Immunity 625 



individual for an indefinite length of time. It can be 

 increased by rapidly injecting the animal with blood con- 

 taining the spirilla. Serum containing the immunizing body 

 imparts passive immunity to other animals into which it is 

 injected, and, according to Novy and Knapp, establishes a 

 solid basis for the prevention and cure of relapsing fever in 

 man. 



40 



