ABSORPTION. 



201 



FIG. 42. 



point the thoracic duct passes upward through the chest, crossing 

 obliquely from right to left, and terminating in 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 everywhere the same in appearance. Its colorless and trans- 

 parent character, the small size of the vessels, and the thinness and 

 delicacy of their coats, make them nearly or quite invisible to the unaided 

 eye. But during the absorption of food the lymphatics of the small 

 intestine are distended with chyle, and thus become visible as opaque 

 white filaments, ramifying in the 

 intestinal walls, converging from 

 the intestine to the receptaculum 

 chyli, and contrasting strongly 

 with the semi-transparent ruddy 

 color of the neighboring tissues. 

 Owing to the appearance thus 

 given to the vessels by 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, only peri- 

 odical. The fatty substances be- 

 gin to be absorbed during diges- 

 tion, as soon as they have been 

 eniulsionedby the digestive fluids. 

 As the process goes on, they ac- 

 cumulate in larger quantity, and 

 gradually fill the whole lacteal 

 system of the abdomen. But as 

 digestion and absorption come to 

 an end, the milky fluid disappears 

 from these vessels, and they re- 

 sume their former transparent 

 appearance. 



The lacteals, accordingly, are 

 the lymphatics of the small intes- 

 tine, which, in addition to the 

 lymph which they usually con- 

 tain, have absorbed a fluid rich 

 in emulsioned fat. They are then 

 distinguished from the lymphatics 

 elsewhere by the milky character of their contents, which accumulate 

 in the receptaculum chyli, and may be followed thence through the 

 thoracic duct, to its termination in the subclavian vein. (Fig. 42.) 



It was owing to the opacity of the lacteals during digestion that 



LACTEALS AND LYMPHATICS, during digestion. 



