338 DIGESTION. 



conversion into sugar, and as it becomes sugar, also dis- 

 solving in the fluids with which it is mixed ; while with, 

 these are mingled gastric fluid, and fluid that has been 

 swallowed, together with such portions of the food as are 

 not digestible, and will be finally expelled as part of the 

 fteces. 



On the entrance of the chyme into the duodenum, it is 

 subjected to the influence of the fluid secreted by Lieber- 

 kuhn's and Brunn's glands, before described, and to that 

 of the bile and pancreatic juice, which are poured into this 

 part of the intestine. 



Without doubt, that part of digestion which it is a chief 

 duty of the small intestine to perform, is the alteration of 

 the fat in such a manner as to make it fit for absorption. 

 And there is no doubt that this change is chiefly effected 

 in the upper part of the small intestine. What is the 

 exact share of the process, however, allotted respectively 

 to the bile, pancreatic secretion, and the secretion of the 

 intestinal glands, is still uncertain. It is most probable, 

 however, that the pancreatic secretion and the bile are 

 the main agents in emulsifying the fat, and that they do 

 this by direct admixture with it. They also promote its 

 absorption by moistening the surface of the villi (p. 331). 



During digestion in the small intestine, the villi become 

 turgid with blood, their epithelial cells become filled, by 

 absorption, with fat-globules, which, after minute division,, 

 transude into the granular basis of the villus, and thence 

 into the lacteal vessel in the centre, by which they are 

 conveyed along the mesentery to the lymphatic glands, 

 and thence into the thoracic duct. A part of the fat is 

 also absorbed by the blood-vessels of the intestine. The 

 term chyle is sometimes applied to the emulsified contents 

 of the intestine after their admixture with, the bile and 

 pancreatic juice ; but more strictly to the fluid contained in 

 the lacteal vessels during digestion, which differs from 

 ordinary lymph contained in the same vessels at other times,. 



