whatever the type of being, in its strictest signification. This is the teaching of Aristotle, as it is the doctrine of modern physiologists; and those functions are always here referred to as the essential conditions of whatever is animated, although, for higher forms of being, other organs and functions are required. The nature, however, of the essence or principle which originates and orders those living functions is hitherto for us, as it was for Aristotle, inscrutable; and it may be that the wide survey which he took of life, by complicating simple functions with sentient and even intellectual faculties, tended only to disturb and pervert the course of his inquiry. But whether Aristotle's mode of inquiry was or not faulty, and whether the principle which animates the world (it may be the universe) is or not among those causes which are inscrutable, it will be ever a topic of deep interest to the learned and the thoughtful of every age.

In an opening chapter, Aristotle has in so clear and succinct a manner reviewed the prevailing doctrines and opinions as well of his own as of a preceding age, that that summary may be regarded as the exposition of all that was then most authoritative; and as, from that time, physiology may be said to have declined, it would be almost supererogatory to

allude to any other writer before the rise of modern science. It may be mentioned, however, in deference to the name, that Cicero1 has alluded, with a just appreciation of Aristotle's superiority, to this treatise; but as the topic was foreign to his pursuits and little in accordance with his talents, we cannot be surprised if he mistook the scope of the design, and perverted thereby the tendency of the argument.

This treatise is, it may be added, both an introduction and a sequel to the other physiological treatises of Aristotle; and, as it treats of all the characteristics of living beings, it may contribute to a clearer understanding of them, as they, in their turn, may serve to elucidate it; for they all proceed from the same hand, maintain the same doctrines, and emanate from the same laborious and original intellect.

This topic engaged the attention of eminent anatomists and physiologists towards the opening of the present century, and their writings will shew the opinions entertained by the moderns concerning it; but it has, generally, been made an incidental rather than a special subject of inquiry, a prelude, as it were, to the teaching of anatomy and physiology. The opinions entertained concerning vital principle

1 Tusc. Disp. Lib. I. I.

by the eminent men here alluded to (Hunter and Barclay, Bichât and Cuvier) may well be collated with those of Aristotle, who wrote at a time when science was in its infancy, and when, for profitable investigation, he had to depend almost exclusively, amid so much hypothesis, upon his own laborious and perspicacious intellect.

In quoting those writers, there is hardly occasion for observing any order of precedence, as they flourished about the same time, and contributed equally to the present development of physiological science,

According to Hunter1, "Animal matter is endowed with a principle called, in common language, life. This principle is perhaps conceived of with more difficulty than any other in nature, which arises from its being more complex in its effects than any other; and it is, therefore, no wonder that it is the least understood. But, although life may appear compounded in its effects in a complicated animal like man, it is as simple in him as in the most simple animal, and is reducible to one simple property in every animal." In another paragraph, he adds, "the first and most simple idea of life is its being the principle of self-preservation, by its preventing

1 On Vital Principle.

matter from falling into dissolution-for dissolution immediately takes place when matter is deprived of it; the second is its being the principle of action. These are two very different properties, though they arise from the same principle."

Barclay1 observes that, "in every living organized structure there is plainly a power that preserves, regulates, and controls the whole; directing, at first, the different processes in forming one part of the organs, afterwards employing the assistance of the organs which it has formed to produce more, till at last it completes the whole of the system in such a manner as to suit its future conveniences and wants. This power, or rather this agent, physiologists have named Vital Principle; though not a few are inclined to suppose it to be the effect, rather than the cause, of the organization. But in all operations that are performed without either volition or consciousness, it appears subordinate to a much higher power-to that Almighty and Omniscient Being, who dispenses his laws to the boundless Universe, and whose laws, except by himself, can never be improved, altered, or abrogated.'

Bichât makes Vital Principle to be "the assemblage of the functions which resist death;" and this

1 Introduction to Anatomical Nomenclature.

3 La Vie et la Mort.

definition was adopted substantively by Cuvier, who, in his introductory lecture to the "Comparative Anatomy," has illustrated the influences of this assumed principle, by a description, alike graphic and beautiful, of what takes place when it has been withdrawn or extinguished. "If1," he observes, "in order to have a correct idea of life, we consider it in simple forms of being, we shall soon perceive that it consists in the faculty possessed by particular corporeal combinations of lasting for a given time and under a determined form; of attracting, incessantly, into their composition a portion of the surrounding substances, and in giving back to the elements portions of their own substance. So long as this series of movements is maintained, the body, in which it is manifested, is a living body; and when it is irrecoverably arrested it is dead."

But although the definition of Bichât involves a great truth, and is a summary of all that has been ever said upon the subject, it is open to the criticism of M. Magendie, that, by its admitting the idea of death, it presupposes life, and thus establishes a vicious circle of reasoning. It is criticised also by M. Comte2, as a fancied antagonism between animate and inanimate matter, a chimerical struggle between 1 Règne Animal. 2 Science Biologique.