PFEIFFER'S PHENOMENON 207 



the microbes by solution, the process being known as 

 bacteriolysis, and the bodies which bring it about being 

 termed " bacteriolysins." The reaction in the guinea-pig 

 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 fresh peritoneal 

 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 peritoneal exudate is unneces- 

 sary 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, normal 

 or immune, and in peritoneal exudate, but is unstable, 

 disappearing on keeping or heating the serum ; the other 

 is a relatively stable body present in the anti-serum. The 

 former, the unstable body present in all fresh sera, ete., 

 is usually termed " complement " (also " alexin " or 

 " addiment ") ; while the stable constituent of immune 

 serum is known as the " amboceptor " or " immune 

 body " (also as " intermediary," " preparer," " fixateur " 

 or " substance sensibilisatrice "). 



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. Attempts 

 have been made to supplement the complement present by 

 injecting fresh normal serum with the anti-serum, but without 

 success, and some anti-microbic sera, e.g. anthrax serum, are not 

 bacteriolytic ; this explanation is, therefore, unsatisfactory. 

 Deflection of complement may occur in some instances, or the 

 complement may not be of the right kind. In other cases, the 



