COMPLEMENT FIXATION 181 



tion with antigen, serves to fix complement, is to be regarded as an 

 amboceptor (sensitizer). As has been shown in the discussion of 

 cytolysins, it is possible at o C. to bring about a selective combination 

 of hemolytic amboceptor with its antigen. Liefmann attempted to 

 bring about a union of complement-fixing body and its antigen in this 

 way but was unsuccessful. It is known that if a considerable excess 

 of antigen or antiserum is present, complement may also be absorbed 

 at o C. and in such an experiment as Liefmann's it is impossible to 

 say that such an excess did not exist. Therefore, the experiment is 

 not conclusive. Neufeld and Handel also attempted selective absorp- 

 tion at 37 C. They showed that cholera vibrios and their specific 

 immune sera fix the hemolytic complement at o C., whereas the 

 bacteriolytic complement remains active. At 37 C. both complements 

 are fixed. They are of the opinion that at o C. the complement-fixing 

 amboceptor is bound to the hemolytic complement and that at 37 C. 

 both the complement-fixing and bacteriolytic amboceptors are active. 

 This experiment has been held to support the hypothesis of the multi- 

 plicity of complements. They also found that an immune serum pro- 

 duced by the injection of a certain water vibrio acted as a complement- 

 fixing body with cholera spirilla but did not serve as a bacteriolytic 

 amboceptor. This may be interpreted as indicating that the two im- 

 mune bodies are distinct but does not prove the amboceptor nature of 

 that body which enters into the phenomenon of complement fixation. 

 It may very well be that the experimental conditions were not optimal 

 to the reactions and that while investigators sought to separate two 

 forms of complement they were working with one and the same body 

 which operates somewhat differently under the diverse conditions. 

 Sachs interprets the amboceptor as a body which brings about the union 

 between antigen and complement but states that certain amboceptors 

 may be toxic (lytic) and others, for example, those serving to fix com- 

 plement, may be considered as atoxic. He considers that the differences 

 in effect may be the result of a number of factors, including mass action 

 and differences in combining avidity of the various reacting bodies. 

 It would appear to us that Zinsser's interpretation in regard to pre- 

 cipitins might also be applied here and that the lysis of cells may be an 

 incident in complement fixation, certain conditions favoring lysis, others 

 merely fixation of complement. If this be accepted, the complement- 

 fixing body must be regarded as an amboceptor or sensitizer in the 

 same sense as are the cytolysins. 



Activation by Complement. The utilization of complement in 

 hemolysis serves so to fix complement that it cannot activate a bac- 

 teriolytic amboceptor. Therefore, hemolysis exhibits the fixation of 

 complement in association with lysis of the cells. Handel found that 

 hemolytic and complement-fixing properties of an immune serum were 

 parallel, but Muir and Martin observed marked differences. The latter 

 investigators produced two immune sera, one against ox serum and the 

 other against ox cells, both of which exhibited hemolytic and comple- 

 ment-fixing properties. The immune serum prepared against ox cells 



