144 BACTERIOLOGY. 



in the preparation were of the same color, but during the 

 application of the decolorizing solution all except the 

 tubercle bacilli gave up their color. This characteristic, 

 together with reactions to be described, as said, serves to 

 differentiate the tubercle bacillus from other organisms 

 with which it might be confounded. A number of 

 different methods have been suggested for the staining 

 of tubercle bacilli, but the original method as employed 

 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 in the occasional em- 

 ployment of ZiehFs carbolic-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 certain 

 number of the bacilli are entirely decolorized by the too 

 energetic action of the strong acids. He recommends 

 the following method of decolorization : After staining 

 the slip or section in the usual way, pass it through three 

 alcohols ; it is then to be washed out in a solution com- 

 posed of 



Water 150 c.c. 



Alcohol 50 c.c. 



Concen. 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 



