290 Chapter IX 



Gamaleia 1 furnished important data on this subject. They showed 

 that animals vaccinated against the Bacillus pyocyaneus and the 

 vibrios of Koch and Gamaleia were even more susceptible to intoxi- 

 cation by the soluble products of these micro-organisms than were 

 normal animals which had acquired no immunity against the corre- 

 sponding bacteria. Shortly afterwards this observation was confirmed 

 by Selander 2 , in his work on hog cholera, carried out under Roux's 

 direction. Rabbits vaccinated against the cocco-bacillus of this disease 

 resisted infection by the virus, but died as a result of the exhibition 

 of the same doses of toxin that killed normal rabbits. I 3 was able 

 not only to verify this, but to add to it the further fact that the 

 blood serum of vaccinated rabbits, although markedly protective 

 against infection, exercised not the slightest antitoxic action. 



When, later, R. Pfeiffer set himself to study the immunity of 

 animals against the cholera vibrio, he, along with his collaborators, 

 was able to furnish numerous data confirming the hypothesis that 

 animals thoroughly vaccinated against this vibrio had not thereby 

 become more resistant to its toxin and that their anti-infective serum 

 exhibited no antitoxic power. These results have been confirmed 

 repeatedly and must be regarded as fully established. 



Von Behring here recognised a general law which, with the aid of 

 his collaborators, he attempted to develop. We owe to him the 

 knowledge that the susceptibility, augmented as regards the toxins, 

 of animals vaccinated against micro-organisms, might even serve in 

 doubtful cases to reveal the presence of their bacterial poisons. 

 Culture products when deprived of micro-organisms often set up no 

 [305] poisoning in normal animals susceptible to infection. From this fact 

 it is generally concluded that the toxin is not present in the products 

 in question. But animals of the same species when immunised 

 against infection by the micro-organism, owing to their "hyper- 

 susceptibility," react much more delicately and allow of the de- 

 monstration of the presence of bacterial poisons in fluids inactive 

 for unvaccinated animals. 



In collaboration with Kifetshima 4 , von Behring immunised guinea- 

 pigs against the diphtheria bacillus, and demonstrated that two or 

 three injections of diphtheria toxin were quite sufficient to render 



1 Compt. rend. Soc. de biol., Paris, 1890, p. 294. 



2 Ann. de VInst. Pasteur, Paris, 1890, t. IT, p. 563. 



3 Ann. de VInst. Pasteur, Paris, 1892, t. VI, p. 295. 



4 Berl kiln. Wchnschr., 1891, p. 157. 



