138 LECTURES ON BIOLOGY 



horse 16 per cent., cow 12 per cent., dog 7 per cent., and kan- 

 garoo only 5 per cent. Correspondingly, anti-pig serum indicated 

 in the pig 100 per cent., in the para 14 per cent., cat 14 per cent., 

 dog 13 per cent., sheep 13 per cent , and kangaroo 5 per cent. 

 An anti-cattle serum produced reactions in other species of cattle 

 and, to a lesser degree, in sheep, goats, antelopes, and gnus. 

 We are, therefore, probably justified in assuming that the phylo- 

 genetic degree of relationship of these animals corresponds to the 

 volume of the precipitates. 



In like manner Nuttall endeavoured to shed light upon man's 

 position in the zoological system, and it is remarkable that these 

 experiments not only led to the same result as those of Frieden- 

 thal, but also agreed with Haeckel's genealogical tree of the 

 princates. For it was shown, as was indeed expected, that an 

 anti-man serum produced the greatest reaction in individuals 

 of different races, weaker results in the anthropoid apes, still 

 less results in guenons and baboons, and least of all in the 

 monkeys of the New World, the Platyrhini. Finally, in the 

 lemurs a very faint turbidity occurred only very rarely and 

 under employment of very strong serum. These experiments 

 seem to indicate that the biochemical differences between 

 man and the chimpanzees and gorillas are less than those 

 between these anthropoid apes and their lower relatives. Though 

 the blood-reaction alone does not supply an incontestable proof 

 of the phylogenetic relation of the various animal species, it 

 forms a most valuable link in the chain of evidence. 



The biochemical method, it may be mentioned in passing, is 

 of the utmost practical value in the detection of crime, for it is 

 often necessary to prove whether blood-stains on a floor or the 

 clothes of an accused person are those of a human being or animal, 

 a question upon the answer to which often depends life and death. 

 To-day such proof is easily furnished, for all that is necessary is 

 to dissolve the blood-stain in water and add a small quantity of 

 anti-man serum. If the blood is that of man, a turbid, flaky 

 precipitate appears after a few minutes, if that of an animal, no 

 reaction takes place. So accurate, indeed, is the effect of the 

 serum that it is even possible to demonstrate with it the origin 

 of blood which is already in a state of putrefaction, or has been 

 in a state of desiccation even for a period of several years. This 



