ANAPHYLAXIS 183 



particular strain of trypanosome and then cured 

 by means of chemo-therapeutic agents, when 

 tested with the original strain was not immune, 

 the disease reappearing after a long incubation. 

 If mice were inoculated with blood from the diseased 

 animal, i.e., with blood containing trypanosomes, 

 they became infected and died. Curiously, how- 

 ever, if the trypanosomes were first removed from 

 this monkey blood, it was found that the serum 

 was able to kill the original strain of trypanosomes. 

 This showed that the trypanosomes had undergone 

 some change in the body of the monkey; they 

 differed from the original strain in their behavior 

 toward the serum; they had become " serum-fast." 

 Similar observations were made at the same time 

 by Kleine, and recently also by Mesnil. 



In explanation of this adaptation, Ehrlich sug- 

 gests that certain particular receptors of the para- 

 site are concerned entirely with the parasite's nutri- 

 tion. Owing to the destruction brought about by 

 the chemical agent, some of these receptors pass 

 into the monkey's body, and, acting as antigens, 

 excite the production of antibodies directed against 

 these particular receptors. When living parasites 

 are brought into contact with this antibody, either 

 in vitro or in vivo, the antibody is anchored by 

 the parasites. As a result of this occupation of 

 its receptors, the parasite undergoes a biological 

 alteration which consists in the disappearance of 



