Re: [Histonet] gomori methenamin silver

From:"J. A. Kiernan"

> 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

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