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Formalin
Formalin
has been used for many years as an all-purpose fixative that
is appropriate for helminth eggs and larvae and for protozoan
cysts. Two concentrations are commonly used: 5% which is recommended
for preservation of protozoan cysts; and 10% which is recommended
for helminth eggs and larvae. Although 5% is often recommended
for all purpose use, most commercial manufacturers provide
10%, which is more likely to kill all helminth eggs. To help
maintain organism morphology, the formalin can be buffered
with sodium phosphate buffers, i.e., neutral (or buffered)
formalin. Selection of specific formalin formulations is at
the user's discretion. Aqueous formalin will permit the examination
of the specimen as a wet mount only, a technique much less
accurate than a permanent stained smear for the identification
of intestinal protozoa. The most common preparation is 10%
formalin. |
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