32 GENERAL BACTERIOLOGY 



over the flame, but it should always be held in fingers to prevent over- 

 heating, which spoils the preparation. 



"When the film is thoroughly dry place the cover-glass in a pair 

 of Cornet or Stewart forceps and "fix" the bacteria in the flame. 

 This is done by passing the prepa.ra.tion 

 through the upper portion of a gas fla 

 film side up. Three passages should be 



made, each consuming about one second forceps. (Muir& Ritchie). 

 of time. The forceps are now placed on the table and the film flooded 

 with one of the anilin dyes. After the stain has acted for five to 

 ten minutes it is washed off into a waste dish with a stream of dis- 

 tilled water, and while the cover-glass is still wet it is placed, bac- 

 teria side down, on a clean glass slide, being careful to avoid air 

 bubbles. The surplus water is then taken up by means of a small 

 piece of blotting or filter paper. 



The preparation is now ready for microscopical examination. 

 (For directions see next exercise). 



The preparation can be made permanent either by allowing the 

 water under the cover-glass to dry before it is removed, or by floating 

 it off with water and afterwards drying. When dry a drop of 

 Canada balsam, dissolved in xylene, is placed on the cover-glass and 

 this is then lowered on to the slide again. 



Resume. 



a. Spread film, 



b. Air dry, 



c. Fix, 



d. Stain, 



e. Mount in water, / \ e. Dry, 



f. Examine, 3 or v /. Mount in balsam, 



g. Dry and mount in balsam. ( ) g. Examine. 



"The great mistake made by beginners is to take too much 

 growth," (M. & K.) and too large a drop. 



REFERENCES. A. 159 ; H. 80 ; M. & R. 98 ; McF. 145 ; P. 198 ; 

 P. B. C. 11. 



SPECIAL DIRECTIONS. 



a. Make cover-glass preparation from agar streak of B. subtilis 

 (13) staining with an aqueous solution of gentian violet for five 

 minutes. 



