2. A striking difference exists between the acetyl and the de-acetylated polysaccharide of Pneumococcus Type I: The de-acetylated carbohydrate fails to react with the group specific A-antiserum, while the acetyl carbohydrate shows a strong reactivity.

3. The minimum amount of the acetyl polysaccharide, which inhibits sheep cell hemolysis by A-antiserum, is almost as small as that of the group specific carbohydrate isolated by Freudenberg and Eichel from urines of group A.

4. The reactivity of the acetyl polysaccharide can be demonstrated not only by the hemolysis inhibition test, but also by complement fixation and by inhibition of group specific iso-agglutination.

5. Feces filtrates, which possess the ability to destroy the blood group specific substances A and B of man, also affect the acetyl polysaccharide of Pneumococcus Type I. After incubation with an effective feces filtrate, the acetyl polysaccharide almost completely loses its potency toward the group specific A-antiserum and also its ability to inhibit the iso-agglutination of A blood cells.

6. Acetyl polysaccharide of Pneumococcus Type I, having lost its reactivity toward the group-specific A-antiserum after treatment with feces filtrate, still reacts with Type I pneumococcus antiserum which was previously absorbed with de-acetylated polysaccharide, Type I. Thus, the essential effect of the feces filtrate on acetyl polysaccharide, Type I, is not the cleavage of acetyl group, but some other chemical alteration.