Observations on the extended use of the Marchi method.

It has previously been reported (Smith, 1951) that the Marchi method applied to human material is useful in demonstrating degeneration in nerve fibres even when the interval between the occurrence of the lesion and death exceeded one year. Also (Smith, Strich, and Sharp, 1956) the Marchi method can be applied when the material has been stored in formol-saline for as long as eight years. This latter observation is contrary to traditional opinion ; it is important because it points to the possible use of the Marchi method on material that would previously have been considered totally unsuitable for this technique. The purpose of this paper is to report an investigation of the effects of storage in formol-saline on degenerating nerve fibres in human material, and to draw attention to the relation between the stage of degeneration and the kind of Marchi staining obtained. The spinal cords from 18 patients were examined. Each patient had had a cordotomy at a known interval before death. In every case Marchi preparations were made after 10 to 14 days' fixation. During the next 15 to 72 months spare blocks of material were stored in 10% or 20% formol-saline. Slices were then cut from the blocks and a second series of Marchi preparations was made. The most satisfactory of these later preparations were found to be uncleared frozen sections prepared by the Swank-Davenport-Glees technique (Glees, 1943) but mounted directly after cutting in glycerine jelly (Smith and others, 1956) ; frozen sections cleared in cedar-wood oil and mounted in Canada balsam, and celloidin sections, some counterstained, were also prepared.