Historical sketch on Immunity 535 



manifestation of Pfeiffer's phenomenon in the peritoneal fluid. When 

 it is suppressed, by preparing the phagocytes by means of injections 

 of various fluids, we find that, instead of Pfeiffer's phenomenon, 

 phagocytosis is almost instantaneously produced. In positions where 

 very few or no leucocytes are pre-existent, as in the subcutaneous 

 tissue, Pfeiffer's phenomenon is never observed. 



Even in the case of the cholera vibrio the extracellular destruction 

 is observed, therefore, only in special cases. Most of the other 

 pathogenic micro-organisms do not undergo this destructive process 

 at all under conditions in which the cholera vibrio exhibits Pfeiffer's 

 phenomenon in a marked degree. These facts appeared to justify me 

 in the conclusion that the destruction of micro-organisms takes place 

 in the animal body by means of soluble ferments, the result of phago- 

 cytic digestion. These ferments are found under the normal condition 

 within these phagocytes and escape from them when they are 

 destroyed or receive some transient injury. This conclusion was in 

 flat contradiction to the theory and statements of Pfeiffer, who 

 attributed an important function to the endothelial secretions. To 

 settle this controversy I tried to obtain Pfeiffer's phenomenon outside 

 the body, that is to say independently of any co-operation from the [559] 

 peritoneal endothelium. It is sufficient to add a little peritoneal 

 lymph, rich in leucocytes, to the inactive anti-infective serum, to 

 obtain in hanging drops the transformation of the cholera vibrios 

 into granules. 



Bordet 1 , in my laboratory, repeated this experiment with the 

 object of determining its essential mechanism. He succeeded in 

 obtaining Pfeiffer's phenomenon in vitro, not only by adding peri- 

 toneal lymph from a normal guinea-pig to the specific serum, but 

 also by adding to it a drop of fresh blood serum from the same 

 animal. The analysis of the phenomena which take place under these 

 conditions led Bordet to the following hypothesis. The destruction 

 of micro-organisms in vaccinated animals takes place by the co- 

 operation of two substances. One of these is Buchner's alexin which 

 is found normally in the phagocytes ; it sets up bacteriolysis properly 

 so-called when it is enclosed within the leucocytes or after it has 

 escaped from them at the time of phagolysis. To attain this end, 

 however, the alexin needs the co-operation of another substance. 

 This is the protective or sensibilising substance of Bordet. It circu- 

 lates in the plasmas and carries a specific character which is absent 



1 Ann. de VInst. Pasteur, Paris, 1895, t. ix, p. 462; 18f)G, t. x, pp. 104, 193. 



