1. In the presence of low concentrations of calcium, ether inhibits the surface precipitation reaction in Arbacia egg cells. 2. Ether and other fat solvents also inhibit the surface precipitation reaction in Stentor protoplasm. 3. The magnesium ion can cause a surface precipitation reaction in Arbacia eggs, but it is far less potent than calcium. The course of the reaction in magnesium solutions is described. 4. There are two ways in which the presence of magnesium might act to prevent the surface precipitation reaction. 5. The relation of these facts to the colloid chemical interpretation of anesthesia is discussed.