THERE are many contenders for the accolade of most important moment in 20th century Scottish history. The beginning and end of two world wars, the reconvening of the Scottish Parliament in 1999 and the first demonstration of television by John Logie Baird in 1926 must be right up there, though no doubt loyal fans of Celtic, Rangers and Aberdeen might argue for their clubs’ European trophy wins.

Yet one incident of genuine scientific breakthrough stands head and shoulders above every other important moment in 20th century Scottish history, and it took place 90 years ago in this week, and it did not even take place in Scotland.

For it was on September 28, 1928, that Scotland’s own Alexander Fleming first produced penicillin. Countless millions have since benefitted from that moment of genius.

It happened largely because Fleming was not the most assiduous scientist at tidying up after himself.

The Kilmarnock Academy scholarship boy had come a long way from his father’s farm near Darvel by the time he discovered penicillin.

A war hero who treated thousands of wounded men in the trenches, he had been studying the relatively new science of bacteriology before the war and became convinced in battlefield hospitals that the then current antiseptics were possibly causing more harm than good.

After the war, Fleming returned to his work as a lecturer and researcher at St Mary’s Hospital, Paddington, in London.

It is often thought that Fleming was relatively unknown when he made his great discovery.

That may have been true in terms of public awareness but he was well known in medical circles for his discovery of the anti-bacterial enzyme Lysozyme in 1922.

It was partly accidental – he treated bacterial cultures with mucus from a cold and described how the enzyme had clear effects on the cultures, thus gaining himself the credit for discovering Lysozyme, which scientists are still working to develop even today.

Fleming, like every other medical scientist, had been appalled by the influenza pandemic after the war which killed many more people than died in the trenches.

He set to work trying to find something to battle the infection, and was making slow progress on his study of the staphylococcus bacteria by the summer of 1928.

Fleming went off to Scotland on holiday in August of that year and, quite typically, he left behind petri dishes that had been used to grow staphylococci bacterial cultures.

Returning on September 3, Fleming happened to notice that the culture in one of the dishes had been enveloped in a fungus around which the staphylococci had stopped growing.

He famously said to himself “that’s funny”, and at that second made a leap of imagination, in effect asking himself if the bacterial-killing mould could halt the spread of infection in humans.

He reasoned that it must have blown in through an open window, and decided to try to grow some of the mould. Just 25 days later he had produced enough of the substance that he at first called “mould juice”, but then named penicillium notatum, or penicillin.

Fleming always said that September 28 was the day of the real discovery, for it was on that date he produced enough of the substance to prove that it was penicillin that was killing staphylococcus.

He later wrote: “One sometimes finds what one is not looking for. When I woke up just after dawn on September 28, 1928, I certainly didn’t plan to revolutionise all medicine by discovering the world’s first antibiotic, or bacteria killer. But I suppose that was exactly what I did.”

While Fleming did not realise the true significance of his discovery at first, he most certainly did see the possibility of what antibiotics could mean for the world, but he was unable for various reasons to take the next steps forward and achieve production of penicillin.

He published his findings in a scientific journal but simply did not have the resources – cash and staff – to take matters further at that time.

It was left to Oxford University scientists Howard Florey and Ernst Chain to show that penicillin really was a wonder drug that could be mass produced.

In truth, Florey, Chain and others did more to develop penicillin, but they always acknowledged Fleming as the initiator.

The awards followed for Fleming, whose story of the accidental discovery was taken up by the press.

He was elected fellow of the Royal Society in 1943 and knighted in 1944. The following year Fleming, Florey and Chain shared the Nobel Prize in Medicine, and there are now many tributes and honours in his name around the world.

Sir Alexander Fleming died of a heart attack at his home in London on March 11, 1955.

All that lay in the future in this week 90 years ago, when an untidy Scotsman began to change the world for the better.