Jim,
    I disagree with you on how long it takes to freeze with liquid nitrogen.
Please don't put your hands in or on liquid nitrogen!!!!!!  It took less
than a second for me to get second degree burns on my left thumb and index
finger in December of 1997.  It was a very painful event and one I
personally never let happen to me again.  Liquid nitrogen will freeze warm
objects faster than blinking your eye.
    Gail Macke, HTL
     Shriners Hospital for Children: Shriners BURNS Hospital--Cincinnati,
Ohio
 P.S. Yes, I did get a lecture on chemical burns, believe I did.

> -----Original Message-----
> From:	Jim at ProSciTech [SMTP:jim@proscitech.com]
> Sent:	Wednesday, October 04, 2000 7:16 AM
> To:	'Greer, Bonnie'; 'Vinnie Della Speranza';
> histonet@pathology.swmed.edu
> Subject:	RE: Freezing tissue
> 
> Sorry Vinnie, better ask for a refund on your tuition- or was that a slip
> of 
> the pen? The gas forming around a warm object inserted into liq N2 forms
> an 
> insulating envelope (Leidenfrost). Freezing speed in liq N2 is slower than
> in 
> near freezing point Iso-pentane.
> You can stick a finger into liq N2 for a couple of seconds and have no
> harm, 
> but don't try that in cold iso-pentane.
> Faster freezing results in smaller (ultimately no) ice crystals. It's
> those 
> crystals that destroy tissues.
> For the light microscopist the goal is to have those crystals small enough
> to 
> not cause tissue damage that is visible under the light microscope. There
> are 
> numerous methods to attain that goal.
> Cheers
> Jim Darley
> ProSciTech                 Microscopy PLUS
> PO Box 111, Thuringowa  QLD  4817  Australia
> Ph +61 7 4774 0370  Fax:+61 7 4789 2313  service@proscitech.com
> Great microscopy catalogue, 500 Links, MSDS, User Notes
> ABN: 99 724 136 560                      www.proscitech.com
> 
> On Wednesday, October 04, 2000 7:59 AM, Greer, Bonnie 
> [SMTP:Bonnie.Greer@stjude.org] wrote:
> > I did muscle bx`s for a long time I used a dewar filled with liquid
> nitrogen
> > and I used another container filled with the isopentane.... suspended
> inside
> > until frozen. You thaw  just enough to freeze your tissue for 20
> seconds. I
> > was taught that the isopentane insulates the tissue causing lee artifact
> > .Email me if I can help.
> >
> > -----Original Message-----
> > From: Vinnie Della Speranza [mailto:dellav@musc.edu]
> > Sent: Monday, October 02, 2000 9:51 AM
> > To: histonet@pathology.swmed.edu
> > Subject: Freezing tissue
> >
> >
> > I would welcome your opinions and feedback.
> >
> > What is the optimal method of freezing tissues with liquid nitrogen?
> with or
> > without isopentane and why?
> >
> > thanks,
> > Vinnie
> >
> >
> >
> > Vinnie Della Speranza
> > Manager for Anatomic Pathology Services
> > Medical University of South Carolina
> > 165 Ashley Avenue
> > Suite 309
> > Charleston, SC  29425
> > ph:  (843) 792-6353
> > fax: (843) 792-8974
> > email: Dellav@musc.edu
> >
> 
>