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An Urban Experience
Correct use of a microscope
1. Always use a coverslip
· You should always use a cover-slip (or cover glass).
· The only exceptions are tape-strip preparations (the acetate backing of the tape acts as its own cover-slip).
· Microscope lenses are designed to look through a cover-slip and fluid layer, which provides a flat optical surface, puts material in a similar focal field, avoids air– fluid interfaces and reduces contrast.
· Curved surfaces (including cell layers, hairs, skin debris, and oil on top of the cover-slip) act as mini- lenses and cause serious distortion.
· Cover-slips can also protect the lenses from scratches and the mounting fluid, and provide a defined search area for skin scrapes and hair plucks.
· It is important to use enough mounting fluid to seal the cover-slip to the slide without gaps or air bubbles, but not so much that it gets onto the microscope lenses or stage.
· I prefer to use immersion oil as it is more viscous – it adheres the cover slip to the slide better with less leakage. However, if you collect material into liquid paraffin use more liquid paraffin if required before placing the cover-slip. Mixing liquid paraffin and immersion oil results in an opaque emulsion.
2. Scanning slides
· Initially, visually examine the slide to orientate it, and appreciate the depth of material, degree of staining and possible areas of interest.
· It is useful to check the quality of staining visually or under low power before placing a cover-slip, as the slide can be re-stained at this stage if necessary.
· Study the slide at progressively higher magnification.
· Low-power lenses (x4–x10) are useful to scan large areas; with skin scrapes, hairs plucks etc., start at one corner of the cover slip, proceed down to the opposite edge, across one visual field and back up again to methodically search all the collected material.
· Use the high-power lens (x40) to close in on areas of interest.
· Use the oil-immersion lens (x100) last of all to avoid getting oil on the other lenses.

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