[Histonet] question of the day - embedding

[Rene J Buesa]

Tracy:
Let me try to dispel some misconceptions:
1- the tissues do not cook if are left in melted paraffin as long as the paraffin is in just its melting point.
2- the tissue are already infiltrated with the paraffin, so there is no additional infiltration to occur
3- the tissues are already dehydrated when they get to the paraffin so they will not "dry out" (they are already dried)
4- the only way there could be some difficulty sectioning later is if the tissues are left a very long time in melted paraffin, like over the weekend.
Otherwise there is no real adverse effect caused by leaving the tissues in melted paraffin during the short time that it takes to embed them, in the same way that if the tissue processor ends the cycle at a given moment and the embedding starts a few hours after that.
I personally consider more problematic leaving the tissues outside the melted paraffin in a warm empty embedding center because there will always be a film of semisolid paraffin surrounding the tissue that will have to melted when the block is casted, and that is what can cause problems.
I know it will very difficult for you to change what it seems you have been doing for years, but I would advise you to fill the holding tank of the embedding center with melted paraffin and place there the tissues until the blocks are done.
René J.

--- On Tue, 2/17/09, Tracy Bergeron <tracy.bergeron <@t> biogenidec.com> wrote:

From: Tracy Bergeron <tracy.bergeron <@t> biogenidec.com>
Subject: [Histonet] question of the day - embedding
To: histonet <@t> lists.utsouthwestern.edu
Date: Tuesday, February 17, 2009, 4:14 PM

Hi all question/dilemma of the day.

        I have been of the view that the longer tissue sat in melted 
paraffin the harder it got, especially animal tissue.  So with that said, 
for the past nearly 10 years I have not used melted paraffin in the 
holding chamber of the embedding center.  I just keep the chamber warm, 
and work that way.  Thus keeping the tissue from continuing to cook and 
harden in the wax.

        Everyone else I am currently working with has never seen the 
method I use, and firmly believe that this causes harm to the tissues if 
they are not in paraffin.

        Thoughts ideas etc.  I am dying to know if I am the only one that 
worries about length of time that animal tissue sits in paraffin.

Thanks.

Sincerely,
Tracy E. Bergeron, B.S., HT, HTL (ASCP)
Associate Scientist III, Pathology
Comparative Pathology Laboratory
Biogen Idec
14 Cambridge Center
Cambridge, MA 02142
Direct:  617-914-1115
Fax:  617-679-3208
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