Anaphylaxis and Immunity. 



87 



the latter part of this period, however, an active sensitization 

 develops towards rabbit serum. It becomes possible, therefore, 

 to test the same uterus for the presence both of the antigen, and 

 of the antibody thereto. The antigen is revealed by the reaction 

 produced by horse serum, which demonstrates that the rabbit 

 component still persists. The antibody is revealed by the reaction 

 to normal rabbit serum. This condition is illustrated in Fig. 1. 



Fig. 1. Guinea-pig passively sensitized Jan. 4 by the intraperitoneal injection 

 of 3 c.c. of the serum of a rabbit highly immunized against horse serum. Killed 

 January 15, and uterine tracing taken. Reactions to both rabbit and horse serum. 



In the same way, guinea-pigs actively sensitized or immunized 

 against rabbit serum may be partially desensitized by means of 

 an injection of the serum of a rabbit immunized against horse 

 serum. The presence of the antigen in the sensitized cells is 

 revealed by the reaction of the uterus to horse serum, while the 

 reaction to rabbit serum shows that the autogenous antibody also 

 persists. This fact is illustrated in Fig. 2. 



The bearing of these data upon the interpretation of certain 



