DIETETICS. 105 



When the yeast has been allowed to act for some time, or if 

 baking powder was used, when the gas formation has ceased, suit- 

 able portions (loaves) of dough are placed in the oven. The heat 

 causes the inclosed bubbles of gas to expand so that the whole 

 mass becomes aerated and further increase of temperature acts 

 on the proteins and starches on the surface coagulating the for- 

 mer and converting the latter into dextrins. Thus is the crust 

 formed. Brown bread is made from wheat from which all the 

 husk has not been removed. There are two possible advantages 

 of this over white bread, namely, the husks act as a mild laxative 

 and they seem to contain traces of vitamines (see p. 121). 



Other Cereals. These include maize or Indian corn, oatmeal 

 and rice, and differ from wheat in that their proteins do not form 

 gluten when mixed with water. They cannot therefore be formed 

 into bread unless they be mixed with some wheat flour. They are 

 relatively rich in ash and maize contains a large proportion of 

 fat. When rice composes a large proportion of the diet, as is the 

 case in tropical countries, the unpolished variety should be used 

 to supply the vitamines. When the diet is a mixed one, however, 

 danger of an insufficiency of vitamines cannot exist. As has 

 been already explained, the protein of cereals is not of first qual- 

 ity, because it does not contain all of the ammo acids (building 

 stones) of tissue proteins. 



Milk and Milk Preparations. Whole milk is as nearly as 

 possible a perfect food, for its protein is of the first quality and 

 it contains a sufficiency of fats and carbohydrates for the growth 

 of the tissues. Where muscular exercise must also be performed, 

 carbohydrates should be added to the milk, and this is best ac- 

 complished by the use of cereals. Milk is an economical food, 

 for one quart nearly equals in nutritive value a pound of steak 

 or eight or nine eggs, and is easily digested and assimulated, but 

 somewhat constipating. The chief protein of milk is caseinogen 

 (phospho protein) and is characterized by being precipitated 

 by weak acids and by the action of gastric juice. When milk soul's 

 some of the milk sugar, or lactose, becomes converted by bacterial 

 action into lactic acid and this precipitates caseinogen. When 

 an extract of the mucous membrane of the stomach is added to 



