82 APPLIED BACTERIOLOGY 



stains, such as gentian violet, fuchsine, and methylene 

 blue, are prepared by allowing a large excess of the dye to 

 digest for some time in strong alcohol, shaking the solution 

 from time to time. The concentrated solutions are then 

 filtered and preserved in stoppered bottles. Most organisms 

 can be stained by means of a simple aqueous solution of 

 the dye, prepared by the addition of a few drops of one of 

 the above concentrated alcoholic solutions to water in the 

 proportion of about 1 to 6. Care should be taken not to 

 have the staining solution too strong, as it is very easy to 

 overstain. The solution can be tested as follows : The dye 

 should be of such a strength that ordinary print is just 

 visible on placing a watch-glass full of the stain upon some 

 ordinary printed matter. This, of course, only holds as a 

 general rule, as a stronger or a weaker solution is some- 

 times required. Stains should always be filtered before 

 use, otherwise granules of colouring matter will be 

 deposited upon the preparation which it is impossible to 

 wash off. 



The best results are obtained by the use of one of the 

 following solutions : 



Ehrlich's Aniline Gentian Violet. — This powerful staining 

 solution is prepared as follows : 



Saturated alcoholic solution of gentian violet 11 c.c. 

 Saturated aqueous solution of aniline . . . 100 c.c. 



The aniline solution is prepared by shaking about 5 c.c. of 

 colourless aniline with 100 c.c. of distilled water for some 

 time, when most of the aniline passes into solution. This 

 solution is now filtered through a wet filter, which will 

 prevent the undissolved aniline from passing through into 

 the filtrate. The gentian violet in this stain can be replaced 

 by fuchsine or methyl violet, using 11 c.c. of saturated 

 alcoholic solution. 



