A wet mount slide is a temporary preparation technique where a specimen is suspended in a liquid medium, typically water or saline, between a glass slide and a coverslip. This method is fundamental in microscopy because it allows for the observation of samples in a hydrated state. The primary purpose of a wet mount is to view living organisms, such as pond water microorganisms, or fresh tissue samples that must remain moist to preserve their natural structure and activity. This quick and simple procedure provides immediate access to the microscopic world.
Necessary Supplies and Setup
The preparation begins with gathering a few simple components, starting with a clean glass slide and a thin glass or plastic coverslip. Clean materials prevent visual obstructions, known as artifacts, that could be mistaken for part of the specimen. A dropper or pipette is used to control the volume of the mounting medium, which is usually distilled water or a buffered saline solution to maintain cell integrity. The specimen, such as a cheek swab or a small piece of plant leaf, is the final component.
The mounting medium serves the dual purpose of suspending the sample and preventing it from drying out under the microscope’s illumination. Saline is often preferred for biological samples because its osmotic pressure is closer to that of cells, reducing cellular distortion. The coverslip flattens the specimen and protects the objective lens from direct contact with the liquid. Before starting, all components should be laid out on a clean, stable surface.
The Wet Mount Preparation Process
The actual construction of the wet mount requires careful attention to ensure a clear preparation. First, a small portion of the specimen is placed directly in the center of the clean glass slide. If the sample is dry, it is positioned first; if it is liquid, such as a culture, a very small drop is applied. Next, add a single, small drop of the mounting medium directly onto the specimen.
Controlling the drop size is important, as too much liquid will cause the coverslip to float or slide excessively. The technique used to lower the coverslip is crucial. The coverslip must be held at approximately a 45-degree angle, with one edge touching the slide next to the liquid. This angle allows the liquid to spread along the bottom edge, creating a seal as the coverslip is slowly lowered over the specimen.
This gradual, angled descent minimizes the inclusion of air, preventing distracting bubbles from becoming trapped. Once the coverslip is flat, the liquid should form a smooth, uniform layer without excessive overflow. A properly prepared slide has the specimen fully immersed and flattened under the coverslip.
Optimizing the Slide and Troubleshooting
After placing the coverslip, the slide may require minor adjustments. If too much mounting medium was used, excess liquid will seep out from under the edges. This excess can be removed by gently touching the edge of absorbent material, like a paper towel, to the liquid, which wicks it away through capillary action. The coverslip should then sit securely without shifting.
A common issue is the presence of air bubbles, which appear under the microscope as perfectly round, dark-rimmed circles. These must be distinguished from actual specimens, which have varying shapes and internal structures. Small, trapped bubbles can sometimes be moved to the edge by gently pressing on the coverslip with the blunt end of a pencil or a mounted needle. Once the slide is secured, the light intensity and focus must be tuned to provide maximum contrast for the specimen.