Immunity against pathogenic micro-organisms 169 



our analysis of this phenomenon. Our review, however, would be 

 incomplete if we omitted to take note of the natural immunity of the [179] 

 animal organism against micro-organisms which are distinguished 

 by an exceptional toxicity. The first place in this group must 

 undoubtedly be assigned to the bacillus of tetanus. 



It may appear very inconsequent to be told that animals very 

 susceptible to tetanus, such as the guinea-pig and rabbit, are endowed 

 with a natural immunity against the tetanus bacillus. And yet this 

 fact, paradoxical as it may seem, has been demonstrated beyond 

 doubt by Yaillard and his collaborators Vincent and Rouget 1 . When 

 a small quantity of a culture of the tetanus bacillus was injected 

 into one of the animals just mentioned, tetanus was not long in 

 declaring itself. After a period of incubation, certain muscles be- 

 came stiff and a tetanus, local at first, soon became general and had 

 a fatal issue. Xow, when much larger quantities of bacilli are 

 inoculated, but care is taken to rid them of the tetanus poison elabo- 

 rated in the culture-fluid, the animals resist without exhibiting any 

 trace of tetanus. This experiment, repeated many times, always 

 with the same result, demonstrates that the tetanus bacillus, when 

 deprived of the co-operation of 

 the toxin, encounters, in these 

 animals so susceptible to the 

 latter, a most effective opposi- 

 tion. Why is this? It was 

 supposed that, in diseases like 

 tetanus so markedly toxic in 

 character, the resistance was 

 in no way dependent on the 

 phagocytic function. Thus 

 Vaillard and Vincent were 

 quite prepared to attribute no 

 share to the phagocytes in the 

 example of natural immunity 

 which they had discovered. A 

 detailed analysis of the facts 

 convinced them, however, that 

 in this they were in error. 



Guinea-pigs and rabbits do not contract tetanus, after the inoculation 

 of a quantity of spores and bacilli of tetanus deprived of their toxin, [180] 

 1 Ann. de VInst. Pasteur, Paris, 1891, t. v, p. 1 ; 1892, t. vi, p. 385; 1893, t. vn, p. 755. 



FIG. 37. Leucocytes of rabbits filled 

 with tetanus spores. 



