CRYSTAL VIOLET-STAINED BACTERIAL FILM 101 



than to endeavor to rinse it off. This jet should be directed from the fine ori- 

 fice of the wash bottle at an angle of about 30 degrees to the slide and should 

 be intended to hit the edge of the drop. The jet will instantly lift off and float 

 away the surface film, as well as wash excess stain out of the preparation. The 

 preparation is now permitted to dry. When dry, it may be touched with im- 

 mersion oil and examined under the oil-immersion lens. If it is desired to 

 maintain this specimen permanently, it may also have a drop of Canada balsam 

 placed on top of it and a very thin coverslip pressed into position. These spec- 

 imens, however, are so easy to prepare that it is rarely necessary to preserve 

 them permanently. The dried smear, if kept free from dust, may be preserved 

 for as long as a year without further preparation. 



Summary 



1. Use a wire loop to make a small, thin smear of a diluted bacterial culture 

 on a clean slide. 



2. Dry smear in air, then pass it two or three times through a flame. 



3. Place a drop of crystal violet stain on the smear, allow it to remain for 

 30 seconds, and wash off with a jet of water from a wash bottle. 



4. Dry smear without heat. 



