MICROSCOPIC EXAMINATION 129 



CARBOLIC GENTIAN VIOLET (NICOLLE) 



Gentian violet (saturated alcoholic solution) 10 cc. 



Carbolic acid (1% solution) 100 cc. 



Mix and filter before storing. 



Aqueous solutions. Aqueous solutions of methyl violet, 

 gentian violet, fuchsin, and the other aniline dyes are pre- 

 pared by adding 1 cc. of the saturated alcoholic solution of the 

 desired dye to 20 cc. of distilled water. This will impart a 

 decided color to the liquid, so that in a pipette it will be 

 barely transparent. 



The true aqueous solutions are made by dissolving the 

 dyes in water, but these are weak and not so effective as those 

 prepared from the alcoholic solutions. These solutions de- 

 teriorate In a short time. The carbol fuchsin and alkaline 

 methylene blue will keep a little longer, but they require fil- 

 tering occasionally. 



STAINS FOR SPECIAL PURPOSES. 



Gram's method of staining bacteria. Stain the cover- 

 glass preparations in gentian violet aniline water, or in a 

 saturated alcoholic solution of gentian violet in 5% carbolic 

 acid in the proportion of 1 to 20 for from 5 to 7 minutes. 

 Rinse in water and transfer them to a watch glass containing 

 Gram's solution until the color becomes quite black. This 

 requires from 1 to 2 minutes; then place the preparations in 

 a watch glass containing alcohol and allow them to remain 

 there until the color has almost entirely disappeared, or has 

 become a pale gray. Rinse in water and examine at once, or 

 allow them to dry and mount in balsam. (Sections of tissues 

 must be dehydrated and cleared before mounting.) 



GRAM'S SOLUTION 



Iodine 1 gram 



Potassium iodide 2 grams 



Distilled water 300 cc. 



Certain bacteria stain deeply and retain the coloring 

 matter when treated by this method, while others are decol- 

 orized by the alcohol. On this account some investigators 



