The one small/simple experiment that Alexander Fleming never did in 1928 and the one small/simple experiment he absolutely needed to do , to become for all time, the fully respected "discoverer" of penicillin.
At least in the eyes of scientists, doctors, historians and knowledgable lay people.
That experiment was to inject some of his mouse juice again into a mouse - but this time a mouse deliberately infected with massive amounts of bacteria, not a healthy mouse.
All to see if his penicillin juice could pricelessly save lives by working internally to root out massive infections, not to merely become another in a long line of antiseptics, to be dabbed on cuts merely as an aid to hurry up their natural scaring and healing.
Fleming never did this experiment.
Crucially, neither did Florey.
Fleming would have to have slowly injected half a gram (cc/ml) of penicillin juice into an acutely ill 20 gram mouse, and since each gram had about 4 units of antibacterial activity in it, that would have been only 2 units of antibacterial activity per dose.
He'd have to repeat this about every 16 hours for perhaps three days to cure the mouse.
By contrast, because Florey first concentrated that penicillin juice down to about one thousandth of its original volume by boiling the water away in a vacuum, he ended up with mere milligrams of a dry brown powder - each mg containing the same antibacterial units as a gram of the original penicillin juice.
But after all this hard work, he also LOST two thirds of the original penicillin activity.
(He'd be fired if he did that for long in a commercial industrial fermentation operation !)
He dissolved 10 of those mgs of dry penicillin powder into .3 cc of distilled water ( back to the future again !) and injected perhaps 20 to 40 units of antibacterial activity into another acutely sick 20 gm mouse, saving its life in one large intense dose.
Luckily his mice did not die of needle fever during that single big dose - Fleming's need to give weaker injections, repeated over a longer period of time, did at least reduce the chance of severe side affects.
Properly handled, Fleming's strain routinely actually will give at least 40 units per gram of juice.
Then one half gram of his juice would give the exact same effect as 10 mg of Florey's dried powder (10 units in both cases.)
So an alternative path to Florey's tiresome and loss-inducing concentrating and purifying of tiny amounts of antibacterial activity in the original juice was to fire the team chemist and hire instead an industrial mycologist (fungus fermentation specialist) who knew how to starve a mold into giving more , not less, penicillin !
Up till Florey, all those who had written scientific articles on penicillin had acted as if it would be used as a non-toxic and wholly natural liquid , much as natural liver extracts were used to save those with pernicious anemia.
Florey introduced a totally new - and totally bogus - wrinkle into the effort to put penicillin to work saving lives.
He suddenly claimed that penicillin juice was NOT non-toxic - unknown parts of it was toxic "impurities" and that only the fully pure penicillin was non-toxic.
Though how he knew this, well in advance of getting anywhere near full purification, I best leave to your wild imagination !
Particularly if you knew some healthy person who died suddenly of anaphylactic shock after a routine dose of 100% pure penicillin.
I am afraid I can never forgive Florey for the wasted years and wasted diversion of effort into purifying penicillin juice instead of simply pouring it - NOW ! - into dying patients.....