THE “FIXATION” OF ELECTRON MICROSCOPIC SPECIMENS BY THE ELECTRON BEAM

Abstract

The pattern of contrast between nuclear sites and cytoplasm seen in electron micrographs of young cells of Escherichia coll fixed in osmic acid vapor resembles the pattern of contrast seen in similarly prepd. cells in light micrographs, and also resembles the pattern seen with the phase contrast microscope in living cells. The contrast pattern appears unchanged in 2d and 3d pictures of the same specimen taken in routine manner with no special precautions against electron bombardment. After micrography in the electron microscope, specimens may be subjected, without undergoing change in appearance, to chemical or thermal influences that would profoundly alter the specimen before exposure to electron irradiation. Thus bacterial protoplasm is "fixed" by electron irradiation so that it is refractory to N HC1 or to cytolysis by dist. water followed by acid treatment. Collodion films and embedding media are refractory to their usual solvents and to high temps, Organic specimens subjected to the electron irradiation of routine micrography are therefore altered in chemical properties if not in visual appearance. This chemical alteration has been attributed to the high energy which a single electron can impart to a molecule of a specimen.