ii6 The Insides and the W or /{i figs of Living Things 



crab has been considered more closely related to the scor- 

 pions than to any other living forms. Now comes the blood 

 test and confirms this in a most striking way. A similar 

 problem for the evolutionist has been the placing of birds 

 and mammals in relation to lower vertebrates. Although 

 birds and mammals are both warm-blooded they differ from 

 each other as classes more than birds differ from reptiles, 

 which are characteristically " cold-blooded." The blood 

 tests very decidedly link the birds with the turtles, which 

 must disturb our poetic sense, since we could hardly find 

 more violent contrasts than are symbolized by the tortoise 

 and the humming bird, for example. 



Another example of important parallelism between the 

 blood tests and the evidences from structure is found on 

 comparing the whales and porpoises with cows and pigs, 

 which of course they do not resemble for the ordinary ob- 

 server. The study of whale anatomy and of whale develop- 

 ment and of fossil whales long ago convinced the biologist 

 that this group of animals represents a progressive divergence 

 from an ancient stock of land animals, in adaptation to life 

 in the water. After millions of years the whales still retain 

 numerous structures and details of organization that link 

 them with the ungulates or hoofed mammals, and today the 

 laboratory discovers that in the fundamental chemical consti- 

 tution they are also related to the hoofed animal. 



Chemical Differences 



We know very little about the fundamental chemistry of 

 living matter. The processes that take place in protoplasm 

 have so far eluded the most delicate chemical research. Yet 

 we have discovered through the study of organic processes 

 themselves the presence of substances which we can point 

 to with certainty, although we have not yet been able to see 

 them in a pure or isolated state. This is true of the vitamins 

 and of the hormones or gland products which have received 

 a great deal of attention in recent years. It is true of toxins 



