GREAT STEPS IN EVOLUTION 81 



all the others depend for their carbon supplies 

 on the sugar, starch, fat, etc., already made 

 by other animals or by plants. As regards 

 nitrogen, most plants take this from nitrates 

 and the like, absorbed along with water by 

 the roots; whereas animals obtain their 

 nitrogenous supplies from the complex pro- 

 teids formed within other organisms. Most 

 plants, therefore, feed at a lower chemical 

 level than do animals, and it is characteristic 

 of them that, in the reduction of carbon 

 dioxide and in the manufacture of starch 

 and proteids, the kinetic energy of sunlight is 

 transformed by the living matter into the 

 potential chemical energy of complex food- 

 stuffs. Animals, on the other hand, get their 

 food ready-made; they take the pounds 

 which plants have, as it were, accumulated 

 in pence, and they spend them. For it is 

 characteristic of animals that they explosively 

 convert the potential chemical energy of food- 

 stuffs into the kinetic energy of locomotion 

 and other activities. In short, the great dis- 

 tinction an average one at best is that 

 most animals are more active than most plants. 

 Changing the point of view a little, we may 

 notice that, because of their mode of nutrition, 

 typical animals are bound to be active and 

 locomotor either in whole or in part. Similarly 



