CHAPTER IV 

 STAINING 



Organisms so small that they are almost or entirely invisible before staining, 

 become distinctly visible when stained. Details unnoticeable in unstained 

 bacteria are apparent in the stained. By staining we are enabled to distinguish 

 some species from others because of differences in their ability to absorb and 

 retain certain stains, and to resist the decolorizing action of acids and alcohol. 



Aqueous solutions of anilin dyes are most commonly employed in staining 

 bacteria. Stains and methods of staining are numerous. Fortunately, how- 

 ever, there are about a half dozen stains and methods of staining which suffice 

 for all ordinary bacteriological examinations. 



The term cubic centimeter (cc.) as used in this volume is synonymous with 

 the term mil. The United States Pharmacopeia IX has brought about a change 

 from the former to the latter, this being an abbreviation for the term milliliter 

 (the first three letters of which are mil). The United States Bureau of Stand- 

 ards regards the term cc. as a misnomer, there being a slight difference between 

 the thousandth part of a liter and the cc. In addition the change was brought 

 about to promote international conformity. 



As this volume will be used by students and practitioners familiar with the 

 term cc., and not so familiar with the better term, mil., it has been thought 

 advisable to still retain cc. in this edition. 



LOEFFLER'S METHYLENE BLUE 



i :io,ooo (Hoo P er cent.) aqueous sol. of potassium hydrate, 10 cc. 

 Saturated alcoholic solution of methylene blue, 3 cc. 



Loeffler's methylene blue is a very satisfactory stain for most bacteria. The 

 method of staining is as follows: 



1. Cover the preparation to be stained with Loeffler's methylene blue, allow 

 the stain to remain on the specimen for i to 5 minutes. 



2. Wash the stain off with water, and allow the slide or cover glass to dry. 



3. Mount. 



4. Examine specimen. 



FUCHSIN 



Saturated alcoholic solution of basic fuchsin, 5 cc. 



Distilled water, 95 cc. 



Apply this stain in the same manner as Loeffler's methylene blue. 



