SENSITIZING ANTIBODIES 291 



two atom groups, 36 a stable haptophore 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 

 precipitins as identical in structure with sensitizer or amboceptor 

 being in fact * ' albuminolysins " in the sense of Gengou. This prob- 

 lem is too complex to be discussed in detail in a summary of im- 

 munity as brief as the one here presented. 



Specificity. The specificity of precipitins is a question of the 

 greatest importance, since, as we shall see, these bodies have been 

 used extensively for the differentiation of animal proteins. In re- 

 gard to bacterial precipitins it may be said that, just as in agglu- 

 tination, there is in precipitation, a certain degree of "group reac- 

 tion." The precipitin obtained with a colon bacillus, for instance, 

 will cause precipitation with culture-filtrates of closely allied or- 

 ganisms, though in a less marked degree. According to Kraus, such 

 confusion may be easily overcome by the proper use of dilution and 

 quantitative adjustment, similar to that used in agglutination tests. 

 Norris 37 found that the precipitates given by immune sera with the 

 filtrates of the homologous bacteria were invariably heavier than 

 those given with allied strains and that the latter could be eliminated 

 entirely by sufficient dilution. 



Specificity becomes of still greater importance in the forensic use 

 of the precipitin reaction introduced by Uhlenhuth, 38 Wassermann 

 and Schiitze, 39 and Stern. 40 These authors found that the precipitin 

 reaction furnished a means of distinguishing the blood of one species 

 from that of another. Thus, blood spots, dissolved out in normal 

 salt solution, could be recognized by this reaction as originating 

 from man or from an animal, even after months of drying and in 

 dilutions as high as 1 :50,000. Since the value of this test depends 

 entirely upon the strict specificity of the reaction, this question has 



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



37 Norris, Jour. Inf. Dis., i, 3, 1904. 



38 Uhlenhuth, Deut. med. Woch., xlvi, 1900; vi and xvii, 1901. 



39 Wassermann und- Schutze, Berl. klin. Woch., vi, 1901. 



40 Stern, Deut. med. Woch., 1901. 



