Suppression of the argyrophil III reaction by mercapto compounds (a prerequisite for the intensification of certain histochemical reactions by physical developers).

The tissue structure catalyse the interaction of silver ions with reducing molecules dissolved in physical developers, producing metallic silver grains bound at the sites of their formation (argyrophil III reaction). This reaction can be considerably slowed by a treatment with thioglycolic acid or certain other mercapto compounds before development. This observation offers a means for intensifying the end-products of certain histochemical reactions through the use of physical developers, without the microscopic image being interfered with or masked by the "unspecific" staining originating from the argyrophil III reaction.