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 If this is elementary life, let us ask what is elementary death—i.e., the death of the cell. And in this connection let us ask the questions which we have to examine in the case of animals high in organization, and of man himself. What are the characteristics of elementary death? When the cell dies, is its death preceded by a growing old or senescence? What are the preliminary signs and the acknowledged symptoms?

Changes Produced by Death.—The state of death is only truly realized when the fundamental properties of living matter enumerated above have entirely disappeared. We must follow step by step this disappearance in all the anatomical elements of the metazoan.

Now the properties of the cell are connected with the physical and chemical organization of living matter. For them to disappear entirely, this organization must be destroyed as far as all that is essential in it is concerned. We cannot admit with the vitalists that there is any material difference between the dead and the living, and that only an immaterial principle which has escaped into the air distinguishes the corpse from the animated being. In fact, the external configuration may be almost preserved, and the corpse may bear the aspect and the forms of the preceding state. But this appearance is deceptive. Something in reality has changed. The structure, the chemical composition of the living substance, have undergone essential changes. What are these changes?

Physical Changes.—Certain physiologists have endeavoured to determine them. Klemm, a botanist, pointed out in 1895 the physical changes which characterize the death of vegetable cells—loss of