In any one strain the occurrence of the previously recognized type-specific protein, M, is usually completely correlated with the presence of the recently recognized type-specific antigen, T. Strain C203 is exceptional in having the T substance of type 1 as well as the two type-specific antigens, M and T, characteristic of type 3. It does not have the M antigen of type 1. While other strains with similar antigenic peculiarities have not been encountered, it is probable that they occur, and the existence of such anomalies must be suspected when unusual serological reactions occur.

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