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" 
To: "Gudrun Lang" 
Cc: "Histonetliste" 
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@uwo.ca
>    http://publish.uwo.ca/~jkiernan/
>
>


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