Facts bearing on acquired immunity 223 



serum produces in vitro Pfeiffer's phenomenon with great rapidity, 

 this phenomenon is not manifested. This experiment has been 

 performed and described by Bordet 1 . Having injected a suspen- 

 sion of this vibrio into the jugular vein of a guinea-pig vaccinated 

 against the cholera vibrio, he killed the animal an hour later and 

 found, in the blood of the heart, vibrios that had kept intact their 

 form and their property of staining with methylene blue. Cultiva- 

 tion of the blood of the heart, liver and spleen gave growths of 

 vibrios. In another guinea-pig, hypervaccinated against the same 

 organism and inoculated by the same method, the blood drawn off 

 shortly (4 15 minutes) afterwards showed, in preparations treated 

 with methylene blue, well-stained vibrios, of normal form and quite 

 intact. This is the most direct proof of the absence of Pfeiffer's 

 phenomenon in the blood fluid of a living animal that enjoys a very [235] 

 marked acquired immunity. The intact vibrios were lodged inside 

 the leucocytes. 



Levaditi 2 repeated these experiments in my laboratory and varied 

 the conditions under which the vibrios were injected into the blood 

 vessels. He was sometimes able to observe phagolysis of the leuco- 

 cytes of the blood and their almost complete disappearance from the 

 the peripheral circulation. In these cases the injured leucocytes 

 accumulated in the pulmonary capillaries and masses of them were 

 seen surrounding groups of vibrios that were transformed into 

 granules. It was, however, easy to exclude phagolysis by preparing 

 the animals by means of injections of physiological saline solution or 

 broth. Under these conditions the leucocytes remained in the blood 

 current and very soon ingested the vibrios. Whilst the vibrios that 

 were still free in the blood plasma retained their form and staining 

 power intact, those found inside microphages were already, in great 

 part, transformed into granules. The rapidity with which these 

 phagocytes ingest the vibrios and set up the changes in them is really 

 extraordinary. 



In this case, which affords a typical example of the reaction of the 

 animal organism in acquired immunity, we see a very marked and 

 immediate phagocytosis. It is this same process that has already 

 been described as occurring in the peritoneal cavity of vaccinated 

 guinea-pigs in which phagolysis was absent as the result of pre- 

 paratory injection. In the subcutaneous tissue and in the anterior 



1 Ann. Soc. d. sc. m6d. et not. de Bruxelles, 1895, t. ir. 

 a Ann. de FInst. Pasteur, Paris, 1901, t xv, p. 894. 



