ABSORPTION IN THE INTESTINES 



391 



which have known osmotic and diffusion properties. The question has been 

 to determine which of the cleavage products are most favorable for absorp- 

 tion and the details of the mechanism. 



The mucous membrane of the small intestine possesses special structures 

 for absorption, the villi. Each villus projects as a finger-like process into 

 the lumen of the intestine. Its single-layered covering of epithelial cells 

 supported by a connective-tissue framework brings a relatively large extent 



Lymphatics of head and 

 neck, right 



Right internal jugular vein 

 Right subclavian vein 



Lymphatics of right arm 



Receptaculum chyli 



Lymphatics of lower ex- 

 tremities 



Lymphatics of head and 

 neck, left 



Thoracic duct 



Left subclavian vein 



Thoracic duct 



Lacteals 



Lymphatics of lower ex- 

 tremities 



FIG. 280. Diagram of the Principal Groups of Lymphatic Vessels. (From Quain.) 



of surface into contact with the digesting food, which is thus separated from 

 a loop of capillaries and lymphatic radicals. 



The capillaries of the villus are connected with the veins which contribute 

 to the portal vein, hence carry blood to the liver. The lacteals of the villus 

 contribute to the mesenteric lacteal system, hence the chyle and lymph pass 

 through the mesenteric glands and the portal duct to the subclavian vein 

 in the neck. There are thus two routes by which absorbed foods may reach 

 the general circulation. These paths can be independently isolated; and a 

 study of the composition of their discharge during active absorption con- 



