To use, emulsify 1 part of faeces in 3 parts of PVA solution. This method will preserve ova, larvae and trophozoites well, but cyts may show some distortion. However some ova and cysts do not concentrate well when preserved in PVA. Faecal smears made from the faeces/PVA mixture and allowed to dry can be used for the permanent staining of trophozoites. Before staining, the slides must be placed in 70% ethyl alcohol containing 5 -10 drops of Lugol’s iodine (see below) to remove the mercuric chloride.