DIGESTION. 113 



bladder, in which it is stored up during the intervals of digestion. 

 As soon as food enters the intestines it is poured out abundantly by 

 the contraction of the walls of the gall-bladder. 



The amount secreted in twenty-four hours is about 2 l /2 pounds. 



Functions of the Bile: 



1. It assists in the emulsification of the fats and promotes their 

 absorption. 



2. It tends to prevent putrefactive changes in the food. 



3. It stimulates the secretion of the intestinal glands, and excites 

 the normal peristaltic movement of the bowels. 



The digested food, the chyme, is a grayish, pultaceous mass, but 

 as it passes through the intestines it becomes yellow from admixture 

 with the bile. It is propelled onward by vermicular motion by the 

 contraction of the circular and longitudinal muscle-fibers. 



During the passage of the digesting food through the intestinal 

 canal the nutritive products the peptones, the dextrose and levulose, 

 the fatty emulsions, the fatty acids and their soaps are absorbed 

 into the blood, while the undigested residue is carried onward by the 

 peristaltic movements through the ileo-cecal valve into the large 

 intestine. 



Intestinal Fermentation. Owing to the favorable conditions for 

 fermentative and putrefactive processes e. g., heat, moisture, oxygen, 

 microorganisms the food, when consumed in excessive quantity or 

 when acted upon by defective secretions, undergoes a series of de- 

 composition changes which are attended by the production of gases 

 and various chemic compounds. Grape-sugar and maltose are par- 

 tially split into lactic acid, this into butyric acid, carbon dioxid, 

 and hydrogen. Fats are reduced to glycerol and fatty acids ; the 

 glycerol, according to the organisms present, yields succinic and 

 other fatty acids, carbon dioxid, and hydrogen. 



The proteids, under the prolonged action of the pancreatic juice, 

 are decomposed, and yield leucin and tyrosin ; the former is split into 

 valerianic acid, ammonia, and carbon dioxid ; the latter is split 

 into indol, which is the antecedent of indican in the urine. Skatol is 

 another proteid derivative constantly present in the fecal substance. 



Intestinal Movements. During intestinal digestion the walls 

 of the intestine exhibit two. kinds of movement, viz., a rhythmic 

 segmentation and a peristalsis. By the former the food is divided 

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