Chapter V 



IMMUNITY TO THE PHENOMENON OF 

 LOCAL SKIN REACTIVITY 



THE facts eml:)odied in the preceding chapter demonstrated 

 that the active principles ot the phenomenon are antigenic 

 bacterial factors specifically neutralized by immune anti- 

 sera. Data concerning natural and actixely and passively acquired 

 immunity to the active principles of the phenomenon are de- 

 scribed in this chapter. 



NATURAL IMMUNITY OF RABBITS 



In experiments previously described it has already been noted 

 that some of the animals remained resistant to the phenomenon 

 of local skin reactivity to B. typhosus cultiue filtrates. Thus, out 

 of 2 12 animals tested with the same doses of B. fyljliosus tryptic 

 digest broth culture filtrates there were 45 negatively reacting 

 rabbits and 167 rabbits which showed severe reactions. In the 

 animals which Avere considered resistant to the phenomenon, 

 there Avas no local hemorrhagic necrosis folloAving the intrave- 

 nous injection. When, prior to the intravenous injection there 

 was erythema at the prepared site, sometimes it became more 

 pronounced four to five hours after the intravenous injection. 

 TAventy-four hours later the skin appeared normal again. In this 

 group of experiments no mild hemorrhagic reactions which 

 Avould constitute an intermediate group bet^veen the negative and 

 positive animals Avere obtained. In further experiments, the use 

 of B. typhosus "agar Avashings" filtrates yielding potent active 

 principles seemed to reduce the number of resistant animals, 

 although a certain percentage of rabbits ahvays remained resistant 

 to B. typJiosus materials. Frequent occurrence of spontaneous 

 immunity to B. typJiosus in rabbits may be presumed to exist 

 from findings of normal agglutinins in a large percentage of 

 animals. Not infrequently B. typhosus agglutinins in a titer as 

 high as 1:1000 Avere encountered in normal bleedings. Conversely. 



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