142 HUM '/IN PHYSIOLOGY 



Water, salts, sugar, and protcids arc absorbed by tJie 

 portal vein; fats are absorbed by the lyinpltatics. After the 

 water, salts, and sugar have traversed the epithelial layer, 

 they pass into the closely adjoining blood capillaries. 

 Thence they are carried with the blood through the portal 

 vein. When great quantities of fluids have been taken, a 

 part may reach the lymph vessels. It has been observed in 

 animals that the lymph in the thoracic duct is increased 

 only when a large quantity of water is imbibed, and that the 

 carbohydrates in the lymph are increased only during the 

 absorption of a large quantity of concentrated sugar solution. 

 The blood of the portal vein, however, always contains, 

 during absorption of carbohydrates, more sugar than arterial 

 blood. Observations upon human beings with thoracic duct 

 fistula, from which all the lymph from the intestine flows, 

 show that the lymph contains at best only traces of the 

 absorbed sugar. 



That the absorbed proteids are carried through the portal 

 vein is proven by the facts that ligaturing the thoracic duct 

 does not interfere with the proteid nutrition and metabolism, 

 and that the lymph flowing from a thoracic duct fistula, as- 

 mentioned above, shows no increase of proteids during their 

 absorption. 



Fats, on the other hand, are mostly absorbed by the 

 lacteals. During the absorption of fats the lacteals and the 

 thoracic duct appear white, because of the milky turbulence 

 due to the absorbed emulsified fat. But as all the fat eaten 

 cannot be demonstrated in the lymph flowing from the 

 thoracic duct or from a chylus fistula during the absorption 

 of fat, it has been assumed that part of the fat is absorbed 

 by the blood vessels. 



2. ABSORPTION AND ASSIMILATION OF PROTEIDS 



Before proteoses are absorbed into the blood, they undergo 

 a change in the wall of the intestine. The blood of the 

 portal vein and the lymph contain no proteoses. If proteoses 



