366 



LECTURE XV. 



instance into contact with the cylindrical epithelium 

 with which every single intestinal villus is invested. On 

 the surface of every epithelial cell we find, as was first 

 discovered by Kolliker, a peculiar border which, when 

 the cell is seen in profile, exhibits minute and fine striae ; 

 when viewed from above, and seen upon the surface, 

 the cell appears hexagonal and, as it were, dotted over 

 with a number of minute points (Comp. the epithelium 

 of the gall-bladder, Fig. 14, and also Fig. 109, A). 

 Kolliker has put forward the conjecture, that these fine 

 striae and dots correspond to minute pore-canals, and 

 that the absorption of the fat is effected by its minute 

 particles being taken up through these minute pores 

 upon the surface of the epithelial cells. * But the object 

 is one which is accessible only to the highest powers of 

 our optical instruments, and it has therefore hitherto 

 been impossible to obtain perfectly clear notions as to 

 whether the striae really correspond to fine canals, or 



FIG. 109. 



Fig. 109. Intestinal villi, showing the absorption of fat. A. Normal human 

 intestinal villus from the jejunum ; at a the cylindrical epithelium in part still 

 investing it with the delicate border and nuclei ; c, the central lacteal vessel ; 

 v, v, blood-vessels ; in the rest of the parenchyma the nuclei of the connective and 

 muscular tissue. B. Villus in a state of contraction, from a dog. C. Human 

 intestinal villus during the absorption of chyle, D, in a case of retention of chyle ; 

 a* the apex a large fat-drop, emerging from a crystalline envelope. 280 diameters. 



