The discovery of viruses

Viruses were first named "filterable infectious agents." Experimentation revealed that these minute entities were capable of passing through filters that caught bacteria and other microorganisms.

In the 19th century, Dutch microbiologist and botanist Martinus Beijerinck demonstrated that viruses cause disease in plants. He applied the sap of sickly tobacco plant leaves to the leaves of healthy plants. The healthy plants produced spots on the leaves and malformed.