Part 2

The performance of vital motions without consciousness;

Eggs freezing with more difficulty from the time they are first laid in proportion to their freshness;――and,

The contraction of muscles after removal from the body;――are I believe the points most relied on as evidence of an independent living principle in the muscular system, and which shall now be considered in the order detailed.

In considering the condition of animals in their nascent state, we may readily understand, that their rudiments, composed of a pellucid congeries of parts, will freely transmit the light, and as there is no analysis of the ray, or proper reflection of it, it can make on the retina no impression, nor convey to the mind any perception of the existence of distinct parts. Soon however the vital energy manifests itself in the formation of red blood, and the motion of a point which being capable of reflecting light presents to the senses marks of distinct organization. Yet from this we derive no evidence that this point is the first to possess life, but only, that it shews itself first, by means of its reflecting powers. And thus though we admit the proposition, it can assist the cause it was adduced to support but little; for the moving energy, we presume may be derived from co-existent parts. And indeed according to some accurate observers, the disproportionate head with other lineaments, appear visible some time before the heart is seen in motion.

That Fœtuses have in a few remarkable instances been ushered into a short lived existence without a brain, is advanced with some degree of elation by the supporters of the principle under consideration. Animals, from equally good authority, have been born without hearts: but will a few cases of lusus naturæ serve to disprove the importance of these organs to the animal economy? I fancy not; in either case above alluded to, we may suppose that the appendages performed, though imperfectly, the offices of their respective organs. And in those particular cases in which the brain is wanted, we may conclude with the learned physiologist, that it was destroyed by disease after the growth of the child, but left the nerves and ganglia (which Doctor Monro considers small or disproportionate brain) endowed with sufficient influence to maintain for a short period its life. If there be an independent vital principle in the muscles; why does not its power support those extremely rare cases, which unfortunately for the doctrine, as well as its advocates, do not generally survive birth any length of time.

No person, at all conversant with the phenomena of the passions, will deny the connexion between the mind and vital functions. It will therefore be only necessary to observe in answer to the third proposition; that sensation is predicated on a comparison of the past, with the present state of impressions, and that all are relative to some change in the percipient organ; heat is only sensible, because it was preceded by a lower temperature. And therefore objects which are equable in their application, and continued for a length of time, affect us but slightly; are unattended to when present, and cannot be recalled when past, must consequently escape our consciousness. Objects of minor importance operate continually on our senses, but may escape the observation when preoccupied, particles of matter passing before our eyes induce us to close the palpebræ, yet the action is not always attended to. Also the common action of the heart and arteries are not the subjects of our consciousness; the stimulus of the contained blood continuing nearly the same, conveys no impression to the mind; but let a fluid, however bland, be injected into them, and the animal will testify by its cries, the acute sensibility of the parts; or suspend their ordinary operation for a few moments, which may be readily done in some of the branches of the arterial system, and the succeeding action becomes very perceptible attended with much uneasiness and anxiety. The common action of the intestines are not generally objects of our attention, yet derange or increase that action and they establish their connexion with the sensitive medium. This is rather a species of abstract reasoning, but we have positive cases on record: in which a British colonel could suspend at pleasure the action of the heart: the stomach likewise appears under the influence of the will, as is evinced in ruminating animals, and Professor Blumenbach gives an instance of a person in whom this organ was under the strictest command; also we have from the same authority, cases in which the Iris has been subjected to the power of volition; and indeed the parrot continually displays something of the kind. For such reasons I would not consider any part of the living body independent of the common sensory, but I can suppose that the mind by disuse or disease may lose its power over some organs, as it sometimes does over even the voluntary muscles. And I can see no reason why those motions called involuntary, could not be gradually withdrawn by want of attention from the direct influence of the mind.

That eggs resist in proportion to their freshness a reduction of temperature, is not in my conception necessarily owing to their vitality; which may be inferred from the circumstance, that as long as they were capable of being hatched, however stale, they must still retain their principle of life, and therefore, a stale egg able to afford a chick by incubation, should freeze no sooner than one newly laid. Another solution of the phenomena can be offered which may have escaped the attention of the ingenious experimenter. In the present state of chemistry, acquainted with the passage of heat through bodies, we know that the change of temperature in a tenacious semifluid must be very slow; caloric passing in such bodies, rather by transposition of particles than by their contact; the heat of the new laid egg is but little below 100° of Fahrenheit and consequently must part with near 70° of heat before it could congeal. And having undergone that change, it would require some time to equalize its temperature with surrounding bodies.

If the egg does contain an independent principle of life why is not the chick evolved without the aid of other agents?

