MOVEMENT OF THE FOOD TUBE 103 



used for cutting or tearing. The long tooth of a dog is an 

 excellent example of a tooth fitted for tearing purposes. 

 Using the diagram, divide the teeth according to their 

 uses, and name them from the chart, as - molars, pre- 

 molars, canines, and incisors. The teeth, with the assist- 

 ance of the tongue, prepare the food for digestion by 

 cutting and crushing it, so that when the tongue pushes 

 it into the gullet, it will be in better condition for digestion. 

 The smaller the particles of food the more surface the en- 

 zymes have to act upon, and consequently the more rapidly 

 digestion takes place in the body. There is, then, a real 

 scientific reason for chewing the food. 



Movement of the food tube as an aid to digestion. 

 Perhaps you have had the experience of losing something 

 held in the mouth by having it slip down the food tube 

 without your being able to get it back again. As this 

 mysterious movement of food through the tube takes place 

 just as well when we are lying down as when we are standing 

 up, it is evidently not due to the force of gravity. The walls 

 of the gullet, the stomach and small intestines are muscular, 

 and are constantly in motion. The stomach itself aids more 

 than the teeth in 

 making the particles 

 of food smaller, for 



the food after it is i ,. . 



swallowed is turned 



Peristaltic waves. 



over and over again 



by the action of this muscular organ, and only very small 

 particles are allowed to go into the small intestine. The 

 large intestine sends along the food by means of wavelike 

 movements. This movement, called peristalsis, occurs in 

 both small and large intestines and is of great importance 



