"I have been accused of being untidy. I confess to being untidy, but I have never allowed my untidiness to interfere with my work."

"I am sometimes asked what I think of the future of penicillin. I think it has a great future, but it must be used wisely."

"It is not often that one finds a substance that is both highly bactericidal and non-toxic to animal tissues."

"I am very grateful for the recognition I have received, but the real credit belongs to the mould."

"I have been very lucky in my scientific career. I have stumbled on things by accident."