n.
Branch of microbiology that deals with the study of viruses .
Viruses were not closely examined until 1892, when a Russian bacteriologist observed that the agent of tobacco mosaic disease could pass through a filter that did not permit the passage of bacteria . Modern virology began in the early 20th century, when the existence of bacteriophages was discovered. Direct visualization of viruses became possible after the electron microscope was introduced ( 0441; 1940).