514 



SPECIAL HISTOLOGY. 



Fig. 210. 



For my own part in fact, I believe that all the narrow cylindrical and 

 filiform villi will be found to present this condition, but that, on the 

 other hand, the number and mode of origin of the lacteals may possibly be 

 different in the broad and foliaceous forms (see Mikr. Anat., ii. 2, p. 160). 

 In addition to these organs, the villi also contain, as Briicke dis- 

 covered a short time ago, a thin layer 

 of longitudinal smooth muscles situ- 

 ated more centrally round the lacteals ; 

 these, however, are not always distinct 

 in man. They produce contractions of 

 the villi (Fig. 210), which are very 

 evident immediately after death, and 

 which, according to Briicke, are also 

 perceptible in the living animal. They 

 have, in all probability, an important 

 influence over the propulsion of the 

 chyle and of the venous blood in the 

 villi always supposing that there is no 

 objection to the assumption that they 

 perform repeated contractions during life. Nothing is known of the 

 nerves in the villi. 



The epithelium of the villi and of the rest of the surface of the 

 mucous membrane, although it is very intimately united with the deeper- 

 seated parts during life, only becoming detached accidentally or by dis- 

 ease, separates very readily in the dead subject, and can only be ob- 

 served in perfectly fresh portions of intestine. It consists everywhere 

 of a simple layer of cylindrical cells slightly narrowed below, of 0-01- 

 0-012 of a line in length, and 0-003-0-004 of a line in breadth, whose 

 contents are usually nothing but fine granules and an oval, clear, vesi- 

 cular nucleus, provided with one or two nucleoli. During life, these 

 cells, which agree in all their chemical characters with the deeper cells 

 of the oral epithelium, are so intimately united, that even after death 

 their contours, in a longitudinal view, are at first either not at all, or 

 only indistinctly distinguishable, though on the surface they have the 

 appearance of a beautiful mosaic. The cylinders only become quite 

 distinct when they are either spontaneously or artificially detaclied, a 

 process which usually takes place in such a manner that they hang 

 together in continuous portions, all the cells covering a villm sometimes 

 coming off together like the calyptra of a moss. The addition of water 

 to these cells produces a separation of the cell contents from the broad 

 end, giving rise, in separate cells, to the appearance of a membrane 

 thickened upon one side and in series of cells or entire villi, to that of 



FIG. 210. Two intestinal villi of the Cat, contracted, and magnified GO diameters. 



