["Diaminobenzidine black" as a new histochemical demonstration of exogenous iron (author's transl)].

A new reaction for the histochemical demonstration of exogenous iron, used as a tracer for the study of connectivity in the central nervous system, is described. It consists of, first, the conversion of iron into Prussian blue, which acts secondarily as a catalyst for the oxidation of diaminobenzidine by hydrogen peroxide. The oxidized diaminobenzidine precipitates by polymerization and gives rise to a brown-colored insoluble reaction product. This reaction has a strikingly better sensitivity and contrast than the classical Perls's reaction.