The growth characteristics of several strains of Staphylococcus aureus in Brain Heart Infusion and in a modified Staphylococcus Medium No. 110 were compared. In the latter medium all of the strains studied showed an increased mucoid character. Some of the strains studied showed a greater potential to synthesize excess slime layer material than others. The highly mucoid strains grew as diffuse-type colonies in modified Staphylococcus Medium No. 110 serum-soft agar and reacted as though they were negative in the test for clumping factor. These strains were also found to be more virulent when used to challenge normal mice intraperitoneally.

In the course of studies of the bactericidal system for the detection of typespecific antibody to group A streptococci (1), a number of strains were found which grew in extremely long chains in the presence of homologous antiserum. This paper reports some preliminary experiments designed to gain further insight into the mechanism of this phenomenon. The results indicate that long chain growth in liquid media of the strains of streptococci studied is dependent in part upon the interaction of type specific antibody and the M protein of the cells. Materials and MetkodsCuRures.--A type 30 strain of group A streptococcus used in most of this work was obtainod from Dr. Rebecca Lancefield and is designated in her laboratory as D-24. This was originally Gri~th's strain "Qulnn." It had been passed through mice repeatedly to enhance its virulence and was received as a lyophilized culture. It grew luxuriantly and resisted phagocytosis in human blood in the absence of antibody. 0.5 ml. of a 10 "e dilution of an 18 hour broth culture was lethal for mice by the intraperitoneal route in less than 5 days. Surface colonies on blood agar were typically large, fiat, matt, with good zones of beta hemolysis after 24 hours incubation.In contrast to the D-24 Q, inn strain of type 30 streptococci, a rabbit-adapted strain of type 30, known in the literature as the "Gay" strain, was also studied.* While this strain was typable, and therefore contained M protein, it failed to grow in long chains in the presence of homologous antiserum. Fourteen additional strains of type 302 were also studied. Several stralfis of type 12 streptococci were screened for the long chain reaction. These included strains recently isolated from the throats of patients at 1%rthwestern University Clinics, Great Lakes Naval Training Center, and Children's Memorial Hospital (Chicago), as well as laboratory strains. Two type 12 strains were selected for detailed study.

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From thesis submitted as partial fulfillment of requirements for the degree oi doctor of philosophy in the University of Michigan.t Present address: a p t .