136 bacteriology: 



lene-blue sulphuric acid solution. This latter con- 

 sists of 



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

 Methylene-Wue, in suhstance .... 1 to 2 grammes. 



They are then rinsed off 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 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-brdwn 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. 



Gi^AciAL Acetic Acid Method. — Another method 

 which may be employed for demonstrating the presence 

 of the capsule surrounding certain organisms, is to 



