"It is not wise to be too dogmatic in science. One must always be prepared to change one's mind."

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

"I am often asked if I foresaw the impact of penicillin. My honest answer is no."

"The mold was there, I just saw it."

"It is a happy accident that the mold grew on my plate, but it was not an accident that I recognized it."