GRAM S METHOD. 



DEMONSTRATION III. 



Examination of pure cultures of Bacteria grown on solid media — 

 Gram's 'method of staining. 



1. With a sterile platinum loop, place a drop of 

 sterile distilled water on a cover glass. Remove then, 

 with due precautions, a minute amount of Bacillus pro- 

 digiosus, and smear with the water, carefully over the 

 cover glass surface. Dry and pass three times through 

 the flame. As a rule no clearing in acetic acid will be 

 needed in examining bacteria from solid media. Float 

 the cover glass in anilin gentian violet for one to two 

 minutes. Wash in water, dry and mount in Canada 

 balsam. 



2. Examine in like manner the potato culture of 

 Bacillus ruber and the gelatine culture of Bacillus 

 cyanogenus. Use either Loeffler's methylene blue or 

 diluted gentian violet for staining. 



Gram's Method. 

 Gram's method of staining is based on the fact that, 

 when some bacteria are stained with certain dyes (of 

 which anilin gentian violet is the principal), and then 

 treated with a solution of iodine, the iodine fixes the 

 stain so that it is not washed out by after treatment 

 with alcohol. It affords a good differential stain, as 

 some species stain, while others do not. Various modi- 

 fications will be noted in this method, for the staining 

 of pus and tissues. 



