Using periodic acid for a fungus stain can present problems.  Read the
publication in june, 1999 J Histotechnology titled Inconsistent detection
of Histoplasma capsulatum with periodic acid oxidation in the Grocott 
methenamine silve nitrate (GMS) fungus stain, F Carson, J Fredenburgh and
J Maxwell.

Time in the periodic acid should be extended to 1 hour at 56-60C, so as to not
miss H capsulatum.  Aspergillus sp/C neoformans at 5 - 30 min/1% periodic acid 
stained consistently.  Beware the false negative, and use good positive tissue
controls of specific fungi you are trying to stain using periodic acid. 

I applaud the authors of this article, very informative and timely!

Gayle Callis