Abstract
Many techniques have been devised to detect helminth ova and/or protozoan cysts. These may be classified according to features of manipulation and physical attributes as follows: direct smear (wet saline mounts,with or without stains, and permanently stained mounts); sedimentation, followed by direct smear; flotation procedures, with or without centrifugation; and ether sedimentation with centrifugation. Another classification based on the range of effectiveness might be as follows: effectiveness limited to helminths; effectiveness limited to protozoa; effective for both helminth eggs and protozoan cysts; effective for specific helminth eggs; and adaptations for making egg counts. At least in the minds of same, direct saline smears and permanent stains for protozoa are relegated to the identification of protozoan trophozoites and for confirmation of findings by concentration methods. A number of the concentration technics have been developed in the last three decades, for which the above classifications are inclusive.
The zinc sulfate flotation technique as developed by Faust et al and Tobie et al(2) has been widely used and considered highly effective. It was the first stool concentration method that acceptably fulfilled the dual role of recovering both eggs and cysts. Recently, a formalin-ether sedimentation procedure(3) has been developed that is also highly effective for concentrating eggs and cysts. This method, a simple modification of Telemann’s,(4) has been extensively used at the 406th Medical General Laboratory since 1946, and has become identified as the 406th table technic.(5) Two other ether sedimentation procedures have been reported for the recovery of cysts as well as eggs, one in 1928 by DeRivas,(6) and the other in 1952 by Larman.(7)
A direct comparison has been made of the formalin-ether and the zinc sulfate technics by means of parallel examinations on 161 “single stool” specimens from a highly parasitized population.