[Histonet] gomori methenamin silver

[John Kiernan]

If you mix the silver nitrate and sodium
tetraborate as you describe, there will be
a white precipitate of silver borate. It is
possible to make a borate-buffered very dilute
silver nitrate solution, as in the Holmes
method (for axons in paraffin sections of
CNS). The mechanism of that technique is
quite different from that of Grocott's or
any other methenamine (hexamine) silver
method. If it stains Pneumocystis that's
fine, but the mechanism will have to be
different.
-- 
-------------------------
John A. Kiernan
Department of Anatomy and Cell Biology
The University of Western Ontario
London,   Canada   N6A 5C1
   kiernan <@t> uwo.ca
   http://publish.uwo.ca/~jkiernan/
-------------------------
Gudrun Lang wrote:
> 
> Dear John,
> thank you, for the answer.
> 
> The origin of my question is, that a fresh histotech in my lab made a
> mistake with the Grocott for Pneumocystis. Her working solution was 5%
> Silvernitrat (80ml) plus Natriumtetraborat (8ml), but without any Hexamin.
> The result was, that the doctor was really enthusiastic about the good
> quality.
> Today she tried it again. Untill now I don't know the result.
> 
> Do you think, Hexamin is really necessary for the proper reaction? And if
> yes, what has happend?
> 
> Gudrun Lang
> 
> ----- Original Message -----
> From: "J. A. Kiernan" <jkiernan <@t> uwo.ca>
> To: "Gudrun Lang" <gudrun.lang <@t> aon.at>
> Cc: "Histonetliste" <histonet <@t> lists.utsouthwestern.edu>
> Sent: Wednesday, December 17, 2003 7:01 PM
> Subject: Re: [Histonet] gomori methenamin silver
> 
> > > Gudrun Lang wrote:
> >
> > > Question 2:
> > > What is the the function of Hexamethenamin? I know it causes
> > > the high pH, but does it make any compound with the
> > > silvernitrate?
> >
> > Methenamine = hexamine = hexamethylenetetramine.
> > It is the soluble solid product of the rapid
> > chemical reaction of formaldehyde with ammonia.
> > It is used therapeutically, as tablets (Urasal) to
> > treat urinary tract infections, and as an antiseptic
> > and antiperspirant cream, Dehydral.
> >
> > Yes, methenamine does form a compound with
> > silver. It is a complex comparable to the silver
> > diammine ion that is formed when enough ammonia
> > is added to a silver nitrate solution to dissolve
> > the brown precipitate (silver oxide) that is
> > first formed. The methenamine-silver complex is
> > reduced to silver metal by reducing groups in
> > the tissue - most notably by aldehyde groups that
> > have been formed by oxidation (eg by dichromate,
> > permanganate or periodate) in an earlier stage of
> > the staining procedure. The methenamine-silver
> > solution does the same job as Schiff's reagent.
> > The black colour of the end product facilitates
> > the detection very small or very thin objects
> > such as bacteria and fungal hyphae.
> > --
> > -------------------------
> > John A. Kiernan
> > Department of Anatomy and Cell Biology
> > The University of Western Ontario
> > London,   Canada   N6A 5C1
> >    kiernan <@t> uwo.ca
> >    http://publish.uwo.ca/~jkiernan/
> >
> >