GRAM-STAINED BACTERIAL FILM 103 



Though this is a Gram preparation by the original technique, it is custom- 

 ary nowadays to provide a counterstain of a contrasting color to bring clearly 

 into evidence any Gram negative organisms which may be mixed with Gram 

 positive. A 1 per cent solution of safranin is widely employed, and in this 

 case, the second red contrasting stain is allowed to act from 5 to 10 seconds, 

 washed off with water, and the slide then dried and examined under an oil- 

 immersion objective. 



Summary 



1 . Follow steps 1 through 3 of Example 6 but allow stain to act for 2 minutes. 

 Then wash it off under tap. 



2. Treat stained smear with Gram's iodine for 1 minute. Rinse under tap and 

 soak in absolute alcohol until no more color comes away. 



3. If desired, counterstain 5 to 10 seconds in 1 per cent safranin and wash it 

 off with water before drying. 



