as though I had ſtood up, in the preſence of the Pope and his Cardinals, to deny the doctrine of the Trinity. I ſhall venture, however, once more to aſſert, that the ſpiritual alluſions of this ſentence are too fine for the groſs conceptions of my material organs. According to my dull comprehenſions, matter and vacuum ſtand preciſely in the ſame degrees of contradiſtinction as ſomething and nothing; and, in the former caſe, as in the latter, it is impoſſible for me to admit the negation of the one, without, at the ſame time, acknowledging the affirmation of the other.—Where there is not matter, there there is vacuum;—where vacuum is not, there there muſt be matter. Thoſe effects, which are not produced by the operations of ſome modification of matter, or, in other words, of ſomething, muſt of courſe be produced by ſome modification of vacuum, or, in other words, of nothing; and how vacuum, or nothing, can be ſo modified as to produce Life, I leave to the conſideration of the Metaphyſicians. It is evident, however, that this is not what the Lecturer means; becauſe, though he denies the modification of matter, he admits the ſuperaddition of ſomething.—But what is this ſomething that is not matter?—Is it Spirit? I certainly do not think it the part of a philoſopher abſolutely to deny the exiſtence of every thing that he cannot demonſtrate; but, as contradictions are not to be admitted, I muſt, for my own part, maintain, that if there is any ſuch thing entering into the animal [36]compoſition (though our ſenſes have never yet been capable of taking cognizance of it) as Spirit, having an exiſtence ſeparate and diſtinct from organization, and that groſs periſhable kind of ſubſtance we call body, that ſuch Spirit, however ſubtile, however refined, muſt ſtill be material: and then, indeed, the abſurdity vaniſhes—becauſe that more ſubtile matter can act upon that which is more groſs and inert, we have ſufficient evidence in the action of air, and of the electric fluid. And that this (a fine and ſubtile, or aeriform eſſence) is the real and genuine meaning of the term Spirit, about which divines and philoſophers have ſo long been contending, is, I conceive, ſufficiently demonſtrable, not only from its etymology, but alſo from the common application of the word in the other ſenſes in which it is ſtill retained: as, for example,—by the ſpirit of any diſtilled or fermented fluid, we always mean to expreſs that more ſubtile and volatile principle (the alkohol of the chemiſts) mixed with, and diffuſed through ſuch fluid, and whoſe materiality (notwithſtanding its ſuperior ſubtility) is no more to be queſtioned than that of the groſſer parts of the fluid with which it enters into combination. In ſhort, it will perhaps be found, that all Nouns, immediately or arbitrarily derived from Verbs,* whether of the ſame, or any other language, ſtill retain, [37]in a conſiderable degree, their paternal ſignification; and ſpirit muſt, perhaps, be admitted to bear no other meaning than the Latin ſpiro (to breathe), from which it is confeſſedly taken: or, if we muſt needs make a diſtinct living exiſtence of it, then can it poſſibly mean no other than a vital aëriform ſubſtance, diffuſed though the frame, and giving animation to the reſpective parts. So that, at any rate, this ſomething ſuperadded to matter, can only be a more refined ſpecies of matter added to that which is more groſs; and, of courſe, it conſtitutes that very modification which the Lecturer denies.—It has been ſtated, in defence of this paſſage, that by ſome thing ſuperadded, no more is meant than ſome quality; but this would by no means mend the matter, ſince nothing can be added but what has a previous and ſeparate exiſtence. Two things brought together may, it is true, occaſion the exiſtence of a third, different from both; but this third is not added, but produced. Now qualities have no ſeparate exiſtence, nor can they even be conceived in the imagination, otherwiſe than as connected with the things of which they deſcribe the ſhades or attributes: they are, in fact, ſolely and purely, modifications of matter, and, conſequently, this interpretation involves all the abſurdity and contradiction of which I have before complained.

But it is much more eaſy to find fault with the definitions of others, than to frame ſuch as are not faulty: I ſhall proceed, [38]therefore, to my taſk with caution; and, beginning with a general, proceed to a particular definition.—Life then, in the animal, we will ſay, is that ſtate of action, by which the functions, or any of the functions of the animal, are carried on. This definition, it is true, neither points out how the action is ſuppoſed to be induced, nor the ſtate of the animal previous to the induction: I proceed, therefore, to add, that, previous to the exiſtence of life, the body muſt have attained a SPECIFIC ORGANIZATION; and that Life, or, in other terms, the Vital Action, is induced by the application of proper ſtimuli: thus, then, life in the animal is that ſtate of action (induced by ſpecific ſtimuli upon matter ſpecifically organized), by which the animal functions, or any of them, are carried on. To the whole of this, I know, may be objected, the aſſertion of that great man, whom, with ſuch repeated arrogance, I have ventured to oppoſe: namely—That Life may exiſt without matter, being in ‘"a ſtate of action, and the property of ſelf-preſervation may alone be preſent, Life being at the ſame time preſent in its full force."’ To the ſolitary inſtance, however, brought in ſupport of this aſſertion, I muſt reply, that the life of the Egg is by no means obvious to my underſtanding; for, although the Egg be ſo far organized as to be endowed with the principle of ſelf-preſervation; ſo, alſo, are various fruits, &c. whoſe Vitality, I ſuppoſe, after they are plucked, will not be contended for*. In ſhort, it does not appear to have any one [39]property or attribute, which, in any other ſubſtance, would be deemed a ſufficient teſt of Vitality, till the ſtimulus of heat, being properly applied, ſo meliorates the arrangement of particles, as to induce the ſpecific organization eſſential to the ſuſceptibility and production of Vital Action.— By this, then, it will appear, that I conſider the preliminary principles of life to be a ſpecific organization and a ſpecific ſtimulus; the perfect contact of theſe to be the immediate cauſe, and life itſelf to be the ſtate of action produced by this union.

