Ernst Chain drew Howard Florey’s attention to Alexander Fleming’s 1929 paper on penicillin. Chain encountered the paper while reviewing earlier research on antibacterial substances and recognized that Fleming’s mould product deserved renewed investigation.
Chain was a German-born biochemist working at Oxford’s Sir William Dunn School of Pathology. Florey was interested in naturally occurring antibacterial substances, and Chain’s discovery of Fleming’s paper helped direct the group toward penicillin. The work began in earnest in 1939, with Chain focusing on the chemistry and purification of the unstable substance.
Chain and his colleagues showed that penicillin could be concentrated and used against bacteria. Norman Heatley developed important culture and extraction techniques, while Florey directed the biological and medical program. In 1940, their experiments in mice provided powerful evidence that penicillin could work inside a living animal, not merely in a laboratory dish.
Arthur Gardner, Norman Heatley and Edward Abraham all made important contributions, but they are not the canonical answer to this question. Gardner was a bacteriologist, Heatley an experimental scientist and Edward Abraham a chemist who helped study penicillin. Chain was the researcher credited with bringing Fleming’s forgotten paper to Florey’s attention.