EXCRETION OF LIPIDS BY WAY OF LARGE INTESTINE 337 



for the excretion of those lipids which still retain their characteristic solu- 

 bility patterns. Mammals, and especially birds, excrete considerable 

 portions of lipids by way of the skin. Various samples of human sweat 

 were reported by Pemberton et al. bn to contain from 20 to 216 milligram 

 per cent of the lipids. An increase in blood lipids occurs prior to sweat- 

 ing. 576 In the case of man, 0.1 to 0.2 g. of cholesterol is excreted through 

 the skin daily. 577 Kayser and Balot 578 reported that the normal human 

 subject excretes about 1 mg. of cholesterol daily in the urine. Hyper- 

 cholesteroluria results when albumin or mucosal casts are present. 



In addition to the lipids in the food which are not capable of absorption 

 and those which fail to be absorbed, the feces contain additional fatty- 

 like material which has been added at various levels in the gastrointestinal 

 tract. These include the lipids present in cell debris, those added in the 

 bile, as well as those secreted through the walls of the small and large 

 intestine. Still another source of fecal lipids is the material synthesized 

 by the intestinal bacteria during the passage of food residues through 

 the lower portion of the small intestine and through the large intestine. 



(1) The Excretion of Lipids in the Bile 



Bile is the external secretion of the liver. Under normal conditions, 

 it is being formed continuously. In the case of animals having a gall 

 bladder, the bile is stored in this organ until a stimulus is evoked for its 

 ejection into the lumen of the intestine. Food in the intestine provides 

 a suitable stimulus; fat and meat are especially efficacious, as are the bile 

 salts. It is evident that a hormone mechanism is responsible for the 

 emptying of the gall bladder, as has been demonstrated by Doubilet and 

 Ivy, 579 who prepared a substance which, on intravenous injection, caused 

 a contraction of the musculature of the walls of the gall bladder. The 

 hormone has been called cholecystokinin. Seager 580 likewise reported the 

 preparation of the purified hormone. It is believed that acid and other 

 substances in the intestine cause the production or liberation of this 

 hormone from the intestinal mucosa. 



Bile contains small amounts of cholesterol, phospholipids, fats, soaps, 



575 R. Pemberton, F. A. Cajori, and C. Y. Crouter, Ann. Internal Med., 2, 1243-1252 

 (1929). 



" 6 H. G. Barbour, M. H. Dawson, and I. Neuwirth, Am. J. Physiol., 7/ t , 204-223 

 (1925). 



577 W. Hueck, Verhandl. deut. path. Ges., 20th meeting, 18-66 (April, 1925). 



578 F. Kayser and R. Balot, Compt. rend. soc. biol, U6, 1598-1600 (1952). 



579 H. Doubilet and A. C. Ivy, Am. J. Physiol. 134, 379-390 (1938). 

 680 L. D. Seager, Proc. Soc. Exptl. Biol. Med., J,7, 257-260 (1941). 



