(2)
Procedure.
STEP 1: Mix a portion of feces with three times the amount of formalin.
STEP 2: Allow to settle for at least one hour and store in screw-cap bottles.
STEP 3: If shipment or prolonged storing is required, dip the top portion of the tightly
fastened container, to include the cap, two or three times into a hot paraffin
bath. This will prevent spillage and reduce the rate of evaporation.
(3)
Notes.
(a) Formalin is the most commonly employed reagent for fixing and
preserving specimens. Formaldehyde solution is a near saturated solution of gas and
water. Such a solution contains from 37 to 40 percent formaldehyde with nine volumes of
water as 10 percent formalin. This 10 percent formalin dilution contains approximately
4.1 to 4.5 parts formaldehyde gas.
(b) Formalin preserved specimens stored for reference material should
have the preservative changed every six months. The formalin volume should be
maintained at all times.
b. Polyvinyl Alcohol (PVA). This is a mixture of fixative and water-soluble resin
that is specifically used to fix and preserve trophozoites of intestinal amoebic organisms.
These trophozoites are very fragile and will become distorted or disintegrate completely
within a few hours after stool passage. This fixative will preserve trophozoites for long
periods of time and will make it easier to identify them. PVA is primarily used for
preserving fresh specimens to be shipped to central laboratories. Permanently stained
films can be prepared from the preserved material. The solution serves as an adhesive
as well as a preservative and prevents the loss of organisms during staining. This is
advantageous when preparing smears from liquid specimens.
(1)
Preparation of reagents. Polyvinyl Alcohol Fixative (PVA)
Modified Schaudinn's Fixative.
Glacial acetic acid ..................................................... 5.0 ml
Glycerol ..... ............................................................... 1.5 ml
Schaudinn's fixative (two parts saturated aqueous
mercury bichloride to one part 955 ethyl alcohol)...... 93.5 ml
Polyvinyl alcohol powder (PVA) ................................ 5.0 gm
(a) While constantly stirring at room temperature, slowly add the 50
grams of PVA to 1,000 milliliters of modified Schaudinn's fixative.
MD0841
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