298 



THE DIGESTIVE SYSTEM 



INTESTINAL ABSORPTION. The absorption of fat consists 

 essentially of three phases : 1, its absorption into the intestinal 

 epithelium ; 2, its secretion into the lymphoid tissue of the villus ; 

 and 3, its entrance into the lacteal vessels. In an animal killed 



FIG. 243. INTESTINAL MUCOSA OF A FKOG DURING THE ABSORPTION OF FAT. 



a, epithelium ; 6, tunica propria ; c, an amoeboid leucocyte. Osmium tetroxid. Highly 



magnified. (After Schafer.) 



during the absorption of fat, the intestinal villi, after fixation by 

 solutions of osmium tetroxid, contain fat in (a) the epithelium, 

 (Z>) the lymphoid tissue, and (c) the central lacteal. 



In the epithelium fat is contained in the form of fine droplets 

 which are most numerous in the distal or free ends of the cells. 

 They are also found in the intercellular spaces. During absorp- 

 tion the epithelial cells of the villi become much swollen and 

 elongated. As the process subsides they return to their former 

 size, relatively they are shrunken. When most distended the 

 intracellular fat droplets are the most abundant; as the cells 

 shrink the intercellular droplets relatively increase in number 

 (Drago*). The relative size of the epithelial cells and the abun- 

 dance of intra-epithelial fat is apparently dependent upon the ac- 

 tivity of the processes of absorption. 



* Richerche d. lab. anat. norm. d. r. univ. d. Roma, 1900. 



