CHAPTER IX. 



STAINING OF BACTERIA IN COVER-GLASS PREPARATIONS AND 



IN TISSUES. 



Anilin Stains. In laboratory work in histology and pathology 

 eosin is used as a so-called counter-stain; this dye is one of the anilin 

 stains. These stains are complicated bodies derived from anilin oil, 

 a heavy liquid which is, however, not a true oil, but, according to 

 its chemical properties, an alkali or a base, like caustic soda, caustic 

 potash, or ammonia. In fact, it contains the ammonia radical in its 

 molecule. By combining the basic anilin oil with various acids in 

 certain proportions either a neutral, an acid, or an alkaline or basic 

 salt may be obtained. Eosin, mentioned above, is an acid anilin 

 stain. Bacteria, however, are particularly well stained by basic or 

 alkaline anilin stains. The most useful of these for work of this 

 kind are gentian violet, fuchsin, and methylene blue. It is best to keep 

 them on hand in the laboratory in the form of filtered saturated 

 alcoholic solutions, since these do not decompose or deteriorate. 

 Saturated alcoholic solutions contain about 25 grams of the dry stain 

 to 100 c.c. of alcohol. Watery solutions are prepared for use from 

 the alcoholic stock solutions by adding to 100 c.c. of distilled water 

 about 5 to 10 c.c. of the saturated alcoholic solution. It should be 

 remembered that a gentian violet in watery solution stains very rapidly, 

 and easily overstains. Methylene blue stains rather slowly, and there- 

 fore does not easily overstain. Fuchsin takes an intermediate position. 

 Hence, the time for staining is as follows : 



With watery gentian violet solution 1J^ to 2 1 A minutes 



With watery fuchsin solution 3 to 4 minutes 



With watery methylene-blue solution 5 minutes or longer 



Staining Bacteria on Cover-glass Preparations. In staining bacteria 

 with the simple watery anilin stains, say in pus or in any other dis- 

 charge or excretion, like urine, feces, etc., proceed as follows: 



1. A cover-glass which has been thoroughly cleaned is held in a 

 Stewart or similar forceps. 



2. Sterilize the platinum loop by holding it over the flame of a 

 Bunsen burner or alcohol lamp. Allow it to cool. 



3. Dip the cool platinum loop into the pus, etc., and spread the 

 drop which adheres to the loop in a thin even film on the cover-glass. 

 Sterilize the platinum loop again and put it aside. 



4. Allow the cover-glass to become air dry, then, holding it in the 

 forceps, draw it, with the prepared side upward, three times through 



