138 INFECTION AND RESISTANCE 



immune animal. This was indeed found to be the case and, al- 

 though such immune serum, like normal serum, is deprived of its 

 in vitro bactericidal power on heating, Pfeiffer found, in his intra- 

 peritoneal experiments, that heated serum is quite as effectual as 

 fresh immune serum in transferring passive immunity to a normal 

 guinea pig. We may summarize the important harvest of facts ob- 

 tained from these experiments of Pfeiffer in the following state- 

 ments: 



1. Rapid dissolution of cholera spirilla takes place in the 

 peritoneal cavity of a cholera-immune guinea pig. Similar lysis 

 takes place not at all, or only to a slight extent, in the peritoneum 

 of a normal pig. In consequence of the lysis the immune pig will 

 survive the injection of quantities of bacteria which invariably kill 

 normal animals of the same weight. 



2. The protection obtained in this way is specific. 



3. The protection may be transferred from an immune to a 

 normal guinea pig, by injecting a little immune serum together with 

 the bacteria into the peritoneum of the normal animal. In a normal 

 animal so treated lysis is in every way similar to that observed in 

 the immune pig. 



4. The transfer of the lytic power and consequent immunity 

 can be brought about not only by means of fresh immune serum but 

 by heated serum as well, although the latter has lost all its alexic 

 power because of the heating. 



Of the phases of this "Pfeiffer phenomenon" the one most diffi- 

 cult to understand, in the light of the knowledge of that time, was 

 the transference of the lytic property with the heated serum. Pfeiffer 

 very naturally took his experiments to signify that the actual de- 

 struction of bacteria in the animal body could take place entirely 

 without the phagocytic participation of the body cells, a view in 

 sharp contrast to that of the Metchnikoff school, and based upon his 

 observation of the complete extracellular disintegration of the spir- 

 illa in the peritoneal exudate. He assumed, however, that there was 

 an indirect participation on the part of the cells. The observation 

 that heated serum, inactive outside the body, was efficient when in- 

 troduced into the peritoneum, persuaded him that the cooperation 

 of the living tissues was a necessary factor, and he assumed a pos- 

 sible activation by substances derived from the endothelial cells lin- 

 ing the peritoneal cavity. In the same way he explained his failure 

 to observe actual bacterial dissolution in hang-drop preparations, 

 even when fresh serum was used in the experiment. 



It will be interesting to examine a protocol of an experiment such 

 as those carried out in the performance of the Pfeiffer phenomenon 

 in order to make the actual occurrences entirely clear. In such 

 experiments the quantity of bacteria used must be chosen with some 

 regard to the virulence and toxicity of the particular culture em- 



