RADIOACTIVITY AND PHYSIOLOGICAL ACTION OF POTASSIUM.

1. The non-radioactive cesium ion can replace the potassium ion almost quantitatively in solutions required for the development of the egg of the sea urchin into swimming blastulae. 2. Thorium chloride and uranium acetate cannot replace the potassium chloride in the solutions required for the development of the egg. 3. Thorium chloride and uranium acetate do not antagonize the action of the potassium contained in sea water upon the development of eggs.