- 532 Chapter XVI 



immunity, and that micro-organisms, introduced into the animal 

 possessing this power, become incapable of any pathogenic manifesta- 

 tion. Certain facts, brought together in Bouchard's laboratory, tell 

 against the hypothesis I have just mentioned. With the object of 

 throwing light on this question I began, immediately after the close 

 of the Congress, to study the acquired immunity of rabbits against 

 the micro-organism of the pneumo-enteritis of pigs. I was able 

 to demonstrate 1 that in this case the resistance of the animal against 

 the micro-organisms does not depend on the acquisition of any anti- 

 toxic property by the body fluids ; such a property is completely 

 absent. At the same time I showed that the serum of vaccinated 

 rabbits possesses a very marked protective power against infection by 

 the coccobacillus of pneumo-enteritis. It was for the first time proved 

 that independently of the antitoxic and bactericidal properties of 

 serums, there exists another special property, the anti-infective 

 property. This I conceived to be of the nature of a stimulant action 

 on the part of the phagocytes. 



It has already been stated in an earlier chapter that before the 

 discovery of antitoxins Richet and Hericourt 2 had observed an 

 immunising action of the serum of animals refractory to staphylococci. 

 These observers were content with this demonstration and did not 

 seek to penetrate more deeply into the mechanism of the action 

 of their serum. For this reason when von Behring and Kitasato 

 [556] announced their discovery of antitoxic serums it was generally 

 thought that the antistaphylococci serums were also antitoxic serums. 

 The immunity against the micro-organism of the pneumo-enteritis of 

 pigs taught us that here we might have to deal with quite a different 

 matter. It was soon demonstrated that the serum from the immunised 

 animal might in fact, without being antitoxic, present the same anti- 

 infective property as in the case of pneumo-enteritis. That was first 

 proved in the case of the experimental disease set up by Koch's 

 cholera vibrio. 



The reappearance of cholera in Europe in 1892 drew the attention 

 of bacteriologists to this disease, and was the occasion of many new 

 researches on immunity against the cholera vibrio. Several important 

 works on this question were published by Pfeiffer 3 , at this period 

 director of the scientific staff of the Koch Institute at Berlin. He 



1 Ann. de Vlnst. Pasteur, Paris, 1892, t. vi, p. 289. 



Compt. rend. Acad. d. sc., Paris, 1888, t. cvn, pp. 690, 748. 

 3 Ztschr.f. Hyg., Leipzig, 1894, Bd. xvi, S. 268. 



