50 



76. Staining tubercle bacteria. Prepare the cover- 

 glass preparations from the culture or the tuberculous mate- 

 rial and flame them as already described. Stain in fresh car- 

 bol 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 car- 

 bol 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 ^. to one 

 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 bacteria or animal tissue in the 

 preparation should be unstained. If desired, a counter stain, 

 such as alkaline methylene-blue can be used after decoloriz- 

 ing. That is, the preparation can be again stained for about 

 one minute in alkaline methylene-blue, rinsed in water and 

 examined as before In these preparations the tubercle bac- 

 teria 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. 



(Gabbett recommended 25 % solution of sulphuric acid.) 

 After staining with the carbol fuchsin treat the prepara- 

 tions with this mixture until the film has a faintly bluish 

 tint. This solution decolorizes and counter stains at the 

 same time. 



