Abstract
A spectrophotometric method using the endpoint of 50% hemolysishas been employed tomeasure the changes in complement activity that occur when a standard suspension of sheep''s erythrocytes is sensitized with graded amts. of a hemolytic antiserum. If x represents hemolytic antiserum, and y the unit of complement, the complement-hemolysin relation is given by the equation: y = x/bx + a. It was also noted that the value of 1/n in the von Krogh equation approaches a minimum in a central range of hemolysin conc. and increases progressively with the use of greater or lesser amts. of the reagent. The minimum was observed in the range of hemolysin conc. which has been taken as optimal for the complement-fixation reaction.