IMMUNOLOGICAL RELATIONSHIPS 331 



initely. Rosenau and Anderson (1909) shelved that mild but 

 definite anaphylactic reactions may be elicited in guinea pigs 

 sensitized Avith horse sertmi as long as two hiuidred forty-five days 

 after the injection. A fe\v guinea pigs gave positive reactions 

 after se\'en hundred thirty-two days and in one case they obtained 

 the reaction after one thousand ninety-six days. 



Passi\e sensitization consists of transfer of the state of liyper- 

 susceptibility to a normal animal by injecting into it serimi from 

 an actively sensitized aninral. Passive sensitization may be accom- 

 blished with homologous and heterologous sera containing specific 

 antibodies. Otto (1907) sho\ved that passive sensitization could 

 be carried out with the serum of an actively sensitized animal 

 eight days after the antigen injection. Friedemann (1907) and 

 Otto found that when the serum of a sensitized animal is injected 

 subcutaneously, the best residts are obtained by administration 

 of the antigen twenty-fom^ to forty-eight hours later. It appears, 

 therefore, that an interval must elapse during which the anti- 

 bodies of the injected serum become associated ^vith the cells of 

 the recipient. 



Nicolle (1907) ^vas able to transfer passively the sensitization 

 to the Arthus phenomenon. Opie (1924^') found that a rabbit 

 passively immiuiized by injection of seriun of an immunized ani- 

 mal may exhibit a severe Arthus reaction. 



There is good evidence that a definite correlation exists be- 

 tween the poAver of a serum to elicit passive sensitization and its 

 precipitating antibody concentration. Doerr and Russ (1909) 

 considered the precipitins and anaphylactic antibody identical. 

 Opie foimd a close but not exact parallelism bet^veen precipitin 

 content of the serum and severity of the Arthus phenomenon in 

 sensitized animals. 



Desensitization to anaphylactic shock was first observed by 

 Otto (1907) and by Rosenau and Anderson (1909), and first 

 confirmed by Gay and Southard and thoroughly studied by 

 Besredka. As defined by Zinsser, desensitization is a specific proc- 

 ess by w^hich antigen is administered to sensitized animals either 

 in sublethal fractional amounts or in a gradual manner so that 

 the reaction takes place ^vithout producing acute injiuy. The 

 sensitive animal so treated loses for a time its capacity to react 

 with the antigen. In guinea pigs the state of desensitization may 

 last t^vo ^veeks or longer and in rabbits, accordino" to Scott, the 

 refractory condition lasts only a short time. 



