CHAPTER X 



THE PHENOMENON OF PRECIPITATION 



(Precipitins) 



THE establishment of the agglutinin reaction as a constant and 

 specific serum-phenomenon by the work of Gruber and Durham led 

 immediately to assiduous investigation of the many problems sug- 

 gested by it, and among them, as we have seen, the question of the 

 nature of the agglutinogen. It was found that agglutinins could be 

 produced, not only by the injection of whole bacteria, but equally 

 as well by treatment with dissolved bacterial extracts or with filtrates 

 from old broth cultures. This naturally led to the thought that there 

 might be a definite reaction if such extracts (instead of the bacteria 

 themselves) were added to agglutinating sera in vitro. Rudolf 

 Kraus l was the first to perform this very logical experiment. He 

 was working with broth filtrates of Bacillus pestis and of the cholera 

 spirillum, and found that when he mixed the perfectly clear filtrates 

 of such cultures with their respective antisera the mixtures would at 

 first become turbid and finally show a light flocculent precipitate. He 

 named the reaction the "precipitin reaction" and, in analogy to 

 agglutinins, spoke of the bodies in the serum which caused the pre- 

 cipitation as "precipitins." The reaction was found, like that of 

 agglutination, to be specific; the cholera serum gave no precipitate 

 with the plague extract and vice versa, and Kraus, after extending 

 his observations to other bacteria, pointed out the practical diagnostic 

 possibilities of his discovery. 



Though Kraus' first observations were made entirely with bac- 

 terial culture filtrates and antibacterial sera, it was soon discovered 

 that his results were merely isolated instances of a broad biological 

 law, and that specific precipitins were produced whenever animals 

 were treated with injections of any kind of foreign protein. Thus 

 Tschistovitch, 2 in 1899, found that the blood serum of rabbits im- 

 munized with eel-serum gave specific precipitates when mixed with 

 eel-serum, and Bordet 3 obtained analogous results by treating rab- 

 bits with defibrinated chicken blood and with milk. Thus rapidly 



1 R. Kraus. Wien. Idin. Woch., No. 32, 1897. 



2 Tschistovitch. Ann. de I'Inst. Past., 13, 1899. 



3 Bordet. Ann. de I'Inst. Past., Vol. 13, 1899, pp. 225-273. 



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