''Contagium vivum fluidum'' (Latin: "contagious living fluid") was a phrase first used to describe a
virus
A virus is a wikt:submicroscopic, submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and ...
, 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
''Tobacco mosaic virus'' (TMV) is a positive-sense single-stranded RNA virus species in the genus '' Tobamovirus'' that infects a wide range of plants, especially tobacco and other members of the family Solanaceae. The infection causes charact ...
, becoming convinced that the virus had a liquid nature.
In 1892,
Dmitri Ivanovsky had discovered that the cause of tobacco mosaic disease could pass through
Chamberland's porcelain filter. He noted these findings but felt that they could only have resulted from a cracked filter. It was left to Beijerinck, in 1898, to put forward the idea that the pathogen was small enough to pass through the filter routinely used to trap bacteria.
Ivanovsky, irked that Beijerinck had not cited him, recreated Beijerinck's experimental set-up and demonstrated that particles of ink were small enough to pass through the filter, thus leaving the particulate or fluid nature of the pathogen unresolved.
[Angela Creager]
''Where Tobacco Mosaic Has Led Us''
/ref> The invention of the electron microscope
An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a ...
in 1931 led to the first virus images in 1935 by the American biochemist and virologist Wendell Meredith Stanley. The second half of the 1900s resulted in the discovery of more than 2,000 virus species
Virus classification is the process of naming viruses and placing them into a taxonomic system similar to the classification systems used for cellular organisms.
Viruses are classified by ph