30 THE ESSENTIALS OF HISTOLOGY. 



LESSON VII. 



COLUMNAR AND CILIATED EPITHELIUM, AND 

 TRANSITIONAL EPITHELIUM. 



1. TAKE a piece of rabbit's intestine which has been two days in chromic 

 acid solution (1 part chromic acid to 2,000 normal saline solution). Scrape the 

 inner surface with a scalpel, break up the scrapings in a drop of water on a 

 slide. Add a small piece of hair to avoid crushing, and cover the preparation. 

 The tissue may then be still further broken up by tapping the cover-glass. 

 Sketch one or two columnar cells and also a row of cells. Measure two or 

 three cells and their nuclei. 



To keep this preparation, place a drop of very dilute hsematoxylin solution 

 at one edge of the cover-glass. When the hsematoxylin has passed in and 

 has stained the cell-nuclei, place a drop of glycerine at the same edge and 

 allow it slowly to diffuse under the cover-glass. Cement this another day. 

 Osmic acid (1 per cent.) may be used in place of hsematoxylin. 



2. Break up in glycerine a shred of epithelium from a piece of frog's 

 intestine that has been treated with osmic acid, and has subsequently 

 macerated in water for a few days. The cells easily separate on tapping the 

 cover-glass. They are larger than those of the rabbit and exhibit certain 

 points of structure better. Measure and sketch one or two cells. 



The cover-glass may be at once fixed by gold size. 



3. Prepare the ciliated epithelium from a trachea that has been in chromic 

 acid solution (1 to 2,000 normal saline) for two days, in the same way as in 

 1. Measure in one or two of the cells (a) the length of the cells, (6) the 

 length of the cilia, (c) the size of the nucleus. Sketch two or three cells. 



This preparation is to be stained and preserved as in 1. 



4. Make a similar teased preparation of the epithelium of the urinary 

 bladder, which is to be distended with bichromate of potash solution (1 part to 

 800 of water), and after an hour or two cut open and placed in more of the 

 same solution. Observe the large flat superficial cells, and the pear-shaped 

 cells of the second layer. Measure and sketch one or two of each kind. The 

 cells will vary greatly in appearance according to the amount of distension' 

 of the organ. 



Stain and preserve as in 1 and 3. 



All the above varieties of epithelium will afterwards be studied in situ 

 when the organs where they occur come under consideration. 



Columnar epithelium. The cells of a columnar epithelium (fig. 28) 

 are prismatic columns, which are set closely side by side, so that when 

 seen from the surface a mosaic appearance is produced. They often 

 taper somewhat towards their attached end, which is generally trun- 

 cated, and set upon a basement membrane. Their free surface is 

 covered by a thick striated border (fig. 29, str), which may sometimes 