The last argument I shall notice on this fanciful hypothesis is not least in importance with the advocates for the independent principle but is one on which they place much reliance, viz., the contraction of muscles after removal from the body. There is little doubt that the contractibility of the muscular fibres is variously disposed in different animals and that particular parts may possess more tenacity of action than others; but if it were a constituent principle of the part, it should continue undiminished in power until the texture be entirely destroyed, and not gradually decrease in energy, as is the case, till it cease to act altogether. It may be strongly urged against this hypothesis that stimuli applied to the nerves soon after the death of an animal, produce more violent action than when applied to the muscles themselves; and much sooner destroy their aptitude for action, which fact, has been shewn true, by a series of ingenious and well conducted experiments, entered on by the learned doctor Whytt, of Edinburgh.

Hence these propositions which have been displayed with no little triumph by the votaries of an independent life, can afford their opinions no support.

But the exertions of physiological speculators did not stop here, while they were seeking with such solicitude for the source of vitality, it is not to be supposed that such an important constituent of the body, as the blood appears to be, should escape unnoticed, nor did it. That the life was in the blood, seems an opinion long since suggested, but it was treated rather as a figurative expression until revived and introduced to notice by the distinguished authority of Harvey. After him it obtained many advocates and zealous supporters in Europe and America. The opinion is entitled to notice, and I shall consider it with that principle of liberality and respect, which I think due to all opinions proceeding from such high sources.

Upon the supposition that the blood was the formative principle first existing in the nascent embryo, from the action of which the various parts of the body are evolved, it was styled the Primum Vivens. But could the blood circulate without vessels? propelled chiefly by a vis atergo, unless moving in tubes or vessels; I apprehend it could never revolve in a circle and perform by secretion, the functions so necessary to the growth and nutrition of the body.

Ingenuity, put upon the stretch, has drawn in support of this visionary speculation, arguments from the coagulum of the blood assuming appearances somewhat resembling muscular contraction, “and” (we are told) “as contraction is the life of the solid, if we find any thing like it, we should call it the living principle of the blood.”――On the same foundation we may assert the vitality of jelly, which can be dissolved and coagulated again, and again, present the same appearance of contraction.

This quality of blood not peculiar to itself, can be referred to physical causes alone, seeing it separates spontaneously when drawn from the body, into crassamentum and serum, we are satisfied its parts are not united by chemical solution, properly so called; but are rather mingled together and kept in intimate mixture by the continual action and agitation of the circulation, for when at rest, the different parts occupy the situation assigned them by their specific gravity, and mutually recede, from the loss of caloric, and by the attraction of aggregation.

An enlightened defender of this opinion of our own country, with his mind apparently more highly imbued by speculative enquiries, than the observation or proper application of facts, endeavored to substantiate a living principle in the blood from the manner in which it is influenced by chemical agents, and has brought forward experiments which, though conducted with some address appear to have been introduced rather to quadrate with preconceived opinions, than with a spirit of impartial investigation.

Portions of blood drawn from the veins of healthy persons were subjected to the influence of electricity, which were observed to separate sooner than other portions set by as standard marks, from which it was inferred that the stimulus must have acted on a principle of life, to increase its action. To this inference I shall only offer general objections. In the present state of our knowledge, we know that the blood though apparently homogeneous is resolvable by agents into several parts; its crassamentum is composed of gelatinous fibres and red particles, kept in intimate mixture with the serosity by a combination of concurring circumstances, which being destroyed by the operation of chemical agents the separation is precipitated.

See observations on albumen, and some other animal fluids, with remarks on the analysis by electro-chemical decomposition. ――――Philosophical Transactions for 1809:――page 373.

The life of the blood has also been inferred from its resistance to a reduction of temperature, similar to that of a fresh egg. In a former part of this work I endeavored to shew the fallacy of such an inference, as the circumstance might arise from its peculiar consistency; but in the case of the blood, its temperature will be maintained sometime during its coagulation, by the latent heat disengaged in its change from the fluid to the denser state.

As Mr. John Bell has in a striking manner contrasted the arguments in question from which a vital power has been inferred, I shall take the opportunity of transcribing his own words. “We are informed that a fresh egg in consequence of being alive resists the cold, and is frozen with greater difficulty; but once frozen and thawed again it loses its living principle and power of resisting cold at once. It freezes now at the same temperature with other animal matter, shewing no longer any power of generating heat, or resisting cold. But we are told (by Mr. Hunter) that the blood having a determined period of coagulating, you may during that time freeze the blood and it will thaw again and yet congeal at its proper time, and he tells us he had very cleverly frozen blood during the time of its flowing from the vein, then thawed the cake, and still in due time it coagulated. Now since the egg resists the cold by its living principle, why did it die or lose that principle during its conversion into ice? or rather since the blood coagulated by a living effort, how did it preserve its living principle after being frozen?” This shews that the coagulation of the blood has no relation to a living power, but is rather a characteristic of some dead animal matters.

