CHAPTER VI 



SOME FAMILIAR FOODSTUFFS SOME 

 IMPORTANT TISSUES 



Some Important Foodstuffs 



The substances considered in the preceding chapters are for 

 the most part foodstuffs. It will be worth while, however, to 

 consider some of the familiar substances usually called ' ' foods. ' ' 

 Most of these materials consist of a mixture, often of several 

 of the classes or individuals of the material bases. We may ask 

 the question, "What is a food?" In a broader sense a food 

 may be denned as any substance which is required by the body. 

 This would include oxygen from the air, water, and inorganic 

 salts, in addition to carbohydrates, fats, proteins, etc. But some 

 substances which are excellent foods, are not indispensable to 

 the body, for example sugar. The body tissues are constantly 

 wearing out and requiring repair. Materials for such repair of 

 worn out tissues, or for the building of new ones, as in growth, 

 are obtained from foods. Also, the body is constantly doing 

 work, either external work, or the work of the heart, the diges- 

 tive organs, glands, etc. Work cannot be done without the 

 expenditure of energy. This energy is obtained by oxidizing, 

 "burning," material derived either directly or indirectly from 

 the foods. Some substances can be burned in the body, but 

 still are harmful because of a poisonous effect upon the cells; 

 such substances should not be classed as foods. Summing up 

 the foregoing statements, a food may be defined as a substance 

 which is necessary to the body or which furnishes it with 

 energy or building material, and which is not harmful to the 

 organism. 



Water and salts, which are very important foods have been 



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