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 
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, 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 time, 
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 