It will now only be expected, that I ſhould give an opinion upon the nature of the ſtimulus required. But, in order to do this, I muſt firſt premiſe, that I conſider the Blood, independent of its nutritive power, as the ſpecific medium by which the ſtimuli muſt be conveyed to the different parts of the organized frame, ſo as to produce the Vital Action. This Blood, then, in its paſſage through the Lungs, collects a ſomething, which generates a ſpecific heat (for it is evident, that heat, unleſs thus generated, will not anſwer the purpoſe), which it diffuſes through the whole vaſcular ſyſtem, and then (exhauſted of its vivifying power) returns again to the lungs, to exhale whatever noxious particles it may have collected, and to inhale a freſh portion of the ſame vivifying principle. But what is this ſomething—this vivifying principle?—Is it atmoſpheric air itſelf?—Certainly not. The coats of the arteries, and the membranous linings of the cells of the lungs, forbid the acceſs of ſuch an element; beſides, it has been [41]proved by experiment, that in the arteries of the living body there is no air. Something, however, it muſt be, that is contained in the atmoſphere, and ſomething of a powerful and exquiſitely ſubtile nature.

If, then, we look upon the component parts of our atmoſphere, what can we diſcover ſo competent to the taſk—ſo ſubtile, ſo powerful, ſo nearly approaching to that idea of an ethereal medium, which ſome philoſophers have ſuppoſed neceſſary to complete the chain of connection between the divine immortal eſſence, and the dull inertion of created matter, as the electrical fluid?—that principle, whoſe preſence, under ſuch a variety of forms, is conſtantly preſenting itſelf to the reſearches of the philoſopher!—whoſe agency, in ſo many of the phenomena of Nature, we are daily detecting! and which, perhaps, will one time be diſcovered to be the real principle by which all heat and action are originally generated and maintained!

FINIS.

Appendix A

BY THE SAME AUTHOR.

In the Preſs, and the Firſt Volume now ready for Delivery, THE PERIPATETIC; Or, SKETCHES of the HEART, of NATURE, and of SOCIETY; In a SERIES of JOURNALS, in VERSE and PROSE, of the ECCENTRIC EXCURSIONS of SYLVANUS THEOPHRASTUS, 3 Vols. Price 9s. in boards.

SCBSCRIPTIONS received by the Author, by the Publiſhers of this Pamphlet, and HOOKHAM and CARPENTER, Bond-Street.

Notes
*
It is an act of juſtice due to the celebrated Lecturer on Comparative Anatomy, to confeſs, that I never was perſonally at his Lectures; and that, except in the inſtance where I have mentioned the authority of the Encyc. Brit. my quotations are taken from the manuſcript copy belonging to a very ingenious pupil, who, a few years ago, was a conſtant and diligent attendant.
*
The Eſſay was diſenſſed for ſix ſucceſſive nights to a theatre particularly thronged; and the following Letter of Thanks was officially addreſſed to the Author:

Theatre, Guy's-Hoſpital, March 2, 1793.

SIR,

I AM deſired, by the Members of the PHYSICAL SOCIETY, to return you their moſt ſincere Thanks for your excellent and very valuable Eſſay, towards a Definition of Animal Vitality, the Abilities you diſplayed during the diſcuſſion, and the inſtruction which this inſtitution has received from your Aſſiſtance in the debates.

I am, SIR, With the greateſt Reſpect. Your moſt obedient humble ſervant, George Johnſon, Secretary. J. Haighton, Praeſes.
Mr. THELWALL,
*
Vide p. 13. of this Eſſay, where it is ſhewn to have been the opinion of Moſes, &c.
*
I treat the word parts here, not as alluding to limbs or proportions, but as referring to the ſeparate and different ſpecies of ſubſtance of which the body is conſtituted—as bone in contradiſtinction to muſcle, muſcle in contradiſtinction to nerve, nerve to membrane, and the like.
*
Vide Note, page 19.
*
The natural mode of derivation ſeems to be of the Verb from the Noun; this being evidently likely to precede in the firſt rude attempts at language: but there are many words now in uſe, which muſt have come to us in the contrary direction—as Heaven, for example, which ſtill retains, ſimply and abſolutely, the meaning (that which is heaved or lifted up), which it brought from the parent verb, to beave.
*
Some, perhaps, will contend for the life of the kernels, ſeeds, &c. I, however, ſhould content myſelf with contending for their ſpecific organization; by which, upon the application of proper ſtimuli, they are rendered ſuſceptible of Life.
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TextGrid Repository (2020). TEI. 5539 An essay towards a definition of animal vitality read at the theatre Guy s Hospital January 26 1793 in which several of the opinions of the celebrated John Hunter are examined and controverted B. University of Oxford Text Archive. . https://hdl.handle.net/21.T11991/0000-001A-6147-7