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, eommences 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 Eeptiles, 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, 45, 
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. 
