THE ANIMAL IN THE WORLD 



537 



its activity is to provide an accumulation of those complex 

 substances which form a necessary part of the food of 

 protoplasm. At the same time it sets free oxygen. The 

 animal, on the other hand, obtains the organic food for its 

 protoplasm by consuming the substances manufactured by 

 plants, either directly from the plant body or after they have 

 been incorporated in a somewhat altered form into the proto- 

 plasm of other animals. In the protoplasm of the animal 

 these substances undergo destruction. Thus the animal 

 destroys organic material without, like the plant, manu- 

 facturing from inorganic matter more to replace it. The 



Rays of the sun absorbed by plants. 



Stored energy of plant substances. 



J 



Stored energy of 

 animal substances. 



Energy freed in 

 the life of plants. 



Energy freed in the life of animals. 

 FIG. 395. — A diagram of the energy of organisms. 



net result of its life is to lessen the amount of organic 

 matter in the world. At the same time it sets free 

 carbon dioxide and simple nitrogen compounds. Thus 

 plants provide food and oxygen for animals, while animals, 

 destroying this food, provide simple nitrogen compounds 1 

 and carbon dioxide for the use of plants. The result is a 

 circulation of nitrogen and of carbon through the bodies of 

 organisms. It will be seen that this circulation of matter 

 is accompanied by a transference of energy. The whole 

 of the energy of the life both of plants and of animals is 

 derived in the long-run from the energy of the sun's rays 



1 These are usually not available for the use of plants till they have 

 been altered by the action of bacteria in the way mentioned on p. 536. 



