82 PATHOGENIC BACTERIA. 



A series of comparative trials has shown that the violet is in 

 this way rendered more intense, and the result of the stain more 

 certain. Or the potash, as suggested by the author, may be 

 added to the dye. The following formula of Mr. Mead's gives 

 excellent results, the specimens being washed in tap water after 

 the use of the stain. 



Potassic gentian violet : 

 Gentian Violet . 1 gram 

 Absolute Alcohol 20 c.c. 



Caustic Potash Solution in dis- 

 tilled water (1 in 10,000) 



100 c.c. 

 Concentrated alcoholic solution of gentian violet : 



Gentian Violet 25 gram | Absolute Alcohol 100 c.c. 



Gram's method : * 



(1) Aniline gentian violet : 



Concentrated alcoholic solu- I Aniline Water 1,000 c.c. 



tion of Gentian Violet 11 c.c. | 



The solution is to be freshly made, and filtered before use. 

 Aniline water is prepared by well shaking 4 c.c. of pure aniline 

 with 100 c.c. of distilled water, and twice filtering through 

 paper, first moistened with distilled water. 



(2) Iodine solution : 



Iodine 1 gram I Distilled Water 300 c.c. 



Iodide of Potassium 2 



The preparation of distilled water for the purpose of 

 making cover-glass films (described on p. 26), may be ex- 

 peditiously carried out by allowing the steam of a beaker or 

 kettle to condense on the clean under side of a flat capsule, par- 

 tially filled with cold water, and afterward quickly inverting the 

 latter, when ample will be found on the side brought uppermost. 



* [The thin smear is dried on the cover-glass, fixed by heat, stained with aniline 

 gentian violet for five minutes, immersed in the iodine solution one or two minutes, 

 washed in strong alcohol until nearly colorless, dried and mounted with balsam. 



