FIXATION OF COMPLEMENT 93 



fixation of a common non-specific substance termed 

 complement, these observers conceived the idea of 

 combining the two phenomena as a means of diagnosis. 

 The components of the first-mentioned reaction, con- 

 sisting of the bacterial suspension or antigen, the spe- 

 cific antibacterial serum or amboceptor, and comple- 

 vient, together form the bacterial system; the second 

 part is known as the hcemolytic system, consisting of 

 blood-corpuscles (antigen), specific hsemolytic serum 

 (amboceptor) , and complement. Bordet and Gengou 

 took a suspension of cholera spirilla as antigen and 

 mixed it with a certain quantity of cholera-immune 

 serum made by injecting a rabbit with cholera spirilla, 

 together with a definite amount of fresh guinea-pig 

 serum as complement. This mixture was incubated at 

 37 "" C. for one hour. At the end of this time it was pre- 

 sumed that the interaction between antigen and ambo- 

 ceptor had taken place with fixation or absorption of 

 complement. But since the reaction was not percepti- 

 ble to the eye, a further procedure became necessary to 

 show the result. For this purpose, a suspension of 

 washed rabbit's blood-corpuscles and a quantity of 

 hsemolytic serum for the rabbit's corpuscles were 

 added, and the whole incubated for another hour. At 

 the end of this time, it was found that no haemolysis of 

 the rabbit's corpuscles had taken place, because the 

 complement had been fixed during the first incubation 



