Reduction of compression artifacts in ultra-thin sections by the application of heat

Cutting compression in ultra-thin sections prepared for electron microscopy was decreased when sections floating in the knife trough were exposed to radiation from a V-shaped, heated wire filament. The apparatus is called a 'heat pen' and consists of a filament mounted in a ball-point pen body and heated by a step-down transformer. The method gave less residual compression than conventional solvent vapour methods without any apparent ill effects on staining properties, specimen stability or resolution. For specimens which were prone to wrinkling caused by shrinkage following vapour stretching, this technique gave much improved results. Heat stretching also eliminates the need to use solvent vapours which may be harmful to the microtomist.