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

"I did not invent penicillin. Nature did that. I only discovered it by accident."

"The greatest reward for a scientist is the advancement of knowledge."

"My greatest satisfaction comes from knowing that my work has saved countless lives."

"The discovery of penicillin was a stroke of luck, but it was also the result of many years of hard work."