Overview

At the beginning of the twentieth century, the term "virus" commonly referred to infectious agents that could not be seen under the microscope, trapped by filters, or grown in laboratory cultures. Today the term refers to a minute entity composed of an inner core of nucleic acid and an envelope of protein. The fundamental difference between a virus and other microbes is that a virus can only reproduce by entering a living host cell and taking over its metabolic apparatus. Studies of tobacco mosaic disease by Adolf Mayer, Martinus Beijerinck, and Dimitri Ivanovski led to the discovery of the tobacco mosaic virus, which was crystallized by Wendell M. Stanley. The discovery of bacterial viruses, or bacteriophages, by Frederick Twort and Félix-Hubert d'Hérelle provided one of the most important experimental tools in the development of molecular biology.

Background

The modern...