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

"My work was not a flash of genius, but a gradual unfolding of facts."

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

"The unprepared mind cannot see the outstretched hand of opportunity."

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