64 EVOLUTION 



there is a harmonious mingling of the two. 

 But when human blood is transfused into eel, 

 pigeon, horse, dog, cat, lemur or " non- 

 anthropoid " ape, there is no harmonious 

 mingling. The human blood serum behaves 

 in a hostile way to the other blood, causing 

 great disturbance, marked, for instance, by 

 the destruction of the red blood corpuscles. 

 The difference in the two sets of cases is 

 that in the first the organisms are closely 

 related, in the second they are not. 



Another form of the same kind of experi- 

 ment is given by Uhlenhuth and Nuttall. 

 The blood-serum of a rabbit which has had 

 human blood injected into it forms a precipi- 

 tate with human blood. It forms almost as 

 marked a precipitate when it is added to the 

 blood of an anthropoid ape. As Schwalbe 

 sums up in the recent Darwin centenary 

 volume : " The reaction to the blood of the 

 lower Eastern monkeys is weaker, that to the 

 Western monkeys weaker still; indeed, in 

 this last case there is only a slight clouding 

 after a considerable time and no actual 

 precipitate. The blood of the Lemuridae 

 (Nuttall) gives no reaction or an extremely 

 weak one, that of the other mammals none 

 whatever. We have in this not only a proof 

 of the literal blood-relationship between man 



