|Basic Malaria Microscopy (part I and II) (WHO - OMS, 1991, 72 p.)|
By the end of this Unit you should be able to:
· describe how microscope slides
for blood films are correctly cleaned, wrapped and stored
Microscope slides are usually supplied in boxes of 50 or 72. They may be described on the box as washed or pre-cleaned, but they will still need to be properly washed, dried and wrapped. It is not possible to make good quality blood films on dirty microscope slides. Blood films made on dirty or greasy slides will wash off easily during staining. It is therefore best to discard slides that:
· have an iridescent bloom or appear white or opaque
· are not properly cleaned
· are old, with surface scratches or chipped edges.
In order to clean slides you will need:
· a large plastic basin
· gauze or cotton wool
· a good quality detergent (powder or liquid)
· 2 - 4 clean, dry, lint-free cotton cloths
· clean water.
All new slides should be washed with detergent and clean water. After being soaked for between 30 minutes and 1 hour, the slides should be rinsed under running tap water or in several changes of clean water. Each slide should be individually wiped dry and polished with the clean, dry, lint-free cloths.
Cleaned slides should be handled only by the edges to avoid finger marks or grease being deposited on the surfaces.
Used, dirty slides should be soaked for a day or two in water containing detergent. (Warm water should be used whenever possible.) After soaking, the slides should be cleaned one by one with a small piece of gauze or cotton wool All traces of the blood film and oil (used during microscopy) should be removed from the slides.
Do not leave the slides in the detergent for too long; soaking should be for a few days only, not weeks. If slides are left in the detergent solution for long periods, the water will evaporate, leaving a deposit on exposed slides that is impossible to remove.
After cleaning, the slides should be transferred to a fresh solution of detergent and later rinsed under running water or in several changes of clean water. They should be individually dried with the clean cotton cloths as described previously.
Slides that are slightly scratched and considered unsuitable for blood films may be handed over to other sections of the laboratory service for routine use.
Wrapping cleaned slides
To wrap cleaned slides correctly you will need:
· sheets of thin, clean paper, about II cm x 15 cm in size
· empty cardboard slide boxes (of the type new slides are packed in)
· rubber bands or adhesive tape.
Cleaned slides should be wrapped with thin paper in packs of 10. Each pack can be secured with adhesive tape or a rubber band. Packs can then be placed in the cardboard slide boxes for later use or dispatch to the field.
Slides should be stored in a dry place such as a warm-air cupboard. If stored at room temperature with high humidity, the slides will stick together after a few weeks. It will then not be possible to use them unless they are rewashed and dried.