Immunity against micro-organisms 305 



these elements still give cholera cultures on nutrient media, a proof 

 that some at least of the intracellular vibrios are alive. Here we 

 have no destruction of the micro-organisms in the fluids of the 

 body, consequently no direct action of the bactericidal substance. 

 This substance, enclosed in the phagocytes, can only act through the 

 intervention of these elements. 



MesniP made analogous experiments with the Massowah vibrio, 

 which, unlike the cholera vibrio, is peculiarly virulent when injected 

 subcutaneously into guinea-pigs. In spite of this difference, this 

 micro-organism, when injected along with protective serum into 

 normal animals, behaves much as does the cholera vibrio proper. 

 Mesnil injected the Massowah vibrios at the same time as the anti- 

 infective specific serum, into the subcutaneous tissue of young and 

 adult guinea-pigs and of young rabbits. In every case he observed the 

 same reaction phenomena in the animal organism. The vibrios caused 

 the formation of oedema at the point of inoculation and remained 

 isolated in the fluid. The majority of these micro-organisms became 

 motionless, but a few remained motile. Pfeiffer's phenomenon was 

 never observed. There was sometimes an aggregation of the vibrios, 

 but this was not comparable with the marked agglutination brought 

 about by the specific serum in vitro. The vibrios retained their power 

 of reproduction, and Mesnil was able to observe them in all phases of 

 division. Some hours (6 — 8) after inoculation the leucocytes began 

 to come up to the seat of injection and set to work at once to ingest 

 the vibrios. This phagocytosis became more and more marked, and 

 finally there was ingestion of the whole of the micro-organisms. Drops 

 of the exudation containing only intraphagocytic vibrios, when placed [321] 

 in the incubator, gave abundant cultures. The leucocytes died out- 

 side the animal body, whilst the vibrios continued to live and grow 

 well under the new conditions. Certain leucocytes became three times 

 their original size, and their contents were seen to be made up of 

 vibrios closely packed together. The subcutaneous exudation, when 

 withdrawn even eight days after the injection of the micro-organisms 

 and sown on nutrient media, still gave colonies of vibrios. 



It is evident, therefore, that the direct action of the protective 

 serum on the vibrios was reduced to a mere trifle. It rendered them 

 motionless and brought about a very slight clumping, but it was 

 incapable of transforming the vibrios into granules or of destroying 

 them. We see, then, that even in the case of the vibrios, the part 

 ^ Ann. de VInst. Pasteur, Paris, 1896, t. x, p. 371. 

 B. 20 



