436 ABSORPTION 



fatty material, both in the small and large intestine, has been found 

 to consist of fatty acids. The reversibility of the reaction under 

 the influence of lipase, which has already been alluded to, does not 

 enter into the question so far as fat-splitting in the intestine is con- 

 cerned, for the products of the reaction can be absorbed as quickly 

 as they are formed. To clinch the matter, it has been proved that 

 when mixtures of paraffin and fat, which can be emulsified in a 

 watery solution of sodium carbonate, are eaten, the paraffin is com- 

 pletely excreted with the faeces, while the greater part of the fat is 

 absorbed. And fatty substances which are not easily split up and 

 saponified (for example, lanolin, the fat of sheep's wool, a mixture 

 of compounds of fatty acids with isocholesterin, a substance closely 

 related to cholesterin and allied bodies) are not absorbed even when 

 they are easily emulsified. Even fats with a melting-point far 

 above the temperature of the body can be absorbed after being split 

 up. The palmitate of cetyl alcohol, the chief constituent of sper- 

 maceti, melting at 53 C, was absorbed to the extent of 15 per 

 cent., 85 per cent, being excreted in the faeces. It appeared as 

 palmitin in the chyle of a human being flowing from a fistula, the 

 palmitic acid having been absorbed as such, or as a sodium soap, and 

 having then united with glycerin to form the neutral fat, palmitin. 



Some observers have endeavoured to show that the fat is absorbed 

 without change by introducing into the intestine fat stained with 

 dyes, such as alkanna red or Sudan III., which are insoluble in 

 water. The stained fat was found in the epithelial cells of the villi, 

 in the lacteals, and, in the case of a patient suffering from chyluria, 

 in the urine. But this evidence is not conclusive, for it has been 

 shown that the pigments might easily have been absorbed after 

 decomposition of the fat, since, although insoluble in water, they are 

 soluble in fatty acids, and therefore to some extent in the intestinal 

 contents, and readily pass into the lymph. 



As already pointed out, the bile plays an important part in the 

 solution of the fatty acids, which may form loose compounds with 

 the amide group of the bile-acids. In these loose combinations, 

 soluble in water, the fatty acids can be absorbed from the intestinal 

 contents (Pfliiger). In whatever way the fat which can be seen 

 in the epithelial cells during absorption of fat gets into them, it 

 must be carefully noted that there is no quantitative proof that it 

 represents all or even the greater part of the absorbed fat. So far 

 as microscopic observations go, much of the fat may pass through 

 the mucosa in the form of soluble decomposition products without 

 appearing in particulate form in the epithelium. 



How the Fat gets out of the Intestinal Epithelium. Leucocytes 

 have been asserted to be active agents in the absorption of fat. 

 They have been described as pushing their way between the 

 epithelial cells, fishing, as it were, for fatty particles in the juices 



