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 two divergent branches, the one thermal and the other mechanical, external the one to the other although both issuing from the same common trunk, and having between them no relation but this, that the sum of their discharges represents the total of the energy in motion. Let us now translate these very simple notions into the more or less barbarous jargon in use in physiology. We shall be convinced as we go on of the truth of the saying of Buffon, that "the language of science is more difficult to learn than the science itself." We shall say, then, that chemical energy, that the unit of weight of the food which may be placed in the organism, constitutes the alimentary potential, the energetic value of this substance, its dynamogenic power. It is measured in units of heat, in Calories, which the substance may leave in the organism. The evaluation is made according to the principles of thermo-chemistry, by means of the numerical tables of Berthelot, Rubner, and Stohmann. The same number also expresses the ''thermogenic power'', virtual or theoretical, of the alimentary substance. This energy being destined to be transformed into vital energies (Chauveau's physiological work, physiological energy), the dynamogenic or thermogenic value of the food is at the same time its biogenetic value. Two weights of different foods which supply the organism with the same number of Calories,—i.e. for which these numerical values are the same,—will be called isodynamic or isodynamogenic, isobiogenetic, isoenergetic weights. They will be equivalent from the point of view of their alimentary value. And finally, if, as is usually the case, the cycle of energy ends in the production of heat, the food which has been utilized for this purpose has a real thermogenic value,