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 ceramic filters then available, giving it almost liquid properties.

This diffusion inspired him to put forward the idea of a non-cellular "contagious living fluid", which he called a "virus".

[2] Ivanovsky, irked that Beijerinck had not cited him, demonstrated that particles of ink could also diffuse through agar gel, thus leaving the particulate or fluid nature of the pathogen unresolved.

[2] Beijerinck's critics including Ivanovsky argued that the idea of a "contagious living fluid" was a contradiction in terms.

[2]: 34  In 1935 American biochemist and virologist Wendell Meredith Stanley was able to crystallize and isolate the tobacco mosaic virus.