116 



DIGESTION 



3. General Plan of Digestion. The great change which food 

 undergoes in digestion is essentially a refining process, re- 

 ducing articles of diet, which are at first more or less solid, 

 crude, and coarse, to a liquid and finely comminuted condition, 



suitable for absorption into the blood. 

 The entire process of digestion takes 

 place in what is called the " alimen- 

 tary canal," a narrow, crooked tube, 

 about thirty feet in its entire length. 

 This canal begins in the mouth, ex- 

 tends thence downward through the 

 gullet to the stomach (a receptacle in 

 which the principal work of digestion 

 is performed), and thence onward 

 through the small and large intes- 

 tines. 



4. The stomach and intestines are 

 situated in the cavity of the abdomen 

 (Fig. 22, C, and Fig. 28), and occupy 

 about two-thirds of its space. The 

 action to which the food is subjected 

 in these organs is of two kinds 

 mechanical and chemical. By the 

 former it is softened, agitated, and 



FIG. 22. -SECTION OF THE TRUNK, carried on ward from one point to 

 SHOWING THE CAVITIES OF THE another j by the latter it is changed 



CHEST AND ABDOMEN 



A, chest c, Abdomen in f orm through the solvent power of 



B, Diaphragm D, Spinal Column the Vai'ioUS digestive fluids. 



E, Spinal Cord 



5. Mastication. As soon as solid 



food is taken into the mouth, it undergoes mastication or 

 chewing. It is caught between the opposite surfaces of the 

 teeth, and by them is cut and crushed into very small frag- 

 ments. In the movements of chewing, the lower jaw plays 

 the chief part; the upper jaw, having almost no motion, acts 



8. Change of food in digestion ? Process of digestion ? Describe the alimentary canal. 



4. Situation of the stomach and intestines ? Action of the food ? Mechanical action ? 

 Chemical ? 



5. Describe the process of mastication. IJow many and what movements ? 



