Barbara,
               There is no question  that tissue dehydrates if a cut
surface of a
paraffin block is stored exposed.  Tissues that were fixed decades ago used
to be
fixed and processed for  longer times compared to current practice.
Assuming that
this resulted in a tissue that was "well fixed" and processed, then we
would expect
to have this tissue impervious to the ravages of fungi etc. However, I have
seen
blocks of tissue where fungus has penetrated throughout the tissue from the cut
surface. As we routinely fix and process for shorter time, it is, I
suggest,  a
reasonable assumption that blocks now processed will be much more
susceptible to
dehydration and also to such attacks.
This does not mean that all blocks or even a moderate percentage may be
attacked.
Chances are that if this does happen it will be to blocks that are critical for
some legal case or for a research project.
 I suspect that you have been lucky with your blocks.
I still feel that the small time expenditure is worth sealing the surface.
Barry

Barbara Davies wrote:

> Barbara Davies/Histology/MEMHOSPCS
>
> Regarding dipping blocks in paraffin before storage:
>
> It is my understanding that this is an antiquated  process, that is also
>quite
> time-consuming.  A properly fixed and processed block should have no
>problem in
> storage.  I would also think that a poorly fixed and/or poorly processed
>block
> is a problem regardless what means you go by to store it.  We quit dipping
> blocks over twenty years ago and have seen no problems.
>
> Barb Davies
> Memorial Hospital
> Colorado Springs, CO