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

3. General laboratory procedures 65Oil residues on the lenses should be removed with special lenstissue paper, absorbent paper or medical-grade cotton wool. Theoptical surfaces may be finally cleaned with a special solution,consisting of the following:— 80% petroleum ether (boiling point 60–80°C)— 20% 2-propanol.Note: Do not use 95% ethanol, xylene or toluene for cleaningthe lenses, since these substances dissolve the cement. They can,however, be used for cleaning mirrors.Cleaning the instrumentHeavy contamination can be removed with mild soapy solutions.Grease and oil can be removed with the special cleaning solutiondescribed above. The instrument should then be cleanedwith a 50:50 mixture of distilled water and 95% ethanol. Thismixture is not suitable for cleaning the optical surfaces.The mechanical parts (coarse adjustment screw, fine adjustmentscrew, condenser focusing and mechanical stage) should beperiodically cleaned and lubricated with machine oil to makethem run freely.Fig. 3.27 Cleaning the objective lenses using asoft camel-hair brushMaintaining the microscopeWhen you carry out repair and maintenance procedures, take care not to confusethe condenser centring screws with the condenser clamp screws. To maintain themicroscope proceed as follows:● Check the mechanical stage.● Check the focusing mechanism.● Remove any fungal growth.● Check the diaphragm.● Clean all mechanical parts.● Lubricate the microscope according to the manufacturer’s instructions.●●Check the spring load on the specimen clamp. Too high a tension may result inbreakage of slides and damage to the clamp.Check the optical alignment. A dim appearance of the specimen is often due tomisalignment of the optical parts rather than to insufficient light.Precautions● Never dip the objectives in xylene or ethanol, as this may cause the lenses tobecome detached.● Never use ordinary paper to clean the lenses.● Never touch the lenses with your fingers.●●●●●Never clean the support or the stage with xylene or acetone.Never clean the inside lenses of the eyepieces and objectives with cloth or paper(this might remove the anti-reflective coating); use a soft camel-hair brush, afine paintbrush or a blower instead.Never leave the microscope without the eyepieces unless the openings are plugged.Never keep the microscope in a closed wooden box in hot humid countries.Never press the objective on to the slide, since both the slide and the objectivemay break. Take care when focusing the microscope.