170 VICTOR BURKE 



tage in adding ether to the acetone. Short exposure of the Gram 

 positive organisms to the ether does not affect their Gram 

 positiveness. 



ADVANTAGES OF ACETONE AS A DECOLORIZER 



1. Reduces time required for the decolorizing process. 



2. Gives a greater time period between decolorization of Gram 

 negative and Gram positive organisms. 



3. Is cheaper and more readily obtained than absolute alcohol. 



4. Gives better results with the poorer dyes. 



5. Makes a cleaner slide as the dye is more thoroughly ex- 

 tracted from the debris and clusters of bacteria. 



6. Gives better results as it decoloiizes the Gram positive 

 organisms more slowly than alcohol. 



7. Makes possible the use of a stronger dye or a mordant such 

 as phenol because any heavy precipitate on the slide is quickly 

 washed away. 



Alcohol has no advantage over acetone as a decolorizer in 

 the Gram process of staining. When these facts become known 

 we believe acetone will come into more general use as a decolor- 

 izer. As has been emphasized by Lyon (1920) acetone can take 

 the place of alcohol in the preparation of pathological sections and 

 in the cleaning and drying of pipettes and other glassware. 



Counter stain 



The choice of a counter stain and the strength of the solution 

 to be used should be determined by a number of factors. With 

 the better violet dyes the choice of a counter stain is relatively 

 unimportant but with the poorer dyes the choice and control 

 of the counter stain largely determines the excellence of the result. 

 Some of the counter stains in general use have a greater tendency 

 than others to mask the violet dye. One has the choice of either, 

 first, shortening the decolorization with the possibility of leaving 

 a trace of the violet dye in the Gram negative organisms and 

 depending upon a strong counter stam or long exposure to cover 

 over any violet dye remaining in the Gram negative organisms 

 or, second, continuing the decolorization until the Gram negative 



