76 ELEMEN TARY PHYSIOLOGY. 



should be well understood. Observe it carefully in 

 this manikin (31). The stomach has three coats or 

 walls. The outer coat is thin and smooth, and fitted 

 for the protection of this organ in its contact with 

 other organs. The inner coat called the mucous 

 wall contains many little glands or cells, which 

 secrete a substance which is very important in the 

 process of digestion. It is called the gastric juice. 



When food comes into the stomach the 



intermixing is made quite thorough by 

 the action of the muscles which compose the middle 

 coat of the stomach. As long as there is food 

 within it, these muscles keep up a churning motion 

 of the organ. The result of the action of the gastric 

 juice is that the food is very much changed in its 

 nature and appearance. It is now called chyme, and 

 the change which has been produced in the stomach, 

 chymification. 



At the right end or discharging open- 

 ing of the stomach is placed a muscular 

 valve called the pylorus. This name 

 means gate-keeper. The pylorus is a door-keeper of 

 the stomach. Such portions of the contents of the 

 stomach which have been properly changed into 

 chyme, it allows to pass out, but refuses passage to 

 other portions. Much depends upon the faithfulness 

 of this pyloric muscle. When from any cause it 

 loses its power, or refuses to act, the food escapes 



