320 IMMUNOLOGICAL METHODS OF DIAGNOSIS 



PRECIPITIN REACTIONS. 



Following the demonstration by Tchistovitch and Bordet (1899) 

 that not only vegetable albumins but animal albumins also are 

 capable of giving rise to precipitin formation, when injected into 

 animals of an alien species, Uhlenhuth especially drew attention 

 to the remarkable specificity of the reaction when applied to the 

 study of the blood of different animals. He thus laid the founda- 

 tion of the modern biological blood-test, which is now recognized as 

 proper evidence regarding the origin of blood-stains, in the courts 

 of practically all civilized countries. The same principle is applied 

 to the examination of various food products for adulterants, insofar 

 as these are of protein nature. If, for example, the question should 

 arise, whether or not eggs have been used in the preparation of 

 certain bakery products, it would only be necessary to test a saline 

 extract of the material in question with a corresponding antiserum, 

 and to note w r hether or not a precipitate or turbidity results on 

 bringing the two together. Or, the question might arise whether a 

 certain meat product were derived from beef or horse, in which case 

 a saline extract of the material would be treated with antibeef serum 

 on the one hand, and antihorse serum on the other, when its origin 

 would be indicated by the antiserum with which a precipitate could 

 be produced. 



Aside from these more practical bearings the precipitin reaction 

 has attracted a great deal of attention owing to the unexpected 

 light which it has thrown upon the biological relationship existing 

 between different animals. For it has been shown that while the 

 precipitins which can be produced in a rabbit, for example, by the 

 injection of the serum of a horse and which naturally will react 

 with the latter, likewise do so with the serum of the donkey and 

 the tapir. An antidog serum will similarly react with the serum of 

 the fox, antichicken serum with pigeon serum, antigoat serum with 

 sheep and bovine serum, antihuman serum with the serum of 

 apes, etc. 



These group reactions are readily explained if we assume the 

 existence in the antigenic sera of "partial 11 precipitinogens, i. e., 

 of precipitinogenic molecular complexes w r hich are peculiar to a 

 special species, besides others which are common to a whole group 



