INFECTION AND IMMUNITY. 565 



otherwise be a fatal dose of the cholera sporillum ; that 

 the peritoneal fluids of the artificially immunized animal 

 had an almost instantaneous bacteriolytic, i. e., disinte- 

 grating, action upon living cholera spirilla that were 

 injected directly into the peritoneal cavity ; that the 

 serum from the immune animal had no such effect upon 

 cholera spirilla in a test tube, but if virulent cholera 

 spirilla were injected into the peritoneum of an animal 

 that is not immune, and that such injection be followed 

 immediately by an intra-peritoneal injection of blood 

 serum from an immune animal, almost instantly the 

 peculiar disintegration of the bacteria that was observed 

 in the peritoneum of the immune animal was to be seen. 

 As we shall learn presently this observation is of the 

 utmost importance and its bearing upon the course of 

 certain subsequent events will soon be manifest. 



The significant features of Pfeiffer's observation are 

 that while the blood serum of an immune animal is cap- 

 able of conferring immunity upon a susceptible animal, 

 yet, in a test tube it exhibits none of the bacteriolytic 

 activity constantly to be noted in the body of the immune 

 animal ; on the other hand if a small quantity of it be 

 injected into the peritoneal cavity of a normal, suscepti- 

 ble animal, the phenomenon of bacteriolysis, hitherto 

 absent, at once makes itself manifest. Clearly the serum 

 requires the co-operation of something within the body 

 of the living animal to bring about the disintegration of 

 bacteria. The phenomenon must therefore be the result 

 of a composite function. 



Though NuttalFs work materially lessened the number 

 of adherents to the phagocytic doctrine of Metschnikoff 

 there was still a group of active workers who retained 



