STAINING AND MOUNTING OF MICRO-ORGANISMS 81 



to different dyes, this property serves to distinguish between 

 various kinds of organisms which are not otherwise to be 

 differentiated by simple microscopical examination. 



Weigert, in 1876, found that bacteria could be stained 

 with the basic anihne dyes, but not by the acid dyes or the 

 natural colouring matters. Koch and other workers at 

 once recognised the value of this discovery, and rapidly 

 investigated the matter, and devised many of the methods 

 now in use. 



All the basic aniline dyes have a very strong affinity for 

 bacteria; whereas the acid coal-tar dyes, such as eosine, 

 safranine, picric acid, and the natural dye stuffs, such 

 as logwood and cochineal, do not possess this property. 



The following are the most commonly used basic aniline 

 stains, dyes used for staining bacteria : 



Gentian violet (syn. benzyl violet, pyoktanin). 

 Methyl violet (syn. Hoffmann's violet, dahlia). 

 Methylene blue (syn. phenylene blue). 

 Thionin blue. 



Fuchsine (basic fuchsin, basic rubin, magenta). 

 Bismarck brown (syn. vesuvin, phenylene brown) . 



Gentian violet and fuchsine are the two dyes most 

 frequently used for the staining of bacteria. These stain 

 quicker and more intensely than any others. In order to 

 increase the staining properties of the dyes, certain reagents 

 are added to the stains to act as mordants. Phenol, aniline 

 oil, and alkalies are amongst the bodies most frequently 

 employed for this purpose. A very large number of stains 

 and staining methods have been devised by various workers 

 from time to time, but we will only give a few of the most 

 approved methods which are applicable to all ordinary 

 purposes. 



Stock solutions of concentrated alcoholic solutions of 



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