CHAPTER XVII. 



COMPLEMENT DEVIATION. 



In 1901, Bordet and Gengou observed that when 

 an antigen was mixed with its specific antibody in 

 the presence of complement, the complement was 

 fixed or bound and thus rendered unavailable .for 

 further reactions. This phenomenon has since be- 

 come widely known as complement deviation, com- 

 plement binding, or complement fixation; and the 

 principle underlying it has become of extreme 

 value in the determination of the presence of 

 substances whose interaction is followed by no 

 readily perceptible result such as lysis or precipi- 

 tation. 



It will be seen that such a reaction is analogous 

 to certain chemical reactions such as the combina- 

 tion of ordinary acids and alkalies in which the 

 presence of the reaction is determined by the use 

 of indicators such as litmus or phenolphthalein. 

 Bordet and Gengou used as an indicator a hem- 

 olytic system of erythrocytes with their specific 

 amboceptor. In this way, for instance, by mixing 

 typhoid bacilli with antityphoid serum, incubating 

 for a time and then adding erythrocytes sensitized 

 with their inactivated antiserum, it was observed 

 that hemolysis did not take place. The comple- 

 ment in the antityphoid serum had been fixed to 

 the typhoid bacilli by the typhoid antibody and 

 was thus rendered unavailable for the hemolysis 

 of the sensitized erythrocytes, subsequently added. 

 Bordet also showed that other indicators such as 



