PART II 

 METHODS OF STAINING OF BACTERIA 



The general structure of bacteria and other microorganisms 

 is most easily seen in stained preparations. The process of 

 staining consists in smearing a suspension of the organisms over 

 a clean slide, drying at room temperature, fixing to the glass by 

 passing through a flame two or three times (do not burn) and 

 staining the film by one of the methods outlined below. After 

 staining, the film is washed in running water, dried with a blotter, 

 and examined. To preserve the mount, a small drop of balsam 

 is placed over the film and the cover glass is pressed down gently 

 to force out the excess of balsam. Set the slide in a warm place 

 to dry. 



Some of the most important laboratory stains are (1) methy- 

 lene blue or thionin, (2) crystal violet, (3) fuchsin, (4) erythrosin, 

 and (5) nigrosin. Stock solutions of methylene blue, thionin, 

 crystal violet, and fuchsin should be prepared and kept on hand. 

 For the stocks, make a saturated solution of the dyes in 95 per 

 cent ethyl alcohol. Filter through paper a small amount of the 

 dye and dilute as given in the directions. 



For quick preparations, not deeply stained, the methylene 

 blue will be found satisfactory. Fuchsin, on the other hand, 

 possesses unusual penetrating power for staining bacterial cells 

 and spores and will be found useful for a great many kinds of 

 bacteria. If heated these dyes penetrate much more rapidly 

 and thus give more deeply stained mounts. 



Loeffler's Alkaline-methylene Blue 



Saturated alcoholic solution of methylene blue 30.0 cc. 



Solution of potassium hydroxide in distilled water 



(1 : 10,000) 100 . cc. 



Ziehl's Carbol-fuchsin 



Saturated alcoholic solution of basic fuchsin 10.0 cc. 



Carbolic acid, 5 per cent aqueous solution 100.0 cc. 



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