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ABC of Safety in the Biological Sciences
BLOCK STORAGE
Celloidin
Celloidin blocks are subject to marked
shrinkage when stored dry in air and for this reason are usually
stored in 70% ethanol. However, after treatment with Gilson's
mixture (equal parts of chloroform and cedar wood oil35),
celloidin blocks can be stored dry in air tight containers. Over a
period of 3 to 10 days cedar wood oil is added to the mixture until
there is approximately 90% of cedar wood oil in the mixture and the
block has become transparent. At this point the block can be dried
in air. Celloidin blocks are highly inflammable and should be stored
with fire safety in mind.
Gelatin
Gelatin is rarely used as an embedding medium,
however it will successfully hold friable material together for
frozen sectioning and will support a specimen in a perspex jar for
museum display. If it is necessary to retain the tissue in gelatin
the block is treated with formalin vapour to render the gelatin
insoluble in water and the block stored in 4% formalin to avoid
shrinkage.
Low Viscosity Nitrocellulose
As for Celloidin.
Methacrylate
Blocks prepared from glycol methacrylates can
be stored dry but are soaked in 70% ethanol overnight before
cutting. Methacrylate blocks are highly inflammable and need to be
stored with fire safety in mind.
Necoloidin
As for Celloidin except that Necoloidin has
explosive properties if allowed to dry out completely.
Paraffin Wax
Paraffin wax blocks are safe under most
conditions of storage except that wax is a flammable substance and
needs to be stored with fire safety in mind. Excessive, prolonged
heat will cause the wax to soften with a resultant deterioration in
the wax and the embedded tissue. Ester wax blocks are hygroscopic
and to avoid deterioration should be stored in air tight containers.
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