ABSORPTION. 197 



inward, between the layers of the mesentery, from the intestine toward 

 the posterior part of the abdomen. During their course through the 

 mesentery, they inosculate with each other by transverse branches, and 

 pass in succession through several ranges of mesenteric glands, which 

 have the same structure with those already mentioned, and which are 

 accordingly the lymphatic glands of the abdominal cavity. On arriving 

 near the attached portion of the mesentery, on the right side of the 

 abdomen, at about the level of the second lumbar vertebra, they terminate 

 iii a saccular dilatation, known as the " receptaculum chyli." From 

 this point the thoracic duct passes upward through the cavity of the 

 chest, crossing obliquely from the right to the left of the median line, 

 and finally discharges its contents into the left subclavian vein, at its 

 junction with the jugular of the same side. 



In the intervals of digestion the fluid contained in the lymphatic 

 vessels is the same in appearance throughout the body. Its colorless 

 and transparent character, together with the small size of the lymphatics 

 themselves, and the thinness and delicacy of their coats, make these 

 vessels nearly or quite invisible to the unaided eye. But during the 

 digestion and absorption of food the elements of the chyle are taken up 

 by the lymphatics of the small intestine, which are distended with a 

 milky fluid, and thus become visible as an abundant network of opaque 

 white filaments, ramifying in the intestinal walls, converging from the 

 intestine to the receptaculum chyli, and contrasting strongly with the 

 ruddy and semi-transparent color of the neighboring tissues. If, when 

 in this condition, one of them be opened with the point of a scalpel, it 

 discharges a chylous liquid, which is easily seen to be the same in 

 character with that contained in the cavity of the intestine itself, namely, 

 an emulsion of fatty molecules and granulations. Owing to the appear- 

 ance thus given to the vessels themselves, and to the milky fluid which 

 they contain, they have received the name of the lacteals, or lactiferous 

 vessels of the abdomen. 



The presence of chyle in the lacteals is, therefore, not a constant, but 

 only a periodical phenomenon. The fatty substances constituting the 

 chyle begin to be absorbed during the process of digestion, as soon as 

 they have been disintegrated and emulsioned by the action of the intes- 

 tinal fluids. As digestion proceeds, they accumulate in larger quantity, 

 and gradually fill the whole lacteal system, giving to its vessels the 

 characteristic aspect above described. But as digestion and absorption 

 from the intestinal cavity come to an end, the milky fluid disappears 

 from the lymphatics, and they resume their former transparent and 

 colorless appearance. 



The lacteals accordingly are nothing more than the lymphatics of the 

 small intestine, which, in addition to the transparent and colorless 

 lymph which they usually contain, have absorbed a fluid rich in fat 

 derived from the process of digestion. While this process is going on, 

 they are distinguished from the lymphatics elsewhere by the milky 

 character of their contents, which accumulate in the receptaculum chyli, 



