174 A MANUAL OF BACTERIOLOGY 



vibrios lose their motility, become distorted and globular, 

 undergo solution, and finally disappear. The protection 

 afforded by the anti-serum is therefore due to the 

 destruction of the microbes by solution, the process 

 being known as bacteriolysis, 1 and the bodies which bring 

 it about being termed " bacteriolysins." The reaction is 

 known as " Pfeiffer's phenomenon " or reaction, from its 

 discoverer. If the serum and the microbes be mixed in 

 vitro the latter are unaffected ; apparently, therefore, 

 some constituent of the living body in addition to the 

 anti-serum is necessary for the solution of the microbes. 

 But in 1895 Metchnikoff showed that the reaction will 

 take place in vitro provided that some of the fresh peri- 

 toneal exudate of a normal guinea-pig be added to the 

 mixture of anti-serum and microbes. The same year 

 Bordet found that the addition of the peritoneal exudate 

 is unnecessary provided the anti- serum be perfectly fresh. 

 These experiments prove that the solution of the microbes 

 is brought about by the interaction of at least two sub- 

 stances, one of which is present in all fresh serum and in 

 the living body, but is unstable, disappearing on keeping 

 or heating the serum, the other is a relatively stable body 

 produced during the process of inoculation. The former, 

 the unstable normal body present in all animals, is usually 

 termed " complement " (Ehrlich and Morgenroth), " alexin " 

 (Buchner and Bordet), or " addiment " ; while the stable 

 constituent produced by immunisation is known as the 

 " amboceptor " (Ehrlich), " immune body," " interme- 

 diary," "preparer" (Gruber), " fixateur " (Metchnikoff), 

 or " substance sensibilisatrice " (Bordet). 



These considerations suggest an explanation why anti-microbic 

 serum neutralises only a limited amount of living culture, viz. the 

 amount of complement present in the body at one time is limited, 

 and when this has been used up bacteriolysis ceases. Anti -micro bic 

 sera are relatively inefficient in practice, insufficiency of complement 



1 See Gruber, " Harbcu Lectures," Journ. State Med., 1902. 



