ABSORPTION OF THE VARIOUS FOOD SUBSTANCES 437 



of the intestine, and then travelling back to discharge their cargo 

 into the lymph. This view, however, is erroneous. But, although 

 the leucocytes do not aid in the absorption of fat from the intestine, 

 they may take up a certain amount of it from the epithelial cells, 

 and convey it through the spaces of the network of adenoid tissue 

 that occupies the interior of the villus, to discharge it into the 

 central lacteal, where it mingles with the lymph and forms the so- 

 called molecular basis of the chyle. It has been supposed that a 

 part of the fat may reach the lacteal in another way. The con- 

 traction of the smooth muscular fibres of the villus and the peristaltic 

 movements of the intestinal walls, which alter the shape of the 

 villi, alter as well the capacity of the lacteal chamber, and so 

 alternately fill it from the lymph of the adenoid reticulum, and 

 empty it into the lymphatic vessel with which it is connected. By 

 this kind of pumping action the passage of fat and other substances 

 into the lymphatics may be aided. There is, however, no proof 

 that all the fat accumulated in the intestinal epithelium leaves 

 it without further change. It is quite as probable that the lipase 

 which is known to be contained in the cells again hydrolyses the 

 fat, or a portion of it, and that the constituents then pass out into 

 the lymph, or even in part into the blood. In the dog most of the 

 fat 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 small fraction of the deficit might be accounted for as fat directly 

 used up for the nutrition of the intestinal wall itself. But even after 

 ligation of the thoracic and right lymphatic ducts a large proportion 

 of a meal of fat (32 to 48 per cent.) is absorbed from the intestine, 

 obviously by the channel of the bloodvessels, since the fat-content 

 of the blood increases up to, it may be, six times the highest amount 

 present in the blood of fasting animals. The statement that only 

 fatty acids can be absorbed under these conditions is erroneous 

 (Munk and Friedenthal). 



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

 three to four hours; 21 to 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-estab- 

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

 the intestine. 



Mechanism of Fat Synthesis in the Intestinal Mucosa. As to the 

 manner in which the synthesis of the fat in the intestinal epithelium 



