_Life is the Sum-total of the Phenomena Common to all Living Beings. Elementary Life._—Living beings differ more in form and configuration than in their manner of being. They are distinguished more by their anatomy than by their physiology. There are, in fact, phenomena common to all, from the highest to the lowest. This is because there is that similar or identical foundation, that _quid commune_ which has enabled us to apply to them the common name of “living beings.” Claude Bernard gave to this sum-total of manifestations common to all (nutrition, reproduction) the name of _elementary life_. To him _general physiology_ was _the study of elementary life_; the two expressions were equivalent, and they were equivalent to a longer formula which the illustrious biologist has given as a title to one of his most celebrated works—_The Study of the Phenomena Common to all Living Beings, Animals, 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_.[4] [4] Le Dantec has objected to this conception of phenomena common to different living beings. He insists that all phenomena which take place in a given living being are proper to him, and differ, however slightly, from those of another individual. The objection is more specious than real. 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.