Protozoan cysts appear as opalescent refractile bodies in the saline preparation; internal structures are easier seen in the iodine suspension. Ova are more readily identified in the saline preparation. Cysts are not easily detected in thick faecal suspensions. Too thin a suspension gives insufficient material for examination. The correct amount is found by experience. Amoeba trophozoites cannot be identified in fixed material but Giardia intestinalis may be recognized. Correct illumination is vital. Too much light causes objects to be missed. When changing to the 40* objective, the light should be increased.
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