TUBERCLE STAINS. 113 



Stain for Tubercle and Leprosy Bacilli. These bacilli 

 cannot be well stained with a simple watery solution of a 

 basic aniline dye. This fact can easily be tested by 

 attempting to stain a film of a tubercle culture with such 

 a solution. They require a powerful stain containing a 

 mordant, and must be exposed to the stain for a long 

 time, or the action of the latter may be aided by a short 

 application of heat. When once stained, however, they 

 resist decolorising with very powerful reagents. The 

 smegma bacillus also resists decolorising with strong acids 

 (p. 255). Any combination of gentian -violet or fuchsin 

 with aniline oil or carbolic acid or other mordant will stain 

 the bacilli named, but the following methods are most 

 commonlv used : 



Ziehl-Neelsen Carbol-Fuchsin Stain. 



Basic fuchsin i part 



Absolute alcohol . . . .10 parts 

 Solution of carbolic acid (i : 20) . 100 parts 



1. Place the specimen in this fluid, and having heated it till steam 

 rises, allow it to remain there for five minutes, or allow it to remain in 

 the cold stain for from twelve to twenty-four hours. (Films and 

 paraffin sections are usually stained with hot stain, loose sections with 

 cold ; in hot stain the latter shrink.) 



2. Decolorise with 20 per cent solution of strong sulphuric acid, 

 nitric acid, or hydrochloric acid, in water. In this the tissues become 

 yellow. 



3. Wash well with water. The tissues will regain a faint pink 

 tint. If the colour is distinctly red, the decolorisation is insufficient, 

 and the specimen must be returned to the acid. As a matter of prac- 

 tice, it is best to remove the preparation from the acid every few 

 seconds and wash in water, replacing the specimen in the acid and 

 re-washing till the proper pale pink tint is obtained. 



4. Contrast stain with a saturated watery solution of methylene- 

 blue for half a minute, or with saturated Bismarck-brown for from two 

 to three minutes. 



5. Wash well with water. In the case of films, dry and mount. 

 In the case of sections, dehydrate, clear and mount. 



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