A New Technique for Carbon Films

In electron microscopy, the films supporting the thin sections should have the following characteristics: (1) a maximum transparency to electrons, (2) a maximum stability when exposed to electron beam, (3) a minimum contamination with dust particles. Formvar films lack stability. If reinforced with evaporated carbon, the transparency to the electron beam is reduced. Removal of the formvar, in order to get a naked carbon film, increases the fragility of the film, and increases also the possibility of contamination, because it requires supplementary manipulations and treatments (e.g. passage through ethylene dichloride, drying, final checking with the light microscope, etc.) Fragility and contamination of the films make some grid squares useless, and this may present a problem, especially when one looks for infrequently occurring components of cells (centrioles, for example), or for rare cytopathologic features (virus particles). The technique recently described by Sj5strand (3) appears difficult to apply to such material, because the chances of finding the desired structure over a hole in metallized net are small. For these reasons, a new technique, offering good conditions for microscopical observation over the largest possible surface appeared necessary, and the following procedure, deriving partially from that indicated by Watson (4), has been devised. Thin sections are cut with a Porter-Blum microtome equipped with a diamond knEO (2).