472 IMMUNOLOGY 



to intervene l)etween the injections. While both injections may- 

 be given snbcntaneonsly, intraperitoneally, or intravenously, the 

 second, i.e., the one to elicit shock, is given as a rule either intra- 

 peritoneally or directly into the blood stream, since it is difficult 

 to produce severe reactions and death wilh even large doses ad- 

 ministered aubcutaneously. 



They found, also, that the reaction is specific, that the specific 

 hypersensitiveness is transmissible from the mother to the off- 

 spring, that the state of hypersusceptibility may be induced by 

 any antigen and persists, when once acquired, for a long time. 

 They observed that the animals which recovered from anaphy- 

 lactic shock are immediately refractory to another injection of 

 antigen. A sensitive animal can be made refractory by injecting, 

 usually subcutaneously, a dose of antigen too small to cause symp- 

 toms of shock. When the animal is thus made refractory to the 

 antigen, it is said to be "desensitized'' and the process of render- 

 ing it refractory is called ''desensitization. " The duration of 

 the refractory state, when once established, varies with the species 

 of animal used in the experiment. In guinea pigs it is said to 

 last two or more weeks, while in rabbits it is very short. Our own 

 experience has indicated that rabbits may become sensitive again 

 within twelve hours. 



Discovery op Passive Sensitization. — In 1907 Nicolle found 

 that when blood from a rabbit that had been sensitized with horse 

 serum was injected into a normal rabliit, the latter became sen- 

 sitive within the next twenty-four hours. The process of trans- 

 ferring to a normal animal specific hypersensitiveness to an 

 antigen by injecting blood taken from a sensitized animal is 

 called ipatisivc sensitizatio7i. 



The information presented thus far enables one to offer a few 

 definitions that may enable the student to better understand the 

 .subject. 



Sensitizing Substance. — Any true antigen as defined in pre- 

 vious chapters can be used as the sensitizing agent. This suggests 

 what is now well established, that sensitization depends upon the 

 development of antibodies. 



Landsteiner and Jacobs (1936) report success in producing 

 anaphylaxis in guinea pigs sensitized with p-chlorobenzoyl chloride 



