THE SELECTIVE ISOLATION OF SMOOTH SUB-STRAINS3 FROM MIXED

The differentiation of "pathogenic " from "non-pathogenic" types of those streptococci that do not produce exotoxin presents a difficult problem. This series of studies was undertaken in the hope of finding a satisfactory method. The strains used were isolated from suspected foci of infection (pharynx, tonsils, teeth, gum margins, feces, and other foci) of patients with chronic diseases (arthritis, upper respiratory tract infection, certain eye diseases, "intestinal intoxication, " "colitis," etc.). Differences in resistance of these strains to certain injuri-ous substances will be described in the present paper. Because of the difficulty of obtaining uniformly dispersed sus-pensions of rough strains, these prelimi ary studies were confined to smooth strains. Because anomalous results were obtained with enterococci (Streptococcus fecalis), the study of this organism will receive treatment in a separate paper