STRUCTURE OF A VILLUS. 



2QL 



elements of the mucosa. The orifices of the glands of Lieberkiihn open between the bases of 

 villi (fig. 207). 



Each villus, be it cylindrical or conical in shape, is covered by a single layer of columnar 

 epithelium, whose protoplasm is reticulated, and contains a well-defined nucleus with an intra- 

 nuclear plexus of fibrils. The ends of the epithelial cells directed towards the gut are polygonal, 

 and present the appearance of a mosaic (fig. 208, D). When looked at from the side, their free 

 surface is seen to be covered with a clear, highly refractive disc or "cuticula," which is marked 

 with vertical stria?. These striae were supposed by Kolliker to represent pores for the absorp- 

 tion of fatty particles, but this has not been confirmed, while Brettauer and Steinach regarded 

 them as produced by prisms placed side by side. 



According to v. Thanhoffer, however, this clear disc is comparable to the thickened flange 

 around the bottom of a vessel, such as is used for collecting gases. On this supposition, the 

 upper end of each cell is open, and from it 

 there project pseudopodia-like bundles of 

 protoplasmic processes (fig. 208, B). These 

 processes are supposed to be extended beyond 

 the margin of the cell, and again rapidly re- 

 tracted, and in so acting they are said to 

 carry the fatty particles into the interior of 

 the cells, much as the pseudopodia of an 

 amoeba entangle its food. [This view has 

 not been confirmed by a sufficient number of 

 observers.] Between the epithelial cells are 

 the so-called goblet-cells (fig. 208, C). [Each 

 goblet-cell is more or less like a chalice, 

 narrower above and below, and broad in the 

 middle, with a tapering fixed extremity. The 

 outer part of these cells is filled with a clear 

 substance or mucigen, which, on the addition 

 of water, yields mucus. The mucigen lies in 

 the intervals of a fine network of fibrils, 

 which pervades the cell-protoplasm, while 

 the protoplasm, containing a globular or tri- 

 angular nucleus, is pushed into the lower 

 part of the cell. Those goblet-cells are simply 

 altered columnar epithelial cells, which secrete 

 mucus in their interior. They are more 

 numerous under certain conditions. Not un- 

 frequently in a section of the mucous mem- 

 brane of the gut, after it is stained with 

 logwood, we may see a deep blue plug of 

 mucus partly exuded from these cells. When H 

 looked at from above they give the appearance 

 seen in fig. 208, D.] The epithelial cells 

 are shed in enormous numbers in cholera, 

 and in poisoning with arsenic and muscarin 

 (Bohm). 



[The epithelial cells covering the villus are 

 placed upon a layer of squamous epithelium 

 (basement membrane) the sub-epithelial 

 membrane of Debove. This basement mem- 

 brane is said to be connected by processes 

 with the so-called branched cells of the adenoid 

 tissue of the villus, while it also sends up pro- 

 cesses between the epithelial covering.] 



Circular 

 muscle. 



Longi- 

 tudinal 

 muscle. 



Fig. 207. 

 Longitudinal section of the small intestine of a 

 dog through a Peyer's patch. 



The villus itself consists of a basis of adenoid tissue, containing in its centre one or more 

 lacteals, closely invested with bundles of longitudinal smooth muscular fibres, derived from the 

 muscularis mucosae, and a plexus of blood-vessels. The adenoid tissue of the villus consists of 

 a reticulum of fibrils with endothelial plates at its nodes. The spaces of the adenoid tissue form 

 a spongy network of inter-communicating. channels containing stroma-cells or leucocytes (fig. 

 208, A, e, e) These leucocytes or lymph-corpuscles have been 3een to contain fatty granules, 

 and they are perhaps concerned in the absorption of fatty particles* 



The lymphatic or lacteal lies in the axis of the villus (fig. 210, d). Some regard the lacteal 

 merely as a space in the centre of the villus, but more probably it has a distinct wall composed 

 of endothelial cells, with apertures or stomata here and there between the cell-plates. These 

 stomata place the interior of the lacteal in direct communication with the spaces of the adenoid 

 tissue. Perhaps, white blood-corpuscles wander out of the blood-vessels of the villi into the 



