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

70 Manual of basic techniques for a health laboratoryFig. 3.36 Components of acentrifugeA: central shaft or spindle;E: centrifuge head;T: centrifuge tubes.Fig. 3.37 A hand-operatedcentrifugeComponents of a centrifuge (Fig. 3.36)A centrifuge consists of:— a central shaft or spindle (A) that rotates at high speed;— a head (E), fixed to the shaft, with buckets for holding the centrifuge tubes;— tubes (T) containing the liquid to be centrifuged.When the spindle rotates the tubes are subjected to centrifugal force. They swingout to the horizontal and the particles in suspension in the liquids in the tubes arethrown to the bottom of the tubes. The particles are compacted at the bottom ofthe centrifuge tubes. These particles form the centrifuge deposit which can be separatedfrom the supernatant fluid and examined. The deposit may contain, for example:— blood cells;— parasite eggs (in diluted stools);— cells from the urinary tract (in urine).3.3.2 Types of centrifugeHand-operated centrifuge (Fig. 3.37)This is operated manually by turning a handle. It takes two or four tubes.The hand-operated centrifuge can be used:— to examine urinary deposits;— to concentrate certain parasites in stools.The speed is insufficient for satisfactory separation of erythrocytes from plasma inblood.Important:●Clamp the centrifuge firmly on a stable support (edge of a table).● Balance the two diametrically opposite tubes perfectly as described in the instructionsfor use, section 3.3.3.● Keep your distance while operating the centrifuge.● To stop the centrifuge, do not slow down the turning of the handle. Pull thehandle out of the machine with a sharp movement.● Remove the tubes slowly and carefully (so as not to disturb the deposit).● Lubricate the spindle of the centrifuge regularly.Warning: The hand-operated centrifuge can cause serious injury, so follow the instructionsabove carefully.Electric centrifugesElectric centrifuges are more accurate than hand-operated centrifuges and shouldbe used whenever possible. Electric centrifuges are used with two types of head —the “swing-out” head and the “angle” head.“Swing-out” head (Fig. 3.38)The head is designed to swing the tubes out to a horizontal position during centrifuging.This is the type most frequently needed.“Angle” head (Fig. 3.39)The “angle” head holds the tubes at an angle of about 45° during centrifuging. It isuseful for certain techniques, e.g. agglutination tests in blood-grouping by the testtubemethod.