Freida Carson observes about methenamine silver demonstration of Histoplasma:

>>With the usual 1% periodic acid oxidation for 5 minutes, you run the risk 
of false negatives with histoplasma. This happen to us, so if you live in an 
area where you are likely to have this organism, you should use chromic acid 
oxidation or perhaps stronger and longer periodic acid oxidation. Jerry 
Fredenburgh and I wrote a paper on this that was published in the Journal of 
Histotechnology a couple of years ago. I do not have the reference handy 
right now, but will put it on histonet if anyone is interested.<<

Please do post the reference, Dr. Carson, so I can excavate my copy of the 
necessary journal out of the garage!

The problem with Histoplasma capsulatum is that the more elderly the 
organism, the more difficult it is to stain, and organisms scattered in 
fibrotic or necrotic material are most difficult of all. Before I would 
believe in a periodic acid oxidation technique, I would want to see someone 
assemble a series of such cases (some university's autopsy files would 
probably contain them) and re-stain them with chromic and periodic acids.

>>so if you live in an area where you are likely to have this organism<< 
Histoplasma is very widely distributed in the eastern half of the USA, and 
given the mobility of Americans, anybody in North America may be infected.

How do you dispose of chromic acid? I would think you'd want to reduce it to 
a lower valence state and precipitate it in some insoluble form that you 
could accumulate in a jug. Does anyone have a method for this? (Thus one can 
precipitate mercury as the sulfide, and silver as the carbonate or sulfate.)

My recycling center now accepts batteries, which contain all kinds of 
unpleasant heavy metals such as cadmium, mercury, and lead. Surely whoever 
carts that stuff off could deal with properly precipitated heavy metal waste 
from histology labs.

Bob Richmond
Samurai Pathologist
Knoxville TN