254 INFECTION AND RESISTANCE 



here again the specificity, like that of bacterial precipitation, ag- 

 glutination, and other serum tests, is relative rather than absolute. 

 Thus a serum which has been obtained by the immunization of an 

 animal with human serum may react, not only with human serum, 

 but also with relatively higher concentrations of the sera of some of 

 the higher apes. However, such non-specific partial reactions can be 

 eliminated entirely by employing higher dilutions of antigen. Thus 

 Uhlenhuth, 23 , 24 ? 25 on the basis of a large experience, has established 

 a -standard of antigen dilution at 1 to 1,000, beyond which no "para" 

 or "minor" precipitation will occur. Since potency far exceeding 

 this is easily procured, absolute specificity can be ensured by the 

 very simple precaution of a sufficient dilution. 



The most important practical use for the reaction has been found 

 in forensic medicine, where it is possible in this way to determine 

 the species of animal from which have emanated the blood, sperm, 

 etc., found in spots on wearing apparel, weapons, or other articles. 

 The extensive investigations of Nuttall 26 upon this subject have inci- 

 dentally been of much value in furnishing a further method for the 

 determination of zoological species relationships. Nuttall carried 

 out 16,000 precipitin tests, with precipitating sera, upon 900 speci- 

 mens of blood which he obtained from various sources. He not only 

 confirmed many of the accepted zoological classifications, but shed 

 much light upon a number of disputed points. In working out the 

 tests upon monkeys he found that the reactions carried out with anti- 

 human serum become weaker as the species examined is farther re- 

 moved from man zoologically. Thus as we read down the column 

 from man to the hapalidsB the precipitate becomes less and less in 

 amount. 



Nuttall's Tests with Antihuman Serum. (Nuttall, loc. cit., p. 165.} 



ANTIHUMAN PRECIPITATING SERUM 

 Tested against Precipitate 



34 Specimens human blood 100% 27 



8 Simiidse, 3 species 100% 



36 Cercopithecidae 92% 



13 Cebidse 78% 



4 Hapalidse 50% 



2 Lemuridse 



23 Uhlenhuth. Deutsche med. Woch., 1900, 1901; Rob. Koch Festschrift, 

 1903. 



24 Uhlenhuth and Weidanz. "Kraus u. Levaditi Handbuch," etc., Vol. 2, 

 1909. 



25 Uhlenhuth and Weidanz. Loc. cit., where other publications are sum- 

 marized. 



26 Nuttall. "Blood Immunity and Blood Relationship," Cambridge Uni- 

 versity Press, 1904. 



27 The percentages refer to the volume of precipitate formed on standing 

 for a given time, the amount formed by the antiserum with its specific antigen 

 being taken as 100 per cent. Antigen dilutions correspond throughout. 



