STUDIES ON THE SERUM OF VACCINATED ANIMALS. 19 



by an adaptation that occurs in them owing to vaccination. If 

 such were the origin of these substances, the appearance of a bac- 

 tericidal power in the serum of vaccinated animals would be indic- 

 ative only of the degree of perfection which phagocytosis has 

 reached. 



Whatever may be the degree of bactericidal activity in animals 

 vaccinated against cholera, phagocytosis can no longer be con- 

 sidered as a phenomenon of secondary importance in the destruction 

 of this organism.* It will be found, to be sure, as Pfeiffer t has 

 recently shown, that vibrios injected into the peritoneal cavity of a 

 vaccinated animal (where leucocytes are always present) may be 

 for the most part destroyed by the fluid without having been taken 

 up by phagocytes, but it is none the less true that many of them 

 are taken up in the manner that Metchnikoff has demonstrated. 

 Metchnikoff injected a culture of cholera into the peritoneal cavity 

 of a vaccinated animal, and then withdrew after a certain time a 

 small amount of exudate, in which phagocytes containing vibrios 

 are to be seen. If the exudate is placed in a moist chamber at body 

 temperature, it is found that phagocytes removed in this manner 

 from the animal body, and subjected to unfavorable conditions, no 

 longer successfully oppose the development of the living organisms 

 that they have taken up; their growth goes on inside the cells, 

 which soon become veritable sacs stuffed with vibrios that finally 

 burst and let the organisms escape into the surrounding fluid. 



Pfeiffer does not consider these facts of great importance. Let us 

 take his point of view for a moment and admit that the phenomena 

 of phagocytosis have only a secondary function and that the 

 destruction of the vibrio in the vaccinated animal is due primarily to 

 the activity of the body fluids apart from cellular activity; it would 

 be reasonable to conclude, then, that this humoral action would occur 

 with greater intensity in those parts of the body most richly endowed 

 with bactericidal substances irrespective of the presence of phago- 

 cytes. If the blood of a rabbit or guinea-pig immunized against 

 cholera contains more of the destructive substances than the peri- 

 toneal exudate, it is reasonable to conclude that it is in the blood 



* See Cantacuzene, Recherches sur le mode de destruction du vibrion chol£rique 

 dans l'organisme, 1894. 



t Pfeiffer, Zeitschrift fur Hygiene, 1894, XVIII, p. 1. 



