96 DIGESTION. 



fluids previously mentioned, viz. : of the saliva in convert- 

 ing starch into sugar, of the gastric juice in digesting the 

 albuminoids, and of the pancreatic juice and bile in 

 emulsifying the fats. 



36. Absorption. With the elaboration of the chyle, 

 the work of digestion is completed ; but, in a certain sense, 

 the food is yet outside of the body ; that is, the blood is not 

 yet enriched by it, and it is not in a position to nourish the 

 tissues. The process by which the liquefied food passes out 

 of the alimentary canal into the blood is called absorption. 

 This is accomplished in two ways ; first, by the blood-vessels. 

 We have seen how the inner membrane of the stomach is 

 underlaid by a tracery of minute and numerous vessels, 

 and how softie portions of the food are by them absorbed. 

 The supply of blood-vessels to the intestines is even 

 greater; particularly to the small intestines, where the 

 work of absorption is more actively carried on. / 



37. The absorbing surface of the small intestines, if con- 

 sidered as a plane surface, amounts to not less than half a 

 square yard. Besides, the mucous membrane is formed in 

 folds with an immense number of thread-like prolongations, 

 called villi, which indefinitely multiply its absorbing capa- 

 city. These minute processes, the villi, give the surface 

 the appearance and smoothness of velvet; and during 

 digestion, they dip into the canal, and, by means of their 

 blood-vessels, absorb its fluid contents, just as the spongi- 

 oles which terminate the rootlets of plants, imbibe moisture 

 from the surrounding soil. 



38. Secondly, absorption is also effected by the lacteals, a 

 set of vessels peculiar to the small intestines. These have 

 their beginnings in the little villi just mentioned, side by 

 side with the blood-vessels. These two sets of absorbents 

 run in different courses, but their destination is the same, 



36, 37. How much thus far has been done with the food ? The next process ? 

 Give the first way. 



38. How is absorption effected in another way? Describe it. Name of the 

 "teals ? Thoracic duct ? 



