EVIDENCE FROM BLOOD TESTS 75 



several days and is then killed and bled, the blood 

 is left until it clots and the serum drained off and 

 preserved. The serum obtained thus from a rabbit 

 is called "anti-human" serum and is an exceedingly 

 delicate test for human blood, not only when the 

 latter is fresh, but also when it is in the form of old 

 and dried blood-stains, or even when the blood is 

 putrid. Stains, for example, are soaked in a very 

 weak solution of common salt and, if necessary, the 

 blood solution is filtered until it is quite limpid and 

 clear. Into the blood solution a few drops of the 

 anti-human serum are conveyed and, if the stains 

 are of human blood, a white precipitate is formed 

 and thrown down, but if the stains are of the blood 

 of some domestic animal, such as a pig, sheep, or 

 fowl, no such reaction follows. In the same manner 

 as above described, we may prepare anti-pig, anti- 

 horse, anti-fowl, etc., etc., sera by injecting the 

 fresh-drawn serum of a pig, horse, fowl, or any other 

 animal into the rabbit, instead of human blood- 

 serum. In some countries, notably in Germany and 

 Austria, this test has already been adopted by the 

 courts of justice and has been found extremely useful 

 in the detection of crime. 



Further investigation showed that these blood 

 tests might be employed to determine the degrees 

 of relationship between different animals, for, al- 

 though a prompt and strong reaction is usually 

 obtained only from the blood of the same species as 

 that from which the original injection into the rabbit 



