"The antagonistic microbe can never be cultivated in media in the absence of the dysentery bacillus. It does not attack heat-killed dysentery bacilli, but is cultivated perfectly in a suspension of washed cells in physiological saline. This indicates that the anti dysentery microbe is an obligate bacteriophage".
Felix d'Herelle (1917) An invisible microbe that is antagonistic to the dysentery bacillus (1917) Comptes rendus Acad. Sci. Paris Retrieved on 2 December 2010