The investigations of Bordet and Gengou first directed attention to the possibility of determining the presence of antibodies by an indirect method known as complement deviation. By this means not only could bacterial antibodies be determined, but likewise their corresponding antigen. (The latter term is applied to any bacterium or substance which, when injected into an organism, gives rise to the formation of an antibody.)
It was found by this method that organ extracts, albumins, peptones, etc., produce antibodies, and that this could be shown in vitro by bringing together the antigen and its corresponding antibody in the presence of complement. The anchoring of complement was demonstrated by failure of hemolysis to occur in an added inactivated hemolytic system.
Wassermann and Bruck used this method to show the presence of bacterial substances in organ extracts and corresponding antibodies in sera of patients immunized against them. They employed this method with
BUTLER WJ. SERUM DIAGNOSIS OF SYPHILIS.. JAMA. 1908;LI(10):824–830. doi:10.1001/jama.1908.25410100024001f