The Identity of the Mechanisms of Type-specific Agglutinin and Precipitin Reactions with Pneumococcus

THE EXPERIMENTAL RESULTS WHICH HAVE BEEN DESCRIBED DEMONSTRATE THE FOLLOWING FACTS: 1. In the type-specific agglutination reaction, when the organisms are not present in sufficient numbers to absorb completely all the antibodies from the serum, more antibody is bound by cellular S than is required for the process of agglutination. 2. The excess of antibody thus bound can then unite with additional amounts of the specific substance when this is added in soluble form to the agglutinated material. 3. If an excess of the free S is added to an agglutinated mass of antibody and bacteria, the organisms are redispersed and in the suspended state are again specifically agglutinable. 4. When a solution of the specific polysaccharide is added in excess to an homologous immune serum, a prozone is created in which precipitation is inhibited; moreover, if, at this point, type-specific pneumococci are added to the mixture, inhibition of agglutination also occurs. 5. The reactive substance in the type-specific agglutination and precipitation reactions is the same, i.e., the capsular polysaccharide. In the former instance it is combined in the bacterial cell; in the latter, it is in a soluble, chemically purified state and entirely separate from the body of the cell.