investigator also claims the presence in the spleen of a related enzyme, called adenase, which transforms adenin into hypoxanthin. The inference is that in many glands and tissues there are specific enzymes, as yet undiscovered, which may be responsible for at least some of the transformations known to occur there.
That autolysis may be a possible explanation of the process of animal metabolism has been suggested by Levene[1] and also by Wells,[2] It has been clearly indicated by such able workers as Salkowski, Jacoby and others, that practically all animal cells contain within themselves ferments or enzymes that are capable, under suitable conditions, of digesting or breaking down the cell contents by a process similar to ordinary proteolysis, and it may perhaps be assumed that all active cells carry forward their ordinary metabolic processes by the agency of these intra-cellular ferments. Moreover, it is not inconceivable that ferments or enzymes of several kinds may exist side by side in a given group of cells, just as they are known to exist in the pancreas, by which we might infer the possibility of a series of transformations taking place at essentially the same time, through the harmonious action of a row of enzymes physiologically quite distinct.
Further, the recently discovered reversible action of enzymes, on which we have at command so much valuable work, suggests the possibility of a maintenance of cell equilibrium through this peculiarity of action, thus affording a tangible explanation of the means by which intra-cellular nitrogenous or proteid equilibrium is maintained, the various cells of the body building up or breaking down the proteid matter of their own tissues as circumstances require. If these ideas are true, then our conception of ferment action must be considerably broadened, and we have before us the possibility of explaining many of the phenomena of tissue metabolism by the action and interaction of intra-cellular enzymes. This is a problem well worthy of broader study, with a view to the elucidation of the general laws that govern tissue changes in general. In this connection we also have suggested the possibility of interaction of another kind, viz., that interdependence of one tissue or gland upon another for the full development of its functional activity, as illustrated by the part played by the enterokinase of the intestinal glands in the development of an active trypsin from the zymogen of the pancreatic cells, and by the action of the internal secretion of the pancreas upon the inert constituents of the muscle to develop in the latter an active glycolytic enzyme. How far this general principle extends in the metabolic phenomena of the body is entirely problematical, but merits careful study. Here, then, we have an
