Contagium vivum fluidum

Contagium vivum fluidum (Latin: "contagious living fluid") was a phrase first used to describe a virus, and underlined its ability to slip through the finest-mesh filters then available, giving it almost liquid properties. Martinus Beijerinck (1851-1931), a Dutch microbiologist and botanist, first used the term when studying the tobacco mosaic virus, becoming convinced that the virus had a liquid nature.