GLACIAL ACETIC ACID METHOD. 133 



mends the following method of decolorization : After 

 staining the slip or section in the usual way, pass it 

 through three alcohols ; it is then to be washed out in a 

 solution composed of 



Water 150 c.c. 



Alcohol . . . . . .50 c.c. 



Concen. sulphuric acid . . . 20 to 30 drops. 



From this they are removed to water and carefully 

 rinsed. The remaining steps in the process are the 

 same as those given in the other methods. 



GRAM'S METHOD. Another differential method of 

 staining which is very commonly employed is that known 

 as Gram's method. In this method the objects to be 

 stained 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 an iodine 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 

 they are still of a violet color they are again treated 

 with the iodine solution followed by alcohol, and this is 

 continued until no trace of violet color 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, 

 particularly the diplococcus of pneumonia. 



GLACIAL ACETIC ACID METHOD. Another method 

 which may be employed for demonstrating the presence 



7 



