XXIV. FOODS AND DIETARIES 



Problem XLII. A study of food values and diets. {Laboror 

 torij Manual , Proh. .YLII.) 

 («-) Food values and cost. 



(b) .yutritive values as compared with cost. 



(c) The family dietary. 



(d) Food values. 



Why we need Food. — ^^W£.Jiave already defined food as anything 

 that forms material for the groiotkior repair of the body of a -plant or 

 animal, or that furnishes energy for it) The millions of cells of which 

 the body is composed must be given material which will form more 

 living matter or material which can be oxidized to release energy 

 when muscle cells move, or gland cells secrete, or brain cells think. 

 Food, then, not only furnishes our body Ti-ith material to grow, but 

 also gives us the energy we expend in the acts of walking, running, 

 breathing, and even in thinking. 



Nutrients. — Certain nutrient materials form the basis of food of 

 both plants and animals. These have been stated to be proteids 

 (such as lean meat, eggs, the gluten of bread), carbohydrates 

 (stai-ches, sugars, gums, etc.), /ate and oils (both animal and vege- 

 table), and mineral matter and water. The parts of the human 

 body, be they muscle, blood, nerve, bone, or gristle, are built up 

 from the nutrients in our food. 



Proteids. — Proteids, in some manner unknown to us, are manu- 

 factured in the bodies of green plants. Proteid substances contain 

 the element nitrogen. Hence such foods are called nitrogenous 

 foods. Man must form the protoplasm of his body (that is, 

 the muscles, tendons, nervous system, blood corpuscles, the living 

 parts of the bone and the skin, etc.) from nitrogenous food. 

 Some of this he obtains by eating the flesh of animals, and some 

 he obtains directly from plants (for example, peas and beans). 

 Because of their chemical composition, proteids are considered to 



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