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

3. General laboratory procedures 533. General laboratoryprocedures3.1 Use of a microscopeThe microscope is an essential instrument for the diagnosis of disease. It is a precisioninstrument and requires careful maintenance to prevent damage to the mechanicaland ocular parts and also to stop fungi from obscuring the lenses.3.1.1 Components of a microscopeThe various components of the microscope can be classified into four systems:— the support system— the magnification system— the illumination system— the adjustment system.Support system (Fig. 3.1)This consists of:— the foot (1)— the limb (2)— the revolving nosepiece (objective changer) (3)— the stage (4)— the mechanical stage (5), which gives a slow controlledmovement to the object slide.Magnification system (Fig. 3.2)This consists of a system of lenses. The lenses of themicroscope are mounted in two groups, one at each endof the long tube — the body tube.● The first group of lenses is at the bottom of the tube,just above the preparation under examination (theobject), and is called the objective.● The second group of lenses is at the top of the tubeand is called the eyepiece.ObjectivesMagnificationThe magnifying power of each objective is shown by afigure engraved on the sleeve of the lens (Fig. 3.3):— the ¥ 10 objective magnifies 10 times;— the ¥ 40 objective magnifies 40 times;— the ¥ 100 objective magnifies 100 times.Fig. 3.1 Components of the support system of amicroscope1: foot; 2: limb; 3: revolving nosepiece; 4: stage;5: mechanical stage.53