Passage: In 1915, British bacteriologist Frederick W. Twort discovered a small agent that infects and kills bacteria, but did not pursue the issue further. Independently, the discovery of "an invisible, antagonistic microbe of the dysentery bacillus" by d'Herelle was announced on 3 September 1917. The isolation of phages by d'Herelle works like this:

Question: What did d'Herelle create?
isolation of phages