Page 280 - parasitology for medical and clinical laboratoryprofessionals

260 CHAPTER 12

PROCEDURE 12-1

(continued)

4. 22-mm cover glasses
5. Lugol’s iodine for demonstrating eggs and cyst structures more easily (iodine will kill
trophozoites, so a preliminary examination for trophozoites should be conducted fi rst)
6. Normal saline for suspension of fecal material
7. Binocular microscope with low- and high-power objectives
8. Ocular micrometer for determining sizes of organisms and ova

Procedural Steps
1. Obtain a standard 1 3 3 inch microscope slide and place one drop of normal
saline on one end of the slide. A drop of iodine (1:5 dilution of Lugol’s iodine)
may be placed on the other end to be incorporated into the feces-saline mixture
after an initial examination for motile trophozoites.
2. A small amount of stool (the amount clinging to the end of a wooden applicator
stick may be sufficient) should be introduced to the drop of saline and another

similar specimen into the diluted iodine.
3. Mix the stool samples and the two solutions with the applicator sticks.
4. Place a #1, 22-mm cover glass over each of the preparations by touching a long
edge of the cover glass to the liquid and then allowing it to gently fall onto the
mixture to avoid air bubbles.

5. The resultant preparation should be sufficiently transparent as to be able to
read newsprint through it.
6. The edges of the cover slip may be sealed with clear nail polish or with equal
mixtures of petroleum jelly (Vaseline) and melted paraffin.

7. Sealing the slides is desirable to avoid drying the specimen, which prevents clear
visualization of the organisms if present. In addition, white and red blood cells, as
well as yeasts, may be visible, all of which may be clinically significant. The cover

glass can be removed from a well-made slide and after drying and fixing the slide,

it can be stained to prepare a permanent slide for further identification and study.
Clinical Precaution:
Use of PVA (polyvinyl alcohol) as a fixative before making the wet mount will

cause a cloudy condition due to exposure to air, so PVA-fixed samples should

not be used for wet mounts.
8. If specimens submitted have been preserved with 10% formalin, saline drops
may be avoided on the unstained sample on the slide.
9. Saline samples with unfixed samples enable more accurate examination of hel-

minth (worm) eggs and larvae, as well as motile trophozoites and cysts, which
are quite refractile.
10. The iodine solution enables the visualization of nuclear detail and darkly stains any
glycogen masses that are diagnostic for some protozoa, but will kill trophozoites.
Sometimes methylene blue is substituted for iodine for wet mounts.