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.

How Parke-Davis could have made a fortune in 1929 from the ultimate in generic drugs : natural penicillin

Parke-Davis, as seen from my folks' homes

A medication made by some natural being out in Nature is the 'ultimate generic drug'  ---- being PD (Public Domain) from its birth, which possibly occurred hundreds of millions of years before Humanity first noticed it.

Penicillin - in theory - is one such 'ultimate generic drug' , but was it in fact, in 1929 ?