As proper subjects of inquiry in Physiological Chemistry we recognize mainly the following: (a) The nutrition of plants and animals and the composition and properties of the nutrient substances. (b) The changes which the nutrients undergo before and during the processes of assimilation. (c) The agents of preparation for assimilation and the general conditions of their activity. (d) The fate of the assimilated nutrients and the nature of the products of degradation. (e) The absorption or liberation of energy.