Objectives

• Preparing a Slide for Observing through the Compound Light Microscope
• Steps to prepare a Light Microscope for observation
• Steps to dye a sample

Apparatus

• Compound Light Microscope
• Clean Glass Slides
• Thin Glass Cover Slips
• Droppers
• Forceps
• Mounted Needle
• Dyes
  • Safranin
  • Methylene Blue
  • Fast Green / Alcian Blue
  • Toluidine Blue O (TBO)
  • Iodine-Potassium Iodide (I2KI)
• Beaker
• Watch Glass or Petri Dish
• Brush
• Tissue Paper

Preparing a Slide

1. Clean a flat glass slide and a coverslip using lens paper or an isopropyl alcohol wipe to remove any dust, fingerprints.
2. If working with a solid specimen (such as plant stems or animal tissues), slice it as thin as possible using a fresh razor blade or microtome. For cellular suspensions or liquid samples (such as pond water or yeast), skip sectioning entirely; the raw suspension is ready for direct pipetting.
3. Use a dropper or pipette to place a single, small drop of distilled water, physiological saline, or an appropriate mounting medium (glycerin, immersion oil) directly onto the center of the clean glass slide. Ensure the drop is small.
4. Use a brush or forceps to pick up the thin tissue slice and gently lay it flat directly into the droplet of liquid medium. Gently tease out any folds or wrinkles, ensuring the sample lies completely flat on the glass surface.
5. If the target specimen is colorless, stain the sample.
6. Hold the clean coverslip by its edges using your fingers. Then slowly reduce the inclination angle using the mounted needle in a way that there are no residual air bubbles trapped inside between the coverslip and the slide.
7. Take a small triangle of paper towel or filter blotting paper and touch it gently to the outer edge of the coverslip. Clean any liquid residue off the bottom of the slide before placing it on the microscope stage to protect the condenser lens from chemical contamination.

Preparing the Microscope

1. Start on the lowest objective lens (4x) first. Never place a slide under a high-power objective initially, as you risk cracking the slide and damaging the delicate glass elements of the lens.
2. Lay the slide flat on the stage, specimen-side up with the coverslip facing upward. Secure it firmly in place using the stage clips, and use the mechanical stage controls to center the specimen directly over the condenser aperture.
3. Use the coarse focus knob only when working with the 4x and 10x objectives. Slowly raise the stage while watching from the side to avoid any contact, then look through the eyepiece and focus upward until the specimen begins to resolve.
4. Switch to the 10x objective to locate and center your specific region of interest. Find an easily recognizable anatomical landmark, such as the outer edge of a stem section, to establish a reference point before escalating the magnification.
5. Switch to the 40x objective and adjust the focus using only the fine adjustment knob. Never use the coarse adjustment knob at 40x, as the microscopic working distance risks cracking the slide. If you require 100x magnification, apply a single drop of specialized immersion oil directly onto the slide before clicking the lens into place to ensure clear refractive index matching.
6. Adjust the height of the condenser and reduce the diaphragm aperture slightly to increase optical contrast. This step is critical for resolving low-contrast boundaries such as cell walls and internal tissue layers.
7. Adjust the illumination using the brightness control knob so the field of view is well-lit but free of glare. Remember that washed-out images indicate excessive light intensity, while dim, dark images indicate insufficient illumination.

Applying Stains to Colorless Specimens

1. Place your cleaned slide on a flat, dry work surface and ensure your tissue slice or cellular smear is positioned flat in the dead center. Select the appropriate dye for the target specimen, keeping in mind that iodine is utilized for plant cell walls and starches, while methylene blue is the ideal agent for animal cell nuclei.
2. Use a dropper pipette to place a single, small drop of the selected staining solution directly over the specimen, ensuring the liquid entirely covers the biological tissue. Avoid adding excessive amounts of the stain, as this will lead to pools of dye overflowing the slide edges and potentially staining the microscope stage.
3. Allow the stain to rest undisturbed on the tissue for thirty to sixty seconds. This dwell time is critical for allowing the ionic dye molecules to diffuse evenly through the membranes and chemically bind to their target biological structures.
4. Tilt the glass slide at a slight angle over a sink or a waste container, and use a pipette to gently rinse away excess dye with a few drops of distilled water. Direct the water flow above the specimen rather than directly onto it to prevent washing the delicate cells off the slide surface.
5. Lower the clean coverslip at a forty-five-degree angle near the edge of the droplet using a mounted needle to slowly release it, which pushes out residual air bubbles. Once the coverslip is down, do not press directly on the glass with your fingers, as this can crush the cells and distort the delicate cellular structures.
6. If you are staining a specimen that has already been mounted with a coverslip, place a single drop of the dye directly against one edge of the coverslip. Place a small, triangular piece of paper towel flat against the opposite edge of the coverslip to draw the water out, pulling the stain across the specimen by capillary action.
7. Use a clean corner of a paper towel to blot any remaining liquid escaping from under the coverslip edges. Wipe the underside of the slide thoroughly with a dry wipe before transferring it to the stage to keep the condenser lens clean and maintain maximum optical clarity.

OR You can also do the below method to stain the specimens

1. Prepare a separate watch glass or dish containing the diluted staining solution, such as safranin or toluidine blue. Use a fine-tipped, wet camel-hair brush rather than forceps to lift the thinnest, most translucent sections out of the water and transfer them into the staining bath to avoid squashing or tearing the delicate cell walls.
2. Allow the sections to incubate in the stain for one to three minutes to ensure the dye molecules fully diffuse through the thick cell walls and bind with lignin or cellulose. After incubation, transfer the sections into a final watch glass containing clean, distilled water to thoroughly rinse away unbound, excess stain before mounting, which eliminates muddy background contrast.