ABSORPTION OF MINERALS AND WATER IN THE INTESTINES 395 



easy to demonstrate the presence of microscopic globules of fat, both in the 

 intercellular substance and in the epithelial cells themselves. But it has 

 been constantly noticed that there is a clear zone along the free borders of 

 the cells. Fat drops exist in the adjacent digesting mass, and in the deeper 

 parts of the cells, but not in this border zone. Since the demonstration of 

 the reversible action of lipase, the view has been strengthened that in the 

 very act of absorption the emulsified fats are decomposed and passed through 

 the cell border only to be resynthesized in the cell protoplasm. This is of 

 course against the strictly mechanical view. The decreasing efficiency of 

 fats when the bile, which wets the mucous 

 surface and dissolves the fatty acids, is 

 withheld from the intestine, also supports 

 this view. As absorption progresses the 

 size of the fat drops in the epithelial cells 

 increases, a fact that is readily explained 

 by supposing a continued synthesis and 

 accumulation of fat. 



The fat drops are ultimately discharged 

 into the connective-tissue spaces and finally 

 pass into the lymph channels, the thoracic 

 duct, and into the blood of the subclavian 

 vein. This is the course taken by the 

 larger percentage of the fat. However, 



some of the fat is absorbed into the capillaries of the villi and passes through 

 the liver. The presence of fat drops in the liver cells at certain times can 

 be ascribed to storage of this absorbed fat. 



It is said that the more readily emulsified fats, those that melt readily at 

 the body temperature, are the more completely absorbed. The efficiency 

 of such absorption is as high as 96 to 98 per cent, for the oils, and decreases 

 sharply for such fats as the tallows. 



The large intestine is capable of absorbing fats, though not so readily as 

 the small intestine. 



Absorption of Minerals and Water in the Intestines. The salts 

 common in the foods are most of them readily soluble, dissociate quite com- 

 pletely in the dilute solutions, and diffuse and dialyze readily. Of the salts 

 of the foods, the sodium and potassium cations and chlorine anion are the 

 most readily dissociated and are most diffusible, while the calcium and 

 magnesium cations and the sulphate anion are least diffusible. The sub- 

 stances pass through the intestinal epithelial cells and the intercellular sub- 

 stance; at least salts easily recognized by microchemical means have been 

 found in both localities during absorption. It seems probable that the forces 

 concerned are largely osmosis and diffusion. 



Yet observers have not been able to show that the rate and character of 



FIG. 285. Mucous Membrane 

 of Frog's Intestine during Fat Ab- 

 sorption, ep, Epithelium; str, 

 striated border; C, lymph corpus- 

 cles; /, lacteal. (E. A. Schafer.) 



