A STUDY OF FOODS 



55 



have learned are present in large quantity in foods of vege- 

 table origin, are usually inclosed in cells, the walls of which 

 are formed of indigestible cellulose. Hence, before starch 

 can be digested, it must be freed from this cellulose envelope. 

 This is largely accomplished by cooking, which causes the 

 starch grains to swell. The cell walls are broken open in 

 this way, and when the grains burst, a larger surface is ex- 

 posed to the action of the digestive juices (Figs. 16 and 17). 

 This is strikingly shown in popping corn. The crust of 

 bread is more easily digested than the softer parts, and 

 toasting bread increases still further its digestibility, because 

 this browned starch (sometimes called soluble starch) requires 

 less change before it can be used by the body. 



Boiling Vegetables. Experiments have shown that a good 

 deal of nutrition is lost by boiling vegetables in water. 

 Much of this waste can be avoided, however, if one heeds 

 the following directions : (1) Vegetables should be cooked 

 as far as possible in their peels, for these outside coverings 

 keep the sugar, proteids, and mineral matters from being 



FIG. 16. Cells of Raw Po- 

 tato with Starch Grains 

 inclosed in the Cellulose 

 Walls. 



FIG. 17. Cells of a Potato 

 well steamed and mashed. 

 Starch Grains have been 

 burst by the Heat. 



drawn out by the water; (2) if, however, the vegetables 

 must be peeled and cut up, the pieces should be as large 

 as possible, as a smaller surface is thus exposed to the 

 water; (3) the amount of water should be as small as 



