274 Chapter IX 



antistimulin gives us another valuable indicatiou. Wassermann, 

 in the work we have just cited, showed that the serum of a rabbit, 

 previously treated with guinea-pig's serum and injected under the 

 same conditions as in the experiment with normal rabbit's serum, has 

 completely lost its protective power. The typhoid bacilli multiply 

 freely in the peritoneal cavity and the organism of the guinea-pig 

 is incapable of opposing a sufficient resistance. Wassermaun thinks 

 that, in this case, the disease becomes grave because of the anticytase 

 found in the serum of rabbits treated with guinea-pig's blood. There 

 is no doubt that this serum is really anticytasic. But as the free 

 cytases found in the peritoneal cavity of a guinea-pig inoculated at 

 the moment of phagolysis, become inactive under the influence of 

 the anticytase and play merely a minor part, it is impossible to ac- 

 [288] cept the German investigator's interpretation. Indeed, Besredka has 

 proved that, in this case, it is the antiphagocytic or antistimulant 

 action of the rabbit's serum which brings about the fatal issue in 

 the case of the typhoid inoculation. 



We have laid stress on the point that an animal, whose serum is 

 protective when introduced into another animal, may itself not be 

 refractory against the specific micro-organism. As regards the serum 

 of normal unvaccinated animals this has been so fully demonstrated 

 that nowadays no one doubts it. The question is more complicated 

 in the case of animals that have acquired immunity. As in the 

 great majority of cases the serum of these animals is found to be 

 endowed with a very great protective power, it has been accepted 

 as proved that the animal which furnishes it must itself possess 

 great immunity. The degree of protective power has even been taken 

 as the measure of the acquired immunity. Thus, the numerous 

 attempts to vaccinate the human subject against typhoid fever, 

 undertaken in consequence of the researches of PfeifFer and Kolle 1 , 

 were based on the fact that in these cases the serum of vaccinated 

 individuals acquires a great protective power. It was argued that 

 if this power is present it can only be due to the acquired immunity 

 of the individuals who furnish such a serum. Undoubtedly the pro- 

 tective property of the fluids and the resistance are often equal ; but 

 it is none the less true that there are cases where; in spite of this 

 property being markedly developed, the animal that furnishes the 

 protective serum is susceptible to the action of the micro-organism 

 and may even succumb to infection therewith. 



1 Ztschr.f. Hyg., Leipzig, 1896, Bd. xxi, S. 203. 



