EVIDENCE FROM BLOOD TESTS 125 



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 

 annual 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, although 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 was taken, the blood of nearly allied species, 

 such as the horse and donkey, for example, gives a weaker and slower 

 precipitation. By using stronger solutions and allowing more tune, 

 quite distant relationships may be brought out. Nuttall and his 

 collaborator, Graham-Smith, made many thousands of such experi- 

 ments bearing upon the problems of relationship and classification 

 and it is of great significance to note that their highly interesting 

 and important results contain few surprises, but, in almost all cases, 

 merely serve to confirm the conclusions previously reached by other 

 methods, such as comparative anatomy and palaeontology. It will 

 be instructive to quote some of these results, the quotations being 

 taken from "Blood Immunity and Blood Relationship, by G. H. F. 

 Nuttall, including Original Researches by G. L. Graham-Smith and 

 T. S. P. Strangeways, " Cambridge, 1904. 



" In the absence of palaeontological evidence the question of the 

 interrelationship amongst animals is based upon similarities of struc- 

 ture in existing forms. In judging of these similarities, the subjective 

 element may largely enter." "The very interesting observations 

 upon the eye made by Johnson also demonstrate the close relationships 

 between the Old World forms and man, the macula lutea tending to 

 disappear as we descend in the scale of New World Monkeys and being 

 absent in the Lemurs. The results which I published upon my tests 

 with precipitins directly supported this evidence, for the reactions 



