THEORIES OF IMMUNITY. 



be secured is by adding the serum of an animal 

 immunized to the cholera vibrio, and that has also 

 been subjected to a temperature of 55° Centi- 

 grade for half an hour, to a culture of active and 

 virulent cholera vibrios, and injecting the mix- 

 ture into the peritoneal cavity of a fresh animal. 

 The bacteria are soon seen to become gathered 

 together, granular, and gradually to disappear. 

 The action is specific and limited to animals 

 immunized to the disease produced by the bac- 

 terium employed — in the case cited, of course, 

 the cholera vibrio. It was at first supposed that 

 a similar reaction could be demonstrated for 

 other bacteria, and that such a reaction could be 

 utilized for differentiating species and races of 

 bacteria from each other. 



The significance of this reaction was not under- 

 stood until the publication of Bordet's results in 

 hemolysis above referred to. In these he found 

 that upon injecting the blood corpuscles of one 

 species of animal into the blood stream of an- 

 other, there resulted in this blood stream the 

 appearance of a substance that was able to de- 

 stroy the blood corpuscles of the first species of 



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