Page:Aristotelous peri psuxes.djvu/89



CH. IV.] after their functions, although in other respects different. But, besides these objections, what is that which is to hold fire and earth, with their opposing tendencies, together? Now, unless there be a restraining force, they must be torn asunder, and if such there be, it ought to be regarded as Vital Principle, and the cause both of nourishment and growth.

The nature of fire seems, to some philosophers, to be the absolute cause of nutrition as well as growth, and that because it alone, among bodies or elements, appears to be nourished and to grow. It might, therefore, be assumed, that it is fire which works out those processes in plants and animals; but although fire is possibly a joint cause, it cannot be the exclusive cause, as this must be assigned rather to the Vital Principle. The increase of fire is infinite, so long as there is any thing combustible, but to all the bodies of nature's constitution there is a limit and a relation both as to bulk and increase; and these are conditions, not of fire but of Vital Principle; not of matter but of design.

Since the same faculty of Vital Principle is at once nutritive and generative, it is necessary first to define nutrition ; for it is by this, compared with other faculties, that Vital Principle is especially distin- guished. Nutrition, then, appears to be a contrary acted upon by a contrary, but this does not imply any kind of contrary by any other contrary; it refers only