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.[A]
[A] 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.