30 ESSENTIALS OF BACTERIOLOGY 



CHAPTER IV 

 STAINING OF BACTERIA 



STAINING or coloring bacteria is done in order to make them 

 prominent and to obtain permanent specimens. It is also 

 necessary to bring out the structure of the bacteria, and 

 serves in many instances as a means of diagnosis; it would be 

 well-nigh impossible to discover them in the tissues without 

 staining. 



Anilin Colors. Of the numerous dyes in the market, nearly 

 all have, at one time or other, been used in staining bacteria. 

 But now only a very few find general use, and with methylene- 

 blue and fuchsin nearly every object can be accomplished. 



Basic and Acid Dyes. Ehrlich was the first to divide the 

 anilin dyes into two groups, the basic colors to which belong 

 Gentian-violet, or pyoktanin. Basic fuchsin. 



Methyl-violet, or dahlia. Bismarck-brown. 



Methylene-blue (not methyl blue). Thionin. 



Safranin. 

 And the acid colors to which eosin and acid fuchsin belong. 



The basic dyes stain the bacteria and the nuclei of cells; the 

 acid dyes stain chiefly the tissue, leaving the bacteria almost 

 untouched. Carmin and hematoxylin are also useful as con- 

 trast stains, affecting bacteria very slightly. The anilin dyes 

 are soluble in alcohol or water or a mixture of the two. 



Staining Solutions. A saturated solution of the dye is 

 made with alcohol. This is called the stock or concentrated 

 solution; i part of this solution to about 100 parts of distilled 

 water constitutes the ordinary aqueous solution in use or weak 

 solution. 



It is readily made by adding to an ounce bottle of distilled 

 water enough of the strong solution until the fluid is still opaque 

 in the body of the bottle, but clear in the neck of the same. 



These weak solutions should be renewed every three or four 

 weeks, otherwise the precipitates formed will interfere with the 

 staining. 



