"The greatest danger in the world is ignorance, and the greatest weapon is knowledge."

"I never thought of myself as a great man, just a man who made a great discovery."

"Many difficulties were encountered in the early attempts to isolate and purify penicillin."

"The discovery of penicillin was a series of small observations, not a single eureka moment."

"I am sometimes asked what I think of the future of penicillin. I think it has a great future, but it must be used wisely."