The Shapes and Sizes of Purified Viruses as Determined by Electron Microscopy

Investigations of the physical properties of viruses have been extensively undertaken only since about 1935, since it had not been clear before then that viruses were particles which could be sufficiently purified to render their physical study significant. In the last two decades, however, a large amount of information has been obtained with the aid of ultrafiltration, analytical ultracentrifugation, electrophoresis, diffusion and viscosity, X-ray diffraction, and electron microscopy. These methods of physical measurement have been combined to give us considerable information about the shape and size of viruses, their density and particle weight, their internal structure, and their degree of hydration.