I use all three of these compounds in my lab, for various types of tissue
and cell fixation and preservation (not specifically molluscan). In general,
ethyl alcohol (ethanol, grain alcohol) is superior for most purposes related
to histological studies (microscopic tissue analysis). This has to do with
its rate of penetration, its ability to denature proteins, its ability to
dissolve lipids and certain other tissue components, and its moderate
hardening effect on tissues. Isopropyl alcohol (isopropanol, 2-propanol)
penetrates more slowly, denatures less effectively, is a poor lipid solvent
(a useful characteristic in certain kinds of studies), and hardens tissues
more than ethanol does (a disadvantage with some tissue types, but an
advantage with others). However, all this relates to microscopic examination
of tissues, not to whole preservation of specimens for display purposes. For
this kind of application, I agree with your assessment - ethanol and
isopropanol generally work equally well, and for certain types of
soft-bodied zoological specimens like polyps, jellyfish, tunicates, etc.,
isopropanol is superior. The few institutional zoological study collections
I was involved with used isopropanol for everything.  Ethyl alcohol must be
used for tissues intended for subsequent DNA studies, and it must be used in
a stronger concentration (95% or preferably 100%). Display specimens, as
well as specimens stored for later histological studies are typically stored
in a 70% solution, though some workers prefer 80% (water making up the
remaining %). Direct preservation in alcohol works well with many kinds of
specimens intended for gross display purposes, especially if they have some
natural rigidity.  However, histological specimens must be fixed in formalin
or another histological fixative prior to storage in alcohol, and ethanol
solution is recommended for storage of such materials. Certain types of soft
zoological specimens also yield better results if formalin fixed before
final storage in alcohol.
That brings us to methyl alcohol (methanol, wood alcohol). For most
tissue-related applications, methanol is noticeably inferior to either
ethanol or isopropanol.  Because of its high affinity for water, methanol is
used in dehydration fixation of thin preparations like blood smears, cell
monolayers, and histological frozen sections. Acetone is also used in such
applications, for the same reason. But both these compounds do a rather poor
job of preserving whole tissue samples that are not previously fixed. In
addition, both of these are more volatile and more toxic than ethanol or
isopropanol, and are more readily absorbed into the body through the skin.
So there is no reason to use either of them for routine preservation of
display specimens, and they are best avoided. Of course if you are in the
field, and you find a specimen you just have to bring home, and you don't
have anything but a can of  gasline antifreeze (methanol), it's better than
nothing. A bottle of vodka or tequilla would do a better job, but is a lot
more expensive.


----- Original Message -----
From: "David Kirsh" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, November 02, 2002 11:20 AM
Subject: isopropyl


> People keep mentioning ethanol or methanol. But what about isopropyl
> alcohol? It seems to be by far the most available and cheapest in the US
and
> works quite reliably for me without buffering.
>
> Although I've decided against trying to preserve animals long-term for
space
> reasons, the specimens I've kept for 25 years don't show any damage to the
> shells. Anyone find differently?
>
> David Kirsh
> Durham, NC