1030 ABSORPTION 



The Absorption of the Fats. In the upper small intestine the fats 

 appear as glycerin and fatty acids, while in its lower segments 

 some of these fatty acids have been combined with alkalies to form 

 soaps. This implies that the neutral fat ingested is hydrolyzed by the 

 gastric, pancreatic and intestinal juices, the end-products of this 

 lipolysis being the substances just mentioned. We know that the 

 alkaline soaps are soluble in water, while those of calcium and mag- 

 nesium are soluble in bile. This is also true of the free fatty acids. 

 Herein really lies the importance of bile as an aid to pancreatic diges- 

 tion; i.e., while it does not dissolve neutral fat, it possesses a power- 

 ful solvent action upon fatty acids and soaps and even upon the 

 otherwise insoluble soaps. From this statement it may be gathered 

 that this secretion is a prerequisite of the normal absorption of fat, 

 because in its absence more than half of this foodstuff is lost to the 

 body and escapes into the feces. It cannot surprise us to find that 

 the accumulation of these masses of unutilized fat also seriously in- 

 terferes with the digestion and absorption of the other foodstuffs. 

 Similar conditions result in the absence of the pancreatic juice, but 

 it seems that the loss of this secretion may be compensated for in a 

 large measure by the secretions still remaining as well as by the 

 activity of micro-organisms. 1 



In its journey through the epithelial cells this material is then 

 synthetized into neutral body-fat. The soaps are split, while the fatty 

 acids thus liberated, are united with glycerin to form neutral fat 

 under elimination of .water. This fat is then diverted into the lacteals 

 of the different villi, whence it reaches the mesenteric lymphatics and 

 eventually the thoracic duct and venous circulation. It is true, how- 

 ever, that only about 60 per cent, of the 95 per cent, of the fat usually 

 absorbed, can be accounted for in this way, whereas the other 40 per 

 cent, must be transferred into the portal radicles directly or be burned 

 up during their passage through the intestinal epithelium. In support 

 of the former view might be mentioned the fact that from 32 to 48 per 

 cent, of the fat enters the system in spite of the ligation of the thoracic 

 duct. Obviously, this absorption can only take place through the 

 portal terminals. As far as the tune is concerned during which this 

 transfer is accomplished, it might be stated that in the dog from 9 to 

 21 per cent, of the fat is absorbed within 3 to 4 hours, 21 to 46 per 

 cent, in 7 hours, and the remaining portion in 18 hours. 



At the height of absorption even the distalmost lymphatics are 

 sharply outlined against the dark red background of the intestine 

 by their milky white contents. Even the blood presents an oily 

 appearance, owing to its admixture with chyle, and if a sample of this 

 blood is allowed to clot, the serum derived therefrom exhibits a white 

 color, and fat globules gradually collect upon its surface. This cannot 

 surprise us, because fat absorption is both abundant as well as rapid, 



1 Leathes, "The Fats," Monographs in Bioch., Longmans, Green & Co., 1912, 

 and Dakin, "Oxidations and Reductions in the Animal Body," ibid., 1912. 



