The Sky of the Night a Mold Changed the Destiny of Humanity
On September 28, 1928, Alexander Fleming, a Scottish bacteriologist at St Mary's Hospital in London, noticed something strange while examining Petri dishes he had left behind before his vacation: a mold had contaminated one of them, and the staphylococcus colonies around it had been destroyed. This chance observation would lead to the discovery of penicillin, the first antibiotic, and save hundreds of millions of human lives. This star map captures the starry vault above London that evening — the sky beneath which modern medicine was born.
Historical context
The story of penicillin is one of the most extraordinary in science — a tale where chance, carelessness, and the genius of observation intertwine to produce a discovery that would save more human lives than any other in the history of medicine.
Alexander Fleming was forty-seven years old in September 1928. Scottish by birth, the son of a Lowland farmer, he had studied medicine in London and served as a captain in the Royal Army Medical Corps during the First World War. In the field hospitals of Flanders, he had watched thousands of soldiers die not from their wounds, but from the infections that developed in them. The antiseptics of the day — phenol, iodine — were almost as destructive to healthy tissue as to bacteria. Fleming emerged from the war with an obsession: to find a substance capable of killing bacteria without destroying human cells.
Back in London after the war, Fleming had joined the bacteriology department at St Mary's Hospital in Paddington, under the direction of Sir Almroth Wright, a pioneer in vaccination. His laboratory, on the second floor, was notoriously untidy — a trait that, through an extraordinary twist of fate, would change the course of history.
In September 1928, Fleming left for a family holiday in Scotland, leaving behind a stack of Petri dishes containing cultures of Staphylococcus aureus — bacteria responsible for many deadly infections. The windows of his laboratory, overlooking Praed Street, were left ajar to circulate air in the lingering summer heat.
When Fleming returned on September 28, he began sorting through his Petri dishes, tossing contaminated ones into a tray of disinfectant. It was then that his former assistant, Merlin Pryce, dropped by for a visit. Fleming, wanting to show his work, retrieved a dish he had just set aside. He examined it more closely. And he saw something that stopped him in his tracks.
A patch of green mold had grown on the agar — a commonplace contamination in laboratories of that era. But around this mold, the staphylococcus colonies had vanished. A transparent circle surrounded the fungus, as though an invisible force had dissolved the bacteria. Fleming then uttered the words that have become legendary, with typical British understatement: "That's funny."
What Fleming was seeing was the effect of a substance secreted by the fungus Penicillium notatum — a substance capable of destroying bacteria at a distance. He named it "penicillin." He spent the following weeks studying it, discovering that it was effective against a broad spectrum of pathogenic bacteria while remaining remarkably harmless to human and animal cells. This was exactly what he had been searching for since the trenches of Flanders.
What sky watched over London that evening of September 28, 1928? London's autumn was just beginning. Twilight fell early on Paddington, the gas lamps of Praed Street casting their yellowish glow on the damp pavements. Above the rooftops of St Mary's Hospital, the September sky offered a remarkable spectacle.
The constellation Sagittarius sat low on the southern horizon, with the heart of the Milky Way — invisible from London's light-polluted sky, but present behind the luminous veil of the city. The Summer Triangle still dominated the firmament: Vega, in Lyra, shone nearly at the zenith with its characteristic blue light; Deneb, in Cygnus, marked the apex of the Northern Cross; and Altair, in Aquila, sparkled to the south. The constellation Pegasus was rising in the east, its Great Square of four stars easily recognizable. Fomalhaut, the solitary star of Piscis Austrinus, twinkled low on the southern horizon — one of the few bright stars in that austere region of the autumn sky.
But Fleming was not gazing at the stars that evening. He was looking at a Petri dish. And in that Petri dish, in the halo of inhibition around a greenish mold, he was seeing something no one before him had understood: the future of medicine.
It would take more than another decade before penicillin became a usable drug. Fleming himself never managed to produce the substance in sufficient quantity or to purify it. It was Howard Florey and Ernst Boris Chain, at Oxford, who accomplished that titanic work between 1939 and 1941, in the midst of the Second World War. By 1944, penicillin was being manufactured on an industrial scale in the United States, and the Allied soldiers of D-Day were the first to benefit from it en masse. Infections that had previously killed within days were conquered within hours.
In 1945, Fleming, Florey, and Chain received the Nobel Prize in Physiology or Medicine. In his acceptance speech, Fleming issued a prophetic warning: if penicillin were used indiscriminately, bacteria would develop resistance. That warning, largely ignored for decades, resonates today with alarming urgency, at a time when antibiotic-resistant "superbugs" constitute one of the gravest threats to global health.
It is estimated that penicillin and the antibiotics derived from it have saved more than 200 million lives since their introduction. Before penicillin, a simple infected cut could be fatal. Bacterial pneumonia was often a death sentence. Tuberculosis, scarlet fever, septicemia — scourges that had decimated humanity for millennia — became treatable conditions resolved within days.
All because one September morning in 1928, a Scottish bacteriologist with a messy laboratory noticed a patch of mold on a forgotten dish. Beneath the autumn sky of London, in a small laboratory in Paddington, chance and observation had conspired to offer humanity its most powerful weapon against disease — born of a mold, beneath the stars.