CULTURAL CHARACTERS OF BACTERIA 31 



and then 30 cc. of a saturated alcoholic solution of methylene 

 blue. Filter. 



4. Ehrlich' s anilin-water fuchsin or gentian violet. To 10-15 

 cc. of distilled water add an excess of anilin oil. Shake 

 vigorously for several minutes and filter. To 10 cc. of the 

 filtrate add i cc. of the standard alcoholic solution ( i ) and filter 

 again. 



5. Ziehl's carbol-fuchsin solution. To 10 cc. of a 5 per cent 

 carbolic acid solution add i cc. of the standard alcoholic solution 

 (i), and filter. 



6. Gabbefs methylene blue solution. To 75 cc. of water add 

 cautiously 25 cc. of concentrated sulphuric acid ; when cool, add 

 2 g. of methylene blue, with frequent stirring until dissolved, 

 and filter. 



7. Gram's mixture. Dissolve 2 g. of potassium iodide in 

 300 cc. of distilled water, and add i g. of iodide. Allow the 

 mixture to stand with occasional stirring until the iodine is dis- 

 solved. Filter and keep in a bottle protected from the light. 



Gram's Method of Staining 



1. Cover film with anilin gentian violet solution (4) for 30 

 seconds, cold. 



2. Wash film in running water. 



3. Immerse in Gram's mixture (7) for 30 seconds. 



4. Immerse in 95 per cent alcohol until decolorized. 



5. Wash in water, and mount. 



Certain bacteria stain by Gram's method, others are decolor- 

 ized. This should be noted in each species under observation. 



Capsnle Staining, Welch's Method 



1. Cover-slip preparations, made without water, see p. 4. 



2. Flood film with glacial acetic acid, and at once allow to 

 drain off. 