Conclusions have likewise been erroneously drawn from the fact of a limb, dying when the supply of blood is cut off from it, but which circumstance serves to prove that blood is the most natural stimulus, and is essential to the perfect organization of the part; but the blood is nothing without its oxygen. Abstract heat, which is an exciting agent next in power, and you produce a like effect; mortification and death, will ensue; yet no one will pretend to say that the principle of caloric which pervades all matter is life.

But let it not be supposed while I thus object to the reputed vitality of the blood, I wish either directly or indirectly to detract from the importance of its use in the animal system. Conveying the principles, which acted on by living organs form the various parts, and presuming it the most general and applicable stimulus of the body, I can still conceive its importance, and appreciate its value though itself be dependent on external agents for its essential qualities.

Thus has the vital influence, passing for ages through all manner of speculations, and tortured in all the variety of fanciful inventions, been secured for a while in a doubtful repository by the ingenuity of its advocates, or the authority of names, but it now comes to be ousted from its local habitations, a dependent wanderer throughout the body, for after all its changes we find it of later days expressed in the excitability of Dr. Brown, acted on by external stimuli. “I say the excitability of Dr. Brown,” though it is asserted that many before him advanced the opinion of the dependent state of life on external substances; because I am willing to allow him the credit, at least, of being the first promulgator, and most zealous supporter of this simple hypothesis.

Dr. Rush tells us in his publication on “animal life” that Dr. Cullen advanced the opinion in 1766, that the Edinburgh professor afterwards deserted it; and that he (Rush) never did, but made it the foundation for many of his rules of practice, and actually advocated the doctrine in his course of lectures in 1771. And thus, we are given to understand, slept unheeded and unapplied, in the manuscript sheets of that professor, this important germ of a grand system, calculated by its simplicity to revolutionize all former theories of medicine, until by the arduous exertions of Dr. Brown an imperfect fabric was reared, serving at least to point to the right path, after enquirers. This digression will be excusable, in an attempt to fix, while adverting to the origin of, the opinion, and however the question of priority may be decided in the minds of gentlemen, whether they give credit to Dr. Cullen for the first suggestion, or to the discriminating mind of Dr. Rush as the strenuous supporter, they will not deny to Dr. Brown the merit of first publishing――of overcoming the prejudices against, and at length drawing the attention of the medical world to this novel doctrine.

In reviewing the ideas of Dr. Brown on the mode of existence of his excitability or vital principle, they appear not sufficiently definite to require much attention. His fundamental principles, though correct in the general, seem not to have been properly investigated by himself, and therefore erroneously applied, and indeed in his own case completely perverted. But I think, on the whole, we may attribute his errors rather to the enthusiasm with which he conducted his speculations than to the fallacy of their nature. Looking forward with eager triumph to the ultimate end of his object, he appeared little solicitous to enquire after the cause, or seat, of vitality. But assuming the principle, that whether it was a quality or substance, it was an indivisible property, a certain quantity of which was assigned to every living being at the commencement of its existence, which quantity determined the duration of life, led him into many inconsistences, and has afforded ground for some of the strongest arguments that can be brought against his hypothesis.

I ought probably, in this place, to pay some attention to the theory of life advanced with much ingenuity by Dr. Darwin. But not feeling disposed unnecessarily to expatiate, I shall avoid a detail on this subject, it being sufficient to remark that his sensorial power appears too physical to solve alone the phenomena of life; it is attributing a power to matter, which I believe, however modified, or refined, it can never assume.

Having thus taken a cursory view of the most prominent opinions which have fallen within my observation, and endeavoured to shew them, rather as the scintillations of imagination, than the effulgent light of reason, suited to guide us through this mazy labyrinth, of metaphysiological investigation. I shall now proceed with what I presume at least the more unexceptionable explanation, and better adapted to the wisdom that regulates all nature.

From the most remote periods of antiquity, philosophers have not been inattentive to the peculiar differences that discriminate animate from inanimate matter, and under some modifications the distinction has been attributed to a principle called life, which not sufficiently understood in its nature, is only to be known by its phenomena, or symptoms.

Writers of high rank in the literary world, have, in their ardour to define its operations, called life a forced state, in consequence probably of observing, that when all external agents are withdrawn, its effects cease to be evinced in a plenitude of action. But were it becoming in me to cavil about modes of expression, I would only call the manifest symptoms of life forced as dependent on external agencies for their continuance. Life being rather the quality that distinguishes dead from living matter, and which may consist in an aptitude to action, and can remain for some time after its active effects cease to be obvious.