68 LABORATORY BACTERIOLOGY 



100. 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 10 to 15 minutes. The preparation is then rinsed 

 in water and decolorized by treating it with a 10% solution 

 of nitric or sulphuric acid for from to i 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 i minute in alkaline methylene blue, 

 rinsed in water, and examined as before. In 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 100 cc. 



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 



1 See Novy's Laboratory Work in Bacteriology, p. 289, for a list of 

 such organisms. 



