CHAPTER XXXVI 

 FOODS 



Introduction. In construction work the building 

 materials which we use depend upon the kind of 

 building which we expect to erect. Sometimes we use 

 bricks and cement, other times we use wood and nails. 

 From time to time the building, after its completion, 

 needs repair. Parts decay or become worn and have 

 to be replaced by new material ; or, sometimes, additions 

 are made to the original building. 



Much the same principle holds true for the living 

 world, plants and animals. Each plant and each animal 

 is constantly being worn out and being added to. The 

 building materials which are supplied to the plant or 

 to the animal we call food. 



Elements in food. This food, obviously, must con- 

 tain the elements of which the plant or animal is com- 

 posed. Since all living material is much the same in 

 chemical composition, both plants and animals need 

 about the same elements. In the human body those 

 elements which are most common are carbon, hydro- 

 gen, oxygen, nitrogen, calcium, phosphorus, sulphur, 

 sodium, chlorine, fluorine, potassium, and iron. 



Use of food. We need food for exactly the same 



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