782 METHODS OF INVESTIGATING BACTERIA. 



fuchsine, magdala, and magenta ; brown, with Bismarck 

 brown, or vesuvine ; green, with methyl green ; blue or 

 violet, with hsematoxyline, methylene blue, iodine violet, 

 methyl violet, dahlia, and gentian violet. Many of the 

 bacilli, however, can only be stained by those aniline 

 dyes which stain nuclei. The following are the materials 

 which are most used. 



Most useful Methylene blue, more especially in faintly alkaline 

 tions! ng " solution (Loeffler's universal staining fluid). This fluid 

 is prepared by mixing 1 ccm. of concentrated alcoholic 

 solution of methylene blue, which can be kept for a long 

 time, with 200 ccm. of distilled water, and then adding 

 two to four drops of a 10 per cent, solution of caustic 

 potash. The mixture must be refiltered every day, and 

 must be freshly prepared about every eight days. 



Gentian violet (B.R. in the catalogue of the Berlin 

 company for the manufacture of aniline dyes) in about 

 1 per cent, watery solution. 



Fuchsine is kept at hand in the form of a concentrated 

 alcoholic solution, and is diluted with about five times 

 the amount of water when required. 



Methyl violet, gentian violet, and dahlia show in a 

 special degree the property of metachromatic staining, 

 i.e., they stain various elements of a shade somewhat 

 different from the primary colour, reddish to red, &c. 

 Methyl green, which is usually contaminated with methyl 

 violet, often gives blue, and at times rose tints. 

 Double stain- In order to differentiate better between nuclei and 

 bacteria double staining is at times very suitable; we 

 may mention, for example, double staining with picro- 

 carmine and gentian violet, w r hich depends on the fact 

 that the carmine can drive out the violet from the nuclei, 

 but not from the bacilli. The sections are placed in the 

 first instance in a solution of gentian violet, then in 

 alcohol, then for a moment in water in order to remove 

 the alcohol, and then in Weigert's picro-carmine solu- 

 tion. After remaining in this solution for a half to one 

 hour they are passed through water, alcohol, oil of 

 cloves, and Canada balsam. The result is that the 

 nuclei of the cells have a red colour, while the bacilli 



