1 42 IMMUNE SERA 



gated by Rosenau and Anderson in the Hygienic 

 Laboratory. Almost simultaneously with the ap- 

 pearance of these studies came a comprehensive 

 monograph on the serum rashes by v. Pirquet and 

 Schick, and this fitted in so well with the labora- 

 tory studies of Otto and of Rosenau and Anderson 

 that a great deal of interest was aroused in this 

 subject. 



The Phenomenon. As a result of all the work 

 that has been done we now know that when an 

 animal is injected with an alien proteid, there 

 develops, after a time, a specific hypersusceptibility 

 for this proteid. After a definite interval if the 

 animal is given a second injection of the same 

 proteid, violent symptoms appear, often leading 

 to the death of the animal. The reaction is specific, 

 so that animals sensitized, for example, to horse 

 serum, manifest little of no hypersusceptibility 

 to other sera. It is possible, however, to sensitize 

 an animal to several proteids simultaneously. The 

 sensitizing dose may be very small -even as little 

 as one millionth cubic centimeter of horse serum 

 has sufficed to render guinea pigs sensitive. A 

 varying length of time must elapse after the sen- 

 sitizing injection before the animal becomes fully 

 sensitized. In guinea pigs injected with small doses 

 of horse serum, from twelve to fourteen days 

 suffices. With larger doses, however, the time 

 required is much longer, and may extend over 



