SYSTEMATIC AND DESCRIPTIVE. 165 



Baumgar tens met hod, Cover-glass-preparations of sputum 

 are made as already described (p. 46), and immersed in 

 a very dilute solution of potash (i 2 drops of a 33 per 

 cent, solution of potash in a watch-glass of distilled water) 

 The cover-glass is pressed down on a slide, and examined 

 with a high power. The bacilli can be thus examined in 

 the unstained condition, and to avoid any mistake from 

 confusion with other species, the cover-glass can be re- 

 moved, dried, passed through the flame, and stained with 

 a drop of an aqueous solution of fuchsine, or gentian-violet. 

 The putrefactive bacteria are stained, but the tubercle 

 bacilli remain absolutely colourless. 



Baumgarteris neiv method. A solution is prepared as 

 follows : Drop 4 5 drops of concentrated alcoholic methyl- 

 violet solution into a small watch-glass full of water. 

 (a) Stain the sections in this solution, wash them in water, and 

 decolorise in absolute alcohol (five to ten minutes), or, before 

 treating with alcohol, immerse the sections for five minutes 

 in a half-saturated solution of carbonate of potash. Pass 

 through clove-oil, and mount in a mixture of Canada balsam, 

 free from chloroform, and clove-oil (equal parts). The object 

 of this process is to differentiate the tubercle bacilli from 

 chance bacteria, inasmuch as the tubercle bacilli gradually 

 are decolorised by the clove-oil, (b) Sections stained in 

 the above solution are placed for five minutes in alcohol, 

 and then in a concentrated solution of bismarck-brown in 

 i per cent, solution of acetic acid. The after-treatment 

 may be conducted as already described. 



Neelseiis method. Cover-glass-preparations may be 

 quickly stained in Neelsen's solution (No. 25) warmed in 

 a watch-glass till steam rises. Sections are left for from 

 five to ten minutes in the solution, and then washed in a 

 watery solution of sulphuric acid (25 per cent.) ; rinsed in 

 distilled water, and immersed in methylene blue solution. 

 After two or three minutes they are passed through alcohol 

 and oil of cloves, and mounted in Canada balsam. 



