DECOLORIZING SOLUTIONS 183 



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 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 employment. 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 subjected to the action of Gabbett's 

 methylene-blue sulphuric acid solution. This latter con- 

 sists of 



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

 Methylene-blue, in substance 1 to 2 grams 



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

 for examination. The tubercle bacilli will be stained red 

 by the fuchsin, while all other bacteria, cell-nuclei, etc., 

 will be tinted blue. 



Pappenheim's Decolorizer and Counter Stain. As with the 

 Gabbett method, the cover-slips are stained for from 5 to 

 10 minutes in cold carbol-fuchsin. They are then rinsed 

 in water and kept, until they are of a pale blue color, in a 

 decolorizing and counter-staining fluid made as follows: 



