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ABSORPTION 



3. ABSORPTION OF FAT 



Because of the ease with which fat can be demonstrated by micro-chemical 

 reactions, much attention has been given to its absorption. 



It has already been stated (page 296) that fat is probably not absorbed 

 as an emulsion, but in the form of a solution of fatty acids effected by the 

 bile acids, or in the form of soaps. 



Since the chyle, even after feeding with free fatty acids, contains neutral 

 fat almost altogether, and free fatty acids only in much smaller amount, and 

 after feeding ethylesters of the higher fatty acids contains only triglycerides 

 and not a trace of the esters fed (Frank), we may deem it fully established 

 that the free fatty acids absorbed from the intestinal canal are synthesized 

 again to neutral fats in the intestinal wall. This is confirmed by the observa- 



FIG. 118. Successive stages in the absorption of fat in the epithelial cells of the frog's intestine, 



after Krehl. 



tion that the intestinal mucosa at the height of digestion contains far more 

 neutral fat than free fatty acids, and that on digestion of the finely divided 

 mucous membrane with a mixture of soaps and glycerin neutral fat is formed. 



This synthesis, like the absorption of fats from the intestinal cavity, is 

 probably carried out by the cellular elements of the mucosa possibly by the 

 numerous leucocytes occurring therein, but more probably by the epithelium 

 of the villi. 



If the intestinal epithelium of the frog in different stages of fat absorption 

 be studied in osmic acid preparations, all transitions are seen from small 

 dustlike gray points to large, black fat droplets (Fig. 118, A to C). In the 

 Mammalia the fat in certain early stages of absorption does not enter in the 

 form of blackened granules, but of small black circles with a clear center. 

 These circles increase in size and depth of color in the further course of 

 absorption just the behavior we should expect if the fat were taken up as 

 a solution of fatty acids and synthesized in the intestinal wall to neutral 

 fat again. 



With regard to the further fate of the absorbed fat, it is supposed that it 

 is free to move inside the parenchyma of the villus only in the pericellular, fluid- 



