100 years of virology: from vitalism via molecular biology to genetic engineering.

The identification of the causative agent of tobacco mosaic disease as a novel pathogen by the Dutch microbiologist Beijerinck is now acknowledged as being the foundation of virology as a discipline distinct from bacteriology. However, as this was contrary to the prevailing theories of the time, it took many years for virology to become firmly established as a separate discipline. The history of virology illustrates how accepted concepts in science evolve by trial and error and the need for a balanced approach when manipulating natural systems.