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SUMMARY

The principle of using reflected light to align knife to specimen block proposed by Gorycki (1965) is applied to the LKB ultrotome. A small mirror mounted on the knife holder base at an angle of 5° reflects light from the fluorescent lamp on to the front of the knife from where it is reflected on to the block face. The width of this band of reflected light at the bottom edge of the block is reduced as the knife approaches the block. At the point at which it is no longer visible the block is 2–3 μm from the knife. When the knife is parallel with the block in the cutting plane the line of reflection is parallel with the knife edge. Using reflected light facilitates alignment between block and knife and makes closing the gap prior to the initial cut a simple and certain operation.