DIGESTION 



21 



into two parts by a sheet of muscle called the diaphragm. 



The upper part is called the chest or thorax, and holds the 



esophagus, lungs, and heart. The lower part is called the 



abdomen, and holds the stomach, intestine, liver, pancreas, 



and kidneys. The stomach is a thin bag of muscle lying 



upon the left side of 



the body, just under the 



lowest ribs. It is lined 



with mucous membrane, 



which contains very 



small tubes. These 



tubes are glands which 



produce a fluid called 



the gastric juice. The 



stomach squeezes and 



stirs the food about in 



a gentle manner, and 



mixes it with the gastric 



juice, so that in the 



course of an hour or two 



the food is ground and 



mixed, much as it was 



in the mouth. 



30. The gastric juice. 

 The glands produce 

 about three quarts of 

 gastric juice daily. It 

 is mostly water, but it 

 contains a small amount 

 of a sour substance called hydrochloric acid, and of a white 

 substance called pepsin. These two substances eat away 

 or dissolve albumin, so that it becomes soft, and finally 

 fully dissolves in the water of the gastric juice. Digested 



Diagram of second part of swallowing. 



a top of tongue arched backward and up- 

 ward. 



b pharynx. 



c morsel of food pushed into the pharynx by 

 the back of the tongue. 



d sliding doors of the pharynx which have 

 come together in the middle. 



e soft palate lifted upward to shut off the nose. 



/ epiglottis folded downward to close the 

 larynx. 



