<P> The history of virology--the scientific study of viruses and the infections they cause--began in the closing years of the 19th century . Although Louis Pasteur and Edward Jenner developed the first vaccines to protect against viral infections, they did not know that viruses existed . The first evidence of the existence of viruses came from experiments with filters that had pores small enough to retain bacteria . In 1892, Dmitry Ivanovsky used one of these filters to show that sap from a diseased tobacco plant remained infectious to healthy tobacco plants despite having been filtered . Martinus Beijerinck called the filtered, infectious substance a "virus" and this discovery is considered to be the beginning of virology . The subsequent discovery and partial characterization of bacteriophages by Felix d'Herelle further catalyzed the field, and by the early 20th century many viruses were discovered . </P> <P> Despite his other successes, Louis Pasteur (1822--1895) was unable to find a causative agent for rabies and speculated about a pathogen too small to be detected using a microscope . In 1884, the French microbiologist Charles Chamberland (1851--1931) invented a filter--known today as the Chamberland filter--that had pores smaller than bacteria . Thus, he could pass a solution containing bacteria through the filter and completely remove them from the solution . </P>

Who discovered the world of bacteria and viruses
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