212 Chapter VIII 



guinea-pig. R. Pfeiffer^ in collaboration with Issaeff sought to fill 

 this gap. But, instead of taking Gamaleia's vibrio, these observers 

 concentrated their attention on the study of the acquired immunity 

 of guinea-pigs against the cholera vibrio. As this vibrio is as a rule 

 less virulent than Gamaleia's vibrio, it was necessary, in order to 

 obtain a fatal infection, to inject it, not into the subcutaneous tissue 

 but into the peritoneal cavity. We have already seen (Chapter VI) 

 that the cholera vibrio when inoculated into the peritoneal cavity of 

 the guinea-pig, there meets with a vigorous resistance on the part 

 of the leucocytes which seize the living and virulent vibrios and 

 digesting them rid the animal of their presence. But when the dose 

 of the vibrios is increased, they multiply in spite of the phagocytic 

 reaction ; they are found swarming in the peritoneal cavity, whence 

 they invade the lymphatic and blood vessels and cause the death 

 of the animal. It is easy, then, to induce a fatal infection of the 

 guinea-pig with the cholera vibrio. But it is also easy to vaccinate 

 these animals against this experimental disease. We have only to 

 inoculate them with a non-fatal quantity of living cholera vibrios, 

 or to inject into them a culture in which the vibrios have been kiUed 

 by heat, or some of the culture fluid from which the vibrios have been 

 removed by filtration. All these methods soon produce an acquired 

 immunity in guinea-pigs. If, when this has been brought about, a 

 little blood is withdrawn and to the serum a small quantity of 

 cholera vibrios is added, in vitro, we can readily demonstrate their 

 disappearance, under the influence of the bactericidal substance dis- 

 solved in the fluid. In this respect there is, then, a marked analogy 

 with the fact established by v. Behring and Nissen as regards 

 Gamaleia's vibrio. 



When into the peritoneal cavity of vaccinated guinea-pigs a 

 certain quantity of cholera culture containing virulent and very 

 [224] motile vibrios is injected, we find that in the peritoneal fluid drawn 

 off" by means of a fine pipette, the vibrios have undergone profound 

 changes in the refractory organism. Even a few minutes after 

 the injection of the vibrios, the leucocytes disappear almost com- 

 pletely from the peritoneal fluid ; and only a few small lymphocytes 

 and a large number of vibrios, the majority of which are already 

 transformed into granules, are found (fig. 39); and there is pre- 

 sented a most typical case of Pfeiffer's phenomenon. Alongside 



^ Ztschr.f. Hyg., Leipzig, 1894, Bd. xvii, S. 355, and Deutsche med. Wchnschr.^ 

 Leipzig, 1896, SS. 97, 119. 



