158 Chapter VI 



a kind of cytase, which resists temperatures approaching 60 C. This 

 cytase is very active against the bacilli, but in the living animal it 

 can only act within the phagocytes, or, in a transitory and incomplete 

 fashion, outside these cells, when phagolysis is taking place in the 

 peritoneal cavity. The resistance offered by the rat to anthrax 

 depends, then, on this phagocytic activity. For its manifestation it is 

 necessary, first of all, that the phagocytes should manifest a positive 

 chemiotaxis for the bacilli, and then that they should seize and ingest 

 these organisms. These are the vital acts that decide the result of 

 the struggle. When the phagocytes show themselves inactive the 

 bacilli multiply in the oedematous fluid which contains no bacteri- 

 cidal cytase, and pass into the plasmas of the lymph and of the blood, 

 which also are incapable of killing these bacteria. The animal may, 

 then, die of anthrax, in spite of the presence in its body of a large 

 quantity of bactericidal cytase which is to be found in situations to 

 which the bacilli have not penetrated. In those cases, on the other 

 hand, where the phagocytes accomplish their function, where they 

 rush up to the menaced point and devour the inoculated bacteria, 

 these bacilli are placed in contact with the intracellular cytase and 

 [168] undergo complete digestion. The organism in this case gets rid of its 

 enemies and victoriously resists infection. 



Anthrax in rats, then, presents one of the most instructive 

 examples of natural immunity. But the detailed analysis of the 

 mechanism of this resistance demonstrates very clearly the great 

 part played by the phagocytes in this process. In this respect the 

 organism of the rat presents, in a general fashion, a great analogy 

 to the natural immunity of the dog, of birds, and of other repre- 

 sentatives of the animal kingdom that we have examined. Under 

 these conditions it is useless to insist at any length on other examples 

 of resistance against anthrax which, moreover, have relation much 

 more often to a natural immunity against attenuated bacilli than to 

 one against true anthrax virus. Rabbits and guinea-pigs, so sensitive 

 to this virus, often resist the inoculation of Pasteur's vaccines. The 

 rabbit is, in general, refractory to the first anthrax vaccine ; it may 

 even resist the second vaccine. The guinea-pig, a more sensitive 

 animal, does not exhibit any natural immunity except against the 

 first vaccine. In all these cases the mechanism is similar to that 

 which the rat and the dog oppose to virulent anthrax. The bacilli, 

 into whatever part of the body they are injected, set up an exudative 

 inflammation which brings up a large number of leucocytes to the 



