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, ...

AN ESSAY, TOWARDS A DEFINITION OF ANIMAL VITALITY.

IT is an apparent paradox, but it is not therefore the less true, that those ideas, or phenomena, that are most fami∣liar 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

eyes, or our imaginations, that a vulgar observer would sneer at the philosopher who should suggest the difficulty of ascertain∣ing 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 exa∣mination 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 pre∣tended 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

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 Prin∣ciple; 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 some∣thing—a phantom of the brain, which, perhaps, has no real existence: and, indeed, if the term is to be literally under∣stood—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 con∣sider it as the ne plus ultra of scepticism: but the philoso∣pher 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

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 mean∣ing 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 whe∣ther 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-ope∣ration of other principles, or natural and pre-existing causes,

I own, for my own part, I must be rather slow in yielding my assent; and, while I bow with respect to superior judg∣ments, 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 con∣siders 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.

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 separa∣tion 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, con∣tinues 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 inven∣tion 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

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 re∣commend it to our imaginations; and is also, to my concep∣tions at least, somewhat more comprehensible than those sys∣tems which refer the operations of gross matter to immaterial agency. It is, however, like all the speculations of the an∣cients upon these subjects, unfounded in experimental en∣quiry, 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 sys∣tems as were reconcileable with this tripartite division, than such as might be consistent with known facts, or maintain∣able on the grounds of reason; and that we should accord∣ingly 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

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 far∣ther—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 sim∣ple 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 sub∣stance, 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 pro∣perly be called, or the power by which the vital functions are performed, being the ultimate effect of these co-operat∣ing causes, is, in reality, as I humbly presume, to be consi∣dered as that Life, or Animal Vitality, for which, under so

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 princi∣ples 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 re∣motest 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 bar∣barism and violence, long before the faculties of man were sufficiently improved for refined speculations, or philosophi∣cal 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 opi∣nion

(for such to me at least it appears) has not wanted sup∣porters among those who will long continue to claim the ap∣plause and admiration of mankind.

And first, I must particularize, that this doctrine has re∣ceived 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 Reve∣lation is not always to be interpreted with philosophical pre∣cision—the enthusiasm of divine inspiration frequently elevat∣ing 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

understood as the opinion of Moses, that the blood is abso∣lutely the Vital Principle.

For this opinion, I am very much inclined to suspect, that no better foundation will be discovered than the acknow∣ledged fact, that when the blood, or any very considerable portion of it, is drawn away, the vital functions of the ani∣mal 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 de∣struction, 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 ac∣quainted 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 imme∣diate susceptibility of injury in the substance of the brain;

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 re∣strained and benumbed, and, of course, its vital functions will be stopped.

From this, and a variety of other considerations, it is evi∣dent 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 sto∣machs; for I know not how the simple cavities of the leech or polipus can, in strict propriety, be considered as sto∣machs.

This objection being founded in truth, it is necessary that we should give it its utmost force, and admit it as a demon∣stration, that animal life neither consists in, nor is absolutely

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 com∣pound fluid, which, in the more perfect animals, we call by the name of blood, as between this ichor and the sap of vege∣tables, and a variety of other simple juices of animal or ve∣getable 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 de∣gree, 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.

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* 1.1),

"the discoverer of the circu∣lation: 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 en∣dowed with a principle of life, in itself, equally with the solid parts."

Now, whether all or any, either of the particular fluid or solid parts,* 1.2 possess in themselves (that is to say, either se∣parately, 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 doc∣trine 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; be∣cause, 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 en∣deavour

to shew, or consider it as nothing more than a spe∣cific fluid, giving nourishment to the various substances, and conveying to the different organized parts the necessary sti∣muli, 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 circula∣tion 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

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 sub∣ject; 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

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 remember∣ed, I do not positively admit), how can this be? since (pre∣vious 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 Prin∣ciple, as residing originally, and in an emphatic sense, in the

blood, and derived from it to the other parts of the system. He even, in the clearest manner, affirms its superior vivifica∣tion over the nerves in particular: for while these, accord∣ing 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 ab∣solutely

"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 reser∣voirs), but from the Vital Principle peculiarly resident in the blood, and deposited there for the purpose of being commu∣nicated and diffused to other parts.

These other parts then being dependant (according to this theory) upon the blood, not only for their support and en∣largement, but, also, in an immediate view, for their Vitali∣ty, 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 stimu∣lus to belong to, or be a property of, the blood; while to the rest of the animal substance, it only belongs in a secondary

signification, as being imparted by the blood. And this, per∣haps, we are the more bound to consider as his real meaning, as he maintains the doctrine of its vitality even after coa∣gulation; and even delivers it as his opinion that this phe∣nomenon

"is owing to an action of self-preservation in the blood, or to an effort for its continuance."

