PFEIFFEFS PHENOMENON. 445 



cavity of another animal. In this case the organisms die 

 an extracellular death, and their destruction is brought 

 about by the medium of a specific substance in the anti- 

 cholera serum. Pfeiffer found that the serum of convales- 

 cent cholera patients gave the same reaction as that of 

 immunised animals, that is, it possesses specific antagonis- 

 ing substances. He obtained the same reaction also in 

 the case of the typhoid bacillus and other organisms. 

 From his observations he concluded that the reaction was 

 specific and could be used as a means of distinguishing 

 organisms which resemble one another. 



The specific property is still possessed by the serum 

 when heated to 6o~ C., a temperature which rapidly destroys 

 all ordinary bactericidal power. Pfeiffer considered that 

 the specific substance in the serum existed chiefly in an 

 inert form, and that it became actively bactericidal 1 by 

 the aid of living cells, probably those of the peritoneal 

 endothelium. He found that if the anti-serum was injected 

 into the peritoneal cavity of a fresh animal, and if, after a 

 time, some of the peritoneal fluid was withdrawn and the 

 corresponding organism added to it, the reaction could be 

 observed outside the body. Metchnikoff, however, showed 

 that the same result was obtained when the organism was 

 simply placed in some fresh peritoneal fluid to which the 

 anti- serum had been added outside the body. In this 

 case the action of the endothelial cells was excluded, and 

 Metchnikoff concluded that the reaction was due to sub- 

 stances derived from the breaking down of leucocytes 

 (these being the only cells in the peritoneal fluid) by the 

 action of the specific substance in the anti-serum. 



This observation of Metchnikoff was confirmed by 

 Bordet, who further improved the method of observing the 

 reaction outside the body, as follows : (a) an emulsion of 

 the living organisms (for example of the cholera vibrio) was 

 made by adding a young culture to about 5 c.c. of bouillon ; 

 (If) two drops of this emulsion were taken, and mixed with 



1 In some cases an antimicrobic serum possesses specific directly bac- 

 tericidal powers, but this is not the general rule. 



