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78 reality. It is manifest, too, that Vital Principle is a cause, in the sense of a final cause; for as the mind acts for some end, so does nature, and that end is her aim; and such an aim has the Vital Principle, by its nature, in living bodies. Thus, all natural bodies, those of animals as well as those of plants, are its instruments, and are what they are for its purposes. The term final cause has a twofold signification, as it implies that for which, as well as that by which, any result is obtained; and Vital Principle is a, final cause, as that whence locomotion is derived, although this is a property which does not belong to all living creatures. Change and growth, moreover, are dependent upon Vital Principle; for sensation seems to be a change of some kind, and whatever is sentient has Vital Principle; and this applies equally to growth and decay, for nothing grows or decays naturally unless it be nourished, and nothing is nourished which does not partake of life. Empedocles has not expressed himself happily upon this point, as, after other observations, he adds that plants take growth downwards, where they strike root, from this being the natural direction of earth, and upwards, from this being the natural direction of fire. Neither has he clearly seized the import of the terms upwards and downwards, as they are not identical for all creatures, or for the universe; for the nead is to animals what the roots are to plants, if we may speak of organs