1. All except two of 106 strains of hemolytic streptococci isolated from man, other animals, milk, and cheese have been classified into five groups, which bear a definite relationship to the sources of the cultures. These broad groups may be subdivided into specific types by methods discussed elsewhere. The specific group classification is made possible by employing two special reagents: (a) extracts prepared by treatment of the bacteria with hot hydrochloric acid, and (b) serum of animals immunized with formalinized cultures. This differentiation is not detected by the agglutination reaction. The grouping agrees with that described by other investigators on the basis of cultural and biochemical characteristics.
2. The group-specific substance present in strains of Group A has been identified chemically as carbohydrate in nature. The chemical composition of the specific substances upon which the specificity of the other groups depends has not been determined. It seems not unlikely, however, that all of them may belong in the general class of carbohydrates, each being chemically distinct and serologically specific in the individual groups.