It is well known that as a result of syphilitic infection various changes occur in blood sera, and that for the detection of these changes several reactions have been elaborated some of which are of great clinical importance. Of these the complement fixation test commonly known as the Wassermann reaction is of particular significance. This test which need not be described in detail depends on the fact that when an antigen consisting of an alcoholic extract of tissue particularly heart or liver added to physiological saline solution,is mixed with syphilitic serum containing complement,part or all of the complement is fixed or inactivated in such a way that it is unable to effect haemolysis of sensitised red blood cells.