to regulate its own structure. The components of the blood plasma, which serve as the deriving material, are the same for all cells. The formation of a specifically acting secretion also requires that every kind of cell should have means and arrangements at its disposal for the specific transformation, under certain circumstances, of the same product. From this point of view we should expect to find that each kind of cell controls particular ferments, of which, however, some will be common to all the cells of the body. These ferments have the task of decomposing the nourishment, brought by the blood plasma to the cell, into simpler products. Investigations on the peculiarities of cell ferments—the tools of the cells—are already in progress, and we shall deal with this question later on. It may be that the result of these investigations will supply the most unequivocal and sure support for the theory of the dependence of cellular function on cellular structure.
For the maintenance of a regular and undisturbed flow in the varied processes of the cell, we must assume that within certain limits constant conditions prevail. When we carry out certain experiments in a laboratory and try to study, for instance, the interaction of two substances upon each other, we choose the most favourable conditions possible, and take particular precautions against the presence of any
