60 MANUAL OF HISTOLOGY. 



After shutting off the carbonic acid gas and admitting oxy- 

 gen, the action will again commence. When the ordinary 

 motion has ceased, the gradual application of heat will cause 

 it to return ; but if the temperature be raised continuously, a 

 point will soon be reached where the excessive heat will cause 

 the motion again to stop. 



Columnar or cylindrical epithelium. This is the epithe- 

 lium par excellence of the digestive tract, clothing the mucous 

 membrane from the cardiac orifice of the stomach to the anus. 

 It is also found at the orifices of the ducts of the large excretory 

 glands, such as the liver and pancreas, in the milk-passages of 

 the nipple, and in some parts of the generative system. These 

 cells are tall and narrow, standing vertical to the surface of the 

 mucous membrane. Sometimes they are broadest at their free 

 extremity, at other times about the middle, so that when viewed 

 from above they appear to be separated from one another. The 

 nuclei are rounded, and are either placed about the middle of 

 the cell or near the attached border. They admit of consider- 

 able variation, however, as to size and shape, some of those in 

 immediate contact being broad at one extremity, and some 

 broad at the others ; the free edge also may be uneven. 



Scrape the surface of a frog's tongue or a rabbit's intestine 

 after washing ; the cells will be seen to advantage. Place 

 some of the scrapings in a drop of glycerine and water to 

 which another drop of dilute acetic aeid (i per cent.) has been 

 added, and mount. In this way the nuclei will be brought 

 clearly into view. The cells closely resemble in their shape 

 the columnar variety, except that they have no cilia. Among 

 them will almost always be found chalice or goblet cells. They 

 lie among the columnar corpuscles, and are usually shorter, 

 but broader, expanding in the centre, and terminating at their 

 attached extremities in a single or double process. The sur- 

 face is cupped. They contain one or more nuclei ; whether 

 they are a distinctive cell or not is as yet uncertain. Some 

 suppose them to be the ordinary columnar cell undergoing 

 mucoid degeneration ; others that they are not epithelial at 

 all. Frey regards them as artificial productions. 1 



1 The most rational explanation is that furnished by F. E. Schultze. The intra- 

 fibrillar substance U, according to this observer, converted into hygroscopic mucin, 

 which swells up. This constitutes a change in the cell which, from being columnar, 

 becomes goblet-shaped. The wall finally ruptures, and the mucin is poured out. 



