THE EVOLUTION OF MAN 



two in Asia, the orang-outangand the gibbon, 

 These four apes strangely resemble human be- 

 ings, even externally. The layman is specially 

 astonished to notice that they, like man, have 

 not jin externally visible JaU. But scientists 

 know that this occurs occasionally even among 

 lower monkeys and so it is not considered a very 

 convincing mark. But there is a very wonderful 

 relation which should convince the most inveter- 

 ate skeptic, and that is the following. 



Whoever has looked at a drop of blood 

 through a very strong microscope knows that 

 this; jpeculiar fluid is a mixture of two things, 

 first, the so-called serum, and then the blood 

 corpuscles floating round in it. Now when we 

 compare the drops of blood of various animal 

 species, we find that the red blood corpuscles 

 have many different forms. Some of them are 

 long, some are round, some are large and some 

 small ; in brief they are different in fish, or newt, 

 or bird, or mammal. This is no ground for sur- 

 prise, for all these animals are very different 

 in many other ways. 



The peculiar significance of this difference is 

 that the attempt to inoculate an animal of one 

 group with the living blood of another group 

 always ends fatally. It is just as if these two 

 kinds of blood carried on a war with one an- 



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