INTESTINAL ABSORPTION. 



155 



Every villus presents on its surface a coat of columnar 

 epithelium continuous with that of the rest of the mucous 

 membrane, and beneath this a network of 

 capillary blood-vessels, while in the centre 

 there is a lacteal. In the lower animals 

 there are sometimes several lacteals forming 

 loops in one villus; but in the human sub- 

 ject there is usually only one in each. 

 This lacteal is somewhat dilated at its ex- 

 tremity, and it does not appear at that part 

 to have any special wall. 



When absorption is going on, the epi- 

 thelial cells of the villi become turbid with 

 molecules of oil, the tissue beneath becomes 

 turbid likewise, and from the tissue the 

 lacteals are filled. The free extremity of 

 each columnar epithelial cell presents a 

 thick layer of substance less consistent than 

 the rest of the cell wall, but more consistent 

 than its contents, and sometimes having a 

 vertically streaked appearance. Through 

 this substance the molecules of emulsified 

 oil find their way; and afterwards they pass 

 onwards through fine prolongations of the deep ends of the 

 epithelial cells : these appear to 

 communicate with branches of a 

 connective - tissue - corpuscles, by 

 which in like manner the mole- 

 cules are carried to the lacteal. 



Only a small quantity of oil 

 is taken into the capillary blood- 

 vessels, by far the greater amount 

 being absorbed by the lacteals ; Z 

 and this, indeed, is the most c 

 notable difference between lacteal j 

 and capillary absorption, so far as 

 nutritive matters are concerned, 

 for it is very certain that sac- 

 charine and albuminoid substances 

 are taken up freely by both sets 



82. COLUM- 

 NAR, EPITHELIAL 

 CELLS OF IN- 

 TESTINE, highly 

 magnified, show- 

 ing the striated 

 substance on 

 their free ex- 

 tremities. 



ig. 83. BLOOD-VESSELS OF 

 Mucous MEMBRANE ov 

 STOMACH : vertical section 

 magnified, a. Venous radi- 

 cles descending from the 

 free surface ; 6, veins ; c, 

 arteries. 



