August 24, 1940

Penicillin

Oxford team publishes penicillin's effectiveness in infected animals

The landmark paper openly admitted its brown powder was impure — and still reported activity at dilutions of one in several hundred thousand.

24 August 1940: three pages in The Lancet

On 24 August 1940 The Lancet published 'Penicillin as a Chemotherapeutic Agent,' a three-page preliminary report from the Sir William Dunn School of Pathology at Oxford. Seven authors were named: Ernst Chain, Howard Florey, Arthur Duncan Gardner, Norman Heatley, Margaret Jennings, Jean Orr-Ewing and Arthur Gordon Sanders.

They described methods for concentrating penicillin from mould-culture medium into a water-soluble brown powder, and reported low observed toxicity in mice, rats and cats alongside therapeutic tests in mice infected with streptococci, staphylococci and Clostridium septique.

What the paper actually claimed

The report repeatedly called its own preparation impure. It also declined the obvious headline: the authors wrote that penicillin was not immediately bactericidal and appeared instead to interfere with bacterial multiplication.

Among the practical findings was an awkward one — at least 40–50% of the administered penicillin emerged in urine still active.

The eight mice behind the paper

The experiment that convinced the team to proceed had run on 25 May: eight infected mice, four given penicillin and four left untreated. By the following morning all four controls were dead and all four treated mice were alive.

No human patient was treated as part of this publication. Oxford's first sustained treatment of a seriously infected patient followed in February 1941, when limited supplies still prevented completion of the course.

Sources

Researched 23 Aug 2026 6 sources 3 audit passes

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