ABC of Safety in the Biological Sciences




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 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.

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.

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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