STAINING THE TUBERCLE BACILLUS. 181 



ing of tubercle bacilli, but the original method as em- 

 ployed by Koch is so satisfactory in its results that it is 

 not advisable to substitute others for it. The above 

 differs from the original Koch-Ehrlich method for the 

 staining of tubercle bacilli in sputum only hi the occa- 

 sional employment of Ziehl's earbol-fuchsin solution 

 and in the method of heating the preparation with the 

 staining-fluid upon it. 



As Nuttall has pointed out, however, the strong acid 

 decolorizer used in this method can, with advantage, 

 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 



Water 150 c.c. 



Alcohol 50 c.c. 



Concentrated sulphuric acid 20 to 30 drops. 



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 earbol-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 cent.) .... 100 c.c. 

 Methylene-hlue, in substance 1 to 2 grammes. 



