TUBERCLE BACILLUS 



431 



The best and most universally applicable stain for the tubercle 

 bacillus is the Ziehl-Neelsen stain. 1 It is used as follows: 



1. A thin smear of the material to be examined for tubercle bacilli 

 is prepared and fixed in the usual manner, then flooded with carbol- 

 fuchsin and steamed gently (not boiled) for five minutes. The pre- 

 paration must be flooded continuously with the stain. 



2. Wash thoroughly with water to remove the excess of stain. 



3. Decolorize with 90 per cent, alcohol containing 3 per cent, 

 hydrochloric acid until the pink color has practically disappeared. 



4. Wash with water. 



5. Counterstain lightly with Loffler's alkaline methylene blue. 



6. Wash, dry, examine. 



* 'l 



FIG. 62. Tubercle bacillus showing branching. X 1800. (Wolbach and Ernst.) 



Tubercle bacilli are colored red; non-acid-fast bacteria are colored 

 blue. It should be remembered that spores may also be stained red 

 by this method, but they are not likely to be confused with tubercle 

 bacilli; they are round or oval; tubercle bacilli are much longer. 



The decolorization and counterstaining may be accomplished by 

 one operation, according to the Frankel-Gabbett method. 2 The 

 preparation of the smear and staining with carbol-fuchsin is carried 

 out as above (Steps 1 and 2). Decolorization and counterstaining are 

 accomplished by flooding the preparation with the Frankel-Gabbett 

 solution (100 c.c. water, 25 c.c. sulphuric acid, 50 c.c. saturated alco- 

 holic solution of methylene blue) for three to five minutes, then wash 



1 Ziehl, Deutsch. med. Wchnschr., 1882, 451; Neelsen, Fortschr. d. Med., 1885, 200. 

 'Frankel, Beil. klin, Woch., 1884; Gabbett, Lancet, 1887. 



