1. The evidence presented indicates that Mg++, or other cation such as Ca++, Ni++, or Co++, is essential for the hemolytic action of C'. Ca++, Ni++, and Co++ are less effective than Mg++. The hemolytic system usually does not contain sufficient Mg++ for optimal hemolytic activity so that a marked enhancement can be obtained by addition of extra Mg++.
2. The enhancing action of tissue fluids can be ascribed to their contribution of Mg++.
3. Substances which bind Mg++ and Ca++ are anticomplementary when added to the usual hemolytic system which contains only a small quantity of Mg++. This type of anticomplementary effect can be overcome by addition of extra Mg++.
4. Ca++ may also be essential to the lytic process but its action is much less pronounced than that of Mg++.
