PRECIPITINS lO/ 



called precipitins. 1 This power of the organism to 

 react to the injection of foreign dissolved albuminous 

 substances has been found to be very extensive. 



Bacterial Precipitins. In 1897, R. Kraus showed 

 that the serum of a rabbit immunized against 

 typhoid often produces a precipitate in the bac- 

 terial-free filtrate of a bouillon culture of typhoid 

 bacilli. This fact has been verified by subsequent 

 investigators and the reaction found to be specific. 

 In general, the best results are obtained with old 

 bouillon cultures which contain a larger proportion 

 of the autolytic products. It was natural that this 

 reaction should at once be applied to the diagnosis 

 of typhoid and other diseases. Numerous experi- 

 ments however have shown that Kraus' phenomenon 

 is not nearly so constantly observed as that of 

 agglutination, and the reaction is therefore but 

 little used. Whether the bacterial precipitins are 

 identical in character with those obtained by 

 injecting an animal with an unrelated serum (zoopre- 

 cipitins), is still undecided. Rostoski, as well as 

 Nuttall, believes that they are probably different. 

 So much for bacterial precipitins. 



Lactoserum Other Specific Precipitins. Bordet, 

 by injecting cows' milk into rabbits', was able to 

 produce a serum which precipitates the casein of 



1 It will be recalled that, besides the production of pre- 

 cipitins, the above procedure causes the formation of other 

 anti-bodies such as anti-complements, anti-agglutinins, etc. 



