ABSORPTION 415 



lymphatic fistula contained a large proportion of the fat given 

 in the food (Munk). But this bare statement would be mis- 

 leading 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 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. 



As to the manner in which the synthesis of the fat in the 

 intestinal epithelium is accomplished, the most fascinating 

 theory is that which attributes it to the reversed action of a fat- 

 splitting ferment or lipase, possibly the very same steapsin as 

 originally split it up in the intestine. The reversibility of the 

 action of various enzymes under changed conditions has been 

 well made out, and it has been stated that even outside of the 

 body the pancreas, intestinal mucous membrane, lymph glands, 

 etc., and even cell-free extracts of these organs have the pofrer of 

 synthesizing the ester, ethyl butyrate from butyric acid, and 

 ethyl alcohol (p. 315). Moore, however, finds that in the case of 

 ordinary fats the synthesis takes place in the intestinal wall 

 only in situ and while the circulation is going on. In the in- 

 testinal mucosa the greater part of the fatty acid is already 

 combined with glycerin as neutral fat, although considerable 

 quantities of free fatty acid are also present. In the lymph 

 coming directly from the mesenteric glands practically the whole 

 of the fatty acids are in the form of neutral fat. 



An additional, and in some respects even more remarkable, 

 illustration of the synthesizing powers of the intestinal wall is the 

 discovery of Munk, already referred to (p. 413), that fatty acids 

 given by the mouth appear in the lymph of the thoracic duct as 

 neutral fats, having somewhere or other, in all probability on 

 their way through the epithelium of the gut, been combined with 

 glycerin. 



