88 LABORATORY BACTERIOLOGY 



(2) The decolorizer and counter stain : — 



Methylene-blue powder 2 grams. 



10% sulphuric acid 100 c.c. 



Stain the preparation with the first solution as described in 

 (86), then rinse in water and stain i minute with the second 

 solution, which decolorizes and counter stains at the same time, 

 and again rinse in water. If the film has a bluish tint, it is 

 ready for examination ; if not, it should be stained a little longer 

 in the second solution. In these preparations the tubercle bac- 

 teria should appear as slender, more or less curved, rod-shaped 

 bodies of a deep reddish cblor, while the surrounding tissue and 

 other bacteria present are stained a more or less intense blue. 

 ■ Sudan III. is reported by Dorset to be a very good differen- 

 tial stain for this organism. A saturated solution in 80 fo alco- 

 hol is used. It is reported to be effective in differentiating the 

 tubercle organism from that of leprosy and from the smegma 

 bacillus. 



