Martinus Beijerinck (1851-1931) uses filtering experiments to show that tobacco mosaic disease is caused by something smaller than a bacteria which he names a virus
Editors. "Discovery of virus". The Literary Encyclopedia. First published 01 May 2009; last revised 30 November -1.
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6383, accessed 26 April 2015.]