304 IMMUNOLOGICAL METHODS OF DIAGNOSIS 



blood serum, this antiserum taking the place of the antibody of the 

 Wassermann reaction. If, then, the suspected substance contains 

 human albumins these will react with the corresponding precipitin 

 of the antiserum, with the result that any complement that may 

 simultaneously be present is bound to a greater or less extent exactly 

 as in the case of the Wassermann reaction. 



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. 



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 w T ill 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" precipitinogens, i. e., 

 of precipitinogenic molecular complexes which are peculiar to a 

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

 of species, all of which will naturally give rise to corresponding 

 "partial" precipitins, in a manner quite analogous to the formation of 

 "partial" agglutinins (which see). That such partial precipitins 

 actually exist in an antiserum may be shown by treating antihuman 

 serum with monkey serum when the antimonkey precipitin will 



