An Instrument to Trim Plastic Specimen Blocks for Electron Microscopy Prior to Sectioning

Two instruments for trimming plastic blocks prior to inserting them into the specimen holder of the microtome have been previously described. One of these is designed to shape the pyramid (1), the other is intended to approach the tissue by trimming the block and leveling the irregular edges of the polymerized plastic from the bottom (2). The usefulness of such instruments is obvious, especially when straight ribbons are required for serial sections. The special grids designed by Anderson (3) to overcome the difficulty of curving ribbons (mainly due to inadequate parallelism of the pyramid sides) is one illustration of the need for such an instrument. The many bleeding fingers seen in electron microscopic laboratories provide another convincing example. The instrument described below serves both to trim the block and shape the pyramid. It is easy to manipulate and no specific skill is required to obtain a rectangular pyramid. It has been used in this laboratory for trimming methacrylate, polyester, and epoxy resin blocks. The location of the specimen in the polymerized block is not critical, for even if not central, no changes in manipulation are required. Furthermore, this instrument can easily be produced in the usual laboratory workshop. Description Illustrated in Fig. 1 is the technical design of the instrument. Fig. 2 shows the view of the instrument when used to trim the top of the block after inserting the accessory brass plate (P). In Fig. 3 the same instrument is depicted as it is used to shape the pyramid. Manipulation The plastic block is inserted into the central hole of the brass cube (C) and secured by the Allen screw (AS) on the side. The lever screw (LS) which regulates the height of the block is unscrewed so that the dome of the block lies below the plate. The brass cube (C) containing the block is then placed into the square hole in the instrument with the dome of the block pointing towards the inclined plane. The plate (P) is inserted into its place in the instrument. The block is raised by turning the screw (LS) while observing the level over the plate. When the dome of the block appears, the narrow bladO is used to slice horizontally along the surface of the brass plate and a thin slice of the plastic is removed (see Fig. 2). The block is elevated slightly and the blade again is slid along …