The Microscope
Materials Needed Wet Mounts and Stained Smears
• Microscope • The microscope is absolutely essential to the microbiology
• Pond water lab: most microorganisms cannot be seen without the aid
• Microscope of a microscope, save some fungi.
• Slides cover • And, of course, there are some microbes which cannot be
• Slip soil seen even with a microscope, unless it is an electron
• Dropper microscope, such as the viruses.
• Prepared slides of Bacillus • Different types of microscopy:
• Toothpicks ⤷ Brightfield microscope
• Dye kits ⤷ Phase-contrast microscope
⤷ Darkfield microscope
• Phase-contrast and darkfield microscopies are used for
wet mounts, whereas brightfield can be used for both wet
mounts and stained specimens.
The Procedures
• Prepare a wet mount of pond water:
1. Go DOWN into the algae and muck to get a really good sample of protozoa and algae.
2. Focus on the sample using 10X, then go to 40X (NOT 100X). Start with brightfield, then switch over
to darkfield and phase-contrast (see directions below).
3. Practice with the microscope, changing condensers settings, using different lenses. It is NOT important
to identify protozoa or algae.
• Prepare a smear and simple stain of the material between your teeth:
1. Take a sterile toothpick, remove some solid material between your wisdom teeth, and mix it into a drop
of water so that you have a suspension spread over the middle third of the microscope slide. NO
COVER SLIP USED!
2. Let the slide air-dry.
3. Heat-fix the dry smear by running the slide quickly through the flame a few times. If your fingers get
hot, you have heat-fixed TOO MUCH.
4. Place the slide on the wire over the stain tray. Flood the smear with crystal violet: let sit for 1 minute.
5. Wash the slide WELL with distilled water. Blot the smear slide with your bibulous paper pad.
6. Focus on the sample using the 10X lens(Be SURE that you are on brightfield microscopy): you should
see masses of purple material, most of it too small to see.
7. Ready to go to 100X now? Do NOT move the stage or the adjustments knobs before you follow the
directions below.
8. Identify the various shapes and arrangements of bacteria in your mouth. Most of them will be bacillus-
shaped or coccus-shaped, but it would not be uncommon to see some spirilla. Notice the
arrangements of the bacteria---pairs, clusters, chains?
9. Any slide that you use for smears is returned to your slide box, to be cleaned and used again.
• Look at a bought prepared bacterial smear
1. Since these are bought stained smears, cover slips are on them. You still use oil on them with the oil-
immersion lens.
2. Be sure to REMOVE any oil before replacing them on the trays.
Materials Needed Wet Mounts and Stained Smears
• Microscope • The microscope is absolutely essential to the microbiology
• Pond water lab: most microorganisms cannot be seen without the aid
• Microscope of a microscope, save some fungi.
• Slides cover • And, of course, there are some microbes which cannot be
• Slip soil seen even with a microscope, unless it is an electron
• Dropper microscope, such as the viruses.
• Prepared slides of Bacillus • Different types of microscopy:
• Toothpicks ⤷ Brightfield microscope
• Dye kits ⤷ Phase-contrast microscope
⤷ Darkfield microscope
• Phase-contrast and darkfield microscopies are used for
wet mounts, whereas brightfield can be used for both wet
mounts and stained specimens.
The Procedures
• Prepare a wet mount of pond water:
1. Go DOWN into the algae and muck to get a really good sample of protozoa and algae.
2. Focus on the sample using 10X, then go to 40X (NOT 100X). Start with brightfield, then switch over
to darkfield and phase-contrast (see directions below).
3. Practice with the microscope, changing condensers settings, using different lenses. It is NOT important
to identify protozoa or algae.
• Prepare a smear and simple stain of the material between your teeth:
1. Take a sterile toothpick, remove some solid material between your wisdom teeth, and mix it into a drop
of water so that you have a suspension spread over the middle third of the microscope slide. NO
COVER SLIP USED!
2. Let the slide air-dry.
3. Heat-fix the dry smear by running the slide quickly through the flame a few times. If your fingers get
hot, you have heat-fixed TOO MUCH.
4. Place the slide on the wire over the stain tray. Flood the smear with crystal violet: let sit for 1 minute.
5. Wash the slide WELL with distilled water. Blot the smear slide with your bibulous paper pad.
6. Focus on the sample using the 10X lens(Be SURE that you are on brightfield microscopy): you should
see masses of purple material, most of it too small to see.
7. Ready to go to 100X now? Do NOT move the stage or the adjustments knobs before you follow the
directions below.
8. Identify the various shapes and arrangements of bacteria in your mouth. Most of them will be bacillus-
shaped or coccus-shaped, but it would not be uncommon to see some spirilla. Notice the
arrangements of the bacteria---pairs, clusters, chains?
9. Any slide that you use for smears is returned to your slide box, to be cleaned and used again.
• Look at a bought prepared bacterial smear
1. Since these are bought stained smears, cover slips are on them. You still use oil on them with the oil-
immersion lens.
2. Be sure to REMOVE any oil before replacing them on the trays.
