A type specific polysaccharide has been isolated from the autolyzed broth of Type I Pneumococcus by a modified Avery and Goebel's method.

The newly prepared polysaccharide reacts with the homologous immune rabbit serum which has been completely absorbed with the acetyl polysaccharide of Avery and Goebel.

The newly prepared polysaccharide produces passive immunity in mice and rats and possibly in rabbits.

The antigenicity is not lost on boiling in acid or alkaline medium, but the precipitative activity is decreased.

In conclusion, it has been shown that the polysaccharide from Type I Pneumococcus, as isolated by a slight modification of Avery and Goebel's method, is a more complete antigen.

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