Racks of glass culture flasks growing penicillin, taken by James Jarche for Illustrated magazine in 1943. The material in the flasks is called the 'felt'. This is the form the penicillin mould takes during the latter stages of its growth before the penicillin antibiotic is extracted. Penicillin is an antibiotic, a chemical effective at very low concentrations which can kill or stop the growth of a disease-causing microbe. Penicillin is produced naturally in moulds of the genus Penicillium, from where the drug gets its name. During WW2 Sir Howard Walter Florey and Ernst Boris Chain developed a means of producing penicillin on an industrial scale. Together with Alexander Fleming they shared the Nobel Prize in 1945. Their work on producing a 'wonder drug' saved millions of lives.
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