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
