316 INFECTION AND IMMUNITY 



mixture. If such a mixture is allowed to stand at temperature for 

 an hour or more, and to it is then added an emulsion of red blood 

 cells together with inactivated hemolytic serum, no hemolysis will 

 take place, since there is no free complement to complete the hemolytio 

 system. If, on the other hand, the original mixture contains no anti- 

 body for the antigen used, the complement present is not fixed and 

 is available for the activation of the hemolytic serum later added. 



The reaction thus depends upon the fact that neither antigen 1S 

 alone, nor amboceptor (antibody) alone, can fix complement, but 

 that this fixation is carried out only by the combination of antigen 

 plus amboceptor. Any specific can be determined by this method, 

 provided the homologous antigen is used ; and vice versa, by the use of 

 a known antibody a suspected antigen may be determined. 



When testing immune sera for antibodies given rise to in man or 

 animals by microorganisms which can be cultivated, either the whole 

 bacteria or extracts of the bacteria may be used as an antigen. 



For the diagnosis of syphilis by this method, in the so-called 

 "Wassermann reaction, " the antigen employed was originally ob- 

 tained by the extraction of syphilitic organs, in which free syphilitic 

 antigens, i.e., uncombined products of Spirochaete pallida, were 

 assumed to be present. 



It has been more recently shown, however, that the Wassermann 

 reaction is not specific in any sense of the word and that suitable 

 antigens can be produced by the alcoholic extraction of lipoids from 

 the normal organs of many animals and man. 



Bacterial extracts for complement-fixation can be made in various 

 ways. The use of thick salt solution suspensions of the cultures them- 

 selves is not advisable because of the anticomplementary action of such 

 suspensions. Good bacterial antigens can be produced by centrifugal- 

 izing them from salt solution suspensions and adding to about 

 20 mgms., 90 mgms. of common salt, rubbing up with" a glass rod 

 for an hour, and then adding distilled water to isotonicity. This is 

 the method of Besredka. This method has been used with success by 

 Miller and Zinsser in the case of tubercle bacilli for complement- 

 fixation in tuberculosis. 



Wassermann and Bruck 1S prepare bacterial antigen by emulsifying 



12 Bordet and Gay, Ann. de 1 'inst. Pasteur, xx, 1906. 



13 Wassermann und Bruck, Med. Klinik, 55, 1905, and Deut. med. Woch., xii, 

 1906. 





