1. No connection can be demonstrated between grouping of non-hemolytic streptococci based upon fermentation reactions, and grouping based upon immunological reactions.

2. A classification of non-hemolytic streptococci can be effected by studying the complement fixation reactions between the streptococci and their antisera.

3. The arrangement of the streptococci in such a classification depends on the fact that two diverse elements are present in the group. Some strains partake entirely of one of these elements, some entirely of the other, while other strains partake of both.

4. The arrangement is further determined by the fact that among the strains composed of one element there are differences in complexity, some strains being made up of many molecules or features, others having much simpler structure. This gives rise to an inverse ratio between the fixing capacity of a serum and the capacity of the corresponding antigen to be fixed.

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