Chemical Basis of Genus and Species 55 



non-treated rabbit is mixed with the serum of the blood 

 of the foreign species. 



In 1897 Kraus discovered that if the filtrates from 

 cultures of bacteria (e. g., typhoid bacillus) are mixed 

 with the serum of an animal immunized with the same 

 serum {e. g., typhoid serum) it causes a precipitate; and 

 that this precipitin reaction is specific. This fact 

 was confirmed and has been extended by the work 

 of many authors. 



Tchistowitch in 1899 observed that the serum of 

 rabbits which had received injections of horse or eel 

 serum caused a precipitate when mixed with the serum 

 of these latter animals. 



Bordet found in 1899 that if milk is injected into a 

 rabbit the serum of such a rabbit acquires the power 

 of precipitating casein, and Fish found that this reac- 

 tion is specific inasmuch as the lactoserum from cow's 

 milk can precipitate only the casein of cow's milk but 

 not that of human or goat milk. Wassermann and 

 Schutze reached the same result independently of each 

 other. 



Myers and later Uhlenhuth showed that if white of 

 egg from a hen's egg is injected into a rabbit, precipitins 

 for white of egg are found in the serum of the latter, 

 and Uhlenhuth' found, by trying the white of egg of 

 different species of birds, that the precipitin reaction 



^ Uhlenhuth, P., and Steffenhagen, K., Kolle-Wassermann, Handh, 

 d. pathol. Mikroorg., 2nd Ed., 1913, iii., 257. 



