GRAM'S METHOD. 145 



it is considered the best method for routine employment. 

 It consists in staining the cover-slips, prepared in the 

 manner given, for from two to five minutes in a cold 

 carbolic-fuchsin solution, after which they are subjected 

 to the action of Gabbett's methylene-blue sulphuric acid 

 solution. This latter consists of 



Sulphuric acid, strength 25 per cent . 100 c.c. 

 Methylene-blue, in substance . . . 1 to 2 grammes. 



They are then rinsed off in water and are ready for ex- 

 amination. 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 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 com- 

 posed 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 micrococcus lanceolatus of pneumonia. 



