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TUBERCULOSIS, 175 



sulphuric or 33 per cent, nitric acid dropped upon it for 

 thirty seconds. The acid is washed off with water, and 

 the specimen is dried and mounted in Canada balsam. 

 Nothing will be colored except the tubercle bacilli, 

 which will appear red. 



Gabbett modified the staining by adding methylene 

 blue to the acid solution, which he makes according to 

 this formula: 



Methyl blue, 2 ; 



Sulphuric acid, 25 ; 



Water, 75. 



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. 



When the tubercle bacilli are to be sought for in sections 

 of tissue, considerable difficulty is at once encountered, 

 partly because of the thickness of the section and partly 

 because of the presence of nuclei which color intensely. 



Again, Khrlich's method must be recommended as the 

 most certain and best method of staining a large number 

 of bacilli. 



The sections of tissue, if imbedded in celloidin or par- 

 affin, should be freed from the foreign substances. Like 

 the cover-glasses, they are placed in the stain for twelve 

 to twenty-four hours at a temperature of 37 C. Upon 

 removal they are allowed to lie in water for about ten 

 minutes to wash away the excess of stain and to soften 

 the tissue, which often shrinks and becomes brittle. The 

 washing in nitric acid (20 per cent.) which follows may 

 have to be continued for as long as two minutes. Thor- 

 ough washing in 60 per cent, alcohol follows, after which 

 the sections can be counter-stained, washed, dehydrated 



