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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