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Microscope Slide Preparation: Mounting Specimens

A slide is a small thin square of glass about 1 X 3 inches. The glass is used to "mount" specimens so that they can be handled and seen under a microscope. There are two major methods for mounting a specimen, dry mount and wet mount.

Image of a Slide on a Microscope

Dry mounting a specimen is fairly easy. It merely involves placing the object to be viewed, or specimen on a glass slide. The object is then normally covered with a coverslip, which is another, smaller piece of glass. When viewing a dry object under the microscope, very thin slices will be best. This allows the light to pass through, from underneath the specimen, and allows the coverslip to be positioned to keep the object from moving about on the slide. Some objects will be too large for a coverslip in which case they should be cut thinner if possible. They also may be viewed under fairly low magnification, with the light source coming from above the object. In this case, when focusing, be sure not to allow the lens tube to touch the specimen.

A wet mount is used to view living organisms. This involves putting water, as well as the specimen, on the slide. It is necessary because most living things require water to survive, and its deprivation will make the object appear different from its natural state. To do a wet mount, be sure to begin with a flat surface. Then put a drop of water in the middle of the slide. Put the specimen on the drop and then apply the coverslip. When holding the coverslip, be sure to hold it by the sides, so that it does not get fingerprints or smudges that might be mistaken for being part of the specimen. If there are bubbles under the coverslip, they can be removed by pressing on it, and forcing the bubbles out through the edges. If there is not enough water under the slip cover, apply a drop on the slide at the edge of the coverslip. The water should be drawn underneath it. Now daub off excess water using a clean paper-towel.

Fast moving organisms in a wet mount can be slowed down using a chemical called "Protoslo". A few strands of cotton may also be added to the mount to trap micro-organisms in a smaller area beneath the lens. To improve resolution on a wet mount, one or another stain may be used, including Lugol's iodine, methylene blue, and crystal violet. Stains may be added at the time the water is dropped on the slide, or it may be added later by adding a drop on the slide near the edge of the coverslip. A piece of paper-towel on the opposite edge of the coverslip will help pull in the dye.

Next Page: The Parts of a Microscope