Herpetological collection

Diana Ruby-Sanderson <dlrs [at] rmh__com> writes

>My husband has worked with preserved herp specimens for about 20
>years now, some as old as late 19th century.  He advises that
>changing out formalin will not hurt the specimens and that you
>should use 50% isopropyl alcohol (70% is too high a concentration
>and may dry them out.)  With regard to rehydrating dry
>specimens--rinse them well in cool, running water to flush the
>residual formalin and then soak them in running water for a least 24
>hours before placing them in the 50% alcohol.

Although the above message is the "traditional" response to such an
inquiry, I believe that there are some better solutions to the
problems.

Specimens in formalin are normally in "10% formalin" which is really
about 3.5% formalin and 96.5% water.  To rinse the specimens in
water and then move them abruptly into alcohol will cause a rapid
hydration-dehydration cycle, which is structurally hard on the
tissues. Studies have shown that you will get less structural damage
to the specimens if you stage them from the formalin through 35%,
then 55% and then 70% ethyl alcohol.  Most of the formalin will be
washed out during this process.  You can test the solution for trace
amounts of formalin with commercially available aldehyde test
strips or make your own.

Ethyl alcohol is highly recommended over isopropyl alcohol.  All
alcohol will cause specimen shrinkage, but isopropyl has been shown
to cause significantly more shrinkage than ethanol.  Also,
isopropanol is twice as toxic as ethanol, and many people are
bothered by its fumes.

Rehydrating completely dehydrated fluid preserved specimens is
problematic.  If the specimens have completely dehydrated, they are
probably best left in that state.  Rehydration is likely to weaken
them further, as it will cause further tissue damage.  If the
specimens are not yet completely dehydrated, then you should try
gently rehydrating one or two via slow steps from water to 70% ethyl
alcohol.  The use of a surfactant may aid rehydration, but will
cause chemical changes in the tissue.

I have discussed these issues at greater length and provide a
bibliography on this subject in "Storage of Fluid-Preserved
Collections,"  pp. 161- 186 in Carolyn L. Rose, Catharine A. Hawks,
and Hugh H. Genoways (editors) 1995.  Storage of Natural History
Collections:  A Preventive Conservation Approach, published by the
Society for the Preservation of Natural History Collections.

John Simmons
Division of Herpetology
Natural History Museum
University of Kansas
Lawrence, Kansas

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                  Conservation DistList Instance 12:61
                Distributed: Wednesday, January 27, 1999
                       Message Id: cdl-12-61-001
                                  ***