Immunity against patJiogenic micro-organisms 163 



In conformity with this result this observer has often noted the 

 ingestion of living spirilla by the macrophages, in hanging drops of 

 the peritoneal exudation of inoculated guinea-pigs. The phenomenon 

 corresponds exactly to that described in connection with the spirillum 

 of the goose. 



In spite of the great difference between the spirillum and the 

 anthrax bacillus from the point of view of their adaptation to 

 surrounding media, the general result is the same with both these 

 microbes : animals endowed with natural immunity get rid of them 

 through the agency of their phagocytes. 



It would be impossible and even useless here to pass in review [173] 

 all the cases of natural immunity against infective micro-organisms. 

 We must consequently limit ourselves to several examples which 

 may have an interesting bearing on the study of the problem as 

 a whole. The spirilla, whose history we have just recorded, remain 

 in the peritoneal fluid, without change of form, up to the moment 

 when they are captured by the macrophages. Let us see by what 

 mechanism the natural immunity against micro-organisms, character- 

 ised by a very special sensitiveness to external influences and by a 

 considerable change of shape, is produced. The cholera vibrio and its 

 allies best satisfy this postulate. When they find themselves placed 

 under unfavourable conditions, these vibrios immediately become 

 transformed into small spherical bodies which are much more like 

 cocci than vibrios. The cholera vibrio is pathogenic for the la- 

 boratory rodents, especially for the guinea-pig, when a fairly large 

 quantity of a culture is injected into the peritoneal cavity. Against 

 smaller doses, however, the natural immunity is a most marked one. 

 If we take a race of the cholera vibrio of medium virulence, and 

 inject into the peritoneal cavity of guinea-pigs a sublethal dose of a 

 culture, the following phenomena may be observed 1 . The inoculated 

 vibrios move actively in the peritoneal fluid, from which almost all 

 the leucocytes have disappeared. There remain only a few lympho- 

 cytes which appear to be indifferent to the influences that set up a 

 real phagolysis. But, little by little, fresh leucocytes come into the 

 exudation and engage in a struggle with the vibrios which, so long as 

 they are free, retain their curved form and complete motility. The 

 microphages, especially, swarm into the peritoneal cavity. Some of 

 them begin to ingest vibrios, but this phagocytosis is at first slight. 

 Later it becomes much more active. The microphages and macro- 

 1 Ann. de FInst. Pasteur, Paris, 1895, t. ix, p. 448. 



112 



