"I have been asked by many people how I came to discover penicillin. The answer is that I did not discover it. I just happened to notice it."

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

"The mere fact that a substance has bactericidal powers does not mean that it can be used for the treatment of septic infections."

"I play with microbes. There are, of course, many rules to this play...but when you have acquired knowledge and experience it is very pleasant to break the rules and to be able to find something nobody…"

"One sometimes finds what one is not looking for."