4i8 



ABSORPTION 



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.) 



Fermentation processes from bacterial growth produce certain acids from 

 the carbohydrates, chiefly in the large intestine. These are readily absorbed. 

 Absorption of Fats by the Intestines. Fats reach the absorbing 

 epithelium in two forms, as soluble glycerol and soaps and as finely emulsi- 

 fied fats. The first two are taken up by the epithelium readily enough, 

 but the proof of absorption of emulsified fats is not so clear. It is compara- 

 tively easy to demonstrate the presence of microscopic globules of fat in the 

 intestinal mucosa both in the epithelial cells themselves and to a less degree 



in the intercellular substance. But it has 

 been constantly noticed that there is a clear 

 zone along the inner or 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. The 

 demonstration of the reversible action of 

 lipase, has strengthened Pfliiger's fat dis- 

 sociation theory which holds that before 

 absorption the emulsified fats too must be 

 decomposed. They can then pass through 

 the cell border and are resynthesized in 

 the cell protoplasm. This is of course 

 against the strictly mechanical view, which 



must be abandoned in the presence of the evidence supporting the newer 

 conception. The decrease in efficiency of fats as foods when the bile, which 

 wets the mucous surface and dissolves the fatty acids, is withheld from the in- 

 testine, supports this view. As absorption progresses the size of the fat 

 drops in the epithelial cells increases, a fact that is readily explained by sup- 

 posing a continued synthesis and accumulation of fat. Pfliiger's view 

 of absorption has recently received strong support in the observations of 

 Bloor that isomannid esters of fatty acids when fed to animals were 

 digested but could not be recovered after absorption. Supposing that 

 lipolytic cleavage occurred in this fat during digestion, it would of course 

 not be rebuilt in the cells of the epithelium after absorption. On the 

 theory that the absorption of fats takes place in the emulsified form, this 

 compound should have reappeared in the chyle, but it did not. 



The fat is ultimately discharged into the connective-tissue spaces, passes 

 through the lymph channels, the thoracic duct, and into the blood of the sub- 

 clavian vein. This is the course taken by the larger percentage of the fat. 

 However, during absorption some of the fat enters 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, the liver 

 exhibiting not only a glycogenic but a lipogenic function. 



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



