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How difficult is the making of permanent slides?

Found in: Labwork

Making permanent slides can be very easy, not much different than making a wet mount. Making permanent slides can also be a time consuming and lengthy process, stretching over several days, and requiring much lab work. As so often the case: It all depends on the specimen.

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Large samples of tissue, for example, have to be first fixed for preservation. The tissue is first placed for several days into an appropriate fixing solution. This solution is often water-based. This water has to be removed before further preparation. The tissue sample is dehydrated by placing it into subsequently higher concentrations of alcohol. Dropping the tissue into concentrated alcohol rit away will cause rapid shrinking, and bad results. Finally, the alcohol has to be removed and the specimen is placed into xylene, which is not healthy when inhaled. Now the tissue is embedded in paraffin wax so that it can be sliced into thin sections with the help of a microtome. The wax has to be removed and the thin sections can now be mounted in appropriate mointing medium. You then have to wait for a few weeks for the medium to dry. Oh, I forgot: You also might want to stain the sample….

Other specimens (which are already sufficiently small and dry) are very easily processed into permanent slides, however. Dry insect parts, such as wings or legs, can be directly mounted in Euparal mounting medium. These specimens do not shrink and deform too much when drying. It is also not necessary to cut them into sections with a microtome. Place a drop of mounting medium on the slide, then place the dry specimen into the medium. Add another small drop on top, then add the cover glass. You still have to wait for several weeks until the mounting medium has dried (store horizontally in a well-ventilated area).

Spores and pollen can also be directly mounted without preparation, glycerine gelatin is the mounting medium of preference here. As glycerine gelatin is water-based, it is not necessary to dry the specimen. Glycerine gelatin is a bit more difficult to use, because it must be warmed (but not too much!) for it to remain liquid. The slide also must be warmed to about 40-45 degrees centigrade. If you warm it too much, and the glycerine gelatin will not cure anymore. Using glycerine gelatin is therefore more difficult, also because it has the tendency to form air bubbles.

Due to the complexity of making some permanent mounts, many amateur microscopists will resort to buying ready-made permanent slides. These were already professionally prcessed and properly stained and cut into sections. For many beginning amateur microscopists, the effort of making one’s own permanent slides of tissue samples might therefore simply not be worth it.

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