PRACTICAL APPLICATIONS 



325 



The precipitin reaction is likewise of great value in rnedicolegal cases 

 in determining the source of blood-stains, the original application and 

 technic having been largely worked out by Wassermann, Schutze, Uh- 

 lenhuth, and Weidanz. Thus in a case where, for example, a bloody 

 towel is found in the possession of a man charged with murder, the prose- 

 cution may see in this a proof of crime, whereas the defendant may claim 

 that the stains are those of dog's blood. Microscopic and chemical 

 tests may show that the stains are blood-stains, but they cannot deter- 

 mine their source. The blood-stained towel is placed in water or salt 

 solution, and a portion of the extract is mixed with the serum of a rabbit- 

 immunized against human serum, and another portion with the serum of 

 a rabbit immunized against dog's serum. If the first mixture shows a 

 precipitate, the stain was made by blood from a human being; if, on 

 the other hand, this mixture remains clear and the second shows a pre- 

 cipitate, this is strongly indicative of the presence of dog's blood. 



This method has also cleared up a number of scientific problems, 

 especially that of showing the blood relationship of man and the lower 

 animals. Just as a group agglutination demonstrates the close relation- 

 ship existing between various bacteria, so, also, serum precipitins prove 

 that a distinct relationship exists between the different species of animals. 



For example, an antihuman serum in low dilution will precipitate the 

 serum of monkeys. The differentiation between human and monkey 

 serum can be accomplished, however, by immunizing the monkey with 

 human serum, when a precipitin is formed that' reacts with human serum 

 alone, an isoprecipitin, or one active against the monkey's own serum, 

 not being developed as a general rule. 



The precipitin tests are likewise of value in food inspection, as, for 

 instance, to determine the nature of meats. For example, in order to 

 detect the presence of dog or horse flesh in sausage, extracts of the sausage 

 are made and tested with anti-dog and anti-horse serum, the presence of 

 precipitates indicating strongly the presence of the meat of these animals. 

 With an appropriate technic even salted and cooked flesh may be recog- 

 nized, although when the meat has been cooked it is necessary to prepare 

 immune serums by immunizing rabbits with extracts of cooked meats. 



In this connection it may be stated that specific organic reactions 

 have been secured by various investigators by prolonged immunization 

 of rabbits with certain organ extracts. Thus it is possible to differen- 

 tiate between the liver and kidney of the same animals; such tests have, 

 however, but limited practical value. Maragliano attempted to apply 

 this test of organic specificity to the serodiagnosis of malignant tumors 

 by preparing immune serums by the injection of tumor juices, securing a 



