>Date:    Mon, 21 Sep 1998 16:57:43 -0400
>From:    Paul Monfils <[log in to unmask]>
>Subject: preserving mollusc tissue/body -Reply
>
>Hi Shireen,
>You mentioned that the museum specimens you saw were STORED in 70%
>isopropyl alcohol.  That is a good long-term STORAGE solution for
>most types of specimens, including those for museum display, for
>eventual dissection, and for histological studies, but NOT for
>materials intended for DNA or other molucular studies.  However,
>long-term storage and initial preservation (or fixation as we call it
>in histological circles) are two different matters.  Tissues for DNA
>work are best preserved by direct immersion in strong, 95% to 100%,
>ethanol (ethyl alcohol), and best stored in the same medium.
>However, this kind of tissue fixation, like most types of fixation,
>is a trade-off.  In this case you gain DNA stability at the expense
>of cellular detail and general tissue morphology.  If histological
>study is the intended purpose, then formalin, or any of several other
>aqueous fixative agents, should normally be used.  These compounds
>form molecular cross-links between protein molecules, and produce
>other submicroscopic effects which stabilize tissue components at the
>microscopic level.  Alcohol, while it stabilizes DNA very well, also
>rapidly extracts water from the tissue, causing cells to shrink and
>become misshapen.  It also dissolves various substances out of the
>cells, which would be stabilized by a good fixative; and it hardens
>tissues excessively.  However, once the tissue is properly fixed in
>something like formalin, it can then be transferred to 70% alcohol,
>safely stored without cellular damage, and later used for
>histological studies.
>If electron microscopy is intended, then neither alcohol nor formalin
>is suitable, and other fixatives, such as glutaraldehyde, must be
>used.  So, there is no general preservative that is suitable for all
>purposes, and you have to know up front what the tissue will be used
>for, in order to preserve it  properly.
 
In general Paul's comments seem right on track, but I'm not sure that I
would call 70% isopropyl alcohol a GOOD long-term storage medium.  Those
institutions that I am familiar with that use isopropyl  use it at 40%
strength.  I would stay away from isopropyl (especially at 70%
concentration) because it tends to shrink and dehydrate specimens more
severely than 70% ethanol. The most common fixation/preservation methodolgy
in the fish/crustacean world is fixation in 10% formalin and preservation
in 70% ETHYL alcohol. As Paul stated the formalin/ethanol combo is great
for anatomical/histological studies but bad for genetic work.  I have been
fixing and storing most everything in 95% ethanol these days for genetic
studies, but I still do some in formalin/ethanol.   The problem most people
face outside of public institutions is that ethanol is heavily taxed (see
Jim Beam or Jack Daniels for further details) and generally not cost
effective to use.  Also, I have used formalin/ethanol treated specimens
with scanning EM.  It's not as good a treatment as glutaraldehyde, but I'm
not sure that MUST BE USED is entirely accurate.
 
Kevin
 
 
Kevin S. Cummings
Illinois Natural History Survey
607 E. Peabody Drive
Champaign, IL 61820
[log in to unmask]
http://www.inhs.uiuc.edu/cbd/collections/mollusk.html