Christine Case, Skyline College

BIOL 240 visual lab guide

BIOL 240

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Preparing a smear for staining. This procedure is used for all stains except the Negative Stain.

1. Sterilize your loop before and after use. Be sure to get the entire wire red hot.

2. Prepare a smear
a. Place a loopful of water on the slide if you have a solid culture	b. A loopful of liquid culture can be place directly on the slide.

3. Let the smear dry completely in the air. Do not apply heat because this can distort the cells.

4. Fix the smear.
a. Smears can be heat-fixed by quickly passing the slide through a flames, three times.	b. Another method of fixing the smear is to cover it with methyl alcohol for 1 min.


5. Stain the smear. Gram stain. Acid fast stain. Structural stains.

6. Observe the slide under low and high-dry lenses to center and focus the image. Place a drop of oil directly on the stained smear (no cover slip). Turn the oil immersion lens into position and observe the cells.