56 LABORATORY BACTERIOLOGY 



permanently in balsam. The tubercle bacteria should be stained 

 a deep reddish color. All other bacteria or animal tissue in 

 the preparation should be unstained. If desired, a counter 

 stain, such as alkaUne methylene-blue, may be used after decol- 

 orizing. 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 preparations the tubercle 

 bacteria are red and the other organisms and cells are blue. 

 A counter stain is of no value in preparations made from pure 

 cultures or for simple diagnostic purposes. When a counter* 

 stain is desired Gabbett's decolorizing and counter-staining 

 solution is very convenient. 

 Formula : — 



Methylene-blue (powder)- 2 grams. 



10% sulphuric acid 100 c.c. 



After staining with the carbol fuchsin treat the preparations 

 with this mixture until the film has a faintly bluish tint. This 

 solution decolorizes and counter stains at the same time. This 

 organism, like some other pathogenic bacteria, takes the Gram 

 stain. See Novy's " Laboratory Work in Bacteriology," p. 289, 

 for a list of such organisms. 



