Ross,
   I believe the recommended use of 70% alcohol is that concentrations of
68% or less allow autolysis to take place.  Thus by using a concentration
slightly higher one preserves the tissue in question.  The problem is that
the difference between 68% and 70% is very small and a small amount of
water in the tissue being preserved or a slight error in making 70%
ethanol and autolysis may begin.  For this reason many researchers are
advocating the use of an 80% ethanol solution; 95-100% if you are planning
on performing DNA studies.
   I have read that propanol, while appropriate as a preservative, leaves
the preserved tissue harder than ethanol does and this makes working with
the tissue more difficult.  The main problem with ethanol is the cost.
Since it can be consumed (at least in the uon-denatured forms) it is taxed
in most jurisdictions (at least in the United States).  This taxation can
be quite high.  When I was a graduate student in the 1970's, a pint
(approximately 500cc) of 100% ethanol, with the tax stamp and purchased at
a liquor store was $6.00; purchased for research use (as a solvent)
without the tax stamp, it cost only $1.00.  Denatured form are cheaper
since they cannot be drunk, however, they also bring additional chemicals
into the preserving solution.
   Formalin, while a good preservating is somewhat acidic.  What some
people do is store the specimen in formalin for several days and then
transfer it to an ethanol solution.  The main problems with formalin are
1) it is carcinogenic - cancer causing and 2) it degrades DNA so DNA
studies cannot be performed on specimens that have been in formalin.

Regards,
Charlie
******************************************************************************
Charlie Sturm, Jr
Research Associate - Section of Invertebrate Zoology
                     Carnegie Museum of Natural History, Pittsburgh, PA
Assistant Professor - Family Medicine

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