CHAPTER XV 

 INTESTINAL DIGESTION. ABSORPTION 



The three secretions which enter the intestine are 

 all alkaline. It does not follow that the contents will 

 be alkaline throughout for there are sources of acidity 

 to be reckoned with. Three of these are notable: there 

 is the acid received from the stomach, more which is 

 formed by the continued fermentation of sugars in the 

 intestine, and still more formed in the normal diges- 

 tion of fats. All these acids may react with the car- 

 bonate of soda present in the juices and there may be 

 an excess of acid in some sections of the canal. But the 

 average condition is not far from neutral. 



Immediately below the stomach the acid material 

 meets the inflowing bile and the pancreatic juice together 

 with some of the succus entericus. When acid reacts 

 with carbonate of soda an evolution of carbon dioxid 

 is to be expected and if this is too abundant to be held 

 in solution there will be an actual effervescence. It has 

 been thought that this may be a useful factor, lightening 

 the texture of the food particles as the gas bubbles in 

 the dough lighten the loaf. 



Movements of the Small Intestine. Four or five 

 hours after a meal the stomach will probably be thrust- 

 ing out the latest portions of its contents to the duo- 

 denum. At about the same time the foremost frac- 

 tions may be entering the large intestine. It is then 

 that food may be undergoing digestion in every loop 

 of the small intestine while absorption will be at its 

 height. The average rate of progress in the intestine 

 is evidently not more than an inch in a minute. This 

 is vastly slower than the rate of travel in the esophagus 

 which is about 2 inches in a second. The mechanical 



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