202 



MANUAL OF PHYSIOLOGY. 



FIG. 89. 



II. Intestinal Absorption. 

 The intestinal absorbents are merely a special department of 



the lymphatic system, which, on account of the white chyle they 

 carry being seen through their trans- 

 parent walls, have been called lacteals, 

 their function being to take up the nutri- 

 ent fluid from the intestinal cavity, as 

 well as to drain the tissue in which they 

 lie. In order to fulfill their function, they 

 are arranged in a particular way, espe- 

 cially adapted to the peculiar construc- 

 tion of the mucous membrane lining this 

 part of the alimentary tract, which must 

 be briefly described before the mechanism 

 of absorption can be understood. 

 Diagram of relation of the Tne m <> s t striking characteristic of the 



epithelium to the lacteal radicle lining membrane of the small intestine is 



in villas. The protoplasmic , . , /> .,,. . < , * j 



e,,itheiiai cells supposed to be * he existence of villi^ which are only found 

 connected to the absorbent ves- in this part of the alimentary tract. They 



Q nip p le . shaped process es pro- 



jectiug into the intestinal cavity, so closely 

 set that they have the appearance of the pile of velvet ; and 

 being just visible to the naked eye, they give the mucous mem- 

 brane, when washed and held under water, a peculiar velvety 

 look. On account of these villi, and also of the ring-like folds 

 of mucous membrane in the upper part of the small intestine, 

 the extent of surface over which the chyme has to travel is 

 greatly increased. 



The surface of the villi is covered over with a simple layer of 

 columnar epithelial cells in continuity with the epithelium lining 

 the rest of the intestinal tract. The free surface of these cells is 

 marked by a clear margin which is composed of a row of minute 

 rods closely packed together, while the deep-seated end of the 

 cells is branched, and appears to be prolonged into the substance 

 of the villus, and in some way to be connected with the support- 

 ing retiform tissue. Some of the cells are seen to swell upon the 

 addition of certain reagents, owing to their containing mucus, 



tissue. (After 



