ABSORPTION. 169 



glands is not precisely understood. Each lymphatic vessel, as it 

 enters the gland, breaks up into a number of minute ramifications, 

 the vasa afferentia and other similar twigs, forming the vctsa effer- 

 entia, pass off in the opposite direction, from the farther side of the 

 gland ; but the exact mode of communication between the two has 

 not been definitely ascertained. The fluids, however, arriving by 

 the vasa afferentia, must pass in some way through the tissue of 

 the gland, before they are carried away again by the vasa efferentia. 

 From the lower extremities the lymphatic vessels enter the abdomen 

 at the groin and converge toward the receptaculum chyli, into 

 which their fluid is discharged, and afterward conveyed, by the 

 thoracic duct, to the left subclavian vein. 



The fluid which these vessels contain is called the lymph. It is 

 a colorless or slightly yellowish transparent fluid, which is absorbed 

 by the lymphatic vessels from the tissues in which they originate. 

 So far as regards its composition, it is known to contain, beside 

 water and saline matters, a small quantity of fibrin and albumen. 

 Its ingredients are evidently derived from the metamorphosis of 

 the tissues, and are returned to the centre of the circulation in 

 order to be eliminated by excretion, or in order to undergo some 

 new transforming or renovating process. We are ignorant, how- 

 ever, with regard to the precise nature of their character and 

 destination. 



The lacteals are simply that portion of the absorbents which 

 originate in the mucous membrane of the small intestine. During 

 the intervals of digestion, these vessels contain a colorless and 

 transparent lymph, entirely similar to that which is found in other 

 parts of the absorbent system. After a meal containing only 

 starchy or albuminoid substances, there is no apparent change in 

 the character of their contents. But after a meal containing fatty 

 matters, these substances are taken up by the absorbents of the 

 intestine, which then become filled with the white chylous emul- 

 sion, and assume the appearance of lacteals. (Fig. 43.) It is for 

 this reason that lacteal vessels do not show themselves upon the 

 stomach nor upon the first few inches of the duodenum ; because 

 oleaginous matters, as we have seen, are not digested in the stomach, 

 but only after they have entered the intestine and passed the orifice 

 of the pancreatic duct. 



The presence of chyle in the lacteals is, therefore, not a con- 

 stant, but only a periodical phenomenon. The fatty substances 

 constituting the chyle begin to be absorbed during the process of 



