"The therapeutic value of penicillin is enormous, but its indiscriminate use could lead to disaster."

"The bacteriologist must be a patient man."

"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…"

"The power of observation is crucial in scientific research."

"The discovery of penicillin was a series of lucky accidents."