1. The order of toxicity of the salts used in these experiments on the surface membrane of a cell, taking as a criterion viability of amebæ immersed in solutions for 1 day, is HgCl2, FeCl3> AlCl3> CuCl2> PbCl2> FeCl2.
Using viability for 5 days as a criterion, the order of toxicity is PbCl2> CuCl2> HgCl2> AlCl3> FeCl3> FeCl2.
2. The rate of toxicity is in the order FeCl3> HgCl2> AlCl3> FeCl2> CuCl2> PbCl2.
3. The ability of amebæ to recover from a marked tear of the plasmalemma in the solutions of the salts occurred in the following order: AlCl3> PbCl2> FeCl2> CuCl2> FeCl3> HgCl2.
II. Internal Protoplasm.
4. The relative toxicity of the salts on the internal protoplasm, judged by the recovery of the amebæ from large injections and the range over which these salts can cause coagulation of the internal protoplasm, is in the following order: PbCl2> CuCl2> FeCl3> HgCl2> FeCl2> AlCl3.
5. AlCl3 in concentrations between M/32 and M/250 causes a marked temporary enlargement of the contractile vacuole. FeCl2, FeCl3, and CuCl3 produce a slight enlargement of the vacuole.
6. PbCl2, in concentrations used in these experiments, appears to form a different type of combination with the internal protoplasm than do the other salts.
7. Using the similarity in appearance of the internal protoplasm after injection and after immersion to indicate that the surface is permeable to a substance in which the ameba is immersed, it is concluded that AlCl3 can easily penetrate the intact plasmalemma. CuCl2 also seems to have some penetrating power. None of the other salts studied give visible internal evidence of penetrability into the ameba.
8. The toxic action of the chlorides of the heavy metals used in these experiments, and of aluminum, is exerted principally upon the surface of the cell and is due not only to the action of the metal cation but also to acid which is produced by hydrolysis.