The Value of the Marchi Method for Staining Tissue Stored in Formalin for Prolonged Periods

This paper reports the demonstration of degener-ating myelin by the Marchi method in material kept in formalin for periods ranging from 22 months to over eight years. It has generally been believed that prolonged immersion in formalin renders material useless for investigation by the Marchi method, because of the constant occurrence of extensive artefacts. Fourteen days has usually been considered the maximum period during which tissue may be exposed to the action of formalin before making Marchi prepara-tions in order to obtain clear incontrovertible evidence of myelin degeneration. In Marchi preparations the presence of abundant black pseudo-Marchi bodies, or of black staining of normal