Facts bearing on acquired immunity 211 



bacilli had been ingested in a living condition. Forty-eight hours 

 after inoculation, no bacilli were to be found in the lymph of the 

 dorsal sac, either inside or outside the cells. But this fluid when 

 sown on nutrient media gave colonies of the Bacillus pyocyanew 

 up to 15 and even 18 days after inoculation. 



We may conclude from these facts that the cold-blooded verte- 

 brata are capable of acquiring immunity to a slight degree and 

 that, in this acquired immunity, a marked phagocytosis may be ob- 

 served, but no bactericidal action of the fluids. 



In order to gain a more complete idea of the mechanism of ac- 

 quired immunity, it is necessary to observe it in higher vertebrates 

 in which a well developed immunity of this type is readily obtained. 

 Here we must have recourse to mammals and pass in review an ample 

 number of examples, before we attempt to give to our readers a 

 general summary of the question. 



For long, researches on acquired immunity were confined almost 

 exclusively to the analysis of the facts observed in animals sub- 

 mitted to anti-anthrax vaccinations by means of the two vaccines 

 of Pasteur. A large number of important facts were thus collected, 

 the more weighty of which must be presented to the reader. But, 

 before entering on the subject, a general orientation on acquired 

 immunity in laboratory animals against vibrios is indispensable as 

 this example dominates, so to speak, the whole of the chapter on 

 acquired immunity against micro-organisms. 



Vou Behring and Nissen 1 , in their researches on the bactericidal 

 power of serums, examined, amongst others, several specimens of 

 serums coming from animals that had been vaccinated against various 

 micro-organisms. In the majority of the examples given by them the 

 acquired immunity produced no increase in this power, but the blood 

 serum of guinea-pigs that had been immunised against Gamaleia's vibrio 

 ( Vibrio metchnikow) was found to be much more bactericidal as regards [223] 

 this micro-organism than the serum of normal susceptible guinea-pigs. 

 These authors came to the conclusion that in acquired immunity, at 

 least as regards the vibrio mentioned, the chief part is played by a 

 bactericidal substance which is developed in the fluids of the vacci- 

 nated animals. They were content with the mere demonstration of this 

 fact without making any attempt to follow the course of events in tlu 

 destruction of the vibrios as it occurs in the organism of the vaccinated 



1 Ztschr.f. Hyg., Leipzig, 1890, Bd. vni, S. 412. 



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