produced in a workshop if machines were suddenly supplied with unsuitable material. All of them would soon refuse to work and come to a standstill. The single workman, who, with his knowledge and his tools, is trained only for a single phase in the production of a complicated whole, would be helpless if he were suddenly ordered to undertake a new task. He would require new tools, and be forced to acquire new experience. If his duties changed without any regularity at all, i.e., were he restricted in his activities to any casual work that might be given to him, then any successful results would be entirely out of the question. We find exactly the same relation in the collective mass of cells which compose our organism. The single cells represent the machines and the workmen who, in an enormous workshop, pursue common aims in separate groups. The cells of the gut and its accessory glands, especially those of the liver, superintend in a certain degree the supply of raw material, which is first prepared in a proper manner, and then recast so as to be "palatable" to all the cells; after which it passes from hand to hand—from one cell to another.
Tn these considerations it is not only the purely chemical processes that have to be taken into account; the physical processes also play an important rôle. Every cell possesses substances which have an
