314 REAGENTS AND PROCESSES 



simple organisms. The central body of the Cyanophyceas may 

 be stained by the above dilute solution if, after twenty-four 

 hours' treatment, the stain is strengthened to a o.i per cent, 

 solution. Methylene-blue and carmine form a good differential 

 stain for bacteria occurring in sections of tissues. 



Methylene-blue and Carbol-fuchsin. This double stain- 

 ing method is used in the differentiation of Bacillus tubercu- 

 losis. The material first coughed up from the lungs by the 

 patient on waking in the morning should be expectorated into 

 a wide-mouthed bottle or covered jar. The person who is to 

 make the examination should afterward pour this out into a 

 shallow glass dish. This should be placed on a dead-black 

 background, and one of the small, yellowish, lenticular bodies 

 which usually occur in tuberculous sputum should be removed 

 and placed on a coverglass. A second coverglass should be 

 placed over this; then press the coverglasses gently between the 

 thumb and forefinger, and rub to and fro until the material 

 is spread out in a thin film on the coverglasses. Then slide 

 the coverglasses apart, and allow them to dry in the open air. 

 When dry, hold them with a pair of forceps and pass them 

 three times through the flame of the Bunsen burner or alcohol 

 lamp. (The film should not be allowed to turn brown, else 

 the preparation will be ruined.) Next pour over them carbol- 

 fuchsin prepared by rubbing i gm. of fuchsin with 100 c.c. 

 of a 5 per cent, aqueous solution of carbolic acid, with the gradual 

 addition of 10 c.c. of alcohol. Hold the coverglasses over a 

 flame with forceps until vapor begins to arise from the surface 

 of the stain. Then hold away from the flame, except in inter- 

 vals of gentle heating, by which they are kept warm for a minute 

 or two. They are next washed in water and decolorized by 

 being moved about in a 25 per cent, solution of nitric or sulphuric 

 acid. When the previously deep red color has changed to a 

 greenish tint, the preparation is washed in 60 per cent, alcohol 

 to remove the color set free by the acid. If any red color still 

 remains, the preparation should be rinsed in water and again 

 treated with the acid-bath. By the above process the fuchsin 



