340 



HUMAN PHYSIOLOGY 



Experiment. — Place filter paper within each of two funnels. In one 

 funnel, wet the filter paper with water. In the second, wet the paper with 

 ox gall dissolved in water (equivalent to bile) . Place olive oil in each funnel. 

 Through which filter does the olive oil pass with greater rapidity ? 



Formation of Glycogen. — Another important function of the liver 

 (which may be taken up in connection with the circulation of the blood) is 

 the formation within it of a material called glycogen or animal sugar. The 

 liver is supplied by blood from two sources. The greater amount of blood 

 received by the liver comes directly from the walls of the stomach and intes- 

 tine to this organ. This blood is very rich in food materials, and from it the 

 cells of the liver take out sugars to form glycogen. Glycogen is stored in the 

 liver until such a time as a food is needed that can be quickly oxidized; 



then the glycogen is carried off by the 

 blood to the tissue which requires it and 

 there used for this purpose. 



The Absorption of Digested Food 

 into the Blood. — The object of diges- 

 tion is to change foods from an in- 

 soluble to a soluble form. This has 

 been seen in the study of the action 

 of the various digestive fluids in the 

 body, each of which is seen to aid in 

 dissolving solid foods, changing them 

 to a fluid, and, in case of the bile, 

 actually assisting them to pass through 

 the wall of the intestine by osmosis. 

 A YQvy small amount of digested food 

 may be absorbed by the blood in the 

 blood vessels of the walls of the stom- 

 ach. Most of the absorption, how- 

 ever, takes place through the walls of 

 the small intestine. Let us examine 

 this structure somewhat closely to 

 see how it is adapted to absorb liquid 

 food. 



A much magnified section through 

 the wall of the small intestine 

 (after Benda). A, B, transverse 

 folds of intestine covered with 

 the fingerlike villi ; note the very 

 great absorbing surface thus 

 gained; C, connective tissue; 

 D, E, circular and longitudinally 

 running muscle fibers. 



Structure of the Small Intestine. — . 

 The small intestine in man is a slender 

 tube nearly twenty feet in length and about one inch in diameter. Its 

 walls contain muscles which, by a series of slow waves of contraction, force 



