A Thermoelectrically Cooled Microtome Table and Knife

Abstract

Thermoelectric cooling units (Frigistor thermoelements) have been used to replace CO₂ gas and solid CO₂ for microtome stage and knife cooling. These units consist of assemblies of series-connected thermoelements, functioning by the Peltier effect. Cooling is controlled by the direct current supply to the units. Current supply is from a double power pack giving 15 amp at 4.8 v for the knife cooling units, and 15 amp at 1 v for the stage. By varying the current flow, the optimum cutting temperature can be obtained and held indefinitely. An 8–couple Frigistor unit replaces the CO₂ stage of a Lipshaw freezing microtome. The stage temperature may be lowered to –36 C in 40–60 sec and at the optimum cutting temperature, 5 μ serial sections of fixed frozen tissue are obtainable. Four 12–couple units are used to cool a 160 mm Jung plane wedge microtome knife fitted to a Reichert sledge microtome, with the stage cooled by one 8–couple unit. The knife temperature can be lowered to –20 C in 5 min; the stage in 1 min. The apparatus has been used to cut a variety of unfixed rat and mouse tissues. The optimum sectioning temperature for such unfixed liver, kidney, spleen, lymph glands, heart, testes, small intestine, pancreas, skin and lung was –20 to –22 C.