STAI N I NU OF BACTERIA. ,31 



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

 add dyes stain chiefly the tissue, leaving the bacteria almost 

 untouched. Carmine and HcematoxyUn 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 ; 

 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 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 chemical agents, 

 the intensity of the aniline dyes can be greatly increased. 



Mordants. Agents that "6rte" 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. 



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

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

 dyes, forming the "anilin water gentian violet" or anilin water 

 fuchsin, etc. 



Carbol Fuchsin. Carbolic acid can be used instead of anilin 

 oil, and forms one of the main ingredients of ZiehPs 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 have in 

 them potassium. 



