PARTS OF THE DIGESTIVE TRACT 367 



excellent dental wash. If one has an acid mouth, a good tooth 

 paste mixed with castile soap may be used to clean the teeth. 



The teeth should be cleaned by a reliable dentist at least every 

 six months. In this way deposits which cover the teeth may be 

 removed and decay prevented. If decay once starts, sooner or 

 later the tooth will be lost. 



Practical Exercises 3. What are the uses of (a) the incisors, (6) the canines, 

 (c) the premolars, and (d) the molars ? 



How many teeth are there in the first set of teeth? When do they begin to 

 come, and when do they go ? 



What makes teeth decay ? Why should we clean the teeth night and morn- 

 ing ? How should we brush them ? 



What is a focal infection ? What harm may it do ? What harm might 

 come from swallowing fluids which pass through a mouth containing decayed 

 teeth? 



How often should one visit the dentist ? Why ? 



Self-Testing Exercise 



Food passes from the (1) into the (2) and (3) 



on its way to the stomach. The enzymes in (4) change 



(5) to sugars. A tooth is composed chiefly of (6). 



The crown of the tooth is covered with (7). The interior of 



the tooth is called the (8) (9). A decayed tooth 



may be the source of a (10) (11). The saliva 



contains the enzyme, (12). 



PROBLEM m. WHAT ARE THE PARTS OF THE DIGESTIVE 



TRACT? 



If we are to understand the work of the parts of the food tube, 

 it is necessary that we know something about their structure. 

 One can learn about the digestive tract through the study of charts 

 or models, but it is much easier to understand if we can see its 

 parts as they would really appear in a living person. This we 

 cannot do, but we have a good substitute in the frog. Let us 

 examine the digestive tract of a frog in order to compare it with 

 man. 



Laboratory Exercise. To compare the digestive system of a frog 

 with that of man. 



Opened frogs preserved in 4 per cent formalin. Manikin showing- 

 digestive tract. 



