298 INFECTION AND IMMUNITY 



when precipitation has taken place, dispersion will again occur, if 

 one or the other component is added in excess. These phenomena 

 are frequently observed in agglutination and precipitation reactions 

 where the highest concentrations of serum will produce less pre- 

 cipitate, or perhaps none at all when greater dilutions produce heavy 

 precipitation. 



Fixation of the Complement. Bordet and Gengou 53 in 1901, de- 

 vised an ingenious method of experimentation by which even very 

 small quantities of any given immune body (amboceptor) can be 

 demonstrated in serum. The term "fixation of complement," by 

 which their method of investigation is now generally known, ex- 

 plains itself, as the steps of experimentation are followed. They 

 prepared the following mixtures : 



(a) (b) 



Bacteriolytic amboceptor Normal serum, heated 



(Plague immune serum, heated) 



+ + 



Plague emulsion Plague emulsion 



+ + 



Complement Complement 



(Fresh normal serum) (Fresh normal serum) 



To both of these after five hours was added 



Hemolytic amboceptor 

 (Heated hemolytic serum) 



+ 



Red blood cells 

 Results : 



(a) showed no hemolysis. 



(b) showed hemolysis -f-. 



The conclusion to be drawn from this was that in (a) the presence 

 of immune body had led to absorption of all the complement. In 

 (b), there being no bacteriolytic immune body to sensitize the 

 bacteria and enable them to absorb complement, the latter substance 

 was left free to activate the subsequently added hemolytic ambo- 

 ceptors. The Bordet-Gengou phenomenon has been extensively used 

 by Wassermann and Bruck, 54 Neisser and Sachs, 55 and others to 



Bordet et Gengou, Ann. de Tinst. Pasteur, 1901. 



64 Wassermann und Bruck, Med. Klin., 1905. 



55 Neisser und Sachs, Berl. klin. Woch., xliv, 1905, and i, 1906. 



