392 PHENOMENON OF COMPLEMENT FIXATION 



it was free in the fluid. Bordet knew that the normal alexin serum used 

 in the experiment could produce hemolysis of corpuscles with a homol- 

 ogous amboceptor, so' he tested for free alexin by subsequently adding 

 to the mixture anti-rabbit hemolysin and rabbit corpuscles. Hemolysis 

 did not occur, because the alexin or complement had been bound by the 

 pest antigen and amboceptor. When a normal serum was substituted 

 for the antipest serum, hemolysis occurred, because the normal serum 

 contained no sensitizers or amboceptors that could unite with the pest 

 bacilli and "fix" the alexin, which, therefore, remained free, and when 

 the hemolysin and red corpuscles were subsequently added, united with 

 them to lyse the red cells. In this way the corpuscles and hemolysin 

 served as indicators for free or unfixed alexin or complement, just as 

 litmus or phenolphthalein may be used as a test for the presence of an 

 acid or an alkali. 



By showing, in this manner, that the complement of a serum could 

 be fixed by either bacteriolytic or hemolytic amboceptors, Bordet 

 endeavored to support his views on the unity of complement. Ehrlich 

 and Morgenroth later verified his findings, and in addition, by more 

 delicate and complicated experiments, showed that many complements 

 may be present in a serum, a fact manifested by a different rate of 

 absorption, by the action of specific anticomplements, etc.-, as mentioned 

 in a previous chapter. 



While Ehrlich's theory as to the multiplicity of complements has 

 been widely accepted, the subject really possesses greater academic 

 than practical interest, for experience has shown that the results are the 

 same in complement-fixation tests at least, regardless of whether we 

 believe in the unity or in the multiplicity of complement, as under 

 ordinary conditions the complement or complements in a given quantity 

 of serum are capable of being absorbed by bacteriolytic, hemolytic, 

 or other amboceptors. 



Gengou showed later that not only cellular antigens, such as bacteria 

 and red blood-cells, are capable of stimulating the production of ambo- 

 ceptors, but that the proteins in solution, such as serum and milk, may 

 produce complement-binding amboceptors in addition to precipitins. 

 This subject was later studied more extensively by Moreschi, whose 

 interest became aroused as the result of his theoretic studies upon 

 anticomplements. This investigator observed that, upon mixing a 

 soluble protein with its antiserum precipitation occurred and the existing 

 complement disappeared, a coincidence that led him to assert that the 

 complement disappeared because it was carried down mechanically in 



