"It is not difficult to make microbes resistant to penicillin in the laboratory by exposing them to concentrations not sufficient to kill them."

"My work was not a flash of genius, but a gradual unfolding of facts."

"The laboratory worker who is not prepared to meet with occasional failures will never achieve success."

"The purification of penicillin was a major triumph of chemistry."

"I was not a great scientist, but I was a careful observer."