418 PHENOMENON OF COMPLEMENT FIXATION 



ogous or suitable antigen, which increases the affinity and fixing power of 

 the amboceptor for the complement. (See Fig. 85) . 



Complement-fixation tests also serve to demonstrate that absorption 

 of complement is not necessarily followed by lysis of the antigen. For 

 example, anthrax and pest bacilli, when mixed with their homologous 

 amboceptors and complement, show no bacteriolysis or but a very 

 slight reaction. The erroneous conclusion thus reached, that these 

 serums contained no amboceptors, was disproved by Bordet, who demon- 

 strated that they contained amboceptors and that complement was 

 absorbed or fixed although bacteriolysis had not taken place. Whether 

 the difference here depends upon variations in the nature of lytic and 

 non-lytic amboceptors or whether it is due to the relative amounts of an 

 amboceptor or the construction and constitution of the antigen is not 

 known. It would appear, however, that the last two possibilities are 

 largely concerned, although, so far as complement fixation is concerned, 

 it is immaterial whether or not bacteriolysis occurs. 



Complement-fixing antibodies, therefore, are probably all in the 

 nature of amboceptors, and these are to be found in varying amounts in 

 practically all immune serums, including antitoxic, agglutinating, and 

 precipitating serums. 



NON-SPECIFIC COMPLEMENT FIXATION 



The importance of having proper controls in practically all tests is 

 especially to be emphasized in complement-fixation work. While the 

 underlying principles are readily understood and the technic is compar- 

 atively simple, there are, however, many sources of error that require a 

 thorough understanding in order that an intelligent and reliable com- 

 plement-fixation reaction may be secured. These refer mainly to non- 

 specific fixation of complement and to quantitative factors governing 

 complement-fixation technic. 



Formed elements, such as bacteria and tissue-cells, as well as various 

 organic and inorganic material, may fix complement by themselves, i. e., 

 in a non-specific manner, and chemicals, such as acids and alkalis, may 

 destroy it. 



I. An antigen alone in certain amounts may absorb complement. This 

 anticomplementary dose of an antigen, as it is called, must be determined 

 beforehand by a process of titration when increasing amounts of antigen 

 are mixed with a constant dose of complement, hemolysin, and corpuscles 

 and the anticomplementary action of the antigen noted by the results 



