36 MANUAL OF BACTERIOLOGY. 



(b) The carbol-fuchsin stain is applied from two to five 

 minutes to the cover-glass, held in forceps or in a watch-crys- 

 tal; it need not be warmed. 



(c) Wash in water. 



(d) Gabbett's solution is applied for one minute. 



(e) Wash in water. The preparation should have a blue 

 color. It may be examined in water directly or after drying 

 and mounting in Canada balsam. 



Gabbett's method has the advantage of decolorizing the 

 preparation and staining the background with methylene-blue 

 at the same time. Tubercle bacilli are colored a brilliant red: 

 most other bacteria and the nuclei of cells are colored blue. 

 The acid-proof bacilli mentioned on page 33 also retain the red 

 stain in most cases, and might be confused with tubercle 

 bacilli. 



Of the numerous methods of staining tubercle bacilli, only 

 a few others can be mentioned. Aniline-water fuchsin, aniline- 

 water gentian-violet or carbol-fuchsin may be used. The 

 intensity of the stain may then be increased by warming the 

 preparation till it steams or boils, and allowing the warm stain 

 to act on the specimens for from three to five minutes; the prep- 

 aration may also be left in the cold stain over night. De- 

 colorization of the background may be effected with a 25 per 

 cent, solution of sulphuric acid used till the color disap- 

 pears, or a 30 per cent, solution of nitric acid, which 

 operates very rapidly. If the color persists after wash- 

 ing in water, it should be dipped in the acid again. After 

 either _ acid the preparation is to be washed in alcohol until 

 the last trace of the stain has been removed. An excellent 

 decolorizing agent is a 3 per cent, solution of hydrochloric acid 

 in alcohol, used for about a minute. With any of these acid 

 solutions the decolorization can be accomplished more per- 

 fectly than with Gabbett's solution, where the operation of the 

 decolorizing agent is -masked. The contrast-stain may be 



