What Is a Microtome?

Jerry Morrison

A microtome is a device used to cut extremely thin slices of material into specimens called sections. Typically, this is performed when preparing items for microscopic examination. Microtomes are available in a number of designs using different cutting components. This is to accommodate the physical properties of the material to be prepared and the type of microscope to be employed. The microscopic study of biological sections is termed histology.

Microtome is a device used to cut extremely thin slices of material into specimens for microscopic examination.
Microtome is a device used to cut extremely thin slices of material into specimens for microscopic examination.

In a sled microtome, the material to be sectioned is held in a sliding shuttle that moves across the surface of a blade. To prepare the material for slicing, an infusion of paraffin wax or an epoxy hardens the sample into a solid. The sample is then fitted into the microtome's shuttle. Several different blade designs are used, depending on the consistency of the sample and the section thickness required. The blades may be metallic, glass or diamond.

The cutting blade, or knife, in a rotary microtome is also in a fixed position relative to the sample. The rotary motion of a flywheel is translated into the horizontal motion of a sample across the knife. Typically, lowering the sample into position is done manually by means of a control wheel. This function has been automated in recent rotary designs, affording more precise sectioning.

A rotary microtome design is usually employed when cryogenic conditions are necessary. Sectioning takes place in a liquid nitrogen chamber, allowing the sample to be hardened into a glass-like state. The rotary design is also used in ultramicrotome sampling where extremely thin sections are needed. Very precise production tolerances are required to ensure the precision necessary to prepare sections for electron microscopy. The cutting blades are usually made from gem quality diamonds.

Unlike mechanical micritomes, which come into physical contact with the specimen, laser microtomes do not require sample preparation. The cutting device is a pulsed infrared laser. This allows very precise control of the sampling and is equally applicable to soft tissue as well as hard material such as bone. The elimination of physical contact with the sample material removes much of the possibility of contamination.

For less rigorous applications, the student or hobbyist might make use of a hand-held microtome. These devises allow tissue sections to be taken for slide preparation, though with far less precision than laboratory instruments. Sample material is firmly held by the device and advanced into cutting position by precise increments. The section is then taken manually with a razor knife.

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