LYSINS, AGGLUTININS, PRECIPITINS, ETC. 237 



complex to be discussed in detail in a summary of immunity 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 proteids. In regard to 

 bacterial precipitins it may be said that, just as in agglutination, there 

 is in precipitation a certain degree of "group reaction." The pre- 

 cipitin obtained with a colon bacillus, for instance, will cause precipita- 

 tion with culture-filtrates of closely allied organisms, 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^ found that the 

 precipitates given by immune sera with the filtrates of the homologous 

 bacteria were invariably heavier than those given with aUied strains 

 and that the latter could be eliminated entirely by sufiicient dilution. 



Specificity becomes of still greater importance in the forensic use 

 of the precipitin reaction introduced by Uhlenhuth,^ Wassermann and 

 Schiitze,' and Stern.^ 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 been studied with especial 

 care, notably by Nuttall.^ All who have investigated the subject find 

 the only important source of confusion in the blood of the anthropoid 

 apes. The specificity of the reaction, too, has been found to depend very 

 closely upon the amount of precipitin in the serum employed. If a 

 highly immune serum is insufiiciently diluted, the reaction loses much 

 of its specific value.' This source of error is easily ehminated in practice 

 by careful control and titration of the sera used for the tests. 



Unlike agglutinins, precipitins have, so far, not been demonstrated 

 in normal sera.' 



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



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

 ' Wassermann und Schiitze, Berl. klin. Woch., vi, 1901. 



■" Stern, Deut. med. Woch., 1901. 



' Nuttall, Brit. Med. Jour., i, 1901; ii, 1902. 



« Kisier und Wolff, Zeit. f. Medizinal-Beamte, 1902. 



' Kraus, loc. cit., and Norris, loc. cit. 



