56 EXPERIMENTAL PHYSIOLOGY 



Examine the mouths of animals, such as the squirrel or 

 rat, the cat or dog, and the horse or cow. How do they 

 differ as to the kind and number of their teeth? What kind 

 of food does each animal eat? Which kind of food requires 

 the most chewing? Do you see any connection between 

 the food and the kind of teeth which predominates in 

 animal? 



B. Structure of a Tooth. Draw J^tion of a molar tooth. 

 Find the following parts : the crown, the neck, roots or fangs, 

 the covering of the crown (enamel), the covering of the fangs 

 (cement), the central or pulp cavity with nerve and blood 

 vessel aperture, the middle layer 

 (dentine). Label all these parts in 

 your drawing. Examine, if possi- 

 ble, the jaw of a human skeleton to 

 show the insertion of the teeth in it. 

 C. The Use of the Teeth. Bite off 

 a piece of apple and chew it. An- 

 swer the following questions: Which 

 teeth are used in the biting off' of 

 the apple? Which to chew it into 

 FIG. 29. A Moiar: k, crown; small pieces? Why are ^these latter 



*S'S** best ada P ted to breakup the food? 



cavity; c, cement. Qf what advantage is it that a 



horse's molars are ridged on the surface? Could you tell 

 from the examination of the teeth the kind of food an ani- 

 mal eats? 



When a tooth decays what part actually decays? What 

 is the difference in the functions of the enamel and of the 

 dentine? How does the location of the nerves in the pulp 

 cavity protect them? Why is a decayed tooth apt to 

 ache? 



