30 MANUAL OF BACTERIOLOGY. 



ate in a short time, and it is best to prepare them freshly each 

 time they are required. A very useful solution, which is 

 permanent, is Loffler's alkaline methylene-blue: 



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

 Potassium hydrate (caustic potash), 1-10,000 watery 



solution 100 c.c. 



Loffler's methylene-blue is a good stain for general purposes. 

 It is perhaps more in use than any other formula for coloring 

 the diphtheria bacillus. 



Aniline-water Staining Solutions. The intensity with 

 which aniline dyes operate may be increased by adding aniline 

 oil to the solution : 



Aniline oil 5 c.c. 



Water 100 c.c. 



Mix, shake vigorously, filter; the fluid after filtration should 

 be perfectly clear; add 



Alcoholic solution of fuchsin (or gentian-violet, or methy- 

 lene-blue) ii c.c. 



Alcohol 10 c.c. 



Aniline-water staining solutions do not keep well, and need 

 to be freshly prepared about every ten days or two weeks. 

 The keeping quality depends probably upon the temperature 

 and possibly on the exposure to light. Sometimes it keeps 

 longer than at others, even when prepared each time alike. It 

 is a good plan to filter it every time before use. Precipitates 

 form during the first twenty-four hours after the stain is made, 

 and for this reason cleaner preparations are obtained with the 

 stain after it has stood for a day. The alcohol advised in the 

 accompanying formula tends to dissolve the precipitate. Vari- 

 ous other formulae are given by different authors for the prep- 

 aration of aniline-water staining solutions, but the one given 

 above will be found to give satisfactory results. The appli- 

 cations of the aniline-water stains will be given under separate 



