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A device used for cutting thin sections (3-5 μm thick) of plant or animal material for examination under the microscope. The specimen is often supported, either by embedding it in a suitable medium, such as paraffin wax, or by freezing it. There are various types of microtome; all have a means of holding the specimen, a knife, and a mechanism for moving the specimen slowly towards the knife. Ultramicrotomes are used for cutting very thin sections (20-100nm) needed for electron microscopy. Glass or diamond knives are used and the specimen advanced by minute increments by thermal expansion. The sections are floated in a water- or water-and-acetone-filled trough surrounding the knife and collected by transferring them onto a fine copper grid. When cutting frozen sections (cryomicrotomy), both the cutting knife and the specimen are enclosed in a cold chamber.
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