Who discovered the bacterial-culture lesions that led to the discovery of bacteriophages?

Felix d’Herelle discovered bacteriophages in 1917, independently of Frederick W. Twort, who had observed them in 1915. D'Herelle noticed clear spots on bacterial cultures, indicating areas where bacteria were destroyed. He later investigated dysentery during World War I and mixed a filtrate from these clear areas with dysentery bacteria, observing that an unknown agent in the filtrate destroyed the bacteria. He termed this agent an "invisible microbe," later renaming it a bacteriophage.123