CHAPTER XII 

 DIGESTION 



Food 



IF bread is analysed it is found to consist of various chemical 

 substances. One of these substances is called glutin. Glutin 

 is a proteid, that is, it is very like the substance albumin and the 

 substance globulin which we have already spoken of as present 

 in blood. Bread also contains starch and a small amount of 

 sugar. These substances mixed in certain proportions with 

 water and a small quantity of certain salts make up bread. 

 In the same way, if lean meat, which is muscle, is examined, it 

 is found to consist largely of proteid matter, with fat and salts, 

 there being also present a considerable amount of water. The 

 substances which are thus found in foods, food-stuffs, as 

 they are called, fall into the following classes. 



1. Proteids. The chief proteids are: 



Glutin, found in flour and all cereals, peas, beans, potatoes. 

 Albumin, found in the white of egg, milk, blood. 

 Globulin, found in yolk of egg, blood. 

 Myosin, found in lean meat. 

 Casein, found in milk, cheese. 

 Fibrin, found in clotted blood. 



Gelatin, obtained from bones, tendon, etc., and chondrin, 

 obtained from cartilage, are substances very like proteids. 



2. Carbohydrates. Examples : 



Starch, found in flour and all cereals, rice, potatoes. 



Sugar, found in bread, potatoes, milk, fruits. There are 

 several different kinds of sugar which, although very 

 like each other, are different chemical substances. The 



