236 INFECTION AND IMMUNITY 



precipitates." It was evident, therefore, that during the process of active 

 immunization with these organisms, a specific antibody had been pro- 

 duced in the serum of the treated animal, which, because of its precipitat- 

 ing 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 precipi- 

 tins in the sera of immunized animals. The phenomenon of precipitation, 

 however, is not limited to bacterial immunization, but has been found, 

 like the phenomena of agglutination and lysis, to depend upon biolog- 

 ical laws of broad application. . Thus, Bordet l found that the blood 

 serum of rabbits treated with the serum of the chicken gave a specific 

 precipitate when mixed with chicken serum. Tchistovitch 2 demon- 

 strated a similar reaction with the sera of rabbits treated with horse and 

 eel sera. By the injection of milk, Wassermann, 3 Schutze, 4 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 "precipitinogens." 



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 precipi- 

 tates, has not lost its power of binding the precipitinogen. This is 

 shown by the fact that the inactivated precipitin, when mixed with pre- 

 cipitinogen, will prevent subsequently added fresh precipitin from caus- 

 ing a reaction. From these facts the conclusion has been drawn that 

 precipitin, like toxin, is built up of two atom groups, 5 a stable hap- 

 tophore and a labile precipitophore group. By the destruction of the 

 latter, an inactive, yet neutralizing substance is produced which is 

 spoken of as "precipitoid." The precipitoids, like protoxoids, have 

 a higher affinity for precipitinogen than the unchanged precipitin, and 

 thus are able to prevent the action of these. 



Our own opinion would rather incline toward regarding the pre- 

 cipitins as identical in structure with sensitizer or amboceptor being 

 in fact " albuminqlysins " in the sense of Gengou. This problem is too 



1 Bordet, Ann. de 1'inst. Pasteur, 1899. 



2 Tchistovitch, Ann. de 1'mst. Pasteur, 1899. 



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



4 Schutze, Zeit. f. Hyg., 1901. 



6 Kraus und v. Pirquet, Cent. f. Bakt., Orig. Bd. xxxii. 



