When the problem of carcinoma is approached from the metabolic aspect, the first question which arises is: how does the metabolism of growing tissue differ from that of resting? The prospects of finding an answer to this question are good. Whether the mass of a given tissue is to remain constant, or, within a short period to increase many-fold, must be determined by the velocity of those processes which supply the driving forces for growth. Our task is to search for such processes and to compare their velocities in resting tissues and growing tissues. If this question is solved, then the further inquiry must be made as to whether the manner of arrangement of growing cells is manifested in their metabolism. Does the metabolism of tumors, growing in a disorganized manner, differ from the metabolism of orderly cells growing at the same rate. The hope of solving this question must be considered slight in general, and rightly so, if it is only the form-building forces which tumors lack. For of all problems of physiology, that of form is the least approachable. Yet it seems doubtful that only minute and unimportant differences should exist between the growth of young cells and those of tumors, instead of considerable physico-chemical differences. Progress in the carcinoma problem implies the adoption of the point of view involved by the latter alternative. This has been done and I shall try to show that it is the correct point of view.