NUTRITION PROPER. 333 



the food would be too much hurried along its way. 

 Slowly, therefore, the digested food is urged along. In 

 the meantime the absorbents are taking up the liquid 

 parts. The percentage of liquids decreases, until finally 

 only solid, indigestible parts remain. This is finally 

 pushed through the ileocoEeal valve (Fig. 204) into the 

 large intestines, and the digestion is substantially done. 

 There are changes of an obscure kind which go on there, 

 but these are too little known to detain us. 



Chemical Work. — The digestive juices of intesti- 

 nal digestion are three — viz., the bile, the pancreatic 

 juice, and the intestinal secretion. The general effect 

 of these is to produce a milky liquid called chyle. 



(a) The bile is secreted by the liver, and during diges- 

 tion is poured out in large quantities into the duodenum 

 a little way below the stomach through a common duct 

 made up of the union of the bile duct with the pancre- 

 atic duct (Fig. 198). The digestive effect of the bile is 

 manifold. 1. It will be remembered that the chyme is 

 acid, and that acidity is unfavorable to the sacchariza- 

 tion of starch. Thus it happens that some starch may 

 escape solution in the stomach. Now, the bile is alka- 

 line, and therefore neutralizes the acidity of the chyme, 

 and thus revives the activity of the ptyalin on the 

 starches. 2. It will be remembered, again, that of the 

 three kinds of food we have had digestive juices for 

 two, viz., ptyalin for starches and pepsin for albumi- 

 noids; but the fats have not yet been touched. Now, 

 the alkalinity of bile partially saponifies the fats, and 

 thus prepares them for emulsification by the pancre- 

 atic and intestinal juices. 3. It is found, too, that in 

 order to be absorbed easily a liquid must be either 

 neutral or a little alkaline. Thus the bile, by neutral- 

 izing the acidity of the chyme, prepares it for easy 

 absorption. 



