Re: [Histonet] Using chromic acid instead of periodic acid with Schiffs - for fungus staining ONLY!
What Rita was asking about PAS-F, I don't know (what does the -F stand for
However, the Bauer reaction (chromic acid oxidation-Schiff) in 1933
was the first ever use in histochemistry of a glycol to aldehyde oxidation
This produces a positive Schiff result in a variety of mucosubstances,
including cellulose, starch and (sorry Gayle) GLYCOGEN!
It also gives a positive result with fungal cell walls.
In fact the Bauer-Schiff was for many years the method of choice for the
demonstration of glycogen and other mucosubstances.
As Gayle correctly pointed out, chromic acid further oxidizes the aldehydes
, probably to carboxyl groups and then to carbon dioxide.
Mucosubstances with a high glycol density (glycogen, starch, fungal cell
walls) are more resistant to this effect.
The resulting Schiff reaction is somewhat paler than a PAS, how much paler
depends on oxidation time, but still positive.
Gomori (1946) used chromic acid oxidation in his method for glycogen and
He detected the resulting aldehydes with hexamine-silver.
Grocott (1955) optimized the Gomori technique for fungal cell walls.
The Gridley stain (1953) was just a Bauer-Schiff/aldehyde fuchsine
Periodic oxidation-Schiff was introduced by both Hotchkiss and McManus in
Periodic acid does not further oxidize the aldehydes produced (at least not
in any reasonable time frame) and rapidly became the oxidation-Schiff method
----- Original Message -----
From: "Gayle Callis"
Sent: Tuesday, August 23, 2005 6:06 PM
Subject: [Histonet] Using chromic acid instead of periodic acid with
Schiffs - for fungus staining ONLY!
> 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)
> Histonet mailing list
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