CHAPTER XII 

 FOOD 



331. Proteids, or Albuminoids. It was learned in an 

 early chapter that protoplasm, the basic life substance, 

 is not always the same in composition, but there is one 

 material that is always found in it and is the test by which 

 it is known to be protoplasm, and that is albuminous 

 material. It was learned in Chapter II that albumin 

 always contains nitrogen, the most inert and inactive of the 

 elements, and that albumin gives strength and stability to 

 the cells and tissues. The fibers of connective tissue, for 

 instance, are albumin. It is the great tissue-building 

 material, and as the activities of cell life are constantly 

 using up the materials of the cells, we are not surprised 

 that albuminous or nitrogenous food is reckoned as the 

 most essential of all foods for sustaining animal life. 

 Albuminous foods are commonly called pro'te-ids, or pro- 

 te-in foods (Greek protos, first or most important). 



332. Carbohydrates, or Sugars and Starches. Why are 

 roasting-ears sweet, although mature corn is not? It is 

 because the sugar in the first has been changed to starch 

 in the second. On the other hand, ripe apples are sweet 

 because the starch of green apples has been changed to 

 sugar. Starch and sugar are so nearly alike in composi- 

 tion and change so readily into each other, that as foods 

 they are classed together. It was learned in Chapter IX 

 that the sugar in the blood -is diminished by muscular 

 exertion. The oxidation of the sugar is accompanied also 



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