364 ABSORPTION. 



of mucous membrane, each containing a delicate net- 

 work of blood-vessels and one or more lacteals, and are 

 invested by a sheath of cylindrical epithelium. In the 

 interspaces of the mucous membrane between the villi, as 

 well as over all the rest of the intestinal canal, the lacteals 

 and blood-vessels are also densely distributed in a close net- 

 work, the lacteals, however, being more sparingly supplied 

 to the large than to the small intestine. 



There seems to be no doubt that absorption of fatty 

 matters during digestion, from the contents of the intes- 

 tines, is effected chiefly by the epithelial cells which line 

 the intestinal tract, and especially by those which clothe 

 the surface of the villi (fig. 8l). From these epithelial 

 cells, again, the fatty particles are passed on into the inte- 

 rior of the lacteal vessels (figs. 8 1 and 82), but how they 

 pass, and what laws govern their so doing, are not at pre- 

 sent exactly known. 



It is probable that the process of absorption by the epi- 

 thelial cells, is assisted by the pressure exercised on the 

 contents of the intestines by their contractile walls ; and 

 that the absorption of fatty particles is also facilitated by 

 the presence of the bile, the pancreatic and intestinal se- 

 cretions which moisten the absorbing surface. For it has 

 been found by experiment, that the passage of oil through 

 an animal membrane is made much easier when the latter 

 is impregnated with an alkaline fluid. 



Absorption by the Lymphatic Vessels. 



The real source of the lymph, and the mode in which its 

 absorption is effected by the lymphatic vessels, were 

 long matters of discussion. But the problem has been 

 much simplified by more accurate knowledge of the anato- 

 mical relations of the lymphatic capillaries. It is most 

 probable that the lymph is derived, in great part, from the 

 liquor sanguinis, which, as before remarked, is always 

 exuding from the blood-capillaries into the interstices of 



