104 STUDIES IN PHYSIOLOGY 



mouth, throat, and gullet all have a moist surface generously 

 supplied with blood vessels, the food does not lie next the 

 mucous membrane for any considerable time, and therefore 

 the amount of absorption in these regions is not great. If 

 one eats slowly, some of the dissolved salts and sugars and 

 water are probably absorbed before reaching the stomach. 



Absorption in the Stomach. In the stomach the food usu- 

 ally remains for several hours, and one would therefore 

 expect that a good deal of absorption would take place during 

 this time. But we must remember that the contraction of 

 the gastric muscles keeps the food in constant motion. This 

 movement, while favorable for digestion, diminishes absorp- 

 tion, because the liquefied food does not remain long enough 

 in one place to soak into the blood. 



Absorption in the Small Intestine. We therefore find that 

 most of our food passes out of the stomach before it is 

 absorbed. In the structure of the small intestine, however, 

 we seem to find every possible provision for gathering up 

 the nutrients. The amount of surface is greatly increased 

 by the crescent-shaped ridges, and still more by the villi, 

 thousands of which project from every square inch of the 

 mucous lining. As the souplike food mass is pushed slowly 

 along through the small intestine, it becomes less and less 

 in bulk, and more and more solid, owing to the fact that the 

 dissolved salts, sugars, peptones, and fats are largely taken 

 up by the blood vessels and lacteals within the villi. 



Absorption in the Large Intestine. The amount of absorp- 

 tion in the large intestine is considerably less, of course, for 

 both villi and crescentic ridges are wanting. Yet even here 

 considerable absorption takes place. When the mass in the 

 intestine reaches the rectum, it consists of little but the 

 indigestible cellulose of vegetable foods, some undigested 

 connective tissue, waste substances from the bile, the solids 

 in the mucous secretion, and some raw starch and fats if 

 large quantities of these nutrients have been eaten. This 

 refuse of the food is thrown off from the body. 



