PAS and Freida's comments

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From:Gayle Callis <>
Date:Thu, 08 Apr 1999 10:40:24 -0600

I think it is also important to know what the pathologists might be looking
for, PAS for fungus, glycogen, basement membrane, mucin, etc indicate to
how I need to do the method.  In fact, when they ask for a PAS for fungus,
I use Chromic acid as the oxidizer, not perodic acid.

Let me count the ways to do PAS!!  I have more than one PAS protocol for 
different things.

I also counterstain with hematoxylin for a shorter time, since the periodic
acid will enhance hematoxylin staining by converting the DNA/RNA COOH groups
to aldehydes, with the chance that you can overwhelm the PAS.  In fact, this
is a way to restore hematoxylin staining when tissues have been stored in
NBF too long, and the pH changes.  A periodic acid step before hematoxylin
staining often restores the nuclear staining.

Full of sidelights today, must be Springtime!

Gayle Callis

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