114 ESSENTIALS OF BACTERIOLOGY 



5 per cent, nitric or 10 per cent, sulphuric acid until, after 

 washing with water, a bright pink remains. The excess of 

 color is then washed out with 95 per cent, alcohol until no 

 further color is imparted to the alcohol, and the smear is a 

 pinkish gray. The preparation is then washed with water and 

 counterstained with aqueous methylene-blue for ten to thirty 

 seconds. A mechanical stage is of great assistance in the 

 search for the bacilli, as it permits every portion of the prepa- 

 ration to be inspected systematically. 



Slow Method. The stain may also be used without heating, 

 though in this case a much longer time is required before the 

 bacilli take up the stain. The preparation is left in a small 

 dish or beaker full of carbol-fuchsin for eight to ten hours, and 

 then decolorized and counterstained in the usual way. The 

 method is less liable to produce artefacts than the quick 

 method, but is not much used on account of the time it 

 takes. 



Examination in Urine. In urine, owing to the almost inevit- 

 able contamination with the smegma bacillus, special methods 

 are necessary to avoid error. The preparation may be left in 

 97 per cent, alcohol for eight hours, when the smegma bacillus 

 will have become decolorized, or Pappenheim's method may be 

 used: (i) Smear and fix as usual; (2) stain with hot carbol-fuch- 

 sin for two minutes, pour off the surplus dye without washing; 

 (3) counterstain and decolorize by pouring five times over the 

 preparation the following solution: A i per cent, alcoholic solu- 

 tion of corallin is saturated with methylene-blue and 20 parts 

 of glycerin added. Wash in water, dry with blotting-paper, 

 then in the air, and examine. The tubercle bacilli are stained 

 red, smegma bacilli, blue. 



Examination of Milk for Tubercle Bacilli. Place a drop 

 of the sample on a cover-glass and mix it with two drops of a i 

 per cent, solution of sodium carbonate. The cover-glass is 

 then gently warmed until evaporation is complete. The 

 saponified fat is then stained, as the ordinary cover-glass prepa- 

 ration. Only a very few persons have succeeded in discovering 

 the bacillus in milk. 



