102 ESSENTIALS OP BACTERIOLOGY. 



second solution, the acid blue, where it remains one minute, 

 then washing in water. The preparation is dried between 

 filter-paper, and mounted best first in water. Examined with 

 oil-immersion. 



A somewhat longer, but preferable, method is to decolorize 

 the carbol-fuchsin with weaker acid. The smear is treated with 

 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 methylin-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. 



In urine, owing to the almost inevitable 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 de- 

 colorized, or Pappenheim's method may be used : (1) Smear 

 and fix as usual ; (2) stain with hot carbol-fuchsin for two 

 minutes, pour off the surplus dye without washing ; (3) counter- 

 stain and decolorize by pouring five times over the preparation 

 the following solution: A 1 per cent, alcoholic solution of 

 corallin is saturated with methylin-blue and 20 parts of gly- 

 cerine added. Wash in water, dry with blotting-paper, then in 

 the air, and examine. The tubercle bacilli are stained red, 

 smegma bacilli, blue. 



The bacillus of leprosy resembles the tubercle bacillus in its 

 staining properties, but gives up the carbol-fuchsin more easily 

 and is usually decolorized by the acid and alcohol. It is colored 

 blue by Pappenheim's method. 



Acid-fast bacilli have also been obtained from timothy grass, 

 butter, milk, manure, and the surfaces of animal bodies, but 

 differ from the tubercle bacillus in cultural characteristics. 



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 



