THE MICROSCOPE AND MICROSCOPIC METHODS 40 



should have been cleaned with bichromate of potassium and sul- 

 phuric acid (see page 37). When the work is completed, the 

 bottle containing the sputum should be sterihzed by steam or 

 boiling. 



Method for staining the tubercle bacillus: 



{a) The cover-glass or slide preparation is made, dried, and 

 fixed by passing through the flame three times. 



(6) The cover-glass, held in forceps or in a watch-crystal is 

 covered with steaming carbol-fuchsin for five minutes, ^f a 

 slide is employed it may be conveniently stained in the Krauss 

 staining dish, being turned face downward. 



(c) Wash in water. 



{d) Wash in alcohol containing 3 per cent of hydrochloric acid 

 one minute, or longer if necessary to remove the red color. 



{e) Wash in water. 



(/") Stain with methylene-blue solution (see page 42) thirty 

 seconds. 



{g) Wash in water. 



{h) Examine in water directly, and after drying and mounting 

 in Canada balsam. If the preparation has been made on a slide 

 it may be dried and examined directly in cedar oil with the ^^'2 in. 

 objective. When the preparation is mounted in water, tubercle 

 bacilli may be obscured by refraction in the thicker portions of 

 the smear. Tubercle bacilli take a brilliant red color; other bac- 

 teria and the nuclei of cells are stained blue. 



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 must then be increased by warming the preparation till 

 it steams or boils, then allowing the warm stain to act on the 

 specimens for from three to five minutes; the preparation may also 

 be left in the cold stain over night. Decolorization may be effected 

 with a 25 per cent solution of sulphuric acid used till the red color 

 disappears, or a 30 per cent solution of nitric acid, which operates 

 very rapidly. If the red color persists after washing in water. 



