Facts bearing on acquired immunity 235 



no longer contains any free bacilli: all are found inside the micro- 

 phages. Nevertheless, if a drop of the exudation now be withdrawn 

 and kept for some time at a temperature of 37 C., it will be found 

 that the bacilli multiply inside the dead phagocytes outside the 

 animal. We thus obtain colonies of bacilli, a fact which clearly 

 proves that these bacilli whilst still alive have been ingested by the 

 leucocytes. This experiment is, therefore, very similar to the one 

 we have described in connection with Gamaleia's vibrio. 



Even at a later period, 24 or 30 hours after the injection of the 

 bacilli, that is to say at a period when an examination of the exu- 

 dation no longer reveals the presence of bacilli, the sowing of a drop 

 of this exudation on a nutrient medium still gives isolated colonies of 

 the Bacillus pyocyaneus capable of producing the characteristic 

 pigments. At a still later period, when the peritoneal exudation 

 remains sterile, a post-mortem examination of the animals enables 

 one to recognise, beneath the peritoneal surface, small white points 

 made up of leucocytes. The sowing of these masses almost invariably 

 gives colonies of the Bacillus pyocyaneus which form blue pigments. 

 We see from this account that, even in the peritoneal cavity of 

 vaccinated animals, matters by no means go on in a uniform fashion, 

 as would appear from Wassermann's statements. Some bactericidal 

 action in the peritoneal fluid there certainly is, but it is quite 

 transient, and is limited to the period of phagolysis. The majority 

 of the bacilli resist this attack of the body fluids to continue their 

 struggle with the phagocytes, which, however, ultimately get the 

 upper hand. In the subcutaneous tissue the part played by this 

 phagocytic reaction is still more general. Gheorghiewsky has studied 

 it not only in vaccinated guinea-pigs but also in a goat which had 

 received several large injections of the Bacillus pyocyaneus. He 

 observed that shortly after the subcutaneous injection of these bacilli, 

 the fluid which accumulates at the seat of inoculation renders them [248] 

 motionless and in part agglutinates them. This fluid is clear and 

 contains a few leucocytes and a number of bacilli which still retain 

 their usual form. Some time later the leucocytes begin to come 

 up to the seat of inoculation and to ingest the bacilli. At the end 

 of 10 to 15 hours all the bacteria have been seized by the micro- 

 phages and we no longer find any of them free. A hanging drop 

 of this exudation, transported to the incubator, soon swarms with 

 bacilli which have sprung from the organisms ingested by the leu- 

 cocytes. 



