FIXATION OF COMPLEMENT 303 



plague antigen. Had the problem involved the identifica- 

 tion of any other antigen — say gonococci, bacillus mallei 

 or others — one would substitute in the mixtures gonorrhea 

 antibodies or glanders antibodies or others as the case may 

 be, and proceed as above. In these cases, however, such 

 antibodies must be artificially produced in animals that 

 react to gonorrhea or glanders antigens. 



In addition to the foregoing the principles involved in 

 these reactions have been employed for the differentiation 

 of closely allied proteins. Such for instance as the differen- 

 tiation of bloods. For instance, if an animal be immunized 

 from human blood its serum will contain amboceptors for 

 human blood corpuscles, the antigen. Such amboceptors 

 in the presence of human corpuscles or their protein extrac- 

 tives and complement fix the complement; on the other 

 hand if the blood under question be from other species than 

 man, no such fixation can occur as there is no specific affinity 

 between such blood and the amboceptors for human blood. 

 Consequently, in the final test for fixation, as determined 

 by + or — hemolysis, no hemolysis occurs after the addition 

 of hemolytic amboceptors and their related corpuscles to 

 the mixture of human blood, its amboceptors and comple- 

 ment, while hemolysis does occur in the mixture of alien 

 blood, human amboceptors, and complement. 



In the former case all complement was fixed to the antigen 

 by the homologous amboceptors, while in the latter this was 

 not possible because of the lack of specific affinity of human 

 blood amboceptors for the alien blood. 



While the principles involved in the practical application 

 of these reactions are very simple, yet there are so many 

 chances for error that each and every step demands the most 

 careful control. 



