SHERWOOD: ON DIFFERENTIAL STAINING METHODS. 27 



As a method typifying the first theory, Gabbet's- is perhaps 

 the best. In this method the preparation is made and stained 

 with steaming carbol-fuchsin from three to five minutes. The 

 excess of staining fluid is drained off without washing and is re- 

 placed by Gabbet's methylene blue solution (2 gi\ M. B.; sul- 

 phuric acid, 25 cc; water, 75 cc). This solution is allowed to act 

 for from one to three minutes and is then washed off with water 

 and the preparation dried and examined. The tubercle bacilli 

 will appear as bright red rods, while all the other organisms are 

 said to be stained blue. 



The Ziehl-Neelsen^ method comes under the second group. In 

 this method the organisms are stained with steaming carbol- 

 fuchsin from three to five minutes and decolorized with acidulated 

 alcohol for several minutes, or until no more color comes from the 

 slide. It is then washed in water and counter-stained with 

 Loeffler's methylene blue. The tubercle bacillus will appear 

 red, while all the other bacteria are supposed to be blue. 



A modification of this method, which is reported to have given 

 greater efficiency, is Pappenheim 's"* method. The preliminary 

 staining is carried out as above. The specimen is then drained 

 and covered with decolorizing solution, which is made by dissolv- 

 ing one gram of rosalic acid in 100 cc. of absolute alcohol, satu- 

 rating the mixture with methylene blue and adding twenty parts 

 of glycerine. The slide is then washed in water, dried between 

 blotting paper, and examined with the immersion lens. The tu- 

 bercle bacilli are stained red and all the other organisms are said 

 to be blue. 



As an example of group IV is Bunge and Trantenroth 's^ method. 

 After fixation of the smear the fat is removed by soaking the speci- 

 mens in absolute alcohol. The preparation is now covered with a 

 5 per cent solution of chromic acid for fifteen minutes, after which 

 it is washed with water. The smear is stained with steaming 

 carbol-fuchsin, decolorized with 16 per cent sulphuric acid for 

 three minutes, and is then counter-stained for five minutes in a 

 concentrated alcoholic solution of methylene blue. This method 

 is said to give the tubercle bacillus a distinct red color, while the 

 smegma bacillus is blue. 



Fonte's^ method for the differentiation of the tubercle bacillus 

 from the rest of the acid-fast group is as follows: 



1. Stain the dried and fixed preparation with steaming carbol- 

 fuchsin for three minutes. 



2. Wash with tap water. 



