In 1892, Iwanowski at St Petersburg discovered a new phenomenon by transmitting the tobacco mosaic disease to health plants by rubbing them with bacteria-free extracts of disease leaves.
Six years later Martinus Beljerinck (1898), a Dutch microbiologist, made the same observation and proposed that tobacco mosaic disease was caused by an entity different from bacteria and called it contagium vivum fluidum – a living infectious fluid that would multiply only in living plant cells, but could survive for long periods in a dried state.
Danish scientists Vilhelm Ellerman and Oluf Bang reported the cell free transmission of chicken leukemia in 1908, and in 1911 Peyton Rous discovered that solid tumors of chicken could be transmitted by cell free filtrates. These were the first indications that some viruses can cause cancer.
A major breakthrough came in 1935 when Stanley , an organic chemist succeeded in purifying TMV. This tobacco mosaic virus multiplies in the laves of tobacco plants and the cells become saturated with it.
The first pictures of viruses were seen using powerful electron microscope was only in the 1930s. It is only in the last 60 years that the most of the different kinds of virus have been discovered.
Discovery of viruses
