298 PATHOGENIC BACTERIA. 



counter-stained in a dilute aqueous solution of Bismarck 

 brown or vesuvin. The excess of stain is then washed 

 off in water, and the specimen dried and mounted in bal- 

 sam. The tubercle bacilli will appear of a fine dark 

 blue, while the pus-corpuscles, epithelial cells, and other 

 bacteria, having been decolorized by the acid, will be 

 colored brown by the counter-stain. 



This method, requiring twenty-four hours for its com- 

 pletion, is naturally one which has fallen into disuse for 

 practitioners who desire in the briefest possible time to 

 know simply whether bacilli are present in the sputum 

 or not. 



Among clinicians Ziehl's method with carbol-fuchsin 

 has met with great favor. After having been spread, 

 dried, and fired, the cover-glass is held in the bite of an 

 appropriate forceps (cover-glass forceps), and the stain 1 

 dropped upon it from a pipette. As soon as the entire 

 cover-glass is covered with stain it is held over the flame 

 of a spirit-lamp or a Bunsen burner until the stain begins 

 to volatilize a little, as indicated by a white vapor. When 

 this is observed, the heating is sufficient, and the temper- 

 ature can be subsequently maintained by intermittent 

 heating. 



If evaporation is allowed to take place, a ring of in- 

 crustation occurs at the edge of the area covered by the 

 stain and prevents the proper action of the acid. To 

 prevent this more stain should now and then be added. 

 The staining is complete in from three to five minutes, 

 after which the specimen is washed off with water, the 

 excess of water absorbed with paper, and 3 per cent, 

 hydrochloric acid in 70 per cent, alcohol, 25 per cent, 

 aqueous sulphuric, or 33 per cent, aqueous nitric acid 

 solution dropped upon it for thirty seconds, or until the 

 red color is just extinguished. The acid is washed off 



1 Carbol-fuchsin: 



