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 and Plants. From this point of view each being is distinguished from another being as a given individual and as a particular species; but all are in some way alike and thus resemble one another: common life, elementary life, the essential phenomena of life; it is life itself.

The manifestations of life may therefore be regarded from the point of view of what is most general among them. As we go down the scale of anatomical organization, as we pass from apparatus (circulatory, digestive, respiratory, nervous) to the organs which compose them, from the organs to the tissues, and finally from the tissues to the anatomical elements or cells of which they are formed, we approach that common, physiological dynamism which is ''elementary life'', but we do not actually reach it. The cell, the anatomical element, is still a complicated structure. The elementary fact is further from us and lower down. It is in the living matter, in the molecule of this matter, and there we must seek it.

Galen gave in days gone by as the object of researches on life, the knowledge of the use of the different organs of the animal machine; "de usu partium." Later, Bichat assigned to them as their end the determination of the properties of tissues. Modern anatomists and zoologists try to reach the constituent element of these tissue—the cell. Their dream is to construct a cellular physiology, a ''physiological cytology''; but we must go further than that.