ABSORPTION OF SPECIAL, MATERIALS. 203 



it appears with the excrement, sometimes giving rise to adipose 

 diarrhoea, thus showing that the amount has exceeded this limit. 



The important question remains, how does the fat emulsion 

 make its way through the intestinal mucous membrane ? That 

 it really does so there can be no shadow of doubt ; for it disap- 

 pears from the intestinal cavity, and can be detected in the chyle 

 with the aid of the microscope more easily than any other of the 

 intestinal contents that are absorbed. 



It has been shown that while a membrane moistened with water 

 acts as a complete barrier to a fat emulsion, and only after pro- 

 longed exposure under high pressure allows traces of fats to pass, 

 the same membrane when saturated with bile will without pres- 

 sure permit the passage of a considerable amount of oil. It has 

 therefore been suggested that the epithelial cells of the mucous 

 membrane are more or less moistened with bile, and the particles 

 of fat in the emulsion are also coated with a film of bile or soap. 

 Thus they are enabled to pass into the epithelial cells, in which 

 they can be detected during digestion. The bile or soapy coating 

 of the fat particles may no doubt aid in their transit through the 

 various obstacles on their way to the lacteal radicles. But the 

 course taken by the fat particles can hardly be explained in this 

 way, and many circumstances force us to the belief that the ac- 

 tivity of the protoplasm of the epithelial or of some special wan- 

 dering cells is the real factor in the case. When the fat is once 

 scattered through the protoplasm of the cells and their prolonga- 

 tion into the delicate connective tissue of the villi, then in all 

 probability other forces, such as the contraction of the villi, may 

 aid in their further movement to the central lacteal space of the 

 villus. 



The exact utility of the marginal bands of rods or pores which 

 characterize the surface of the intestinal epithelium is not known, 

 though it is supposed to be connected with the absorption of fats. 



We may conclude then that the passage through the intestinal 

 wall of some of the materials taken as food may possibly be ac- 

 complished by mere physical processes, but it is probable that the 

 vital activity of the epithelial cells modifies or controls their 

 absorption. The passage of the fat can only be explained by the 



