Coverslipping unstained (Was: polarized/slides)

From:"J. A. Kiernan" <>

On Fri, 1 Jun 2001, P. Emry wrote:

> When you want to coverslip an unstained slide do you do 
> anything to remove the paraffin first?

Yes. I remove the paraffin (2 xylenes) than go into a 3rd
xylene (the one that normally comes before coverslipping)
and then apply the mounting medium. I haven't done this
for a while, but straight paraffin --> resinous mountant
is needed after some in-the-block staining methods (which
can be wonderful; I hope they are still being used). 
Going straight from wax to mountant also provides an
honest picture of the autofluorescence - lipofuscin,
general background etc.

The only other circumstance I can think of when the wax isn't
(or should I say wasn't) routinely removed was an en bloc 
o-phthalaldehyde-induced fluorescence method for histamine.
The paraffin sections had to be mounted and flattened without
using water (Yes it's possible, but I won't say how unless
someone really wants to know) and then coverslipped under
liquid paraffin (= mineral oil). The original Falck-Hillarp
methods for formaldehyde-induced fluorescence of catecholamines
(dopamine, noradrenaline) and serotonin required liquid paraffin
as a combined paraffin solvent and mounting medium for sections 
of the freeze-dried reacted specimens. Methods of this kind were 
developed to the level of a fine art in the 1970s and excellent
methods became available for ordinary cryostat sections. These
histochemical methods for amines died suddenly, circa 1982,
with the commercial availability of antibodies to the synthetic
enzymes and, later, even to the amines themselves. 
Sic transit gloria.

John A. Kiernan
Department of Anatomy & Cell Biology
The University of Western Ontario
London,  Canada   N6A 5C1

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