كتاب النفس

of this essay is that something which gives to matter those attributes. The processes, then, of reproduction, growth, and decay, that is, generation, life, and death, are the essential characteristics of living beings, and conferred upon them, as has been said, by that something which is designated Vital Principle. Now, to homogeneous forms and solitary functions others of more complex nature are superadded, and these give rise to that long chain of being of which man may be regarded as the head; but yet, amid all the simplicity of organs, of action, and of reaction, those two functions still prevail, and constitute life, 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.