Paul's advice is very good. I've never seen an oxalosis
kidney, but I have looked at sections of bits of
plants; they often contain layers of cells that are 
almost filled with star-like growths of calcium oxalate.
Each limb of a star is bright with crossed polars, and
the birefringence changes as you rotate the stage.

The principal von Kossa variant for Ca oxalate is that 
of Pizzolato (1964). Sections are treated with 1% silver 
nitrate in 15% (Yes! 15%) hydrogen peroxide in bright
light. This must be done after removing calcium carbonate
and phosphate deposits (12% acetic acid, 15 minutes 
at 22C; a warm room temp). If the acid treatment is 
omitted, water-insoluble carbonates and phosphates also 
yield black deposits of silver. Pure calcium oxalate does 
not give a dark deposit with the usual von Kossa method.

Refs.
Pizzolato P (1964) J Histochem Cytochem 12: 333
Pearse AGE (1985) Histochemistry Theoretical and Applied,
4th edn, Vol 2. Chapter 20.
Plant histology books, especially by Berlyn and by Ruzin.

John Kiernan
Dept of anatomy & Cell Biology
University of Western Ontario
London,  Canada.
----------------------------------
Paul Bradbury wrote:
> 
> The quickest and easiest approach is to view your existing H&E sections
> using a polarized light microscope. Calcium oxalate crystals are
> strongly birefringest and are impossible to miss. Would I be correct to
> assume you have sections of kidney from an ethylene glycol (antifreeze)
> poisoning?
> 
> The "stains" suggested in some texts are essentially modifications of
> von Kossa's silver substitution method for  the calcium salts usually
> associated with bone or chronic inflammatory reactions. They work, but
> are not specific for calcium oxalate as they will also react with any
> other insoluble calcium salts that happen to be present.
> 
> Give the polarizer a try, I think you will be happy with the results.
> 
> Best of luck,
> 
> Paul Bradbury
> Kamloops, BC,
> Canada
> 
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