HOST RESPONSE TO ANTIGENIC ACTION 459 



elicit reactions of significance either in normal rabbits or in rab- 

 bits previously immunized with killed pneumococci of the same 

 type. 



When a mixture of equal parts of 1 to 1,000 Type II polysac- 

 charide and undiluted homologous immune rabbit serum was in- 

 jected intradermally into normal rabbits, there developed a cu- 

 taneous reaction similar to that observed in actively immunized 

 rabbits when similarly injected with the carbohydrate alone. In 

 the few animals tested, the reaction following the antigen-antibody 

 mixture was not so severe or so lasting as that evoked by the in- 

 jection of polysaccharide into the skin of an actively immunized 

 rabbit. 



In another experiment the precipitin titer was determined on a 

 sample of serum from a rabbit which had been actively immunized 

 with Type II pneumococci and which exhibited a typical cuta- 

 neous reaction to the corresponding polysaccharide. Then, on the 

 basis of body weight, a normal rabbit was given an intravenous in- 

 jection of concentrated Type II antipneumococcic horse serum in 

 an amount calculated to establish in the serum of the rabbit so 

 treated a precipitin titer corresponding to that of the serum of 

 the actively immunized animal. A precipitin test on serum from a 

 test bleeding, taken one hour after the injection of immune serum, 

 indicated that the desired result had been obtained. Skin tests with 

 Type II polysaccharide performed at one-half-hour, one-hour, and 

 two-hour intervals after the serum injection yielded reactions ap- 

 parently identical with those observed when the same antigen was 

 injected intradermally into rabbits actively immunized with Type 

 II pneumococci. A repetition of the skin tests showed that positive 

 reactions could be elicited for at least four days after the injec- 

 tion of serum. It was found, however, when normal horse serum 

 was substituted for the specific, concentrated, immune horse se- 

 rum, that no reaction took place. 



In horses during the course of active immunization, positive 

 cutaneous reactions could be obtained by the intradermal injec- 



