Producing penicillin, 1943.
© NMeM / Daily Herald Archive / Science & Society Picture Library
'In this great rack is a single day's output from the proces at the factory where penicillin is prepared. In each of these flasks, 24 square inches in area, a single dose of penicillin is being made. Three hundred flasks - three hundred doses. But it will be at least 3 weeks before the pure penicillin is eventually extracted.' Each glas flask contains penicillin mould growing in a wrinkled layer called a 'felt'. During this proces the mould exudes penicillin into the growing solution from which it can later be extracted.