108 LECTURE VI. 



Let us follow the progress of the fat, that has been absorbed by the 

 walls of the intestine, and which has undoubtedly been re-formed to some 

 extent, in its further passage through the organism. If we examine the 

 viscera of a fasting or starving animal, we observe the chyle proceeding 

 in a transparent vessel from the intestine to the mesenteric lymphatics. 

 We obtain an entirely different appearance if we feed the animal a diet 

 rich in fat just prior to death. The lacteals are then plainly visible. They 

 have become milky and opaque. If we investigate their nature, we find 

 that they are permeated with fat, even if no fat, as such, but only fatty 

 acids have been administered. In the latter case the glycerin was 

 necessarily missing for a fat synthesis, which must therefore be provided 

 by the organism in some other manner. If we make a fistula at the 

 entrance of the thoracic duct into the vena anonyma of a dog, we can esti- 

 mate the amount of chyle which escapes in a given period of time. In 

 a mixed diet we do not observe any increase in the quantity of chyle. 

 Its appearance only changes when the food contains fat. Although 

 ordinarily transparent, it then becomes white and opaque. In this process 

 of digestion the fats behave differently from other food materials, all of 

 which are poured directly into the blood-stream, and thence conveyed to 

 the liver. The chyle itself retains the fat in the form of a finely 

 divided emulsion. 



I. Munk and Rosenstein * observed in a girl, who was afflicted with a 

 fistula of the thoracic duct, that over 60 per cent of the fat consumed 

 flowed out of the fistula in less than twelve hours. Only about one 

 twenty-fifth of the fat administered had been saponified. Certainly, all 

 fats do not follow such an indirect course, for on feeding a diet rich in fat 

 a direct transmission into the blood-stream occurs. If the thoracic duct 

 is ligated, larger quantities of fat are carried into the blood. I. Munk and 

 Friedenthal 2 found that after a liberal consumption of cream, the fat con- 

 tent of the blood increased to six times the normal. As much as this had 

 passed into the blood, although only 32-48 per cent of the fat had been 

 assimilated. Fat also appeared in the blood after administering fatty 

 acids, about four-fifths of these having been converted into normal fat. 



The amount of fat absorbed depends, as previously indicated, on its 

 composition. For instance, 97.7 per cent of olive oil is utilized, and 

 97.5 per cent of fats, which melt at temperatures between 25-34 degrees 

 (goose-grease and lard). On the other hand, 90-91.5 per cent of mut- 

 ton-tallow, melting at 49-51 degrees, and only about 15 per cent of sper- 

 maceti melting at 53 degrees, are absorbed by human beings. 



Pettenkofer and Voit 3 as well as Rubner 4 have studied the absorption 



1 Virchow's Arch. 123, 230 and 484 (1891); Arch. Anat. Physiol. 1890, 376 and 581. 



2 Zent. Physiol. 15, 297 (1901). 



8 Z. Biol. 9, 1 (1873). 4 Ibid. 15, 115 (1879). 



