THE EVOLUTION OF MAN 



other. The serum of one group destroys the 

 blood corpuscles of another group. If an animal 

 is inoculated with the blood of another group, 

 it quickly feels the fatal effects of this struggle 

 in its veins. It falls into convulsions and finally 

 collapses entirely, just as a conflagration con- 

 sumes a city in whose streets a violent civil war 

 is raging. And this happens often in the case 

 of animals which are relatively close to one 

 another, for instance, many mammals. The 

 blood of a cat kills a rabbit which is inoculated 

 with it, and vice versa. But finally there is a cer- 

 tain limit. The blood of a cat naturally does not 

 kill another cat. Indeed, peace is guaranteed 

 often among more distant relatives. Closely re- 

 lated animals may mix their blood without dan- 

 ger. A dog is so close to a wolf that the living 

 blood of the one may mix with that of the other 

 without harm. It is the same with a horse and 

 a donkey. Now a short time ago a certain scien- 

 tist, Friedenthal in Berlin, mixed human blood 

 and monkey blood. At first one blood acted as 

 a poison for the other; that is to say, as long 

 as the objects of the experiment were man and 

 a lower monkey. But when human blood came 

 o the blood of the chimpanzee, peace was sud- 

 denly established. The boundary of antagonisms 

 had been crossed. The blood of man and that of 

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