ORDINARY STAIN ING-SOLUTIONS. 175 



saturated alcoholic solution and 95 parts of distilled 

 water proves, as a general thing, to he satisfactory. 



The above represent the staining-solutions in every- 

 day use. They may be kept in bottles supplied with 

 stoppers and pipettes (Fig. 34), and when used are 

 dropped upon the preparation to be stained. 



For certain bacteria which stain only imperfectly 

 with these simple solutions it is necessary to employ 

 some agent that will increase the penetrating action of 

 the dyes. Experience has taught us that this can be 

 accomplished by the addition to the solutions of small 

 quantities of alkaline substances, or by dissolving the 

 staining-materials -in strong watery solutions of either 

 aniline oil or carbolic acid, instead of water in other 

 words, by employing special solvents and mordants 

 with the stains. 



Of the solutions thus prepared which may always be 

 employed upon bacteria that show a tendency to stain 

 imperfectly, there are three in common use Loffler's 

 alkaline methylene-blue solution ; the Koch-Ehrlich 

 aniline-water solution of either fuchsin, gentian-violet, 

 or methylene-blue ; and Ziehl's solution of fuchsin in 

 carbolic acid. These solutions are as follows : 



Loffler's alkaline methylene-blue solution : 



Concentrated alcoholic solution of methylene-blue . . 30 c.c. 

 Caustic potash in 1 : 10,000 solution 100 c.c. 



Koch-Ehrlich aniline-water solution. To about 100 

 c.c. of distilled water aniline oil is added drop by drop 

 until the solution has an opaque appearance, the vessel 

 containing the solution being thoroughly shaken after 

 the addition of each drop. It is then filtered through 

 moistened filter-paper until the filtrate is perfectly 



