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From:Rebecca S Smith <>
To:The Histonet <>
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My two cents on this issue:

If you use periodic acid instead of chromic acid, what you are really doing 
is the PAS stain and not the GMS.  Periodic acid oxidizes to a certain 
point and then STOPS.  Chromic acid continues oxidizing the newly formed 
groups, until all that are left are items that contained HIGH amounts of 
carbohydrates in the first place, such as fungi.  This reduces background 
staining.  If your pathologist complain about weak PAS's not identifying 
all fungal elements, then they will not be happy with switching to periodic 
acid.  But, if they are satisfied with the possible false negatives, the 
background staining and the probable weak staining, then GO FOR IT.  I'm 
always for getting rid of hazards that we don't NEED in the 
laboratory.  However, our pathologists were not happy with the switch and 
we returned to offering two stains.  GMS and PAS that are actually 
"different" stains, rather than GMS and PAS which actually are the same 
stain with one demonstrating with silver and one demonstrating with 
Schiff's reagent.  I guess that's enough said before I end up with my foot 
in my mouth!

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