Vital Principle is divisible or without parts, and whether every Vital Principle is or is not the same in kind, and, if not the same, whether the difference is generic or specific; but they who now are engaged in discussing and exploring Vital Principle seem to give exclusive attention to that of man. We must be on our guard against this, however, so that it may not escape us whether there is but one definition for Vital Principle as for animal, or whether it must be different for each creature, as for a horse, a dog, or a man. The term animal, besides, taken in an universal sense, is either without meaning, or of very secondary value; and so equally is every other common term which might be predicated of this subject. If, on the other hand, there are not several Vital Principles, but parts only of a single Principle, we have to settle whether we should commence the inquiry with the Principle as a whole, or, contrariwise, with its parts; and, with respect to the parts, it is difficult to determine which of them have been constituted differently from others; it is difficult also to say whether we should study the parts before their functions, as the mind before thought, or sensibility before sensation; and so for other faculties and functions. If it be expedient to commence the inquiry with functions, it may be a question whether it would not be better here also to study first their opposites; as the object of perception before that which perceives, and thought
