Manual of basic techniques for a health laboratory - libdoc.who.int

4. Parasitology 1771. Allow the thick film to dry thoroughly; if results are required urgently, dryingmay be hastened by fanning, or briefly exposing the slide to gentle heat such asthat from a microscope lamp. Care should be taken to avoid overheating, otherwisethe thick film will be heat-fixed.2. Fix the thin film by adding three drops of methanol, or by dipping it into acontainer of methanol for a few seconds. To permit dehaemoglobinization, thethick film should not be fixed; therefore avoid exposure of the thick film to methanolor methanol vapour.3. Prepare a 10% Giemsa solution in buffered or distilled water, pH 7.2; if a smallquantity is being used, three drops of stain per ml of buffered water will give thecorrect concentration of Giemsa solution. One slide requires about 3ml of madeupstain. Mix the stain well with a glass rod.4. Gently pour the stain on to the slides or use a pipette. Stain for 5–10 minutes.5. Gently flush the stain off the slides by adding drops of clean water. Do not tip offthe stain and then wash, as this will leave a deposit of scum over the smears.6. Place the slides in the slide rack to drain and dry, film side downwards, makingsure that the film does not touch the slide rack.Staining blood films with Field stainStaining with Field stain allows rapid detection of malaria parasites (but it does notalways stain Schüffner’s dots).Materials and reagents● Microscope●●●Glass jarsSlide racksMethanol● Field stain (reagent no. 25)● Buffered water, pH 7.2 (reagent no. 15).Method for staining thick films1. Dip the unfixed film into a jar containing Field stain A solution for 3 seconds.2. Wash gently by dipping (once) into a jar of clean water for 5 seconds.3. Dip the slide into a jar containing Field stain B solution for 3 seconds.4. Wash the slide gently as in step 2.5. Place the slide upright in a slide rack to air-dry.Method for staining thin films1. Fix the film in methanol for 1 minute.2. Wash off the methanol with buffered water.3. Using a pipette, cover the film with diluted Field stain B (one volume of stainplus four volumes of buffered water).4. Immediately add an equal volume of Field stain A solution and mix well bytilting the slide.5. Allow to stain for 1 minute.6. Wash off the stain with clean water.7. Place the slide upright in a slide rack to air-dry.