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

186 Manual of basic techniques for a health laboratoryFig. 4.148 Collecting a capillary blood sample on each of twoslidesFig. 4.149 Collecting a capillary bloodsample on filter-paper●●●CoverslipsBlood lancetsFilter-paper● Sodium chloride, 0.85% solution (reagent no. 53)● Giemsa stain (reagent no. 29) or Field stain (reagent no. 25)● Buffered water, pH 7.2 (reagent no. 15)●70% Ethanol.Method1. Sterilize the pad of the third finger then prick with the blood lancet. Wipe awaythe first drop of blood with filter-paper. Collect two drops of blood (Fig. 4.148):— one drop on one slide— one drop on a second slide.2. Collect two drops of blood on a piece of filter-paper (Fig. 4.149). Leave to dry.3. On the first slide, place one drop of sodium chloride solution beside the drop ofblood.Mix, using the corner of a slide (Fig. 4.150). Cover with a coverslip.4. On the other slide, spread the blood to make a thick film (see page 174).Stain with Giemsa stain (see page 175) or Field stain (see page 177).Note: Blood films must be stained and examined immediately after collection ofblood samples, since trypanosomes lyse and disappear within a few hours.Microscopic examinationWet preparation. Examine the first slide (with the wet preparation) under themicroscope, using the ¥ 40 objective and reducing the condenser aperture.Examine the edges of the smear first. Look for movement among the erythrocytes;trypanosomes will displace them with their flagellum as they move forward.Make sure that the organisms are trypanosomes:Length: 15–25mm (2–3 erythrocytes).Width: 3 mm (half an erythrocyte).Shape: like an elongated fish.Motility: trypanosomes move rapidly, advancing and contracting like a snake, andhave an undulating membrane extending from a motile flagellum at the anteriorend (Fig. 4.151).