106 ANIMAI, FUNCTIONS. 



MASTICATION. 



303. This word comes from the Latin mastico, which 

 signifies to chew. Chewing is one of the natural functions 

 of animals, the object of which is to divide the food into 

 minute pieces, and thus to prepare it for passing through 

 the esophagus into the stomach, to undergo the process of 

 digestion. 



304. While the food is masticating, it is at the same 

 time intermixing with a fluid called saliva, which is pre- 

 pared by glands situated around the mouth, and into the 

 cavity of which it is poured through small ducts, coming 

 from the glands by which it is secreted. The action of 

 the muscles concerned in mastication, serve to stimulate 

 these glands; in consequence of which they afford a 

 larger quantity of the fluid at the time when it is most 

 necessary. The same action also facilitates the passage 

 of the saliva into the mouth. 



305. If the mouth had been constructed without this 

 provision for moistening the food, it is obvious that dry, 

 absorbent substances could not have been swallowed ; 

 since it is absolutely necessary, as our experience teaches, 

 to reduce such substances to a soft pulpy mass, before they 

 can be forced through the esophagus. 



306. There is a great difference in the form, structure, 

 position, and number of the teeth of different animals ; all 

 of which bear a direct and intimate relation to the kind 

 of food on which they subsist. Thus the teeth of the lion, 

 the wolf, and the cat, are constructed for tearing the flesh 

 of animals ; while those of the cow, sheep, and deer, are 

 made to crop the tender herbs. 



307. The teeth of the lion could no better perform the 

 office assigned to those of the cow, than the cow could 

 rend the skin, and divide the muscles of a living victim, in 

 the manner of the lion. 



308. Teeth of Man. In the human subject the number 



What is meant by mastication ? Is chewing, a vital, or a natural func- 

 tion? What is the use of mastication? How is the food moistened dur- 

 ing mastication? What is said of the form of the teeth, in relation to the 

 kind of food on which the animal lives ? 



