Ultra-microtomy by a new method.

Polymerization of n-butyl methacrylate monomer is used as a rapid and simple means for embedding fixed biological material. The solid resin provides an optically clear matrix for cutting very thin sections, one at a time, with a slightly modified conventional rotary microtome. Advance of the embedded specimen toward the knife is obtained from the thermal expansion of a brass specimen holder. These ultrathin sections have uniform thickness, large area, and integrity of tissue structure. They are suitable for producing transmission images at the higher magnifications of the conventional light, phase-contrast, and electron microscopes. Metallic shadowing of the sections provides greater contrast as well as a threedimensional aspect to the structural details of the tissue. Micrographs and a bibliography are presented.