(c) Dip the screwcap and top portion of the bottle two or three times in a
hot, melted paraffin bath. This will prevent leakage and reduce the rate of evaporation.
2-19. PROCESSING OF GASTROINTESTINAL SPECIMENS
There are many laboratory procedures used in the identification of human
parasites. Each method has advantages and disadvantages--not one can be used for all
occasions. There are some criteria that govern the choice of technique--the most
common parasites encountered in the area, the amount of daily specimens, the
resources available, the desirability of quantitative results, etc. Some of these
procedures are suited to the most primitive conditions and others require the best
equipped laboratories.
a. Direct Smears. The direct microscopic examination of fresh stools for the
observation and examination of parasitic organisms should be performed on all samples.
If this preparation does not show any organisms, concentration of the stool must be done
prior to any other procedure.
(1) Saline solution. This preparation is particularly useful for the detection of
motility and examination of all intestinal parasites. Chromatoidal bodies are very
refractile and easily detected in saline direct smears. Place one drop (approximately 0.05
milliliter) of warm (37 C) physiological (0.85 percent) saline on one end of a 25 by 75
milliliter plain glass slide. Using an applicator stick, place a small portion of feces
(approximately 0.1 milligram) in the saline drop and mix until the suspension becomes
homogenous. The other end of the slide may be used for a stained direct preparation.
(2) Iodine. The iodine film is employed primarily to study the diagnostic
morphological features of protozoan cysts. If the iodine solution is too strong, the fecal
material becomes clumped and the refractile nature of the organisms is altered.
However, a weak solution does not stain the organism well. Gram's iodine is too weak,
while Lugol's iodine is considered too strong by some workers.
(a) Dobell and O'Connor's iodine.
Iodine (powdered crystals) ................................ 0.5 gm
Potassium iodine ............................................... 1.0 gm
Distilled water .................................................... 50.0 ml
Mix the potassium iodide in distilled water, add the iodine, and mix
well. This concentration produces a "dark tea" color. Store in a
stoppered brown glass bottle and filter before use. Formalin
preserved specimens require a slightly darker solution. This solution
is stable for 10 days.
MD0841
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