060304.HTML???????? c╣.■¡╣.■¡üü 1 Microtomy

 

Early rotary instrument

Sections of tissue must be cut thin enough for light to travel through them in light microscopy, and much thinner still for sufficient detail (resolution) using electron microscopy. Instruments designed for sectioning are called microtomes. Such instruments were first designed in the mid and late 19th century and included versions specialized for cutting frozen sections, sliding knives over stationary specimens for cutting wood, and ones employing a rotary action in which the knife typically remains stationary and the specimen, mounted on an arm, is moved in a reciprocal manner while advancing a small increment for each cycle.

Shown here is one of the earliest (c. 1880) rotary microtomes designed for cutting sections of paraffin-embedded specimens. Biological material is chemically prepared so that water in the tissue is replaced by molten paraffin that is solidified upon cooling into small blocks. As succeeding sections are cut, they stick to each other and form a ribbon of sections. By examining each section in ordered sequence, it is possible to study the third dimension of structural organization.

Modern sectioning usually produces sections at a thickness of 1 to 3 micrometers (╡m) for light microscopy if resin plastics are employed. Ultramicrotomes are used to obtain sections about 60 to 80 nanometers (nm) in thickness for transmission electron microscopy.

 
   
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