182 BACTERIOLOGY. 



The cover-slips are then rinsed in water and are ready 

 for examination. . The tubercle bacilli will be stained 

 red by the fuchsin, while all other bacteria, cell-nuclei, 

 etc., will be tinted blue. 



GRAM'S METHOD. Another important differential 

 method of staining which is very commonly employed 

 is that recommended by Gram. In this method the 

 objects are treated with an aniline-water solution of 

 gentian-violet made after the formula of Koch-Ehrlich. 

 After remaining in this for twenty to thirty minutes 

 they are immersed in a solution composed of 



Iodine 1 gramme. 



Potassium iodide 2 grammes. 



Distilled water 300 c.c. 



In this they remain for about five minutes ; they are 

 then transferred to alcohol and thoroughly rinsed. If 

 still of a violet color, they are again treated with the 

 iodine solution, followed by alcohol, and this is con- 

 tinued until no trace of violet is visible to the naked 

 eye. They may then be examined, or a contrast-color 

 of carmine or Bismarck-brown may be given them. 



This method is particularly useful in demonstrating 

 the capsule which is seen to surround some bacteria, 

 especially micrococcus lanceolatus of pneumonia. 



GLACIAL ACETIC ACID METHOD. Another method 

 that may be employed for demonstrating the presence 

 of the capsule surrounding certain organisms is to pre- 

 pare the cover-slips in the ordinary way, then cover the 

 layer of bacteria upon them with glacial acetic acid, 

 which is instantly poured off (not washed off in water), 

 and the aniline-water gentian-violet solution dropped 

 upon them ; this is allowed to remain three or four 



