134 PRACTICAL HISTOLOGY. [V. 



next layer are somewhat pyriform (fig." 95, ?>), while the deepest layers 



are composed of smaller polyhedral cells. 



4. Transitional Epithelium of Bladder (H). Place the dis- 



tended bladder of a frog or cat in dilute alcohol for twenty-four 

 hours, stain it en masse for the same time in 

 picro-carmine, scrape off a little of the mucous 

 surface and diffuse it in glycerine, add a hair 

 and cover. The cells may also be macerated 

 by using instead J per cent, bichromate of 

 potash solution. 



(a.) Observe various forms of cells, some 

 of them more or less flattened with facets on 

 their surfaces (fig. 95, a, a'), others elongated 

 with finger-shaped processes (6), some pear- 



Fie. 95 . isolated Transi- shaped, and others cubical. All arc 



tional Cells from the rmplpqfp/l 

 Bladder of a Guinea-pig, nucleated. ^ 



a. A superficial ceil seen 5. To Distend a Frog s Bladder. By 

 means of a pin transfix the skin at the 



the deeper layers. Dilute margins of the anus, and tie round the pin 



alcohol and picro-car- ,-r -, *, , i 



mine, x 3 oo. a thread so as to completely occlude the 



aperture. Open the abdomen, make a slit 



into the rectum, and from the latter, after removing its contents, 

 inject dilute alcohol (p. 25) into the bladder. When the bladder is 

 distended, ligature it, cut it out, and suspend it in its inflated con- 

 dition in dilute alcohol for twenty-four hours. 



If the bladder of a cat or guinea-pig be used, it is distended from 

 the urethra with dilute alcohol, and suspended for twenty-four 

 hours in a large volume of the same liquid. 



ADDITIONAL EXERCISES. 



6. To Silver the Free Ends of Columnar Epithelium. A small piece of 

 the mucous surface of the small intestine of a cat is washed in distilled water, 

 and then placed for ten minutes in a ^ per cent, silver nitrate solution, and 

 silvered in the usual way (Method, p. 77). After hardening in alcohol, if the 

 epithelium be detached and mounted in glycerine, it is easy to obtain a view 

 of the free ends of the epithelial cells, with the cement substance between them 

 indicated by "silver lines," and also to see the open mouths of the goblet-cells. 

 The view obtained is that shown in fig. 92, d. 



N.B. Other preparations of these, forms of epithelium will be obtained in 

 sections of the organs in which they occur. 



