"My own work was really quite simple. I just observed what was happening."

"It is not the man who first sees a thing who is the discoverer, but he who sees into a thing."

"The thoughtless person playing with penicillin treatment is morally responsible for the death of the man who succumbs to infection with the penicillin-resistant organism."

"The mould grew, and then I saw the clear space around it."

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