1904-5.] ON THE: ABSORPTION OF FAT IN THE INTESTINE. 245 
III.—STRUCTURE OF A VILLUS. 
Before dealing with the subject proper I wish to refer briefly to the 
structure of certain cellular elements of a normal villus of the duodenum 
of a guinea-pig. 
The epithelial cells covering the villus are columnar, their length being 
approximately three to four times their width at the outer edge. They 
lie upon a basement membrane in which there are no nuclei. The majority 
of histologists describe this membrane as containing nuclei, but I have 
never been able to satisfy myself that they are present. It is true that 
in many cases nuclei appear to be present, but on very careful examination 
one will invariably find that such a nucleus belongs to an adjacent capil- 
lary. It is an easy matter to demonstrate blood capillaries lying adjacent 
to the basement membrane, and in specimens where the red corpuscles do 
not stand out prominently it is not difficult to fall into error. 
When the epithelial cells are at rest, no demonstrable space exists be- 
tween adjacent cells, their edges being closely approximated from upper 
to lower end. During their active stage, however, as I shall point out fur- 
ther on, their lower ends become separated. This separation I believe 
to be due to the contraction of the lower end of the cell so that the length 
of the cell is increased. The reasons for this view I will give later on when 
discussing the extrusion of the fat from the epithelial cells. 
The striated border is particularly interesting inasmuch as no one, 
heretofore, except Kischensky, has been able to demonstrate fat within 
it. In the literature of the subject it is usually represented as having a 
distinct and clearly defined outline both above and below. It is a simple 
matter to demonstrate the sharply defined lower margin of this striated 
border; in fact one can readily see it in teased out preparations, but the 
distal edge is not equally well defined. Heidenhain* has indeed called 
attention to the changeable character of the outer edge and Kischensky 
and others have noted the same fact. I have examined a great many 
specimens of epithelium from various animals, and as a result, find that 
the striae are unequal at their distal ends. Further, I have on many 
occasions seen striae terminating as rodets distally. And it is perhaps 
what one might regard as probable, for in the higher invertebrates the 
epithelial cells of the intestine are ciliated, and in the larvae of frogs, also 
the epithelium is ciliated, while that of the adult frog is only striated. 
Again as I shall show later on these striae are able to pick up particulate 
*Pfliiger’s Arch, Vol, 43, Supplement, p. 91. 
