"I can only warn. It is up to others to heed the warning."

"My only merit is that I did not discard the cultures at an early stage."

"The public looks for miracles. We scientists look for facts."

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

"The greatest tragedy is the misuse of a good thing."

"I was just a dirty old man who left his dishes unwashed."

"The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantitie…"

"The mold was a lucky accident, but the observation was not."

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

"It is a remarkable fact that this substance, which is so potent against bacteria, is almost harmless to animal tissues."