I. The Plasmalemma.
1. On the plasmalemma of amebæ CaCl2 antagonizes the toxic action of LiCl better than it does NaCl, and still better than it does KCl. MgCl2 antagonizes the toxic action of NaCl better than it does LiCl and still better than it does KCl.
2. CaCl2 antagonizes the toxic action of LiCl and of KCl better than does MgCl2: MgCl2 antagonizes NaCl better than does CaCl2.
II. The Internal Protoplasm.
3. The antagonizing efficiency of CaCl2 and of MgCl2 are highest against the toxic action of KCl on the internal protoplasm, less against that of NaCl, and least against that of LiCl.
4. CaCl2 antagonizes the toxic action of LiCl better than does MgCl2: MgCl2 antagonizes the toxic action of NaCl and of KCl better than does CaCl2.
5. LiCl antagonizes the toxic action of MgCl2 on the internal protoplasm more effectively than do NaCl or KCl, which have an equal antagonizing effect on the MgCl2 action.
III. The Nature of Antagonism.
6. When the concentration of an antagonizing salt is increased to a toxic value, it acts synergistically with a toxic salt.
7. No case was found in which a potentially antagonistic salt abolishes the toxic action of a salt unless it is present at the site (surface or interior) of toxic action.
8. Antagonistic actions of the salts used in these experiments are of differing effectiveness on the internal protoplasm and on the surface membrane.