CHAPTER XVII 

 PRECIPITINS 



CLOSELY allied to the agglutinins are antibodies known as precipitins. 

 They act on dissolved albuminous bodies in a manner quite similar to 

 the action of agglutinins upon formed cellular elements. For example: 

 (1) If typhoid immune serum is added to a bouillon culture of typhoid 

 bacilli, agglutination occurs; (2) if the culture is filtered and the im- 

 mune serum is added to the clear sterile filtrate, cloudiness appears and 

 finally a precipitate forms. The first is an example of the action of 

 agglutinins upon the formed bacilli, and the second illustrates the ac- 

 tion of precipitins upon the albumins of dead and dissolved bacilli. 



Precipitins are formed not only for bacterial albumins, but for most 

 any soluble animal (zooprecipitin) and vegetable protein (phytoprecipi- 

 tiri) as well. If the serum of a rabbit immunized with horse serum is 

 added to horse serum, a precipitate forms, owing to the presence of a 

 specific precipitin in the immune serum. Normal rabbit serum does not 

 possess this power. 



Definition. The precipitins are specific antibodies that develop in the 

 serum of animals inoculated with bacteria or with solutions of animal or 

 vegetable albumins, which possess the power of producing a precipitate in a 

 . dear solution of the particular albumin or culture filtrate against which the 

 animal has been immunized. 



Historic. Kraus (1897) was the first to study and describe the bac- 

 terial precipitins. He observed that when the serums of animals that 

 have been immunized against cholera, typhoid, or plague are added to a 

 clear filtrate of the respective bouillon cultures of their bacteria, instead 

 of to the bacteria themselves, the clear solution becomes turbid and a 

 precipitate forms. 



This reaction was found to be quite specific, i. e., it occurs best with 

 the filtrate of the homologous bacteria, and to a much less extent with 

 closely allied species. For example, the typhoid immune serum does 

 not produce a precipitate with a filtrate of Spirillum cholerse, and simi- 

 larly a cholera immune serum does not produce a precipitate with the 

 filtrate of Bacillus typhosus. Kraus advocated the precipitin reaction 



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