Abstract
In the course of the study on the antibody response to human streptococcal infections, it was needed to prepare a standard antistreptolysin O and to establish a standard procedure for the measurement of antistreptolysin O (ASL) titer in human sera. As the first step of the investigation, the fundamental studies on measuring the hemolytic activity of streptolysin O (SL) were undertaken. As was performed by several investigators (Herbert, 1941; Gillen and Feldman, 1954; Halbert, Swick and Sonn, 1955), the 50% hemolysis end-point was determined by the spectrophotometric measurement, in order to achieve an accurate estimation of the hemolytic activity of SL. For setting up the standardized conditions, several variables which would influence HD50 of SL were investigated in details.
