Standardization of the Wassermann test using preserved complement titrated to 50 per cent haemolysis.

This paper describes a modification of the Wassermann test giving an improved standardization of the complement titration and of the haemolytic system which is suitable to the resources of a small laboratory. Advantage has been taken of the stability of complement preserved by the method of Richardson (1941), so that modern methods for the standardization of the haemolytic system can be included in the routine without sacrifice of simplicity in technique. The improved methods that have been advocated for the titration of complement and the standardization of the haemolytic system may be briefly reviewed. Increased accuracy is obtained in the complement titration by the determination of the point of 50 per cent. haemolysis rather than that of the minimum haemolytic dose (MHD), giving 100 per cent. haemolysis. The curve of haemolysis is a sigmoid one, and at the point of 50 per cent. haemolysis the rate of change of the degree of haemolysis for a given small change in the amount of complement employed is maximal, whereas at the 100 per cent. point it is minimal. Further accuracy can be obtained by photometric determination of the degree of haemolysis in all tubes of the titration showing partial haemolysis. By mathematical analysis or graphical construction, all the measurements can contribute to the determination of the 50 per cent. point (Kent, Bukantz, and Rein 1946; Mayer, Eaton, and Heidelberger, 1946). Some authorities consider that the employment of a more accurate method for the complement titration should be accompanied by a similar increase in accuracy of the amboceptor titration. Thus Whillans (1950) employs an amboceptor titration similar to the simple method of Wyler (1929), but measures the degree of haemolysis in the tubes showing partial haemolysis and constructs a graph from the results. Wadsworth (1947a) employs a different and more logical principle. A series of