1. A variant arising in a culture of hemolytic streptococcus was shown to have lost the properties of producing pigment and hemolyzing blood. Despite the loss of these two functions, it had in common with the strain from which it was derived certain other distinguishing biochemical characteristics, as follows: Both attained the same hydrogen ion concentration in dextrose broth; both hydrolyzed sodium hippurate, grew on bile agar, and fermented trehalose but not sorbitol; both failed to reduce methylene blue in milk cultures, and were insusceptible to the action of streptococcus bacteriophage. In addition, the virulence of the variant remained the same as that of the original culture.
2. The antigenic and serological specificity of the variant was identical with the group and type specificity of the original strain (Group B, Type I). These specificities were established by the use of immune sera prepared by immunization of rabbits with each form. The immunological reactions employed were reciprocal agglutination, precipitation, agglutinin and precipitin absorption, and passive mouse protection.