ABSORPTION 



413 



acids, is absorbed as neutral fat by the epithelial cells covering 

 the villi. If an animal is killed during digestion of a fatty 

 meal, these cells are found to contain globules of different sizes, 

 which stain black with osmic acid, are dissolved out by ether, 

 leaving vacuoles in the cell substance, and are therefore fat 

 (Fig. 156). It has always been difficult to explain how droplets 

 of emulsified fat could get into the interior of the epithelial cells, 

 although, perhaps, no more difficult than to explain the passage 

 of living tubercle bacilli from the contents of the intestine into 

 the chyle of the thoracic duct a fact which has been clearly 

 demonstrated (Ravenel). The fat certainly passes into the cells, 

 and not between them. When fat is found in the cement substance 

 between the cells, it has been mechanically squeezed out of 

 them by the shrinking of the villi in preparation. This difficulty 

 is obviated if we suppose that the 

 whole of the fat is split up in the 

 intestine, the products being ab- 

 sorbed in solution, the glycerin 

 as such, and the fatty acids either 

 as soaps or in the free state, or 

 partly free and partly saponified. 

 If this is the true theory and 

 the evidence of its truth has of 

 late years been continually grow- 

 ing neutral fat must again be 

 built up in the epithelial cells from 

 the absorbed glycerin and the 

 fatty acids or soaps. Now, it has 



J 





sir 



SORPTION OF FAT (SCHAFER). 



ep, epithelial cells ; str, striated 

 been shown that when an animal border ; c , lymph corpuscles ; /, lac- 

 is fed with fatty acids they are teal. 

 not only absorbed, but appear as 



neutral fats in the chyle of the thoracic duct, having combined 

 with glycerin in the intestinal wall ; and the epithelial cells 

 contain globules of fat, just as they do when 'the animal is fed 

 with neutral fat. Further, it is known that fat-splitting goes 

 on in the alimentary canal to a much greater extent than would 

 be necessary merely for the formation of a quantity ol soap 

 sufficient to emulsify the whole of the fat in the food. Indeed, 

 at certain stages of digestion most of the fatty material, both 

 in the small and large intestine, has been found to consist of 

 fatty acids. 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, 



