100 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



as they stain with reagents that stain protoplasmic granules ; but as 

 they also stain darkly with osmic acid, they are apt to be mistaken 

 for fat. There is, however, no doubt that the particles found during 

 fat-absorption are composed of fat. There is also no doubt that the 

 epithelial cells have the power of again forming fat out of the fatty 

 acids and glycerin into which it has been broken up in the intestine. 

 Munk, who performed a large number of experiments on the subject, 

 showed that the splitting of fats into glyceiin and fatty acids occurs 

 to a much greater extent than was formerly supposed : these sub- 

 stances, being soluble, pass readily into the epithelium cells, and these 

 cells perform the synthetic act of building them into fat once more ; 

 the fat so formed appears in the form of small globules, surrounding 

 or becoming mixed with the protoplasmic granules that are ordinarily 

 present. Another remarkable fact which he made out is that after 

 feeding an animal on fatty acids the chyle contains fat. The 

 necessary glycerin must have been formed by protoplasmic activity 

 during absorption. The more recent work of Moore and Eockwood 

 has shown that fat is absorbed entirely as glycerin and either fatty 

 acid or soap ; and that preliminary emulsification, though advan- 

 tageous for the formation of these substances, is not essential. 



Bile aids the digestion of fat, in virtue of its being a solvent of fatty 

 acids, and it probably assists fat- absorption by reducing the surface 

 tension of the intestinal contents ; membranes moistened with bile 

 allow fatty materials to pass through them more readily than would 

 otherwise be the case. In cases of disease in which bile is absent 

 from the intestines a large proportion of the fat in the food passes 

 into the faeces. 



