290 INFECTION AND IMMUNITY 



cholerae, when mixed with the clear filtrate of bouillon cultures of 

 the respective organisms, produce microscopically visible precipi- 

 tates. These precipitates occurred only when filtrate and immune 

 serum were homologous, i. e., when the animal from which the serum 

 had been obtained had been immunized by the same species of 

 microorganism as that which was used in the test ; it was for this 

 reason Kraus spoke of them as "specific precipitates." It was 

 evident, therefore, that during the process of active immunization 

 with these organisms, a specific antibody had been produced in the 

 serum of the treated animal, which, because of its precipitating 

 quality, was named "precipitin. " This peculiar reaction was soon 

 found to hold good, not only for the bacteria used by Kraus, but 

 also for other bacteria, few failing to stimulate the production of 

 specific precipitins in the sera of immunized animals. The phenom- 

 enon of precipitation, however, is not limited to bacterial immuniza- 

 tion, but has been found, like the phenomena of agglutination and 

 lysis, to depend upon biological laws of broad application. Thus, 

 Bordet 32 found that the blood serum of rabbits treated with the 

 serum of the chicken gave a specific precipitate when mixed with 

 chicken serum. Tchistovitch 33 demonstrated a similar reaction with 

 the sera of rabbits treated with horse and eel sera. By the injection 

 of milk, Wassermann, 34 Schutze, 35 and others produced an antibody 

 which precipitated the casein of the particular variety of milk 

 employed for immunization. The reaction was thus applicable to 

 many albuminous substances. These substances, because of their 

 precipitin-stimulating quality, are called "preeipitinogens." 



Nature of Precipitins. The precipitins, like the agglutinins, may 

 be inactivated by heating to from 60 to 70 C., and can not be 

 reactivated by the addition of normal serum or by any other known 

 method. Such inactivated precipitin, however, while unable to 

 produce precipitates, has not lost its power of binding the precipi- 

 tinogen. This is shown by the fact that the inactivated precipitin, 

 when mixed with precipitinogen, will prevent subsequently added 

 fresh precipitin from causing a reaction. From these facts the con- 

 clusion has been drawn that precipitin, like toxin, is built up of 



32 Bordet, Ann. de Pinst. Pasteur, 1899. 



83 Tchistovitch, Ann. de 1'inst. Pasteur, 1899. 



84 Wassermann, Deut. med. Woch., 29, 1900. 

 K Schiitse, Zeit. f. Hyg., 1901. 



