NEEDS OF THE ANIMAL 355 



the body. The process of making food liquid is called 

 digestion. Let us see how some simple food, such as 

 wheat, is digested or made liquid in the body. 



If you chew grains of wheat, they soon begin to taste 

 sweet, because some of the starch of the wheat has been 

 changed into sugar. The saliva of the mouth contains 

 a substance which has the power of helping to change 

 starch into sugar. The sugar dissolves or becomes 

 liquid in the water of the mouth. Substances which 

 have the power to make foods liquid are called ferments, 

 and they are of the very greatest importance to all 

 living things, both plants and animals. 



After chewing the wheat a little longer a white 

 gummy substance remains. This substance is gluten 

 (protein), the muscle-making part of the wheat (see 

 page 273). The saliva softens this, but cannot make it 

 liquid. When it is swallowed, it passes down through the 

 gullet into the stomach (which is merely a pear-shaped 

 sac, holding about three pints when moderately filled). 

 By its motion the stomach churns the food and mixes 

 it with a ferment (called pepsin) which helps to make 

 protein liquid. The pepsin, together with acid and 

 other substances secreted by the stomach, forms the 

 gastric juice. 



The fat of the wheat is not digested in the mouth or 

 stomach, but passes unchanged into the small intestine. 

 Into this the pancreas, or sweetbread (a tongue-shaped 

 organ about six inches long, lying close to the stomach), 



