74 FOOD MATERIALS 



in an outer covering, or capsule, of hard cellulose. Just 

 within the capsules lie large cells which contain the 

 proteid part of the wheat, the gluten. The rest of the 

 kernel consists mainly of starch cells, which lie in a fine 

 meshwork of cellulose. In addition, each kernel con- 

 tains an embryo plant for which the starch and gluten 

 have been prepared as food and which is itself nutritious. 

 Certain of the cereals, especially wheat, oats and corn, 

 are of special value as foods, because they contain about 

 the right proportions of proteid and starch for a full 

 diet. With the addition of a hydrocarbon in the form 

 of butter or oil, an almost complete food l may be 

 obtained. 



Bread. Bread 2 is a favorite method of using cereals, 

 especially wheat, because of its ease of digestion and its 

 agreeable flavor. Its digestibility depends upon its 

 sponginess, which is due to the myriads of small bubbles 

 caught in the dough because of the tenacity imparted 

 to it by the gluten. The bubbles themselves are ordi- 

 narily produced by yeast, which consists of a large num- 

 ber of microscopic one-celled plants. These develop 

 rapidly in the warm dough and during their growth give 

 off bubbles of carbon dioxide. 3 



The fact that wheat flour makes a light bread has 

 caused the other cereals which do not make so light a 

 bread, to be undervalued as food, when, as a matter of 



1 A complete food is one that furnishes in their proper pro- 

 portions all the carbohydrate, hydrocarbon and proteid necessary 

 to sustain life and activity. " According to recently accepted 

 standards, bread and butter lack only a small amount of proteid. 



* There are many kinds of bread, both leavened ( raised ) and un- 

 leavened. A primitive form is a mere flour paste baked by being 

 spread thinly upon a hot stone. Certain hard crackers resemble 

 this. 



8 Carbon dioxide may also be produced by the union of the two 

 chemicals cream of tartar and bicarbonate of soda, as in the best 

 baking powders. 



