VEGETABLE FOODS. 



165 



albumen, 2 per cent, fat, 53 per cent. carbo-h}'drates, and 17.5 per cent, 

 cellulose. 



The preparation of bread depends upon the fermentation produced 

 through the action of the yeast-plant in rye- or wheat-meal mixed to a 

 thick paste with water, the so-called dough, and allowed to ferment at 

 about 30 C. Through the action of the yeast part of the starch is 

 converted into dextrin and sugar, of which a part again undergoes 

 further decomposition into carbon dioxide and alcohol. The bubbles of 

 the former serve to render the dough light and porous. In baking the 

 gas-bubbles expand through the heat and render the bread still more 



FIG. 55. SECTION OF A WHEAT-GRAIN, MAGNIFIED 610 DIAMETERS, AFTER 



PEKAR. (Thanhoffer.) 

 1, epidermis ; 2, epicarpium ; 3, endocarpium ; 4, testa ; 5, tegmen ; 6, perisperm ; 1, endosperm. 



porous, and therefore more permeable to the digestive juices and more 

 readity digestible, while in the action of the heat a certain amount of 

 starch is still further converted into dextrin and sugar. The nutritive 

 properties of bread depend upon the starch, dextrin, sugar, and 

 albumen which are contained within it. Bread, therefore, contains all 

 the nutritive principles in some amount, as a certain amount of oils and 

 inorganic salts are also present, although the carbohydrates are present 

 in the largest proportion. It has been estimated that a man, to obtain 

 the necessary amount of albumen required for his daily ration, would 

 have to consume three pounds of bread daily. 



Oats, rye, and corn also have their various constituents arranged 



