DIGESTION OF FOOD: THE MOUTH 



83 



In eating, food is usually kept for so short a time in the 

 mouth, is so imperfectly chewed and broken up that the 

 ptyalin solution acts upon only a small portion of the starch. 

 iSaliva does not at all affect other foods, i.e. fats or proteids. 

 In its chemical reaction it is slightly alkaline, due to traces 

 of inorganic salts. Ptyalin will not act at all if the food mass 

 is acid, as when it is mixed with vinegar. 



THE THROAT 



The Pharynx. Back of the mouth and partly shut off 

 from it is a considerable cavity called the pharynx, or throat, 

 through which food must go before it reaches the gullet; 



Citfa 



FIG. 43. CILIATED CELLS THAT 

 LINE THE PHARYNX 



Fig. 40. In a person of average 

 size this cavity is about four and 

 a half inches in length and of 

 varying width. 



It is partly shut off from the 

 mouth by the tongue below, by 

 the soft palate and uvula above, 

 and by the pillars of the fauces 

 at the sides. These last are ver- 

 tically placed folds of tissue which can be easily seen by 

 opening the mouth widely before a mirror. They are 

 somewhat like thick curtains hanging down at the sides of 

 the opening into the throat. 



The Tonsils. To one who thinks that there is a use for 

 everything in the world, it is interesting to find that there 

 are several structures in the human body which are appar- 

 ently of no value. Among these are the tonsils, which are 

 frequently removed by a slight surgical operation. These 

 growths are located on each side of the passage from the 

 mouth to the throat, one between each pair of the pillars of 

 fauces; Fig. 40. They vary much in size, though in most 

 cases they are about as large as half a walnut. From their 



dtion they are much exposed tQ currents of air taken iii 



