CHAPTER XIV 



Nitrogen 



MAN'S EXISTENCE AS RELATED TO PLANT AND 

 ANIMAL LIFE, FOODS, 



Fundamental Foods. The elements which enter into 

 the structure of the human body, such as oxygen, hydrogen, 

 nitrogen, carbon, etc., are comparatively few and are abun- 

 dant in the world about us, either separately or in compounds. 

 But with all of man's ingenuity, he has never learned to 

 manufacture these ele- 

 ments into compounds Sulphur 

 that will serve as food for 

 the human body. 



The leaves of plants 

 are the fundamental food 

 factories of the world. 

 Here carbon, hydrogen, 

 and oxygen are united by 

 the aid of the sun into 

 plant foods called carbohy- 



r I 

 horusl 



tm \ 



0ygen 



PROPORTIONS OF ELEMENTS IN COMPOSI- 

 TION OF LIVING THINGS 



j 4 , T? 4 A 4 ' 

 drates. Fate and proteins 



are two other kinds of 



foods that are also manufactured in the bodies of both 

 plants arid animals, but the carbohydrates are the original 

 material out of which the living organism, whether plant 

 or animal, first produces fats and proteins. 



Air, water, and salt are necessary to the processes of life, 



425 



