Science's faith-based belief in the non-toxicity of pure natural Penicillin

For an entire generation of scientists, doctors and science reporters (those working between 1929 and 1949), it was an article of absolute faith that pure penicillin was non-toxic.

But how did they know? How in the hell did they know ?

For during most of those years they had never seen anything like pure penicillin , let alone given it an extensive work-out down in the hospital wards.