Crystalline ovalbumin, when heated under controlled conditions, promoted growth of Streptococcus hemolyticus in a synthetic medium. A similar activation of albumin also was produced by ultraviolet irradiation or by shaking under nitrogen. Untreated albumin failed to permit growth under the same conditions. The activity of treated albumin was destroyed by aeration or by reaction with iodoacetate.

The data suggest that the activity of ovalbumin for the streptococcus depends on the presence of "exposed" SH groups. However, other sulfhydryl-containing compounds (thioglycolate, glutathione, cysteine) could not replace ovalbumin.

A number of crude and crystalline proteins, and di- and tripeptides were inactive. Strepogenin and crystalline bovine serum albumin produced a weak growth response on extended incubation.

Approximately 50 per cent of the original protein in the culture disappeared during growth. Ovalbumin labelled with C14 was added to the synthetic medium. After growth of the culture the isotope was found associated with the cells and in the culture fluid in both dialyzable and non-dialyzable forms.

Under the conditions described, luxuriant growth of 15 strains (10 serological types) of Group A streptococci was obtained in 10 hours from small inocula. The growth was capable of repeated subcultivation.

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