THE RECOGNITION AND PREVENTION OF ARTEFACTS OF THE MARCHI METHOD

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Abstract
Three distinct types of artifacts are recognized. "Pseudo-Marchi dust" consists of fine or coarse particles (1-30[mu]) or a network and is usually scattered throughout the whole section in random distribution. Pseudo-Marchi staining of normal fibers resembles true degeneration but diameter is constant throughout instead of irregular. The 2d, 5th, 7th and 8th cranial nerves and the corpus collosum are especially susceptible. Massive, localized pseudo-Marchi staining occurs in dense patches, often deep in a large block. No method of prevention is certain but gentle handling of tissue, thin blocks, rapid mixing and adequate volume of OSO4, postfixation washing and use of frozen preparation wherever possible all seem to help.