Heidenhain's SuSa

Please read this article about the disposal of used mercuric chloride first.
Then read these comments about safe working with mercury compounds and cleanup of spills.

Distilled water    800 mL
Mercuric chloride 45 g
Trichloracetic acid 20 g
Sodium chloride 5 g
Strong formalin 200 mL
Acetic acid, glacial 40 mL

The name "SuSa" is a contraction of the German words "sublimat" and "saure". Sublimat is a reference to an older name for mercuric chloride of "corrosive sublimate", given because of its ability to corrode mucosa when used as a treatment in medicine in the past and its ability to sublime when heated. Saure is a reference to the trichloracetic acid content, a strong protein precipitant.

This is a rapid fixative and gives good morphological preservation, although it is not significantly better than formal sublimate or B5, both of which have much simpler formulae.

It has been observed that Weigert's elastic fibre stain is not always successful on tissues fixed with this solution.

Small pieces of tissue can be fixed in two to three hours. Very small pieces may be adequately fixed in about an hour and some of the improved staining effects will be obtained after that time, but full fixation requires up to 24 hours.

This solution is generally considered to be an intolerant fixative and tissues should be removed from it when fixation is complete.

It is sometimes said that mercury pigment does not form in tissues fixed with this solution, possibly because of the acid content. This is unreliable, and the iodine thiosluphate sequence should always be used on sections. Tissues should be transferred directly to 95% ethanol as this solution has a reputation for swollen collagen fibres when more aqueous post fixation treatment is applied.

Secondary fixation
This is a suitable fixatives for secondary fixation following primary fixation in 10% formalin variants. Treatment of trimmed and fixed tissues will give most of the effects noted and enhance staining.

Due to its mercuric chloride content this fixative will corrode metal. Metal cassettes, metal jar lids, metal forceps, metal rulers, metal countertops and all other metal objects must be avoided. This includes stainless steel, which may resist corrosion better than other metals but will still be affected. Dry paper towels are an effective barrier. Do not forget to dispose of them safely.


Drury, R.A.B. and Wallington, E.A.,
Carleton's Histological Technique, Ed. 5,
Oxford University Press, Oxford, UK.




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