48 ESSENTIALS OF BACTERIOLOGY 



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 aniline dyes stain the bacteria and the nuclei of 

 cells; the acid dyes stain chiefly the tissue, leaving the bac- 

 teria almost untouched. Carmin and hematoxylin are also 

 useful as contrast 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 10 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. 



Compound Solutions. By means of certain chemic 

 agents the intensity of the anilin dyes can be greatly increased. 



Intensifiers or Mordants. Agents that "bite" into the 

 specimen, carrying the stain with them, depositing it in the 

 deeper layers, are called mordants or etchers. 



Various metallic salts and vegetable acids are used for such 

 purpose. 



The mother liquid of the anilin dyes, anilin-oil, a member 

 of the aromatic benzol group, has also this property. 



