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Biology LibreTexts

3.4: Exercise 1 - using the compound light microscope

  • Page ID
    17506
  • Note

    Lenses are fragile and expensive—treat them with care!

    objectives should never touch the slide!
    clean lenses with lens paper only.
    KimwipestM and other paper may scratch a lens.

    1. Identify the parts of the microscope. Note the positions of the objectives, the coarse and fine focus adjustments, the adjustable light switch and the condenser diaphragm. Adjust the positions of the eyepieces to fit the distance between your eyes.

    2. Locate the four objective lenses on the microscopes. The magnification of each lens (4x, 10x, 40x, and 100x) is stamped on its casing. Rotate the 4x objective into position. Adjust the position of the iris diaphragm on the condenser to its corresponding 4x position.

    3. Turn on the microscope lamp and adjust the dimmer switch until the light is not too intense when you look through the eyepieces. You may need to adjust the distance between the eyepieces to fit your eyes.

    4. Place the slide with the stained human blood smear on the microscope stage. Use the coarse focus knob to bring the ruler into focus. You may also need to adjust the light. Make additional adjustments with the fine focus knob.

    5. Use the stage manipulators to move the ruler to either the right or the left. What direction does the image move?

    6. Dial the 10x objective into position. Adjust the condenser diaphragm. Adjust the focus with the coarse and fine focus adjustment knobs. How does the distance between the specimen and the objective change?

    7. Swing the 40x objective into position and adjust the condenser diaphragm. Adjust the focus using ONLY the fine focus knob. What happens to the working distance and the size of the field of view?

    8. Take some time to make some observations on the blood cells. The major cell type in blood
    is the erythrocyte, or red blood cell (RBC). RBCs are biconcave disk shape and are ~7 μm in diameter. There are 4-6 billion RBCs in every milliliter of blood. The oxygen-binding protein, hemoglobin, gives RBCs their red color. Various kinds of white blood cells (WBCs), which are part of the body’s immune system, make up the remaining cells in blood. Together, the WBCs comprise less than 1% of blood cells. Compare the RBCs and the WBCs.

    What major differences do you notice between the two types of cells?

    WBCs have distinctive morphologies. Move the slide to find additional WBCs. Neutrophils, aka polymorphonuclear leukocytes, are 12-14 μm in diameter with multi-lobed nuclei. Neutrophils are usually the most abundant WBC. Lymphocytes, 6-9 μm in diameter, have a large, uniformly-stained nucleus surrounded by a thin layer of cytoplasm. You may find smaller numbers of basophils and eosinophils, which have a 2-lobed nucleus and many granules that stain with hematoxylin (purple) or eosin (pink), respectively. Record your observations.​​​​​​​