Tu berciilosis . 411 



elongated rope-like colonies having a waving outline. Other 

 evolution forms have been already noted. 



Staining . The resistance to staining is overcome by a heated 

 alkaline watery solution of methylene blue (Koch), or better by 

 a carbolated solution of fuchsin (Ziehl-Neelsen). To a 5 per 

 cent, watery solution of carbolic acid add one-tenth of its volume 

 of saturated alcoholic solution of fuchsin. The suspected 

 sputum or scraping from a section of a lesion is spread in a thin 

 layer on a cover glass by drawing over it the straight edge of a 

 second cover glass, dried in the air, and passed three times 

 through an alcohol flame with the smeared side up. It may then 

 be floated on the surface of the staining fluid w'itli the specimen 

 side down, then gently heated for three or four minutes almost 

 to ebulition, drying being prevented by the addition of more of 

 the carbol-fuchsin solution as required. It is then washed in 

 water to remove excess of the staining fluid and treated with a 

 bleaching acid solution (sulphuric acid 5 per cent, or nitric acid 

 15 per cent.) When decolorized it is well rinsed in two or more 

 portions of a 60 or 70 per cent, alcohol and then in water. Next 

 stain with a i or 2 per cent, aqueous solution of methylene blue 

 for one minute and wash off the excess with water. The tubercle 

 bacilli will appear of a deep red and other bacteria blue. 



GabbeW s counter-staining and decolorizing solution is especi- 

 ally useful in economizing time. After staining, as above direct- 

 ed, in the carbol-fuchsin solution for one minute, wash in water, 

 then cover with a solution of 2 grams methylene blue (powder) 

 in 100 cc. of 10 per cent, sulphuric acid, until the film has a 

 faintly bluish tint : then wash thoroughly in water and examine. 

 Tubercle bacilli come out red, others blue. 



In examination of tissues the microscopic sections are steeped 

 for twenty-four hours in the carbol-fuchsin solution (or i hour at 

 a temperature of 45° to 50° C), then decolorized in a 5 per cent, 

 sulphuric acid for a few seconds, then in a 70 per cent, alcohol : 

 they are then counter-stained in an aqueous solution of methylene 

 blue, washed in water dehydrated with absolute alcohol, cleared 

 up in xyol or oil of cedar, and mounted in Canada balsam. 



Biology. The bacillus tuberculosis is notorious for its variant 

 forms, assumed in adapting itself to given environments, and 

 which it retains with considerable tenacity for a time, even when 



