From the evidence presented in tables 2 and 3, it is seen that the 8668-WM form has lost its ability to produce demonstrable streptolysin-O under these conditions, whereas the 8668-S form retains this capacity.Production of reptolygin-S. Streptolysin-S was prepared by making a heavy suspension of bacterial cells from a 20 hour blood agar plate in inactivated horse serum for 5 hours at 37 C, followed by centrifugation. The supernatant was titrated for streptolysin-S as presented in table 4. The hemolysin thus formed was assssed for 326 on July 31, 2020 by guest http://jb.asm.org/ Downloaded from VARIATION IN GROUP A STREPTOCOCCI 1955]