Laboratory technician testing the purity of pencillin, taken by James Jarche for Illustrated magazine in 1943. The technician is testing manufactured penicillin solutions in a laboratory at St Mary's Hospital, Paddington, London. Different dilutions are used to test the strength of the penicillin. A drop of staphylococus culture is put in the penicillin solution. The test tubes are then incubated and the growth, if any, of the bacteria noted. 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.
© NMeM / Daily Herald Archive / Science & Society Picture Library