From thermodynamical considerations expressions are derived for the forces which will act on a liquid drop suspended in another liquid, if the latter contains in solution a substance whose concentration is non-uniform. It is shown that forces of attraction and repulsion between two such drops may result, if the drops are seats of chemical reactions, which produce substances diffusing into the surrounding medium.

An estimate of the order of magnitude of such forces is made, and it is found that they may exceed the electrical forces which would result from the charges which the drops may possess.

A possible experimental method of studying such forces is suggested.

The possible connection of the above forces with those observed in the phenomena of "cytotropism," and their bearing on the physical explanation of organic form, especially of the phenomena of "induction," is briefly discussed.

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