DIGESTION IN SMALL INTESTINE. 271 



secretion, and the secretion of the intestinal glands, is still un- 

 certain. 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. 265). 



During digestion in the small intestine, the villi become 

 turgid with blood, their epithelial cells become filled, by ab- 

 sorption, with fat-globules, which, after minute division, trans- 

 ude 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, chiefly in the greatly increased quantity of fat 

 particles which have been absorbed from the small intestine. 



Although the most evident function of the small intestine is 

 the digestion of fat, it must not be forgotten that a great part 

 of the other constituents of the food is by no means completely 

 digested when it leaves the stomach. Indeed, its leaving it 

 unabsorbed would, alone, be proof of this fact. 



The albuminous substances which have been partly dissolved 

 in the stomach continue to be acted on by the gastric juice 

 which passes into the duodenum with them, and the effect of 

 the last-named secretion is assisted or complemented by that 

 of the pancreas and intestinal glands. As the albuminous 

 matters are dissolved, they are absorbed chiefly by the blood- 

 vessels, and only to a small extent, probably, by the lacteals. 



The starchy, or amylaceous portion of the food, the conver- 

 sion of which into dextrin and sugar was more or less inter- 

 rupted during its stay in the stomach, is now acted on briskly 

 by the secretion of the pancreas, and of Brunn's glands, and 

 perhaps of Lieberkuhn's glands also, and the sugar as it is 

 formed dissolves in the intestinal fluids, and afterwards, like 

 the albumen, is absorbed chiefly by the bloodvessels. 



The liquids, swallowed as such, which may have escaped 

 absorption in the stomach, are absorbed probably very soon 

 after their entrance into the intestine ; the fluidity of the con- 

 tents of the latter being preserved more by the constant secre- 

 tion of fluid by the intestinal glands, pancreas, and liver, than 

 by any given portion of fluid, whether swallowed or secreted, 

 remaining long unabsorbed. From this fact, therefore, it may 



