III. PRECIPITINS. 



Definition. All of the foregoing experiments have 

 concerned themselves with the results obtained by 

 injection of cellular material of one animal into 

 another. In the further study of this subject, ex- 

 periments were made to discover what happens 

 when dissolved albuminous bodies of one species are 

 injected into animals of another species. This line 

 of investigation was first pursued by Tsistowitsch, <^~ 

 who injected rabbits with ,the serum of horses and 

 of eels. On withdrawing serum from such rabbits 

 and mixing it with horse or eel serum, the mix- 

 ture became cloudy, owing to the precipitation of L 

 part of the albumin of the horse or eel serum by 

 that of the rabbit. Normal rabbit serum does not 

 possess this property. Bordet was able to demon- 

 strate that the same thing takes place if rabbits are 

 treated with chicken blood. On mixing such a 

 serum with chicken serum a precipitate formed. 

 These substances which develop in the serum by 

 treating an animal with albuminous bodies of an- 

 other animal, and which precipitate these albumins ^ 

 when the sera of the two animals are mixed, are 



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