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Rh definition was adopted substantively by Cuvier, who, in his introductory lecture to the "Comparative Anatomy," has illustrated the influences of this assumed principle, by a description, alike graphic and beautiful, of what takes place when it has been withdrawn or extinguished. "If ," he observes, "in order to have a correct idea of life, we consider it in simple forms of being, we shall soon perceive that it consists in the faculty possessed by particular corporeal combinations of lasting for a given time and under a determined form; of attracting, incessantly, into their composition a portion of the surrounding substances, and in giving back to the elements portions of their own substance. So long as this series of movements is maintained, the body, in which it is manifested, is a living body; and when it is irrecoverably arrested it is dead."

But although the definition of Bichât involves a great truth, and is a summary of all that has been ever said upon the subject, it is open to the criticism of M. Magendie, that, by its admitting the idea of death, it presupposes life, and thus establishes a vicious circle of reasoning. It is criticised also by M. Comte, as a fancied antagonism between animate and inanimate matter, a chimerical struggle between