An image observed by Transmission Electron Microscopy is produced by electrons emitted from a heated filament. Electrons are scattered or deflected by the specimen whilst others pass through and produce an image on the flourescent screen.
Fixation is the first stage which aims to preserve the tissue in the original state.
The fixatives are buffered and osmotically balanced. Glutaraldehyde is the commonly used primary fixative which penetrates and stabilises proteins whilst osmium tetroxide is a secondary fixative used to react with the lipids. An image seen by the Scanning Electron Microscope is produced by a small focus of electrons that sequentially scans the surface of the specimen. The physical effects caused by the incident beam are detected and displayed on the monitor. The image is a visual enlargement of the topography of the specimen being scanned.