Re: GMS vs PAS

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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.
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

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