20 ENVIRONMENT OF PLANTS AND ANIMALS 



ment in the same manner. Air, water, light, a certain amount of 

 heat, soil to live in or on, and food form parts of the surroundings 

 of every living thing. 



The Same Elements found in Plants 

 and Animals as in their Environment. 

 It has been found by chemists that 

 the plants and animals as well as their 

 environment may be reduced to about 

 eighty very simple substances known 

 as chemical elements. For example, 

 the air is made up largely of two ele- 

 ments, oxygen and nitrogen. Water, 

 by means of an electric current, may 

 be broken up into two elements, oxygen 

 and hydrogen. The elements in water 

 are combined to make a chemical com- 

 pound. The oxygen and nitrogen of 

 the air are not so united, but exist as 

 separate gases. If we were to study 



Aa experiment that shows the 

 air contains about four fifths 

 nitrogen. 



Apparatus for separating 

 water by means of an 

 electric current into the 

 two elements, hydrogen 

 and oxygen. 



ihe chemistry of the bodies of plants and animals and of their 

 foods, we would find them to be made up of certain chemical 

 elements combined in various complex compounds. These ele- 

 ments are principally carbon, hydrogen, oxygen, nitrogen, and 

 perhaps a dozen others in very minute proportions. But the 

 same elements present in the living things might also be found 



