STAINING OF BACTERIA. 31 



1 part of this solution to about 100 parts of distilled water con- 

 stitutes 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 just 

 opaque in the body of the bottle, but still 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 chemical agents, 

 the intensity of the aniline dyes can be greatly increased. 



Mordants. Agents that "frrte" 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 aniline dyes, aniline oi7, a member 

 of the aromatic benzol group, has also this property. 



Aniline Oil Water. Aniline oil is shaken up with water and 

 then filtered ; the aniline water so obtained is mixed with the 

 dyes forming the "aniline water gentian violet" or aniline 

 water fuchsin, etc. 



Carbol Fuchsin. Carbolic acid can be used instead of aniline 

 oil, and forms one of the main ingredients of Ziehl's or Neelsen's 

 solution, used principally in staining bacillus tuberculosis. 

 Kiihne has a carbol-methylin blue made similar to the carbol 

 fuchsin. 



Alkaline Stains. Alkalies have the same object as the above 

 agents ; namely, to intensify the picture. Potassium hydrate, 

 ammon. carbonate, and sodium hydrate are used. 



Loffler's alkaline blue and Koch's weak alkaline blue make 

 use of potassium. 



Heat. Warming or boiling the stains during the process of 

 staining increases their intensity. 



Decolorizing Agent's. The object is usually over-colored in 

 some part, and then decolorizing agents are employed. Water is 

 sufficient for many cases ; alcohol and strong mineral acids com- 

 bined are necessary in some. 



