STOMACH OF MAN 



153 



Opening into 

 stomach 



After food leaves the mouth cavity, it gets beyond our direct con- 

 trol, and the muscles of the gullet, stimulated to activity by the 

 presence of food in the tube, push the food down by a series of con- 

 tractions until it reaches the stomach. These wavelike movements 

 (called peristal' tic movements) occur also in other parts of the food 

 tube, food being pushed along in the stomach and the small intes- 

 tine by a series of these slow-moving muscular waves. Peristaltic 

 movement is caused by muscles which are not under voluntary 

 nervous control, although anger, fear, or other unpleasant emotions 

 have the effect of slowing them or even stopping them entirely. 



Stomach of Man. — The stomach is a pear-shaped organ capable 

 of holding about three pints. The end opposite to the gullet, 

 which empties into the small intestine, is provided with a ring of 

 muscle called the pylo'rus. When this muscle relaxes, it permits 

 the passage of food from the stomach. 

 There is also another ring of muscle 

 guarding the entrance to the stomach. 



Gastric Glands. — If we open the 

 stomach of a frog and remove its contents 

 by careful washing, its wall is seen to be 

 thrown into folds internally. Between 

 the folds in the stomach of man, as well 

 as in the frog, are 1 ocated a great number 

 of tiny pits. These form the mouths of 

 the gastric glands, which pour into the 

 stomach a secretion known as the gastric 

 juice. The gastric glands are little tubes, 

 the lining of which secretes the fluid. 

 When we think of or see appetizing food, 

 this secretion is given out in considerable quantity. The stomach, 

 like the mouth, " waters " at the sight of food, as the glands are 

 controlled by nerves. Gastric juice is slightly acid in its chemical 

 reaction, containing about 0.2 per cent free hydrochloric acid. It 

 also contains two enzymes : one very important, called pepsin^ and 

 the other, less important, called rennin. Rennin curdles or coagu- 

 lates a protein found in milk ; after the milk is curdled, the pepsin 

 is able to act upon it. " Junket " tablets, which contain rennin, 

 are used sometimes in the preparation of a dessert from milk. 



Neck of 

 gland 



H CI secreting eel/ 

 on inner margin 

 of gland 



Cells secreting 

 fluid containing 

 pepsin 



Body of gland 

 where most of 

 secreting is 

 done 



A gastric gland. 



