PRECIPITINS 83 



pork, contain horse meat. Preparation for the test 

 consists in the immunization of animals, of which rab- 

 bits are the most suitable, by injections of extracts 

 made from the various meats to be tested for, as horse, 

 beef, pork, etc., each of which has a specific protein. 

 The immune serum, on being brought in contact with 

 an extract of the particular meat whose protein is 

 specific for it, will bring about precipitation. 



(II) Medicolegal Identification of Blood 



This test occasionally assumes the utmost impor- 

 tance when the question arises in murder cases as to 

 whether blood stains are human or not. The chemical 

 tests for blood do not distinguish one species from 

 another, while microscopical examination of dried 

 blood is unsatisfactory. Dried blood in very small 

 quantities, however, will respond to the precipitation 

 reaction, and by this means we can differentiate 

 human blood from that of the lower animals. Uhlen- 

 huth, Wassermann, and Schiiltz were the first to make 

 use of the precipitation test in this connection. 



The Precipitin Reaction 



The technic of the reaction is divided into two 

 parts. 



( a ) Production of the Precipitating Serum, — For 

 this purpose rabbits are employed. Three or four in- 



