340 PHYSIOLOGICAL CHEMISTRY 



transforming guanin into xanthin. The same 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 ani- 

 mal metabolism has been suggested by Levene 1 and also by Wells. 2 

 It has been clearly indicated by such able workers as Salkowski, Ja- 

 coby, and others, that practically all animal cells contain within them- 

 selves 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 intracellular 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 pos- 

 sibility of a maintenance of cell-equilibrium through this peculiarity 

 of action, thus affording a tangible explanation of the means by which 

 intracellular 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 intracellular 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 interdepend- 

 ence of one tissue or gland upon another for the full development of its 

 functional activity, as illustrated by the part played by the entero- 

 kinase of the intestinal glands in the development of an active tryp- 

 sin 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 



1 Die Endprodukte der Selbsiverdauung tierischer Organe, Zeitschrift fur physio- 

 logische Chemie, Band 41, p. 393. 



2 On the Relation of Autolysis to Proteid Metabolism, Amer. Journal of Physi- 

 ology, vol. 11, p. 351. 



