XXV. DIGESTION AND ABSORPTION 



Purpose of Digestion. We have learned that starch and proteid 

 food of plants are formed in the leaves. A plant, however, is 

 unable to make use of the food in this condition. Before it can 

 be transported from one part of the plant body to another, it is 

 changed into a soluble form. In this state it can be passed from 

 cell to cell by the process of osmosis. Much the same condition 

 exists in animals. In order that food may be of use to man, it must 



be changed into a state that 

 will allow of its passage in a 

 soluble form through the walls 

 of the alimentary canal, or 

 food tube. Digestion consists 

 in the changing of foods from 

 an insoluble to a soluble form, 

 so that they may pass through 

 the walls of the alimentary canal 

 and become part of the blood. 



Problem XLV. Study of 

 the digestive system of a frog 

 in order better to understand 

 that of man. (Laboratory 

 Manual, Prob. XLV.} 



Alimentary Canal. In all 

 vertebrate animals, including 

 man, food is normally taken in 

 the mouth and passed through 

 a food tube during the process 

 of digestion. This tube is 

 composed of different portions, 

 named, respectively, as we 

 the gullet, stomach, small and 



Picture of the organs of digestion : a, in- 

 testine, leading out of the pylorus ; b, liver ; 

 c, esophagus ; d, 'pancreas ; e, stomach ; 

 /, spleen ; g, i, j, k, m, n, parts of large 

 intestine : h, I, small intestine. (From 

 Johonnot and Bouton.) 



pass from the mouth, posteriorly, 

 large intestine, and rectum. 



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