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TEXT-BOOK OF PHYSIOLOGY. 



woody fiber which envelops and penetrates the grain, they are some- 

 what difficult of digestion. A section of a grain of wheat shows the 

 external cellulose envelope, the husk, beneath which is a layer of large 

 cells containing the chief proteid the gluten. The interior of the 

 grain consists of small cavities, the walls of which are formed of cellu- 

 lose and which contain the granules of starch, fat, small quantities of 

 proteid, and inorganic salts. All other cereals have a similar structure. 



In the preparation of white flour from wheat it is customary to 

 remove the husk, a process which involves the removal also of a por- 

 tion, if not all, of the gluten cells, so that such flour contains less nitrog- 

 enized material than the original grain. It is possible, however, in 

 the milling of wheat, to remove only the husk and retain the gluten in 

 the flour, as in the preparation of whole wheat flour. 



Bread is an artificially prepared food made either of wheat or 

 rye. Owing to the fact that the proteids of the other cereals do not 

 possess the same adhesive properties when kneaded with water, they 

 can not be used for bread-making purposes. In the making of bread, 

 the flour is kneaded with water until a glutinous mass dough is 

 formed. During this process, salt, sugar, and yeast are added. It 

 is then placed in a temperature of about 100 F. In the presence of 

 heat and moisture the natural ferment of the flour diastase con- 

 verts a portion of the starch into sugar, which in turn is split up into 

 carbon dioxid and alcohol by the yeast plant. The bubbles of 

 carbon dioxid, becoming entangled in the dough, cause it to swell 

 or rise and subsequently give the porous or spongy character to the 

 bread. When baked at a temperature of 400 F., the alcohol is 

 driven off; yeast cells and other organisms are destroyed; the starch, 

 particularly that on the surface, is dextrinized. Thus prepared, 

 white bread consists of water, 32 per cent.; proteid, 8.8 per cent.; 

 fat, 1.7 per cent. ; carbohydrate, 56.3 per cent. ; salts, 0.9 per cent. The 

 principal salts are potassium and magnesium phosphate. Whole 

 wheat bread consists of water, 40 per cent.; proteid, 12.2 per cent.; 

 fat, 1.2 per cent.; carbohydrate, 43.5 percent.; salts, 1.3 percent.; 

 cellulose, 1.8 per cent. 



Composition of Vegetable Foods. The average composition 

 of some of the principal vegetables is shown in the following table : 



