I heard you can substitute Periodic Acid for Chromic Acid in the GMS 
stain. How long do you leave the slide in the Periodic Acid, and does anyone 
have a procedure for it?  Also I heard that while using Periodic Acid false 
negatives may be obtained. Has anyone come into that problem while using 
Period Acid? If so, are there any precaution steps to take to minimize the 
risk?