210 MANUAL OF PHYSIOLOGY. 



tides of fat in the emulsion are also coated with a film of bile or 

 soap. Thus they are enabled to pass into the epithelial cells, in 

 which they can be detected during digestion. The bile or soapy 

 coating of the fat particles may no doubt aid in their transit 

 through the various obstacles on their way to the lacteal radicles. 

 But the course taken by the fat particles can hardly be explained 

 in this way, and many circumstances force us to the belief that 

 the activity of the protoplasm of the epithelial or of some special 

 wandering cells is the real factor in the case. When the fat is 

 once scattered through the protoplasm of the cells and their pro- 

 longation into the delicate connective tissue of the villi, then in 

 all probability other forces, such as the contraction of the villi, 

 may aid in their further movement to the central lacteal space 

 of the villus. 



The exact utility of the marginal bands of rods or pores which 

 characterize the surface of the intestinal epithelium is not 

 known, though it is supposed to be connected with the absorp- 

 tion of fats. 



We may conclude, then, that the passage through the intestinal 

 wall of some of the materials taken as food may possibly be ac- 

 complished by mere physical processes, but it is probable that the 

 vital activity of the epithelial cells modifies or controls their 

 absorption. The passage of the fat can only be explained by the 

 aid of the direct activity of cells which by amoeboid movement 

 take up the fine particles and pass them on to the interstices of 

 the connective tissue of the villi. 



LYMPH AND CHYLE. 



As these two fluids are mixed together in the thoracic duct, 

 whence the lymph is commonly obtained for examination, they 

 had better be considered at the same time. 



As we should expect, the fluids coming from the tissue drain- 

 age, from the lymphatic glands, and from the lacteals of the 

 alimentary tract form an opaque mixture which holds a consid- 

 erable quantity of proteid in solution, and contains a number of 

 morphological elements, viz. : (1), protoplasmic cells similar to 

 those found in the lymph follicles, and in most essential points 



