ABSORPTION. 



193 



intestine into that of the lacteal vessels. Its transmission is facilitated 

 by the alkaline condition of the blood and of the intestinal juices. Oil 

 by itself is a non-diffusible substance; that is, it is incapable of 

 passing through an animal membrane by endosmosis. If a fluid con- 

 taining oil be placed on one side of an animal membrane, and pure 

 water on the other, the water will readily penetrate the substance of 

 the membrane, while the oily particles cannot be made to pass under 

 any ordinary pressure. Though this be true, however, for pure water, 

 it is not true for slightly alkaline fluids like the serum of blood or the 

 lymph. This has been demonstrated by the experiments of Matteucci, 

 in which he made an emulsion with an alkaline fluid containing 4.3 

 parts per thousand of potassium hydrate. Such a solution has no per- 

 ceptible alkaline taste, and its action on reddened litmus paper is about 

 equal to that of the lymph and chyle. If this emulsion were placed in 

 an endosmometer, together with a watery alkaline solution of similar, 

 strength, it was found that the oily particles penetrated the animal 

 membrane without much difficulty, and mingled with the fluid on the 

 opposite side. Endosmosis will thus take place with a fatty emulsion, 

 provided the fluids used in the experiment be slightly alkaline in re- 

 action. 



The fatty molecules of the chyle, accordingly, are taken up by the 

 layer of epithelium cells covering the surface of the villi, and their 

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

 tion in the physical appearance of the cells composing it. In the inter- 

 vals of digestion these cells are nearly transparent and homogeneous- 



60. 



Fig. 61. 



INTESTINAL EPITHELIUM; from the 

 Dog, while fasting. 



INTESTINAL EPITHELIUM; from the Dog, 

 during the digestion of fat. 



looking, presenting under the microscope only the appearance of a very 

 fine and delicate granulation. (Fig. 60.) But if examined during the 

 digestion and absorption of fatty matters, their substance is seen to be 



