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Exercise 6. Making Stained Preparations of Bacteria 
MATERIALS: 
Hay infusion 
Cultures of bacteria on agar 
Clean slides 
Clean cover glasses 
Canada balsam 
Tooth picks 
1. Examine the infusion with the naked eye. Note whether it has changed 
since it was used in Exercise 4. Look up the meaning of zoogloeae in Appen¬ 
dix B. 
2. Wet the tip of one finger, rub it on a cake of Bon Ami, and with the same 
finger spread the paste thus formed over the surface of the slide. Allow the 
paste to dry, and wipe it off with a clean dry cloth or paper towel. If the slide 
is clean, a drop of water placed on it will spread in an even film over the glass. 
Grease causes water to collect in tiny drops. 
Place a small drop of the infusion in the center of the clean slide. Spread 
the drop over an area about the size of a dime. (See Fig. 8.) The wire loop 
can best be used for this purpose. 
3. Permit the spread on the slide to dry. Do not heat the slide to hasten 
the drying. 
4. Pass the slide, film side up, quickly three times through the Bunsen flame. 
(See Fig. 9.) The heat kills the organisms and causes them to adhere to the 
glass throughout subsequent operations. It is termed “fixing” the prepara¬ 
tion. 
