CHAPTER V 



DIGESTION OF FOOD: THE MOUTH AND THROAT 



FIG. 35. SCALE- 

 LIKE CELLS FROM 

 THE LINING OF THE 

 MOUTH 



IN their original condition most of our foods are of no more 

 value to the body than are the trees of the forest or the stones 

 of the quarry to the builder, good as raw 

 material, but not immediately available. 

 Before they can be taken into the blood 

 they must be softened, ground up into 

 small bits and at least partially dissolved 

 into liquid form. This process is a long 

 one beginning, perhaps, when the food 

 is in the hands of the butcher or miller, 

 and carried further, by some process 

 of cooking. The chief part of this prep- 

 aration, however, is performed by the alimentary canal, 

 whose main function is to grind and dissolve the food masses 

 into readiness for absorption. This process of disintegra- 

 tion is partly mechanical and partly chemical, and we call 

 it digestion. The digestive canal is, in a sense, a chemical 

 laboratory. 



THE MOUTH 



The preparation of food for absorption begins in the mouth. 

 The whole mouth cavity is lined with a smooth, moist mem- 

 brane, consisting of cells (Fig. 35), which secrete a transparent 

 liquid somewhat thicker than water and called mucus. 

 Mucus is of no value as a factor in digestion, but it keeps the 

 lining membranes soft and flexible, and lubricates dry foods 



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