28 STAINING AGENTS. 



Aniline Blue. 



This stain is much used in connection with the staining of 

 bacillus tuberculosis, but is also very satisfactory as a stain for 

 sieve plates and sieve tissue. Cellulose takes a blue color while the 

 sieve plates become azure. Sections treated with this color are 

 liable to fade after a time. The stain is good in double staining. 



flagenta. 



Magenta is used both as a general and selective stain. It 

 should be applied in an aqueous solution, containing a little acetic 

 acid. The tissue will need to be left in the solution for some time, 

 before the proper depth of staining is secured. 



Picric Acid. 



This is a very convenient and useful ground or general stain 

 and is usually applied in weak alcoholic solutions. It must be borne 

 in mind, however, that picric acid will wash out to quite an extent 

 many of the aniline colors, but in use with haematoxylin, borax, or 

 alum carmine, it makes a most excellent general stain. In connec- 

 tion with hydrochloric acid it will readily wash out the carmine 

 colors. 



Silver Nitrate. 



In a dilute alkaline aqueous solution this is often used as a test 

 for living protoplasm, since it colors it black, while dead protoplasm 

 remains unchanged. The reaction is very delicate and positive. 

 Tannic acid also colors less dilute alkaline solutions black, while 

 cells containing glucose are colored brown. As a general stain 

 the action of silver nitrate is too uncertain for positive directions. 



