Ultrastructural visualization of unfixed and unstained whole mounts by high-voltage electron microscopy at low temperatures.

A physical procedure for the visualization of cellular fine structures is described as an alternative to chemical preparative techniques. It consists of fixation by fast freezing followed by controlled etching in the cryostage of a million-volt transmission electron microscope. Whole mounts were thus observed under stable conditions with no use of chemical fixatives, solvents, or stains, with no exposure to the atmosphere, and with the improved penetration and resolution in thick specimens that characterize high-voltage electron microscopy. The preservation, contrast, and resolution exhibited by images of preparations obtained by this procedure are discussed.