200 



COLUMNAR EPITHELIUM. 



Hum. There is always a distinct oval nucleus which contains a network of chromato- 

 plasm. The nucleus may cause a bulging in the part of the cell in which it is 

 situated, and the nuclei of adjacent cells are on this account often seated in different 

 planes. The substance of the cell usually appears granular, but on closer inspection 

 with higher powers it may be seen that the granular appearance is caused by vacuo- 

 lation and reticulation of the protoplasm. The cell may contain fatty globules and 

 other substances, among which the most deserving of mention is mucin, the chief 

 organic constituent of mucus. The mucin (or mucigen) usually takes the form of a 

 granular deposit within the cell, especially in the part nearest the free border ; when 

 fully formed the granules swell, and their substance escapes in the form of mucus ; 

 the nucleus is often pressed down towards the finer extremity of the cell. Columnar 

 epithelium cells which are thus altered by distension of the outer or free part of the 

 cell by mucus are termed from their shape " goblet or chalice cells " (figs. 232, 233). 



In typical columnar epithe- 

 lium cells, such as those lining 

 the mucous membrane of the 

 small intestine, the free border 

 differs from the rest of the cell 

 in being more refracting and 

 finely striated. This striated 

 border of the cell (figs. 230 and 

 231, sir.) is often spoken of as the 

 cuticular layer, and it is thereby 

 assumed that it is composed of 



Fig. 234. ISOLATED CELLS FROM THE CONVOLUTED TUBTJLES OP THE RAT'S KIDNEY. (Heidenhain). 



Fig. 235. SECTION OF A RACEMOSE GLAND, SHOWING THE COMMENCEMENT OF A DUCT IN THE ALVEOLI. 

 MAGNIFIED 425 DIAMETERS. (E. A. S.) 



a, one of the alveoli, several of which are in the section shown grouped around the commencement of 

 the duct, d' ; a', an alveolus, not opened by the section ; b, basement membrane in section ; c, interstitial 

 connective tissue of the gland ; d, section of a duct which has passed away from its alveoli, and is now 

 lined with characteristically-striated columnar cells ; s, semilunar group of darkly-stained cells at the 

 periphery of an alveolus. 



something different from the cell-protoplasm. The border does not however, appear 

 to offer a greater resistance than does the cell-protoplasm to the action of reagents, 

 for those which destroy the protoplasm of the cell destroy also the striated border. 

 After having been hardened by reagents it may be detached from the rest of the 

 cell, and since the striated free borders of adjacent cells often adhere together, 

 a continuous membrane may thus be obtained, marked by a mosaic of fine 

 lines indicating the division between the cells from which this " cuticula " has 

 become detached. The fine strias appear to be caused by the existence of 

 fibrils or septa (perhaps spongioplasmic). The striated cuticula is not imme- 

 diately in contact with the protoplasm of the cell, but is separated from it by a 

 thin disk composed of a substance which refracts the light even more than the striated 

 border. This disk (shown in fig. 230) corresponds in situation to the bright border of 

 the ciliated epithelium cells (see below), and it is possible that the striated border is 

 the morphological equivalent of the bunch of cilia upon those cells. Columnar epithe- 



