124 THE INVISIBLE WORLD 



of oxygen are taken from the atmosphere every 

 day. 



But, day by day, moment by moment, all this 

 stream of vital fluid, is poured back again into the 

 air. While in the breathing organs of all animal 

 life oxygen seizes upon the waste material, or used 

 up carbon, loads up with it, and returns to the 

 air as carbon-dioxide. While in the flame of every 

 fire that burns oxygen seizes the carbon of the fuel, 

 loads up with it, and returns to the air, as carbon 

 dioxide. While, too, in every slow fire of decaying 

 vegetable or animal body oxygen again seizes the 

 carbon of that body and carries its burden back to 

 the air as carbon dioxide. 



Then, all this carbon dioxide returned to the 

 air, day by day, moment by moment, yields up its 

 carbon as food to the vegetable kingdom, and, day 

 by day, moment by moment, the 7,000,000 tons of 

 oxygen are being set free in the air, ready to speed 

 again on its journey through the rounds of its 

 food cycle. 



So as the air presses deeply into the soil, great 

 quantities of its nitrogen are absorbed by the roots 

 of plants as food. As animals devour the plants, 

 the nitrogen becomes a part of their systems. As 

 plants and animals die, and their bodies are de- 

 composed, all this nitrogen is liberated, and again 

 finds its way into the soil, ready for another round 

 in its food cycle. 



All these food cycles are constant, eternal. No 

 break in the endless chains. To their keeping is 



