(c) Procedure. Using an applicator stick, mix a small amount of fecal
material with a drop of Buffered Methylene on a slide. Mix well, coverslip, seal with a 1:1
vaseline/paraffin mixture. Examine for intestinal parasites.
b. Concentration Techniques. Intestinal parasites are readily found in direct
smears when present in large quantities. However, in most cases, concentration is
required for the detection of these parasites. Concentration procedures, when properly
performed, are more reliable by ensuring a higher recovery ratio for protozoans as well
as for helminths.
(1) Zinc sulfate. This is a simple and efficient method for the recovery of ova,
larvae, and protozoan cysts. This method is recommended for mass examination of
roundworm eggs and protozoan cysts. The procedure is not suitable for the recovery of
eggs from Ascaris, Trichuris, trematodes, and pseudophyllids. Another drawback of the
procedure is that it is not convenient when working with fatty stools.
(a) Reagent--zinc sulfate solution, specific gravity 1.18 to 1.20. Add 331
grams of zinc sulfate (USP) to 1,000 milliliters of warm tap water. Check the specific
gravity with a hydrometer and adjust if needed by adding zinc sulfate or water.
(b) Procedure for concentration.
STEP 1: Place 0.3 to 0.5 grams (1/3 to 1/2 milliliters if liquid) of feces in a disposable
container and emulsify with 1.0 milliliters of tap water.
STEP 2: Add 8.0 milliliters of tap water, mix well, and strain through two layers of wet
gauze into a 15 milliliter centrifuge tube.
STEP 4: Decant supernatant and add one milliliter of zinc sulfate solution. Mix well.
STEP 5: Fill the tube to the 13 or 14 milliliter mark with zinc sulfate.
STEP 7: Carefully and without shaking or spilling, place the tube in a rack vertically and
away from any vibrations caused by machinery.