316 DIGESTION. 



These cells, though closely adherent to the subjacent parts 

 during life, are easily removed after death, and are almost 

 always destroyed and removed in injected preparations. 

 They adhere firmly to each other, and are isolated with diffi- 

 culty in miscroscopic preparations. Kolliker has shown that 

 the membranes on the free surfaces of these cells are thick- 

 ened and finely striated, forming, as it were, a special mem- 

 brane covering the villus and external to the cells. This 

 membrane may be raised up from the cells and exhibited by 

 the action of water. 1 



The substance of the villus is composed of a stroma of 

 amorphous matter, in which are embedded nuclei and a 

 few fibres, fibro-plastic cells, and numerous non-striated mus- 

 cular fibres. The blood-vessels are very numerous ; four or 

 five, and sometimes as many as twelve or fifteen artereoles 

 entering at the base, ramifying through the substance of the 

 villus, but not branching or anastamosing, or even diminish- 

 ing in calibre, until by a slightly wavy turn or loop they 

 communicate with the venous radicles, each of which is some- 

 what larger than the arterioles. The veins all converge to 

 two or three branches, finally emptying into a large trunk 

 which occupies the centre of the villus. 2 



The nuclei of the muscular fibres of the villi may be 

 shown by treating them with acetic acid after the epithelium 

 has been removed. These fibres appear to be longitudinal, 

 forming a thin layer surrounding the villus, about half way 

 between the periphery and the centre, and continuous with 

 the muscular coat of the intestine. The muscular fibres, 

 from their arrangement, would seem to be capable of short- 



1 KOLLIKER, op. cit., p. 328. These observations were made by Kolliker in 

 1855. In 1842, Goodsir described and figured an appearance on the free ends 

 of the epithelium covering the villi, which he said was like a membrane cover- 

 ing the cells, though he did not distinctly assert the existence of such a mem- 

 brane. ( On the Structure of the Intestinal Villi in Man and certain of the Mam- 

 malia, with some Observations on Digestion, and the Absorption of Chyle. TJie 

 Edinburgh New PhilosophicalJournal, 1842, vol. xxxiii., p. 167.) 



2 SAPPEY, Traite d" 1 Anatomic Descriptive, Paris, 185V, tome iii., pp. 144, 145. 



