308 Chapter X 



by the phagocytes show no appreciable change; they are always 

 stained very uniformly and intensely by Gram's method, and they 

 never swell up. The bacilli undergo no agglutination in the body 

 of the mouse, a fact of which we can convince ourselves by examining 

 hanging drops of the exudation. The phenomenon which strikes the 

 observer most is the very pronounced phagocytosis, due principally 

 to the activity of the microphages. Some hours after inoculation 

 these cells are found to be crammed with bacilli, a large number 

 of which no longer stain in the normal fashion. Without being trans- 

 formed into granules, these micro-organisms undergo intracellular 

 digestion which at the end of a few days is complete. This de- 

 struction is more rapid and complete in the microphages, slower in 

 the macrophages. Drops of exudation collected from these mice, at 

 a stage when the ingestion is completed, produce fatal septicaemia 

 in untreated mice. This is proof that at the moment when they were 

 seized by the phagocytes the bacilli still retained their virulence. 

 Mesnil, as the result of his experiments, concludes that "the effect 

 of the serum is to stimulate the phagocytes and especially the poly- 

 nuclear forms ; they ingest more quickly, they digest more quickly. 

 The serum is, therefore, a stimulant of the cells charged with the 

 defence of the animal " (p. 496). 

 [324] We need not describe the phenomena produced in mice inoculated 

 subcutaneously and treated with protective serum, for even in the 

 peritoneal cavity neither Pfeiffer's phenomenon nor any extracellular 

 destruction of the bacilli can be observed. The micro-organisms, 

 when subjected to the influence of the specific serum, readily absorb 

 the fixative, as demonstrated by Bordet and Gengou\ This absorp- 

 tion must certainly favour the action of the intraphagocytic cytases. 

 It is not, however, sufficient to explain the protective, anti-infective 

 action of the serum. Such explanation was given by the experiments 

 which Gengou, at my request, was good enough to make. He inocu- 

 lated mice with the bacilli of swine erysipelas, mixed with specific 

 serum heated to 55° C, to which was added some normal guinea-pig's 

 serum. The mice so treated resisted the infection but controls died 

 in a few days. Being thus assured of the protective action of the 

 serum, Gengou prepared the same mixtures of swine erysipelas 

 bacilli and of the two serums ; but, instead of injecting the whole of 

 the mixture, he removed the bacilli from the serums, after a pro- 

 longed contact, and injected the bacilli alone into the mice. The 

 1 Ann. de VInst. Pasteur, Paris, 1901, t. xv, p. 289. 



