274 BACTERIOLOGY 



cellular poisons as may be bound up as integral portions of 

 their constituent protoplasm. 



Furthermore, in so far at least as induced immunity is 

 concerned, the bulk of the experimental testimony supports 

 the opinion that the reaction is specific; that is to say, be 

 the systemic reaction evidenced as the elaboration of an 

 antidote to a soluble poison or as increased facility to destroy 

 living bacteria, it is called forth only through the specific 

 stimulus afforded by the injection of the animal with the 

 particular poison or bacterium from which we desire to 

 protect it. Thus, for instance, an animal rendered immune 

 from tetanus toxin, is not immune from diphtheria toxin 

 or from the inroads of diphtheria bacilli; similarly an animal 

 immune from any of the pathogenic species of bacteria is 

 immune from that species only and not necessarily from any 

 others. 



An observation of fundamental importance to an under- 

 standing of the mechanism of immunity was made by R. 

 Pfeiffer in 1895. While investigating Asiatic cholera he 

 found that animals could be immunized from the specific 

 endotoxin of the organism causing that disease; that the 

 blood-serum of such immune animals when injected into 

 normal animals protected them from what would otherwise 

 be a fatal dose of the cholera spirillum; that the peritoneal 

 fluids of the artificially immunized animal had an almost 

 instantaneous bacteriolytic, i. e., disintegrating, 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 intraperitoneal injection of 



