198 



FUNCTIONS OF NUTRITION. 



the other, the water will readily penetrate the substance of the mem- 

 brane, while the oily particles cannot be made to pass under any ordi- 

 nary pressure. But though this be true for pure water, it is not true 

 for slightly alkaline fluids like the serum of blood or the lymph. This 

 was shown by the experiments of Matteucci, with an oily emulsion 

 in an alkaline fluid containing 4.3 parts of potassium hydrate per thou- 

 sand. Such a solution has no alkaline taste, and its action on reddened 

 litmus-paper is about equal to that of the lymph and chyle. If such 

 an emulsion be placed in an endosmometer, together with a watery 

 alkaline solution of similar strength, the oily particles penetrate the 

 animal membrane without much difficulty, and mingle with the exterior 

 fluid. Endosmosis will therefore take place with a fatty emulsion, pro- 

 vided the fluids be slightly alkaline in reaction. 



When the molecules of the chyle are taken up by the villi, their 



FIG. 39. 



FIG. 40. 



INTESTINAL EPITHELIUM; from the Dog 

 while fasting. 



INTESTINAL EPITHELIUM ; from the Dog 

 during the digestion of fat. 



passage into and through the epithelial layer produces a marked altera- 

 tion in the appearance of its cells. In the intervals of digestion these 

 cells are nearly transparent and homogeneous-looking, presenting under 

 the microscope the appearance of a very delicate granulation. (Fig. 

 39.) But during the digestion and absorption of fatty matters, their 

 substance is crowded with oily particles. (Fig. 40.) The oily matter 

 then passes onward, penetrating deeper into the substance of the villus, 

 until received by the capillary vessels in its interior. 



Absorption by the Blood-vessels. The final absorption of the digested 

 fluids is accomplished mainly by the blood-vessels of the intestinal 

 villi. Their situation, their numbers, and the rapid movement of the 

 blood, are all favorable conditions for the performance of this function. 

 The capillary plexus of each villus is situated in its superficial part, im- 

 mediately beneath the epithelium cells, so that the absorbed fluids, after 



