Re: [Histonet] Using chromic acid instead of periodic acid with Schiffs - for fungus staining ONLY!

From:Bryan Llewellyn

I think the person wanted the details for Bauer's stain, or CAS (chromic 
acid Schiff).  It was originally published for glycogen, I believe, but PAS 
is better for that.  The method is simple.

Oxidise with 1% chromium trioxide in water for 1 hour (or 5% for 10 
Bleach with 5% metabisulphite and wash.
Schiff's reagent 20 minutes or so.
Finish off as you would a PAS.

Bryan Llewellyn

----- Original Message ----- 
From: "Gayle Callis" 
Sent: Tuesday, August 23, 2005 3:06 PM
Subject: [Histonet] Using chromic acid instead of periodic acid with 
Schiffs - for fungus staining ONLY!

> Histonetters,
> I hope I didn't confuse people with my answer about PAS-F (what the F 
> meant escapes me??? for fungus, fluorescence?) where the person was asking 
> about using chromic acid instead of periodic acid i.e in PAS. 
> Theoretically, one could not call this PAS - maybe chromic acid-Schiff or 
> CAS??  The key word was the mention of Gridley staining, a method for 
> fungus staining, and I assumed this person wanted to use a chromic acid 
> oxidizer followed by Schiffs reagent for that purpose i.e fungus stain.
> Whatever you do, do NOT use chromic acid for a standard PAS stain if 
> staining for mucosubstances, glycogen, basement membranes or  other 
> components that are PAS positive.  Chromic acid is a much stronger 
> oxidizer than periodic acid, and will over-oxidize these components to the 
> point of them NOT staining after Schiffs application - not a good idea. 
> However chromic acid with Schiffs does work for fungus staining.  Freida 
> Carson et al wrote a publication on false negative  fungus staining by 
> using Periodic acid -Schiffs reagent, and mentioned using chromic acid in 
> place of periodic acid.  This can be found in J of Histotechnology, and an 
> excellent bit of information.
> Chromic acid oxidation with Schiffs reagents is reserved for those who do 
> not want use periodic acid as the oxidizing agent for fungus staining.
> Gayle Callis
> Research Histopathology Supervisor
> Veterinary Molecular Biology
> Montana State University - Bozeman
> PO Box 173610
> Bozeman MT 59717-3610
> 406 994-6367
> 406 994-4303 (FAX)
> _______________________________________________
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