STUDIES ON THE HEMOLYTIC STREPTOCOCCUS OF HUMAN ORIGIN : I. OBSERVATIONS ON THE VIRULENT, ATTENUATED, AND AVIRULENT VARIANTS.

1. Four common variants of the hemolytic streptococcus of human origin have been described. These have been designated the F, M, attenuated M, and C variants. 2. The F and M variants only have been isolated from the blood stream in streptococcal infections. Only the M, however, has any primary virulence for the mouse. 3. Both these variants resist phagocytosis in human blood under suitable conditions, and this appears to be a reliable test for human virulence. 4. The attenuated M variant, found only in laboratory cultures, has a capsule as well developed as that of the virulent variants, and yet does not resist phagocytosis. 5. The C variant has no capsule and is readily phagocyted. It appears to correspond to the avirulent variant in other species. 6. An attempt has been made to correlate these four variants with those already described in the literature. 7. The application of these findings to the problem of virulence has been discussed.