THEORIES OF IMMUNITY. 



result of " the activity of the endothelial cells," 

 changes to an active condition, and becomes 

 capable of destroying great numbers of the 

 spirilla. This activity of the endothelial cells 

 was developed into a "new fundamental law" of 

 immunity (Deut. Med. Woch., 1896, pp. 97, 119), 

 and the discovery renewed the vitality of the 

 " humoral theory." 



As Metchnikoff (I. c.) himself goes on to say, 

 it may be easily supposed that he undertook 

 the investigation of this phenomenon of extra- 

 cellular destruction of the bacteria as soon as 

 possible, with a view of determining its real im- 

 portance in the question of immunity. He was 

 soon able to show that Pfeiffer's phenomenon 

 takes place in special circumstances only; previ- 

 ously existing phagocytes must undergo much 

 damage before the spirilla can become trans- 

 formed into granules; such " phagolysis " is in- 

 dispensable in order that Pfeiffer's phenomenon 

 may occur in the peritoneal fluids. If it be sup- 

 pressed by preparing the phagocytes beforehand 

 — by the injection of various liquids — an in- 

 stantaneous phagocytosis is produced instead of 



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