1. The lipocarbohydrate or F polysaccharide derived from a rough variant of Type I pneumococcus (I R) is antigenic in rabbits and gives rise to precipitins and sheep cell hemolysins. The somatic or C carbohydrate on the other hand is not antigenic.
2. Antisera for the rough variant of Type 1 pneumococcus contain also bacterial agglutinins immunologically unrelated to the C and F precipitins and the heterophile antibody.
3. A study has been made of the quantitative precipitin reaction of the C and F polysaccharides in the serum of rabbits immunized with the IR pneumococcus clarifying certain of these relationships.