74 BACTEEIOLOGY 



colour used is plainly visible on the cover-glass, after which 

 this is washed in water, dried, and mounted in Canada 

 balsam. After washing in water the cover-glasses may 

 also be brought into alcohol and then treated with oil of 

 cloves and Canada balsam. 



In this staining process the nitric acid acts as a bleaching 

 agent on the different micro-organisms contained in the 

 mass under examination. The tubercle-bacilli alone refuse 

 to yield up their stain to the acid unless it has acted for 

 a long time. 



Ziehl and Neelsen's method of staining^. — The Koch-Ehrlich 

 method was modified by Ziehl and Neelsen by using car- 

 bolic fuchsine instead of aniline water fuchsine. Here, also, 

 either the stain is applied on the cover-glass, or this is laid 

 prepared side downwards in the warm dye. It is after- 

 wards washed with water and decolorised in 33 per cent, 

 nitric or 5 per cent, sulphuric acid. In all other particulars 

 the process resembles the Koch-Ehrlich method, and 

 secondary staining is effected by means of malachite green, 

 picric acid, or methyl blue. 



Ehrlich's method of staining. — For demonstrating tubercle- 

 bacilli in pus, Ehrlich recommends that it be spread out 

 very thinly, and the preparation placed for one to two hours 

 in cold aniline fuchsine and decolorised with sulphanil-nitric 

 acid (1 part nitric acid to 3 to 6 parts saturated solution of 

 sulphanilic acid). The double staining is done with methyl 

 blue. 



Gunther's method of staining. — In this process the stain- 

 ing is effected with warm aniline water fuchsine, from which 

 the cover-glass is conveyed with the prepared side upper- 

 most into alcohol containing 3 to 100 of hydrochloric acid, 

 in which it is moved about for a minute £^nd then rinsed in 

 water. By means of a pipette a few drops of dilute alco- 

 holic solution of methyl blue are now allowed to fall upon 



