Ampoule of penicillin, by Merck & Co., Inc., Rahway, New Jersey, 5000 Florey Units

The label on this glass ampoule of penicillin powder reads “Caution – New Drug, Limited by Federal Law to Investigation Use”. The sample was used as part of clinical trials before the new drug could be used in hospitals, clinics and by medics during the Second World War. The powder would be diluted and then injected.

The amount of penicillin in the powder was at that time measured in Oxford units or Florey units, which were named after Howard Florey (1898-1968). Florey was the leader of the team at Oxford University that, in the early 1940s, discovered the potential of penicillin as an antibiotic to fight a wide variety of infections. Later, penicillin was measured in International Units.