The Relationship of Microtome Knife Facet Bevels to Edge Effectiveness in Cutting Paraffin Sections

Abstract

Paraffin sections cut by microtome knives having the usual cutting facet bevels of 31d` showed major amounts of gross paraffin compression at 4 μ or thinner. In such sections, folding was not eliminated by floating out for mounting. A knife with a 21d` facet bevel, hand honed on a ground glass plate, produced a superior 4 μ ribbon, and finished slides of sections from this ribbon were relatively free of folding. Individual cells showed no ill effects from the more obtuse cutting edge, since photomicrographs of frog liver cells taken from properly flattened areas of ribbons with gross folding defects were indistinguishable from those of cells from unfolded ribbons cut with the 21d` knife. The 21d` facet bevel may be obtained by replacing the original 13 mm diameter back with one of 9 mm and hand honing with coarse, then fine American Optical abrasives. Honing was done on a 6 × 18″ ground glass plate previously dressed by rubbing against another identical plate with a water suspension of American Optical honing-plate compound between them. Hand honing was carried out by back-and-forth movements of the knife on the plate, with a minimum of pressure, and with the knife turned over after six complete strokes.