ABSORPTION BY LACTEALS AND BLOOD-VESSELS. 197 



epithelium-cells, which clothe the extremity of each villus 

 (fig. 9), become distended with an opalescent fluid, the chyle 

 ( 222), which they select from the contents of the small 

 intestine ; and this is subsequently given up by them to a 

 lacteal tube, which, without any open mouth, commences in 

 the midst of each villus. The vessels which thus originate, 

 unite into minute trunks, and these again into larger ones ; and 

 these pass between the two layers of the mesentery (or fold of 

 peritoneum by which the intestines are suspended, 212) 

 towards the lower part of the spinal column : where they 

 deliver their contents into a sort of reservoir, which thus 

 becomes the receptacle for all the chyle that has been collected 

 from the alimentary canal (fig. 114). In traversing the me- 

 sentery, the lacteals of the higher animals pass through little 

 knot-like bodies of a peculiar nature, which are called mesen- 

 teric glands. These appear to afford the means for the per- 

 formance, within a more concentrated space, of the assimi- 

 lating action which is carried on during the passage of the 

 chyle through the lacteal system ; for in Reptiles, in which 

 these glands do not exist, the absorbent vessels are much 

 more extended and spread out than they are in Birds and 

 Mammals. 



218. Near the surface of each of these villi, moreover, lies 

 a minute network of Blood-vessels ; and there is now no 

 longer any doubt that these receive, by simple imbibition,* 

 any substances, whether alimentary or otherwise, which exist 

 in a state of perfect solution in the contents of the intestinal 

 canal. For a great variety of such substances have been 

 detected, by chemical analysis, in the blood which is returned 

 from the walls of the intestines by the mesenteric veins ; 

 whilst it is seldom that anything is found in the lacteals, 

 save the proper constituents of chyle. It is through this 

 channel that poisonous substances are taken into the circula- 

 tion; and these may be absorbed from the walls of the 

 stomach (on which there are no villi or lacteals), without ever 

 passing from it into the intestinal tube. Hence it is a great 



* That tendency called Endosmose which thinner liquids have to 

 pass-towards and mix-with such as are more viscid, even through an 

 intervening membrane, seems to be the physical cause (as experi- 

 ment indicates) of this imbibition ; which is greatly promoted by the 

 movement of blood in the vessels. 



