Worthy of special notice is the fact that cell protoplasm is essentially proteid in nature; water and proteid make up the larger part of its substance, to which are added small proportions of carbohydrate, fat, and mineral matter. Proteid is the basis of cell protoplasm; it is the chemical nucleus of living matter, and owing to the large size of its molecule, with its large number of contained atoms, is capable of many combinations and many alterations. Most of the reactions characteristic of katabolism centre around this proteid, but the disruptive changes that occur undoubtedly involve more largely the circulating materials present in the blood and lymph, and which bathe the cells, rather than the so-called fixed, or organ proteid, of the cell substance itself. Still, while the circulating blood and lymph furnish largely the substances which are made to undergo disintegration in katabolism, the living protoplasmic cell is the controlling power which regulates the extent and character of the decompositions, and proteid matter is the chemical basis of protoplasm. From these statements, we again have suggested the significant importance of the proteid foods in nutrition, since they alone can furnish the material which constitutes the chemical basis of living cells. The human body, which represents the highest form of animal life, is merely, as stated by another, “literally a nation of cells derived from a single cell called the ovum, living together, but dividing the work, transformed variously into tissues and organs, and variously surrounded by protoplasm products” (Waller). The processes involved in metabolism are not easily unravelled. The word itself is simple, but it is employed to designate that complex of “chemical changes in living organisms which constitute their life, the changes by which their food is assimilated and becomes part of them, the changes which it undergoes while it shares their life, and finally those by which it is returned to the condition of inanimate matter. Gathered together under this one phrase are some of the most intricate and inaccessible of natural phenomena. It implies also, and gently insists on the idea, that all the phenomena of life are at bottom chemical reactions” (Leathes). Regarding the processes of anabolism, as in the construction of living protoplasm out of inert food materials, we can say nothing. This is altogether beyond our ken at present, and doubtless will remain so, since it involves a chemical alteration, or change, akin to that of bringing the dead to life. With the processes of katabolism, however, we may hope for more satisfactory results; and, indeed, to-day we have considerable information of value as to some of the methods, at least, which are the cause of this phase of nutrition. This knowledge, however, has been slow of attainment.