Re: GMS vs PAS
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From: | RUSS ALLISON <Allison@Cardiff.ac.uk> |
To: | histonet@pathology.swmed.edu |
Reply-To: | |
Content-Type: | text/plain; charset=US-ASCII |
The reason for using silver, rather than a dye, in certain of the
variations of the Feulgen method, which is essentially what is being
debated, is that silver provides a much greater contrast and
therefore shows more easily lower concentrations of groups in
which dialdehydes can be induced. This, of course, is useful for
demonstrating the relatively low concentrations in basement
membranes (kidney) and fungi.
The oxidising agents chosen reflect the preferred - even optimal -
oxidation. The Gridley, for example uses chromic acid, yet still, to
my mind, still produces a relatively small amount of oxidation
product (because there were few oxidisable group yielding
dialdehydes to begin with) and thus produces a weak, pale end
product. That is a feature of basic fuchsin (or any other dye) when
compared with reduced silver nitrate.
Staining for mucin in goblet cells using a silver-Schiff would lead to
totally unsuitable results in my humble opinion.
There are, of course, even more powerful oxidising agents such as
peracetic and performic acid, used for the demonstration of
phospholipids and cerebrosides.
I
t is not only in Schiff reactions that such oxidising agents are used.
There is also a plethora of dyes that can be used to demonstrate a
whole variety of tissue entities in similar oxidation methods, as
Culling and his co-workers in Vancouver have so comprehensively
described. Furthermore, a whole variety of dyes may be used in a
modified "Shiff" reaction with the intention of providing a colour
different to that of basic fuchsin. Most, if not all, require
differentiation because of the other miscellaneous tissue groups
stained. Acid alcohol will usually do the trick.
In summary, it is my opinion that if you use the methods for the
specific groups given in the standard textbooks, you will save
yourself heartache and , at the same time, get the optimal results.
No need to re-invent the wheel when somebody else has already
done the hard work for you.
Finally, remember that the Schiff reaction, originally applied by
Feulgen (who I believe ended up enjoying a life as lecturer to
people like us), was devised to demonstrate DNA for which it is
happily a stoichiometric method; i.e. the stain intensity is
proportional to the amount of substrate (DA) present. Hence its
use in quantitative histochemistry. It was probably also the first
histological method in which the chemistry of the reaction was first
truly understood and thus the foundation of histochemistry.
Hardly a Valentine's message, but from the heart nevertheless!
Russ Allison,
Dental School
Cardiff
Wales
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