In order to, avoid disadvantages attendant upon the use of fresh frozen sections, or of block impregnation with silver, in staining climbing or mossy fibers of the cerebellum, Rio Hortega's double impregnation method for nerve fibers is useful. This consists of prolonged formalin fixation prior to cutting frozen sections (which thereafter are easier to cut) and preliminary treatment with ammoniacal aqueous and alcoholic washes, mordanting in pyridine silver, and treatment with pyridine-silver-carbonate. Following this, sections are handled individually through one of several reduction methods after which they may be directly mounted or gold toned.