A wet mount is a fundamental microscopy technique for quick specimen examination. It involves placing a biological sample in a drop of liquid, usually water, directly onto a microscope slide. A thin glass coverslip then gently rests over the liquid and specimen. This simple method provides a temporary view of the sample and is widely used in basic biological and clinical settings.
Why Use a Wet Mount
Wet mounts offer distinct advantages for observing biological samples. They are particularly valuable for studying living organisms like pond water protists or bacteria, as the liquid medium maintains their natural environment and also prevents delicate specimens from drying out, which can distort their natural shape. This allows for real-time observation of movement, feeding behaviors, and interactions, which is not possible with dry preparations.
The quick preparation time of a wet mount makes it ideal for immediate analysis. It requires no complex staining or lengthy drying processes, though stains can be added to enhance contrast. This simplicity enables rapid diagnostic observations and initial surveys of a sample, providing quick insights into its composition and activity.
How to Prepare a Wet Mount
Preparing a wet mount requires a few basic laboratory materials: a clean microscope slide, a thin glass coverslip, a dropper or pipette, a liquid medium (like distilled water or saline solution), and the specimen. Clean materials are essential to prevent contamination and ensure clear viewing.
Begin by placing a small amount of the specimen in the center of the clean microscope slide. For solid samples, such as plant epidermal cells or fibers, ensure the specimen is thin enough for light to pass through. Next, add one or two drops of the chosen liquid medium directly onto the specimen. The liquid selection depends on the specimen; water is common for freshwater organisms, while saline solutions might be used for animal cells to maintain osmotic balance.
Carefully position the coverslip at a 45-degree angle, touching one edge to the slide just outside the liquid drop. Slowly lower the coverslip over the liquid and specimen, allowing the liquid to spread evenly underneath by capillary action. This angled approach minimizes trapped air bubbles, which can obstruct the view. Blot any excess liquid from under the coverslip with filter paper or a paper towel, drawing the liquid from the edge without disturbing the coverslip.
Common Observations
Wet mounts reveal a diverse range of microscopic life and cellular structures. Pond water, for instance, is a rich source of microorganisms. Viewers can identify various protozoa, such as the rapidly moving Paramecium with its cilia, or the shape-shifting Amoeba extending its pseudopods. Algae, like filamentous Spirogyra with its spiral chloroplasts, are commonly seen. These observations provide insight into microbial ecology and cellular locomotion.
Plant tissues also offer good subjects for wet mounts. A thin epidermal layer from an onion scale, for example, shows rectangular plant cells with distinct cell walls and nuclei. Observing leaf cross-sections can reveal chloroplasts within palisade cells, illustrating the sites of photosynthesis. The movement of cytoplasm, known as cytoplasmic streaming, can be observed in larger plant cells, showcasing dynamic cellular processes.
Wet mounts are also useful for examining non-living particulate matter. Hair and various types of fibers, such as cotton or synthetic threads, can be mounted in water to observe their unique structural characteristics, aiding in identification.