STAINING THE TUBERCLE BACILLUS. 169 



be replaced by much more dilute solutions, as a number 

 of the bacilli are entirely decolorized by the too energetic 

 action of the strong acids. He recommends the follow- 

 ing method of decolorization : after staining the slip or 

 section in the usual way, pass it through three alcohols ; 

 it is then to be washed in a solution composed of 



From this it is removed to water and carefully rinsed. 

 The remaining steps in the process are the same as those 

 given in the other methods. 



Gabbett's Method for the staining of tubercle 

 bacilli recommends itself because of its simplicity and 

 the rapidity with which it can be performed. By many 

 it is considered the best method for routine employ- 

 ment. It consists in staining the cover-slips, prepared 

 in the manner given, for from two to five minutes in 

 a cold carbol-fuchsin solution, after which they are sub- 

 jected to the action of Gabbett's methylene-blue sul- 

 phuric acid solution. This latter consists of 



Sulphuric acid (strength 25 per Qent.) . . 100 c.c. 



Methylene-blue, in substance . . 1 to 2 grammes. 



The cover-slips are then rinsed in water and are ready 

 for examination. The tubercle bacilli will be stained 

 red by the fuchsm, while all other bacteria, cell-nuclei, 

 etc., will be tinted blue. 



Gram's Method. — Another important differential 



method of staining which is very commonly employed 



is that recommended by Gram. In this method the 



objects are treated with an aniline-water solution of 



3ntian-violet made after the formula of Koch-Ehrlich. 



