Penicillin

Penicillin's journey from accidental observation to life-saving medicine spans thirteen years, three countries, and a world war. The discovery came in 1928; the adjacent possible for mass production didn't open until 1941. The gap reveals how an insight can await its moment.

Alexander Fleming, a Scottish physician at St. Mary's Hospital in London, returned from holiday in September 1928 to find mold growing on a Petri dish of Staphylococcus bacteria. The mold—Penicillium notatum—had created a clear zone where bacteria could not survive. Fleming recognized the antibacterial effect and named the active substance penicillin. He published his findings in 1929.

Then nothing happened. Fleming lacked the chemistry background to isolate the active compound and the laboratory resources to purify it at scale. He tried briefly to interest chemists in the problem but found no takers. By 1929, work on penicillin at St. Mary's had ended. The discovery sat dormant for a decade.

The adjacent possible reopened in 1939 at Oxford. Howard Florey, an Australian pathologist, and Ernst Chain, a German-Jewish biochemist who had fled Nazi Germany, assembled a team at the Sir William Dunn School of Pathology. Chain rediscovered Fleming's paper while searching for antibacterial substances. On May 25, 1940, they injected eight mice with lethal doses of Streptococcus, then treated half with penicillin. By morning, all untreated mice were dead; all treated mice survived. Chain called it "a miracle."

The first human trial came on February 12, 1941. Albert Alexander, a 43-year-old policeman, had developed a life-threatening infection from a rose thorn scratch. Penicillin brought remarkable recovery—but supplies ran out. He died five days later. The lesson was clear: penicillin worked, but only if you had enough.

With Britain consumed by war, Florey and Norman Heatley sailed to America in June 1941, carrying Penicillium cultures smeared on their coat linings for security. The U.S. Department of Agriculture's laboratory in Peoria, Illinois, became the scale-up site. Researchers discovered that corn steep liquor—a waste product from cornstarch manufacturing—dramatically improved mold growth. A new strain found on a moldy cantaloupe produced six times more penicillin than Fleming's original.

By 1943, unprecedented Anglo-American cooperation had solved the production problem. American pharmaceutical companies—Pfizer, Merck, Squibb—built fermentation tanks the size of swimming pools. By D-Day in 1944, enough penicillin existed to treat all Allied wounded. The antibiotic era had begun.

Fleming, Florey, and Chain shared the 1945 Nobel Prize in Physiology or Medicine. But penicillin's cascade extended far beyond its inventors. The antibiotic revolution that followed—streptomycin, tetracycline, erythromycin—transformed medicine from a profession largely helpless against infection into one that could cure diseases that had killed for millennia. Penicillin opened the adjacent possible for all antibiotics that followed.