STAINING OF BACTERIA 31 



Compound Solutions. By means of certain chemical agents 

 the intensity of the anilin dyes can be greatly increased. 



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. 



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 or phenol can be used 

 instead of anilin-oil, and forms one of the main ingredients of 

 Ziehl's or Neelsen's solution, used principally in staining Bacil- 

 lus tuberculosis. Kiihne has a carbol-methylene-blue made 

 similar to the carbol-fuchsin. 



Alkaline Stains. Alkalis have the same object as the above 

 agents, namely, to intensify the picture. Potassium hydroxid, 

 ammonium carbonate, and sodium hydroxid are used. 



Lofrler's alkaline blue and Koch's weak alkaline blue have 

 in them potassium. 



Heat. Warming or boiling the stains during the process of 

 staining increases their intensity. 



Decolorizing Agents. The object after staining is usually 

 overcolored in some part, and then decolorizing agents are em- 

 ployed. Water is sufficient in many cases; alcohol and strong 

 mineral acids combined are necessary in some. 



lodin as Used in Gram's Method. Belonging to this group, 

 but used more in the sense of a protective, is tincture of iodin. 

 It picks out certain bacteria, which it coats; prevents them from 

 being decolorized, but allows all else to be faded. Then, by 

 using one of the acid or tissue dyes, a contrast color or double 

 staining is obtained. Many of the more important bacteria are 

 not acted upon by the iodin, and it thus becomes a very useful 

 means of diagnosis. 



