96 METHODS USED IN THE STUDY OF BACTERIA 



Violet 



Methyl-violet (Hoffman's violet, dahlia) 



Gentian-violet (benzyl-violet, Pyoktanin) 

 Blue 



Methylene blue (phenylene blue) 



Victoria blue 



Thionin blue 

 Red 



Basic fuchsin (basic rubin, magenta) 



Safranin (fuchsin, Girofle) 

 Brown 



Bismarck brown (vesuvin, phenylene brown) 



These dyes are usually used in a weak aqueous solution, 

 and in preparing the bacteria for microscopical examination 

 they are spread in a thin film on a grease-free cover-glass, 

 fixed by heat, stained, washed in water, and mounted in Canada 

 balsam, the exact details for which must be gotten from a lab- 

 oratory guide. Instead of spreading the bacteria promiscu- 

 ously over the surface of a cover-glass, a cover-glass may be 

 lowered on to the culture and an impression preparation made, 

 which is fixed and stained as usual. This is a difficult prepara- 

 tion to make, but when properly made gives the relation which 

 individuals bear to one another in the colony. In staining 

 it is necessary for certain purposes to add substances that are 

 known as mordants. Anilin oil, weak alkalies, carbolic acid, 

 and tannic acid are the mordants most frequently used. 

 These mordants hasten the action of the dyes, and are neces- 

 sary with certain bacteria, and are frequently used even for 



