218 A MANUAL OF BACTERIOLOGY 



2. FIXATION OR ABSORPTION OF COMPLEMENT TEST. 1 



Complement being absorbed or fixed only in the presence of 

 both antigen and its homologous amboceptor, the fixation of 

 complement may be employed to determine the nature of either 

 antigen or amboceptor, the other constituent, amboceptor or 

 antigen, being known. Thus, for the determination of the nature 

 of a bacterium, a known amboceptor is used, for the determina- 

 tion of an amboceptor (e.g. the serum of a patient suffering from 

 an infection) a known antigen is required. The Wassermann 

 reaction in syphilis (which see) is an example of the application 

 of the latter reaction, which is that more frequently employed, as 

 agglutination and absorption tests are generally satisfactory and 

 simpler for the determination of the nature of a bacterium. Inas- 

 much as the complement which takes part in a complement fixa- 

 tion reaction is the same as that which hsemolyses in the presence 

 of red corpuscles and the homologous hsemolytic amboceptor, a 

 mixture of red corpuscles and hsemolytic serum forms the reagent 

 by which the fixation or non-fixation of complement in the mix- 

 ture is determined. If the amboceptor be known, the antigen 

 can be determined ; if the antigen be known, the amboceptor 

 can be determined, the detection in either case depending upon 

 whether or no complement is absorbed, this being ascertained by 

 adding corpuscles and haemolytic serum to the mixture, the 

 absence or occurrence of haemolysis being the indicator. 



COMPLEMENT FIXATION WITH BACTERIAL ANTIGENS. This 

 may be employed for the differentiation of bacterial species, a 

 known anti-serum being used, or for the recognition of bacterial 

 infections, a known bacterial antigen being employed and the 

 patient's serum being used as the anti-serum, as in tuberculosis 

 and gonococcal infections. In either case the principles involved 

 are the same and the technique is as follows : 



1. Preparation of the bacterial antigen. If a bacterium is to be 

 tested, the antigen is prepared from it ; if the diagnosis of a 

 bacterial infection is desired, the antigen should be prepared from 

 a number of different strains of the particular micro-organism, 

 i.e. the antigen should be polyvalent. 



(a) A simple bacterial antigen may be prepared by cultivating 



1 Often termed " deviation of complement " test. 



