402 SPECIAL MICROSCOPIC TECHNIQUE. 



5. For investigating fertilization, one may use the eggs of 

 Ascaris megalocephala. The whole egg is fixed in Zenker's 

 fluid, sectioned, and stained with iron haematoxylin. 



2. EPITHELIAL TISSUE. 



6. Epithelium may be studied advantageously in the fresh 

 state by scraping the cells from mucous surfaces, etc. In a 

 drop of the saliva placed on a slide, large flat epithelial cells 

 are found. They may be stained in methylene-blue and 

 mounted in glycerin. 



7. By the methods of maceration, epithelial cells can be 

 isolated. These may be studied unstained or colored by 

 methylene-blue. Picro-carmine may be used with cells which 

 have been fixed or hardened. A drop can be drawn under the 

 cover glass by placing a piece of filter-paper on the opposite 

 side; and the coloring material may be washed out in the same 

 way. 



Goblet cells may be obtained from the bronchus or intes- 

 tine ; ciliated epithelium, from the bronchus, nasal mucous 

 membrane, etc. An excellent method of isolating the cells 

 of the nasal mucous membrane consists in exposing it to the 

 vapors of osmic acid for from six to eight hours, and then 

 macerating in dilute alcohol. These cells may be stained in 

 picro-carmine. 



8. The cement lines are demonstrated best by the silver 

 nitrate method. A membrane covered with endothelium, 

 such as the mesentery, is stretched over a cork or cover 

 glass and placed in a 0.1-1 per cent, aqueous silver nitrate 

 solution. After from one to ten minutes to one hour the object 

 becomes somewhat opaque. It is then placed in a large quan- 

 tity of water and exposed to direct sunlight. Reduction usually 

 occurs in from five to fifteen minutes. After this, it may be 

 treated as an ordinary section and mounted in glycerin or 

 Canada balsam. Many modifications of this method have 

 been employed. 



9. A special method for the demonstration of protoplasmic 

 bridges has been suggested by Kolossow. This consists in fix- 



