372 A MANUAL OF PHYSIOLOGY 



the dog no fat is absorbed by the bloodvessels, except per- 

 haps a small quantity in the form of soaps ; it nearly all 

 goes into the lacteals, and thence by the general lymph 

 stream through the thoracic duct into the blood. And in 

 man the chyle collected from a lymphatic fistula contained 

 a large proportion of the fat given in the food (Munk). But 

 this bare statement would be misleading if we did not add 

 that the fat taken in can never be entirely recovered in the 

 chyle collected from the thoracic duct. A portion of it dis- 

 appears, and its fate is unknown. And even after ligature of 

 the thoracic duct a large proportion of a meal of fatty acids 

 is absorbed from the intestine, by what channel is uncertain 

 (Frank). 



A dog normally absorbs 9 21 per cent, of the fat in a 

 meal in three to four hours; 21 46 per cent, in seven 

 hours; and 86 per cent, in eighteen hours (Harley). After 

 excision of the pancreas the absorption of fat is hindered, 

 though not abolished. More fat, indeed, can be recovered 

 from the intestine than is given in the food. This at first 

 sight paradoxical reSult is explained by the well-established 

 fact that a certain amount of fat is normally excreted into- 

 the intestine. 



Absorption of Water, Salts, and Sugar. The water, salts, 

 and sugar pass normally into the rootlets of the portal vein, 

 not into the chyle, for no increase in the quantity of these 

 substances flowing through the thoracic duct takes place 

 during digestion, while the sugar in the portal blood is- 

 increased after a starchy meal. In man not I per cent, of 

 the sugar corresponding to the carbohydrates of the food 

 could be recovered in the chyle escaping from a lymphatic 

 fistula. But when a large amount of a dilute solution of 

 sugar is introduced into the intestine some of it is taken 

 up by the lacteals. 



Absorption of Proteids. The proteids of the food and 

 their digested products also pass directly into the blood- 

 capillaries which feed the portal system. For it has been 

 shown that after ligature of the thoracic duct proteid sub- 

 stances are still absorbed from the intestine, and the urea 

 corresponding to their nitrogen appears in the urine. And 



