MODIFICATION OF THE GRAM STAIN 323 



of the more uncommon aniline salts with the hope that one 

 may be found which will be entirely stable and have great pene- 

 trating power. 



As an alternative method, aniline oxalate may be used in place 

 of aniline sulphate in this modified stain. This salt seems to have 

 slightly better penetrating power than the aniline sulphate and 

 has the advantage that staining may be accomplished in thirty 

 seconds instead of one minute. This stain was kept for six weeks 

 in the sunlight out doors and in the incubator for two months 

 and no change could be detected in its staining qualities. It is 

 thought, however, that the aniline oxalate stain would not be 

 as stable as the aniline sulphate stain because aniline oxalate 

 very slowly decomposes in solution, liberating free aniline, while 

 aniline sulphate solution is stable. 



The aniline-sulphate-gentian-violet stain as here outlined was 

 tried on various kinds of bacteria and in all cases the results were 

 similar to those obtained with the Gram stain. Control slides of 

 Gram positive organisms made according to the usual Gram 

 method, showed the bacteria slightly less densely stained by this 

 modified method. This difference was no greater than the dif- 

 ference detected in a comparison of slides made with American 

 and Gruebler dye-stuff in the customary manner. Gram nega- 

 tive bacteria with this modified stain seem to be more nearly 

 colorless than the consols made by the Gram method. The 

 degree of difference between a Gram negative and a Gram posi- 

 tive stain seems to be entirely comparable in the two methods. 

 Different strengths of solutions, imported and domestic dye-stuff 

 and various time elements of staining, washing and decolorizing 

 were tried and there seemed to be a fairly wide range of 

 limits, with the production of apparently the same result in 

 the finished specimen. Two points should be noted; first, the 

 primary washing of the slide after staining with aniline-sulphate- 

 gentian-violet should be brief (a long washing of more than half 

 a minute tending, on account of the solubility of the aniline salt, 

 to reduce the brilliancy of the preparation) ; second, the modified 

 iodine solution should be left in contact with the slide for one min- 



