TUBERCULOSIS. 299 



with water, and the specimen is dried and mounted in 

 Canada balsam. Nothing will be colored except the tu- 

 bercle bacilli, which will appear red. 



Gabbett modified the staining by adding methylene 

 blue to the acid solution, which he makes according to 

 this formula: 



In Gabbett's method, after staining with carbol-fuch- 

 sin the specimen is washed with water, acted upon by 

 the methylene-blue solution for exactly thirty seconds, 

 washed with water until only a very faint blue remains, 

 dried, and finally mounted in Canada balsam. By this 

 method the tubercle bacilli are colored red, and the pus- 

 corpuscles, epithelial cells, and the unimportant bacteria 

 blue. Taking into consideration that the tubercle bacil- 

 lus contains a large amount of fat (40 per cent, of ether- 

 soluble constituents, de Schweinitz and Dorset), Dorset 1 

 suggests the use of Soudan III. as the best stain for the 

 differential staining of tubercle bacillus. The method 

 which he recommends is as follows : Cover-glass prepa- 

 rations are made and fixed in the ordinary way and then 

 immersed for ten minutes in a cold, saturated, 80 per cent, 

 alcoholic solution of Soudan III. The excess is then re- 

 moved by washing in several changes of 70 per cent, 

 alcohol for five minutes, or in 95 per cent, alcohol. The 

 bacilli appear bright red, and the beaded appearance 

 is said to be very distinct. 



Tissues are stained and decolorized in the same manner 

 and subsequently counter-stained with methylene blue, 

 dehydrated with absolute alcohol, cleared in clove oil, 

 and mounted in Canada balsam. 



Dorset found that Soudan III. is selective for the 

 tubercle bacillus, and does not stain other micro- 



1 New York Medical Journal, Feb. 4, 1899, p. 148. 