So that, ac∣cording to this position, and the arguments that follow upon the circumstance of coagula becoming vascular under parti∣cular circumstances, we are not to consider the vitality of the blood as the consequence of its state, condition, and har∣mony, with the other parts* 1.3 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 con∣sidered 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

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 pre∣served in that condition (as other dead animal substances may) for a considerable time; and yet, after it is again re∣duced, by an increase of temperature, to its fluid form, it will coagulate just as usual.

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, how∣ever, (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 in∣stances 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 com∣bination, its glutinous texture, and a variety of obvious reasons, it may naturally be supposed to form the best cement∣ing medium; and the healing of wounds, by other applica∣tions, 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, extra∣neous particles, till Nature has a sufficient opportunity of ex∣erting her restoring powers.

The blood, yet warm, and fluid from the wound, may na∣turally enough be expected to enter intimately into the dif∣ferent 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 circum∣stances 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 resto∣ration.—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 sup∣port this argument, have only suggested a process similar to that observable in vegetation, where the moist earth, in contact

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 appear∣ance 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 pre∣serve an equal degree of temperature in the living body, dur∣ing the prevalence of different temperatures of the atmos∣phere—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 pheno∣menon, 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 expect∣ed 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

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 pre∣serves life in different parts of the body,"

is equally applica∣cable to the Theory of the Lecturer, and to my own; for, whether it be considered as retaining in itself the Vital Prin∣ciple, 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, per∣haps, 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 con∣fessedly

and palpably alive. Now, that the nerves (for ex∣ample), 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, nou∣rishing and sustaining a living part, must of necessity be itself alive, is what I cannot readily admit, because it seems to con∣tradict 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 ex∣pire; 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, con∣sequently, 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 sensi∣tive 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 philoso∣phers,

who maintained, that all things contain the compo∣nent 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 pos∣sessed 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 scien∣tific world, I shall proceed to the professed object of my Essay; namely—to consider of the Definition. Of this un∣dertaking the difficulty must be readily admitted; or, should pride or petulance be inclined to deny it, the subterfuges to

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 nega∣tive 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 en∣quirer: 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 parch∣men, 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 orga∣nization, this I consider to be no other than that arrangement

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 en∣tirely 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 dis∣pensed

with, and which may not, this, I believe, has never been successfully attempted.

The definition of John Hunter appears to me particu∣larly vague and unsatisfactory.

"Life,"

says he,

"does not consist in any modification of matter: it either is something su∣peradded to matter, or else it consists in a peculiar arrange∣ment 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, per∣haps, 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

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 Tri∣nity. 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, acknow∣ledging 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 contradic∣tions are not to be admitted, I must, for my own part, main∣tain, that if there is any such thing entering into the animal

composition (though our senses have never yet been capable of taking cognizance of it) as Spirit, having an existence se∣parate and distinct from organization, and that gross perish∣able kind of substance we call body, that such Spirit, how∣ever subtile, however refined, must still be material: and then, indeed, the absurdity vanishes—because that more sub∣tile 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 con∣tending, 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 vola∣tile principle (the alkohol of the chemists) mixed with, and dif∣fused through such fluid, and whose materiality (notwith∣standing its superior subtility) is no more to be questioned than that of the grosser parts of the fluid with which it en∣ters into combination. In short, it will perhaps be found, that all Nouns, immediately or arbitrarily derived from Verbs,* 1.4 whether of the same, or any other language, still re∣tain,

in a considerable degree, their paternal signification; and spirit must, perhaps, be admitted to bear no other mean∣ing than the Latin spiro (to breathe), from which it is con∣fessedly 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 giv∣ing animation to the respective parts. So that, at any rate, this something superadded to matter, can only be a more re∣fined 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 attri∣butes: 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 com∣plained.

But it is much more easy to find fault with the definitions of others, than to frame such as are not faulty: I shall pro∣ceed,

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 sti∣muli 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 op∣pose: 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* 1.5. In short, it does not appear to have any one

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 par∣ticles, 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 prelimi∣nary 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 opi∣nion upon the nature of the stimulus required. But, in order to do this, I must first premise, that I consider the Blood, in∣dependent 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 ar∣teries, and the membranous linings of the cells of the lungs, forbid the access of such an element; besides, it has been

proved by experiment, that in the arteries of the living body there is no air. Something, however, it must be, that is con∣tained in the atmosphere, and something of a powerful and exquisitely subtile nature.

If, then, we look upon the component parts of our atmos∣phere, 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 ne∣cessary to complete the chain of connection between the di∣vine immortal essence, and the dull inertion of created mat∣ter, 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.

Notes

• * 1.1

  Vide p. 13. of this Essay, where it is shewn to have been the opinion of Moses, &c.
• * 1.2

  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.
• * 1.3

  Vide Note, page 19.
• * 1.4

  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.
• * 1.5

  Some, perhaps, will contend for the life of the kernels, seeds, &c. I, how∣ever, should content myself with contending for their specific organization; by which, upon the application of proper stimuli, they are rendered susceptible of Life.