Two samples of mould that legendary scientist Sir Alexander Fleming used to produce penicillin have sold for almost £25,000.
Both specimens of the yellow-green Penicillium Notatum fungus are contained on a glass disc and date back to the 1930s, when Fleming was developing his 1928 discovery of penicillin.
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The samples helped pave the way for the development of antibiotics, which people first started to use in 1942 to treat infections which would previously have proved fatal. The treatment has gone on to save millions of lives.
Part of an archive that formed part of the sale was a poignant letter of thanks from a father to the biologist for helping to save his daughter's life.
One of the two moulds Fleming gave to his niece
The collection also included an ironic letter from Fleming to a relative in which he professed to being in good health 'thanks to penicillin.'
The archive was assembled by Fleming's niece Mary Anne Johnston and was sold by a direct descendant.
One lot containing one of the moulds, letters, photographs and a journal sold for £12,500 to a private overseas buyer on internet at the London auction.
A self portrait by Fleming is also being sold
A second mould sold for £11,875 to a private overseas buyer on telephone.
Matthew Haley, of auctioneers Bonhams, said: "The high prices paid for these lots reflect their importance and the enduring fascination with Alexander Fleming's crucial discovery, to which so many millions of people all over the world owe their lives.
"They might not be much to look at now but they are of humongous significance in the world of medicine.
Fleming at work in his laboratoryThe revered scientist with his second wife Amalia
"These samples were used by Alexander Fleming to develop penicillin and bring us to where we are today in terms in curing people from bacterial infections and saving lives.
"Fleming was awarded the Nobel Prize in 1945 and actually gave a few samples like these to celebrities."
Fleming's breakthrough in discovering penicillin was a complete accident.The Nobel prize bronze medal
He was researching staphylococcus bacteria when he went on holiday, leaving his samples on a bench in his laboratory at St Mary's Hospital, London.
When he returned he noticed that one sample was contaminated with a fungus and the colonies of staphylococci around it had been killed.
Fleming grew the mould in a pure culture and found that it produced a substance that killed a number of disease-causing bacteria.
He identified the mould as being Penicillium Notatum.