64 LABORATORY BACTERIOLOGY 
96. Staining tubercle bacteria. Prepare the cover-glass 
preparations from the culture of tubercle bacteria and flame 
them as already described. Stain in fresh carbol fuchsin. 
Place a few drops of the stain on the film side of the cover 
glass and hold it over a flame with forceps until steam is given 
off. Allow the hot stain to act for from 3 to 5 minutes, or 
the preparation may be floated on the carbol fuchsin in a 
watch glass without heat. In this case it is allowed to act 
for from ro to 15 minutes. The preparation is then rinsed 
in water and decolorized by treating it with a 3% solution 
of HCl in 95% alcohol for from } to 1 minute. It is again 
rinsed in water, when it is ready for examination. It can be 
dried and mounted permanently in balsam. The tubercle 
bacteria should be stained a deep reddish color. All other bac- 
teria or animal tissue in the preparation should be unstained. 
If desired, a counterstain, such as alkaline methylene blue, may 
be used after decolorizing; that is, the preparation should be 
again stained for about 1 minute in alkaline methylene blue, 
rinsed in water, and examined as before. Im these prepara- 
tions the tubercle bacteria are red and the other organisms 
and cells are blue. A counterstain is of no value in prepara- 
tions made from pure cultures or for simple diagnostic pur- 
poses. When a counterstain is desired Gabbett’s decolorizing 
and counterstaining solution is very convenient. 
GABBETT’S SOLUTION 
Methylene blue (powder) . . . . . . . 2 grams 
10% sulphuric acid. SS a ae a ee MOREE; 
After staining with the carbol fuchsin treat the preparations 
with this mixture until the film has a faintly bluish tint. This 
solution decolorizes and counterstains at the same time. This 
organism, like some other pathogenic bacteria, takes the Gram 
stain.} 
1 See Novy’s Laboratory Work in Bacteriology, p. 289, for a list of 
such organisms. 
