STAIN FOR TUBERCLE BACILLI. 105 



3. Wash well with water. The tissues will regain a faint pink tint. If 

 the colour is distinctly red, the decolorisation is insufficient, and the specimen 

 must be returned to the acid. As a matter of practice, it is best to remove 

 the preparation from the acid every few seconds and wash in water, replacing 

 the specimen in the acid and re-washing till the proper pale pink tint is ob- 

 tained. Then wash in alcohol for half a minute and replace in water. 



4. Contrast stain with a saturated watery solution of methylene-blue 

 for half a minute, or with saturated Bismarck-brown for from two to three 

 minutes. 



J. Wash well with water. In the case of films, dry and mount. In the 

 case of sections, dehydrate, clear, and mount. 



Fraenkel's Modification of the Ziehl-Neelsen Stain. 



Here the process is shortened by using a mixture containing 

 both the decolorising agent and the contrast stain. 



The sections or films are stained with the carbol-fuchsin as above de- 

 scribed, and then placed in the following decolorising solution : — 



Distilled water 50 parts. 



Absolute alcohol 30 » 



Nitric acid 20 „ 



Methylene-blue in crystals to saturation. 



They are treated with this till the red colour has quite disappeared and been 

 replaced by blue. The subsequent staJIs are the same as in No. 5, supra. 



Leprosy bacilli are stained in the same way, but are rather 

 more easily decolorised than tubercle bacilli, and it is better to 

 use only 5%)er cent sulphuric acid in decolorising. 



In the case of specimens stained either by the original Ziehl- 

 Neelsen method, or by Fraenkel's modification, the tubercle or 

 leprosy bacilli ought to be bright red, and the tissue blue or 

 brown, according to the contrast stain used. Other bacteria 

 which may be present are also coloured with the contrast stain. 



Gabbett's Methylene-blite Solution. 



Methylene-blue . . . . 2 grms. 

 Sulphuric acid . . . . -25 c.c. 

 Distilled water 75 c.c. 



This is very similar to Fraenkel's decoloriser and contrast 

 stain, and is used in the same manner. It has this one disad- 

 vantage, that it will not decolorise smegma bacilli should these 

 be present in urinary sediments or in tissues from portions of 

 the genito-urinary tract. 



