RE: oxidation of paraffin sections. Thickness!

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From:Pam Marcum <>
To:"J. A. Kiernan" <>,
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The only time I have heard this type of problem was when the pathologist
thought thin sections were staining "to light".  They weren't taking into
consideration the fact that there was less to stain with a thin section.
They were accustom to looking at 4 to 6u paraffin sections and wanted the
same appearance in .5u to 2u sections.  Plastics in particular were
interesting to explain early on.  Pam Marcum

-----Original Message-----
From: J. A. Kiernan []
Sent: Tuesday, April 11, 2000 1:25 AM
Cc: ''
Subject: Re: oxidation of paraffin sections. Thickness!

On Mon, 10 Apr 2000 wrote:

> For staining sections I know that it takes longer to stain thin sections
> than thick sections.

How did you come by this idea? It certainly isn't a general
rule. For most methods you need longer times for thicker sections.
This makes sense, because molecules of dyes, solvents etc take
longer to diffuse through a thick than through a thin slice of

I'm trying to think of a method that needs longer times for thinner
sections but can't, unless the embedding medium is changed. Some
plastic embedding media, often preferred for really thin sections,
cannot be dissolved out before staining. The plastic retards
permeation of dyes etc, but nevertheless it takes longer to stain
a thick plastic section than a thin one. It could therefore take
longer to stain a thin plastic section than a thicker paraffin
or (unembedded) frozen section.

Are there some staining methods that take longer for thinner
sections in the same embedding medium?

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1

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