Acquired immunity against micro-organisms 277 



cinated against anthrax, gave a serum whose protective power was 

 quite distinct. Realising the great importance of these facts I asked 

 M. de Xittis 1 to repeat these experiments in my laboratory. The 

 vaccination of pigeons is an easy matter, but that of guinea-pigs 

 presents great difficulties. He succeeded, nevertheless, in vaccinating 

 some of these rodents very highly, and this enabled him to compare 

 the protective power of the blood serum in the two species. That of 

 the vaccinated pigeon was found to be endowed with this power and 

 protected guinea-pigs and mice against virulent anthrax. The serum 

 of the immunised guinea-pigs, on the contrary, exhibited no pro-[29i] 

 tective property, just as in Wernicke's experiments. The guinea-pigs 

 and mice, into which this serum was injected at the same time as 

 the anthrax bacilli, died even when attenuated anthrax was used. 

 We have, then, in this case, an example of acquired immunity, inde- 

 pendent of any protective power of the fluids of the body. 



In the course of their researches on the bacillus isolated by 

 R. Pfeiffer from persons attacked by influenza, Delius and Kolle 2 

 tried to vaccinate susceptible animals (guinea-pigs) against this 

 minute organism and to immunise animals naturally refractory (dog, 

 sheep, goat) against fairly large doses of cultures. They succeeded 

 in vaccinating guinea-pigs against ten times the lethal dose, but 

 never obtained any protective serum. Nor did the other animals 

 that were treated furnish a protective serum. "From the whole of 

 our experiments carried on for several years " conclude Delius and 

 Kolle "it is quite evident that we were unable to produce any 

 appreciable change in the blood by the use of those methods which 

 have produced specific immunising serums against other bacteria 

 such as the bacilli of diphtheria, cholera, typhoid fever, and 'blue 

 pus'" (p. 345). Slatineano undertook a detailed study of Pfeifier's 

 bacillus in my laboratory, but he found it impossible to demonstrate 

 any unquestionable protective effect exerted by the blood serum of 

 vaccinated guinea-pigs upon normal guinea-pigs inoculated with a 

 fatal dose of this organism. We are not justified, therefore, in classing 

 this bacillus with the anthrax bacillus ; we may, however, cite it as 

 an argument illustrating the difficulty that is met with, in certain 

 examples of acquired immunity, of discovering the protective power, 

 when feeble and masked. 



The inoculation with micro-organisms of animal nature causes the 



1 Ann. de llnst. Pasteur, Paris, 1901, t. xv, p. 769. 



2 Ztschr.f. Hyg., Leipzig, 1897, Bd. xxiv S. 327. 



