A Method for the Titration of Complement

A major difficulty in the quantitative study of complement is the accurate determination of the amount remaining after various manipulations. The method usually employed is to compare the minimal quantity of solution which will completely hemolyze a measured volume of sensitized cells with the corresponding quant i ty of the original serum. The method is cumbersome and time-consuming, necessitating multiple tests for each determination, and the results are only approximate. Recently, Brooks I has suggested a method based on the colorimetric estimation of the proportion of cells hemolyzed by a given quantity of solution within an arbitrarily fixed time. By the use of a curve correlating the percentage of hemolysis with the quantity of complement he obtains results accurate to 1 per cent. Needing a simple but accurate method adapted to making many determinations within a relatively short time, we have made use of the fact that the time required for hemolysis i's a function of the quantity of complement. The data for a reference curve similar to Fig. 1 are first obtained with known quantities of complement, using a fixed amount of a standard sensitized cell suspension. The time required for an unknown solution to cause hemolysis under the same conditions of temperature and volume is then determined, and its complement content obtained by graphic interpolation on the timecomplement curve (Fig. 1). *