THE IMMUNOLOGICAL RELATIONSHIP OF THE CAPSULAR POLYSACCHARIDE OF TYPE XIV PNEUMOCOCCUS TO THE BLOOD GROUP A SPECIFIC SUBSTANCE.

1. The agglutination of human erythrocytes and the precipitation of the blood group A substance by Type XIV antipneumococcus horse serum are properties of the specific anticarbohydrate immune bodies in the serum. 2. Absorption of Type XIV antipneumococcus horse serum with the homologous bacterial polysaccharide removes the agglutinins for human erythrocytes as well as the precipitins for the group A substance. 3. Absorption of Type XIV antipneumococcus horse serum with the group A substance markedly diminishes the ability of the serum to agglutinate erythrocytes of all groups. 4. Absorption of Type XIV antipneumococcus horse serum with human erythrocytes causes a marked diminution in the precipitation with group A substance. 5. The chemical and immunological relationship between the specific substances of blood group A and the Type XIV Pneumococcus is discussed.