Immunity against pathogenic micro-organisms 171 



up septicaemia ; in order to do this it needs the co-operation of other 

 micro-organisms. Leclainche and Vallee 1 have extended the same 

 rule to the bacillus of symptomatic anthrax (Bacillus chauvaei), so 

 important as being the cause of an epizootic disease of the Bovidae. 

 The spores of this bacillus when heated to 80 85 C. lose the pre- 

 formed toxin and at once become incapable of producing infection. 

 In this case also, these spores soon after injection become the prey 

 of phagocytes, which seize them, prevent their germination and check 

 their pathogenic action. If to these heated spores, however, we add 

 a small quantity of toxin, they are enabled to germinate in the 

 tissues and set up a typical infection. If heated spores are mixed 

 with sterile sand, and the mixture introduced into guinea-pigs, these 

 animals almost invariably acquire a fatal symptomatic anthrax. The 

 spores in the superficial part of the sandy mass are readily devoured 

 by the phagocytes ; but those which are included within the central 

 part of the mass, being protected for some time against these cells, 

 germinate as soon as they become permeated with the fluids of 

 the animal organism. If we envelope the sand in a paper sac the 

 protection against the phagocytes is still more complete and allows 

 almost all the spores to germinate and in every case to set up a fatal 

 infection. Leclainche and Vallee conclude from their experiments 

 " that we only require to protect the spore mechanically in order to 

 see an infection produced; here we cannot allege an increase of its 

 virulence, as when we associate a chemical substance with the virus, 

 and the exclusive part played by the phagocytosis in the protective 

 process stands out clearly " (p. 221). 



The history of these three anaerobic organisms clearly proves that 

 the natural immunity against them cannot be made dependent on 

 either the bactericidal power of the fluids, or on any antitoxic property, 

 or on the incapacity of the micro-organism to secrete its toxin in the 

 fluids of the refractory animal. The cause of this immunity resolves 

 itself into the reaction of the phagocytes which prevent the micro- 

 organisms from producing their poisons. 



All that has been said on the subject of the natural immunity of 

 the Vertebrates has had reference to cases of resistance against [182] 

 Bacteria. But may not the immunity against micro-organisms be- 

 longing to other groups depend on other factors with which the 

 reader has not yet been made sufficiently acquainted ? Amongst the 

 lower plants there are Blastomycetes (Torulae and Yeasts) which are 

 1 Ann. de Vlnst. Pasteur, Paris, 1900, t. xiv, p. 202. 



