CH.VIII FROM THE ALIMENTARY CANAL TO THE HEART 97 



pick up those things that may enter the blood. There 

 is no way of getting from the alimentary canal into the 

 blood except by passing through this membrane. 



77. Absorption. Foods in the form of a liquid can 

 pass through the mucous membrane in any part of the 

 alimentary canal, through the delicate walls of the blood 

 capillaries, and become part of the plasma. The word 

 absorption refers to this soaking through the walls, but 

 it is not simply a soaking process, for the cells are active 

 in picking up the little particles of food and passing 

 them on into the plasma of the blood. We know that 

 the sap of trees goes up through the little plant cells to 

 the leaves by passing from cell to cell by a process 

 called osmosis. Now, in a similar way, the foods enter 

 the plasma. We may say that absorption is in part 

 soaking through the walls, in part osmosis, and in 

 part due to the action of the living cells of the walls 

 themselves. 



Foods may be absorbed all along the alimentary canal, 

 but there are some places where absorption occurs more 

 readily than at others. TJie largest amount is absorbed 

 from the small intestine. Here we have a very large 

 surface of mucous membrane so made as to favor rapid 

 absorption of all kinds of foods. Next in importance 

 is the large intestine, where water and salt are absorbed 

 chiefly. Water, salt, some sugars, and some peptones 

 may be absorbed from the stomach, but the amount is 

 comparatively small. A very little water, salt, and sugar 

 may enter the blood from the mouth and even from the 

 oesophagus. 



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