The compound hexamethylenetetramine, (CH ₂) ₆ N ₄, or a derivative of this (often with mandelic acid), especially when used as a urinary antiseptic.
In full "methenamine silver". A solution of methenamine and silver nitrate, used in several histological stains.
1920s; earliest use found in Pharmacopeia United States. From methene + amine.