Immunity against micro-organisms 311 



appear to be produced under all circumstances " (p. 117). As, how- 

 ever, his researches on this subject were made on guinea-pigs which, 

 in spite of the treatment with specific serum, always ended by 

 succumbing to anthrax, we readily understand that his results cannot 

 be compared with those obtained by Marchoux. I was present at the 

 experiments of this observer and convinced myself of the accuracy of 

 the facts recorded in his memoir. 



Most of the examples here studied justify fully the hypothesis 

 of the stimulant action of protective serums, a view that I formu- 

 lated as the result of my researches on the immunity of rabbits 

 against the Gentilly cocco-bacillus 1 . In this the first case of anti- 

 infective immunity, due to the serum elaborated by an immunised 

 animal, I could not find either a bactericidal action, however slight, 

 or any agglutinative or attenuating property of the fluids of the 

 body. As, on the other hand, this serum had no antitoxic power, [327] 

 everything indicated that we must look for its action, which was 

 nil or very slight on the micro-organism, as being exerted on the 

 organism of the animal into which it was injected for protective 

 purposes. A comparative examination of the course of the pheno- 

 mena in the subcutaneous tissue of the ear in rabbits, some of 

 which received an injection of the specific serum into the veins whilst 

 others were kept as controls, at once showed how widely different 

 were the two cases. In the control animals, the cocco-bacilli im- 

 mediately began to multiply without meeting with any opposition on 

 the part of the organism of the animal ; on the other hand, in the 

 rabbits treated with serum, the serum became rich in leucocytes 

 which at once set to work to ingest the micro-organisms. In course 

 of time the latter gradually diminished in numbers, whilst the leuco- 

 cytes went on increasing. The phagocytosis, also, became more and 

 more marked. This struggle was continued for more than 24 hours, 

 after which the purulent exudation, containing masses of leucocytes, 

 no longer included any cocco-bacilli visible under the microscope 

 either outside or inside cells. Nevertheless, this pus was still capable 

 of producing a fatal septicaemia in untreated rabbits, clearly proving 

 that it still contained some living and virulent micro-organisms. 

 These cocco-bacilli persisted for a long time inside the phagocytes ; 

 their presence being demonstrated by injecting the exudation into 

 unprotected rabbits and thus setting up a fatal infection. Finally, 

 however, they disappear completely. On consideration of such facts 

 1 Ann. de I'Inst. Pasteur, Paris, 1892, t. vi, p. 308. 



