One hundred years of virology.

One hundred years ago a young Russian scientist, Dimitri Ivanovsky (1864 to 1920), presented a paper before the Academy of Sciences of St. Petersburg in which he stated that "the sap of leaves infected with tobacco mosaic disease retains its infectious properties even after filtration through Chamberland filter candles" (10). This observation suggested a disease agent smaller than any known before and was the first step in a long series of observations and experiments that led to the discovery of viruses. While it is often difficult to assign a single date to the discovery of viruses, Ivanovsky is generally given credit for first recognizing an entity that is filterable and submicroscopic in size that might well be the cause of a disease. Indeed, the term filterable agent was the name used to describe these organisms well before the term viruses was specifically applied to them. Filtration became an experimental definition. Ivanovsky's contributions and priority for the discovery were "willingly acknowledged" by Martinus Beijerinck who, unaware of Ivanovsky's work, published similar findings 6 years later in 1898 (3). Fifty years later, in 1944, Wendell Stanley writing in Science stated that "there is considerable justification for regarding Ivanovsky as the father of the new science of Virology" (17). The nineteenth century saw the final defeat of the concept favoring spontaneous generation of organisms and an acceptance of the germ theory of disease. The new definition of causality for a disease inherent in Robert Koch's postulates and the proof that anthrax in cattle was caused by Bacillus anthraxus had a powerful impact on the scientists working in the last decades of the nineteenth century. Although some, like the great anatomist Jacob Henle (a teacher of Robert Koch and grandfather of Werner Henle), had the imagination to conceive of infectious agents with the properties of viruses as early as 1840, these ideas failed to gain acceptance for a lack of experimental evidence. The path to that evidence begins with three scientists independently working on the tobacco mosaic disease, Adolf Mayer, Dimitri Ivanovsky, and Martinus Beijerinck (Fig. 1). Dimitri Ivanovsky, son of a landowner in Kherson Guberniya, was born in the village of Nix near St. Petersburg on 28 October 1864. After the death of his father when Ivanovsky and his siblings were still young, the family moved to a poor section of St. Petersburg. There Ivanovsky attended secondary school and served as a tutor to supplement his mother's pension. Ivanovsky was educated at the gymnasium of Gdov and at St. Petersburg, graduating as a gold medalist in the spring of 1883. After defending his thesis "On Two Diseases of Tobacco Plants," Ivanovsky was awarded the degree of candidate of science in 1888 by St.