[The Marchi reaction: ultrastructural aspects (author's transl)].

A secondary demyelination process was brought about in the optic tract by unilateral enucleation of 10 adult rats which were sacrificed at 8, 15, 20, 30 and 45 days respectively, after the intervention. The Marchi reaction, which is identifiable by the presence of granular bodies, is positive at all stages, but tends to lessen towards the 45th day. The granular bodies are inside the disintegrating myelin sheath, and gradually fill the space made available by the degenerate axoplasm. The granular bodies are at first bulky and compact before breaking up and disappearing. The remains of the myelin sheath are then resorbed. Satellite cells occur from the 15th day onwards. The interest of the Marchi reaction for the tracing of nervous pathways is confirmed by these findings.