ABSORPTION 



285 



readily account for the appearance characteristic of chyle 

 (p. 278), the minuteness of the fat particles it contains being 

 probably intended to prevent embolism by plugging of the 

 capillaries. The view thus indicated was the one formerly most 

 prevalent. On the other hand, bile has, in virtue of its bile-salts, 

 an extremely active solvent action on both fatty acids and soaps : 

 hence the possibility that fat is split up so as to give rise to 

 variable relative amounts of substances, which pass in solution 

 into the cells of the villi, as do the proteids and carbohydrates. 

 We shall see that the chemical view is the one now generally 

 adopted. 



If the intestinal mucous membrane of an animal in full fat 

 absorption is stained with osmic acid, the epithelial cells are found 

 to be crowded with minute particles of varying size, whose black- 

 ness shows them to be fat (Fig. 88). This fact provided the chief 

 support for the view that fat 

 reaches the lacteals in a state of 

 minute mechanical subdivision 

 not necessarily involving much 

 chemical change. If this were so 

 we should expect to see some of 

 the fat particles in transit through 

 the striated border of the epithe- 

 lial cells, and this is never ob- 

 served. 



It is generally accepted that the 

 fat passes into the cell and not 

 between the cells, and the ques- 

 tion arises as to whether this 

 passage into the wall of the 

 bowel is a physical or a secretive 



process. Leucocytes are not credited with absorption, though 

 as carriers of fat between the epithelial cells and the central 

 lacteal — viz., through the arterial network of the villus — they 

 undoubtedly assist. On the other hand, the absorption of anthrax 

 bacilli from the intestine, a process which is undoubted, must 

 occur by their being engulfed by cells. The wandering cells 

 of the body are, we know, capable of ingesting bacteria in 

 other places, and there appears no reason why it should be 

 different in the intestines. Nevertheless, there are good reasons 

 for believing that the fat is dissolved and absorbed by the 

 epithelium of the intestine, its solution into fatty acids and 

 glycerin being effected by the combined action of the bile-salts 

 and pancreatic lipase. These split products are readily absorbed, 

 glycerin presenting no difficulties, while the fatty acids are taken 

 up either as such or as soaps. It has been stated that osmic 



Fig. 88. — Mucous Membrane of 

 Frog's Intestine during Ab- 

 sorption of Fat (Schafer). 



ep. Epithelial cells ; sir, striated 

 border ; c, lymph corpuscles ; 

 I. lacteal. 



