A series of experiments was carried out on various strains of streptococci in order to ascertain the changes which bacteriophage produces in the phenomena of agglutination of these organisms. The results can be placed in the following categories.
1. Loss of specific agglutinability was observed with partial and with what appeared as complete loss of specific agglutinin absorption and agglutinogenic properties.
2. Partial modification of the antigen, bringing about inagglutinability of the strains with complete preservation of agglutinogenic and agglutinin-absorption properties. Coincidentally, additional components appeared. Some of these were related to the specific antigens of the organisms from which they were derived, while others were not. In two instances these components were of "group" character.
3. "Complete" modification observed with two strains consisting of complete transformation of the normal culture agglutinogens into antigens of an entirely different specificity.
It appears from these studies that the bacteriophage phenomenon may play an intricate rô1e in serological grouping of various strains of pathogenic streptococci.