An original sample of Alexander Fleming's penicillin mould culture could make $10,000-20,000 at Bonhams.
Penicillin was among the greatest medical breakthroughs of all time.
This is already the most valuable piece of mould on the planet
Its discovery led to the development of antibiotics, which have eradicated some of the worst diseases known to man and increased life expectancy around the world.
But, remarkably, it was all a happy accident.
Fleming actually discovered the effects of the mould while researching a strain of bacteria that causes disease. He saw that wherever the mould grew, it killed off the bacteria.
As Fleming put it: "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."
This lot consists of part of that original mould culture preserved between two pieces of glass.
It's tiny (measuring 50mm across) and is bound together with sellotape, but what it lacks in size and looks it more than makes up for in its significance to human progress.
Fleming actually gave it to his neighbours in 1955, after they scared off some burglars. He writes in a letter accompanying the piece: "I have to thank you for a great service when on Saturday night you scared the burglars and so saved my safe and its contents.
"I should have been very sorry to have lost all the various medals which have been given to me and after this experience I do not trust the safe - they are in the bank.
Other exciting items in the December 7 auction include one of the earliest TVs on the market.
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