376 



THE DIGESTIVE SYSTEM 



most abundant ; as the cells shrink the intercellular droplets increase 

 relatively in number (Drago, Richerche d. lab. ant. norm. d. r. univ. d. 

 Roma, 1900). The relative size of the epithelial cells and the abun- 

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

 of the processes of absorption. 



As to the manner in which the fat enters the epithelium there is 

 some doubt. Schafer (Internat. Monatsch. f. Anat. u. Physiol., 1885) 

 suggested that the leukocytes by their ameboid activity inclose the 



emulsified droplets in the 

 intestinal lumen and convey 

 them into the substance of 

 the villi. It seems more 

 probable that the fats are 

 saponified in the intestinal 

 tract, and enter the epithe- 

 lium in solution (White- 

 head, Amer. Jour. Physiol., 

 24, 2, 1909). Here they 

 are again synthesized into 

 neutral fat by the activity 

 of the epithelium (Pflliger, 

 Arch. f. d. ges. Physiol., 

 1900). Such a process ac- 

 counts for the abundance of 

 fat within the distal por- 

 tions of the cells. The drop- 

 lets are then secreted into 

 the intercellular and subja- 

 cent tissue spaces. 



The second phase of absorption includes the transference of the 

 fat particles to the lacteal. This process appears to depend partially, at 

 least, upon the activity of the leukocytes, as suggested by Schafer, the 

 particles of fat thus finding their way through the diffuse lymphoid 

 tissue. According to Renter (Anat. Hefte, 1902), fat droplets are 

 found in the tissue spaces as well as in the lymph corpuscles of the 

 diffuse lymphoid tissue, a fact which would seem to indicate that other 

 agencies aid in the transit of the fat from the epithelium to the lacteal 

 than are accounted for by the purely mechanical theory of Schafer. 

 The third phase includes the secretion of the fat into the lumen of 

 the lacteal; this is, at least partially, accomplished by the disintegra- 



FIG. 349. APEX OF AN INTESTINAL VILLUS OF A 

 RABBIT WHICH HAD BEEN FED WITH MILK. 



The fat droplets have been blackened by fixa- 

 tion with picric acid and osmium tetroxid. The 

 figure shows the distribution of fat during certain 

 stages of absorption. Alum carmin stain. High- 

 ly magnified. (After R. Heidenhain, from 

 Oppel.) 



