Acquired immunity against micro-organisms 289 



With the object of gaining some idea of the changes that the 

 micro-organisms undergo in the immunised animal, Vallee 1 carried 

 out a series of experiments on rabbits vaccinated against the bacillus 

 of swine erysipelas. He enclosed these bacilli in sacs of collodion 

 which he introduced into the peritoneal cavity of susceptible rabbits 

 and of others that were hyperimmunised. The bacillus developed well 

 in both cases. It gave homogeneous non-agglutinated cultures in the 

 sacs placed in normal animals, whilst in the sacs introduced into 

 the peritoneal cavity of hyperimmunised rabbits the bacilli grew into 

 agglutinated filaments. This proves that the wall of the sacs per- 

 mitted of the passage of the active substances elaborated in the 

 immunised animal. Different from the point of view of agglutination, 

 the cultures likewise exhibited a considerable difference in their 

 pathogenic activity. The cultures developed in the sacs in hyper- 

 immunised rabbits were found to be much more virulent than those 

 grown in the sacs in control animals. This augmentation of virulence 

 depends, probably, on the influence of the active substances which 

 pass through the walls of the sacs. In any case, this experiment 

 affords further confirmation of the impossibility of maintaining the 

 theory of the attenuation of micro-organisms by the fluids of an 

 animal enjoying acquired immunity. 



Since the discovery of the antitoxic property of the fluids of the 

 body, it has been accepted that its manifestation was indispensable 

 for the acquisition of immunity. It was thought that in order to get 

 rid of pathogenic micro-organisms the animal had first to develop 

 the means of neutralising their toxins. These substances once pre- 

 vented from exerting their toxic action, the micro-organisms were 

 left without their weapon of attack and found themselves reduced 

 to the condition of simple saprophytes. It was accepted, therefore, 

 that an effective antitoxic power was always to be found in the fluids 

 of animals that had acquired immunity. Against this explanation, [304] 

 however, are certain established facts. Chauveau 2 had observed that 

 Algerian sheep, whose natural immunity was further strengthened 

 by considerable doses of anthrax bacilli, exhibited a susceptibility 

 to injections of anthrax blood quite as marked as that of normal 

 sheep. The immunity against the virus, then, did not progress 

 pari passu with that against the poison. Later, Charrin and 



1 Compt. rend. Soc. de biol., Paris, 1899, p. 432. 



8 Compt. rend. Acad. d. sc., Paris, 1880, t. xc, p. 1526. 



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