THE FAT-ABSORBING FUNCTION OF THE ALIMENTARY 

 TRACT OF THE KING SALMON. 



By CHARLES W. GREENE, Ph. D., 

 Department of Physiology and Pharmacology, Laboratory of Physiology, University of Missouri. 



REVIEW OF THE LITERATURE. 



The absorption of fats by ihe alimentary tract of man and animals has been a 

 subject for discussion and investigation for many decades. Our present views con- 

 cerning the topic have been arrived at almost exclusively by the study of the higher 

 mammals. Few observations along this line, especially of an experimental nature, 

 have been made on fishes. The setting of the problem which has led to the investiga- 

 tions here presented is found in our current views of fat absorption. These views have 

 been concisely and admirably summarized by Wells." 



In the intestines fat is split into a mixture of fat, fatty acid, and gjlcerin; but as the fatty acid 

 and glycerin are diffusible, while the fat is not, they are separated from the fat by absorption into the 

 wall of the intestine. Hence an equilibrium is not reached in the intestine, so the splitting continues 

 txntil practically all the fat has been decomposed and the products absorbed. When this mixture of 

 fatty acid and glycerin first enters the epithelial cells lining the intestines there is no equilibrium, for 

 there is no fat absorbed with them as such. Therefore the lipase, which Kastle and Loevenhart showed 

 was present in these cells, sets about to establish equilibrium by combining them. As a result we 

 have in the cell a mixture of fat, fatty acid, and glycerin, which will attain equilibrium only when 

 new additions of the two last substances cease to enter the cell. Now another factor also appears, for 

 on the other side of the cell is the tissue fluid, containing relatively little fatty acid and glycerin. Into 

 this the diffusible contents of the cell will tend to pass to establish an osmotic equilibrium, which is 

 quite independent of the chemical equilibrium. This abstraction of part of the cell contents tends to 

 again overthrow chemical equilibrium, there now being an excess of fat in the cell. Of course, the 

 lipase will, under this condition, reverse its action and split the fat it has just built into fatty acid and 

 glycerin. It is evident that these processes are all going on together, and that, as the composition of 

 the contents of tlie intestines and of the blood vessels varies, the direction of the enzyme action will 

 also vary. In the blood serum, and also in the lymphatic fluid, there is more lipase, which will unite 

 part of the fatty acid and glycerin, and bj- removing them from the fluid about the cells favor osmotic 

 diffusion from the intestinal epithelium, thus facilitating absorption. 



Quite similar must be the process that takes place in the tissue cells throughout the body. In 

 the blood-serum bathing the cells is a mixture of fat and its constituents, probably nearly in equilibrium, 

 since lipase accompanies them. If the diffusible substances enter a cell containing lipase, e. g., a liver 

 cell, the process of building and splitting will be quite the same as in the intestinal epithelium. The 

 only difference is that here the fatty acid may be removed from the cell by being utilized by oxidation 

 or some other chemical transformation. 



a Wells, H. C: Chemical Pathology, p. 67, Philadelphia. 1907. 



IS3 



