DIGESTION OF THE CARBOHYDRATES 235 



formed by mixing them with small quantities of an emulsifiable fat 

 or oil, over ninety-five per cent, of the 'hydrocarbon is recoverable, 

 unaltered, in the feces. The same is true of Lanoline which consists 

 of a mixture of cholesterol esters of fatty acids and is not saponifiable 

 by lipase. These esters are not absorbed; they pass into the feces 

 unaltered, although free cholesterol itself can be shown to undergo 

 absorption. 



Fatty acids which are normally foreign to animal tissues are absorbed, 

 but only when the fat is previously split into its constituents by lipase. 

 This has been most conclusively shown by the following very beautiful 

 experiment of Bloor's. Bloor prepared the fatty-acid compounds of 

 the polyatomic alcohols derivable from sugars by reduction. Among 

 these Dilaurate of Isomannitol has a high dextrorotation, while the normal 

 body-fats are optically inactive. On administering this substance to dogs 

 in their food and collecting the chyle from the thoracic duct a large 

 proportion of fat was obtained which yielded Laurie Acid on hydrolysis. 

 Laurie acid isnot found normally in animal fats, and it must therefore 

 have been derived from the isomannitol dilaurate which had been 

 administered. But the fat obtained from the thoracic duct was also 

 Optically Inactive; therefore, it cannot have consisted of isomannitol 

 dilaurate. The accuracy of the method was sufficient to have detected 

 the absorption of 0.5 per cent, of the isomannitol dilaurate which had 

 been administered. Not more than this proportion therefore can have 

 been absorbed without previous hydrolysis by the pancreatic lipase. 



The carbohydrates, and, as we shall see, the proteins are absorbed 

 in the form of the simplest components into which they can be con- 

 verted by the hydrolyzing enzymes, and are distributed to the tissues 

 after having passed through the liver. The fats, on the contrary, are 

 thrown directly into the circulation in a comparatively complex form. 

 Corresponding to this difference in the method of distribution we find 

 that the composition of the tissue-fats is very much more dependent 

 ' upon the varying nature of the diet than the tissue-carbohydrates or 

 the tissue-proteins. Thus Erucic Acid, C 2 iH 4 iCOOH, is never normally 

 present in the tissue-fats of dogs. Yet if rape-seed oil, which contains 

 notable quantities of erucic acid glyceride, be given to starving dogs, 

 this fatty acid may subsequently be isolated from their tissues. The 

 normal melting-point of dog-fat is 20 C. Munk allowed a dog to fast 

 for nineteen days, until the tissues were presumably free of reserve- 

 stores of fat. The dog then weighed sixteen kilograms. It was now 

 fed for fourteen days with mutton tallow. The weight of the animal 

 increased during this period by seventeen per cent. On "trying out" 

 the tissues 1100 grams of fat were obtained and its melting-point was 

 40 C. The administration of the fat of high melting-point had, under 

 these conditions, led to an abnormally high melting-point of the fats 

 laid up in the tissues. 



The results which we have quoted were obtained with starving 

 animals. Under normal conditions, however, when the tissues are not 



