influence upon osmotic pressure, together with others which are without this influence. In this respect, too, the cell is always laid down on the most delicate lines. Sometimes it decomposes colloidal substances and transforms them into others, which increase the osmotic pressure of the cell; at other times it synthesizes materials in solution into larger, more complicated molecules, until a body appears which is more and more extracted from the solution, and by this means loses its influence upon the osmotic pressure of the cell. This variety of function is of great importance to the cell in quite a different direction. We know that single ions exhibit very specific activities. Here also the cell must be equipped with arrangements to accelerate in one case the action of a separate ion and to check those of another, or else to entirely exclude them. The cell is able to effect this in diverse ways. Sometimes an ion is combined with a protein, for instance, or with other substances, and so is robbed of its own characteristics; at other times an ion is set free through decomposition or simple dissociation. Or else the cell induces antagonistically acting ions to react mutually on each other in finely graduated stages.
Numerous experiments have shown, as has already been mentioned, that definite cells depend upon definite secretions having their origin in other organs. If we remove certain organs, for instance the thyroid
