84 



MANUAL OF HISTOLOGY. 



Fig. 74. Columnar cells from the 

 small intestine of the rabbit, a, 

 side view of cells with thickened 

 raised lids traversed by pores ; 6, 

 view from above, in which the 

 orifices of the pores appear like 

 dots. 



SO. 



It had long been known that the free surfaces of the columnar cells in 

 question were covered with transparent borders. 

 These, however, were held to be the optical 

 expression of thickened cell -membranes. We 

 now know, however, beyond doubt, that each 

 cell is topped by a kind of lid as it were. In 

 this fine streaks or pore-canals may, as a rule, 

 be distinctly recognised (figs. 74 a, 75 b) seen 

 from above, also, the cells are observed to be 

 finely dotted (fig. 74 b). At times, however, 

 the markings on the borders of the cells are 

 not distinguishable, or only very indistinctly 



This transparent lid may be loosened from the surface of the cells 



by the action of water or 

 pressure ; either in the 

 form of one continuous band 

 (figs. 74 a, 75 a), or, only 

 specially attached to each 

 cell (figs. 75 c-/). Then 

 again, the delicate sub- 

 stance of the lid, composed 

 of some unstable albumin- 

 ous matter, splits up fre- 

 quently on imbibing water, 

 or under slight pressure, 

 into a number of rod- 

 like pieces, which may 

 give to the columnar epi- 

 thelial cells in question 



Fig. 75. The same cells. At o, the border is loosened by 

 water and slight pressure; 6, natural condition; c, a portion 

 of the lid destroyed; d e /, the latter is resolved into a 

 number of rod-like or prismatic pieces, by maceration in 

 water. 



very much the appearance of ciliated elements. 



53. 



The nature of this cell-border on the free surface of the columnar 

 epithelia just mentioned, leaves no room to doubt that the layer is 

 produced by the cell itself, and not deposited on its membrane from with- 

 out in some way or other. 



But many other formations leave us less cer- 

 tain as to their origin. These may occur lying 

 beneath cells, or again, on the exterior of large 

 collections of the latter, in which case they re- 

 present continuous layers, capsules, sacs, blind 

 follicles, tubes, &c., formations which all cor- 

 respond in their structureless transparent appear- 

 ance, and usually in their insolubility, and in 

 consisting of some material allied to, if not iden- 

 tical with el as tin. 



Thus; underneath the coatings of epithelial 

 cells which, cover different mucous membranes of the body, a transparent 

 layer may frequently be observed with varying degrees of distinctness 

 (fig. 76 c c). This is the so-called intermediate membrane of Henle or 

 basement membrane of the English investigators, Todd and Bowman. 

 There appear in like manner transparent Iamina3 underneath the epithe- 

 lium, clothing the anterior and posterior surfaces of the cornea. 



Fig. 76. Diagram of a mucous 

 membrane covered with 

 columnar epithelium, a, the 

 cells ; 6 ft, interstitial sub- 

 stance between their lower 

 ends^ cc, transparent, layer ; 

 d, fibrous tissue of the 

 mucous membrane. 



