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CH. I.] every natural body partaking of life may be regarded as an essence; but then it is an essence in combination, as has been said. And since the body is such a combination, being possessed of life, it cannot be Vital Principle; for as it is itself more truly subject and matter, it cannot be among the subordinates of a subject. It follows, then, that the Vital Principle must be an essence, as being the form of a natural body holding life in potentiality; but essence is a reality,—the reality, that is, of a body such as has been described. Now reality is, in the twofold signification, either of knowledge or of reflexion; and that it may be regarded as knowledge is manifest in that sleep and watching co-exist as original properties, in Vital Principle; and equally manifest that watching is analogous to reflexion upon knowledge, as that sleep represents knowledge possessed but not employed. But knowledge pre-exists in the same individual, and the Vital Principle is, therefore, the original reality of a natural body endowed with life in potentiality; only this is to be understood of a body which may be organised. Thus, the parts even of plants are organs, but then they are organs which are altogether simple, as the leaf is the covering of the pericarp, and the pericarp of the fruit; and the roots are analogous to the mouth, for both take in food. If, then, there be any general expression for every kind of Vital Principle, it may be set down as "the