"I had no idea that I had stumbled on to a subject that would prove to be of such immense importance."

"The therapeutic value of penicillin is enormous, but its indiscriminate use could lead to disaster."

"Some people have been very enthusiastic about penicillin, others less so."

"It is not the discovery of a new substance that is important, but the recognition of its properties."

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