Laboratory technician examining flasks of penicillin culture, taken by James Jarche for Illustrated magazine in 1943. As the penicillin mould grows in the glass flask it develops a distinctive appearance. It grows into a crinkled layer which is called a 'felt'. During this process of growth the mould exudes peniciliin into the growth solution. Each flask contains enough mould to produce a single dose of penicillin. However it takes another three weeks to extract and purify the drug.
© NMeM / Daily Herald Archive / Science & Society Picture Library