THE DIGESTION OF FOOD 



III 



157. Digestion in the Stomach. The moment the food 

 reaches the stomach, the muscles begin to contract, and a 

 spiral wave of motion begins, becoming more rapid as 

 digestion goes on. The food is 



rolled over and over, and thor- 

 oughly mixed with the gastric 

 juice. Two rings, one at the 

 entrance and the other at the out- 

 let, keep the food in the stomach 

 while it is being churned about 

 and digested. 



158. The Gastric Juice. Soon 

 after food enters the stomach, 

 drops of fluid collect at the 

 mouths of the gastric glands 

 and trickle down its walls to 

 mix with the food. This fluid is 

 known as the gastric juice. 



The gastric juice is a clear, almost colorless fluid, with a 

 sour taste and odor. It contains a peculiar substance called 

 pepsin, and an acid, both of which are necessary to the 

 digestion of food in the stomach. The amount of gastric 

 juice has been variously estimated, all the way from five 

 to fourteen pounds daily. 



Experiment 34. To show how the wall of the stomach looks. 

 The wall of the pig's stomach resembles^ that of the human stomach. 

 Get from the market a piece of a pig's stomach. Cut off bits of it 

 and examine it thoroughly with a hand lens. Scrape off the inner, 

 or mucous, coat with the edge of a very sharp knife. Find the 

 openings of the gastric tubes with the help of a magnifying glass. 

 Pick with fine needles until the fibers of the muscular coat are 

 found. Contrast the appearance of the pig's stomach with that of 

 a cow by examining a piece of tripe. 



FIG. 72. The Inner Surface 

 of the Stomach, from which 

 the Epithelium has been re- 

 moved, showing the Open- 

 ings of Gastric Glands. 

 Magnified 20 diameters. 



