On Chemical Reactions and Staining Mechanisms

What is the difference between argentaffin and argyrophilic reactions? Both terms relate to the formation of colloidal metallic silver (latin argentum, Greek argyros) (1), which may range in color from yellow through brown to black depending on particle size and density, in specific structural components of tissues. the metal is formed at sites of reduction of silver ions derived from a staining solution. these ions may be simple ag+, as in a solution of silver nitrate, or they may be complex ions such as silver diammine, [ag(nh3)2] + or silver methenamine, [ag3(c6h12n4)2] 3+, which are formed respectively by adding ammonium hydroxide or hexamethylenetetramine to solutions of silver nitrate. (hexamethylenetetramine, the reaction product of formaldehyde and ammonia, is also used as a urinary antiseptic; its pharmaceutical name is methenamine in the Usa and hexamine in the UK.) these complex silver ions are more easily reduced than ag+. By convention, argentaffin is used when the reducing agent is present in the tissue. structures are said to be argyrophilic when bright light or a solution of a reducing agent is applied to the object after exposure to a silver solution.