A Petri ish is a shallow glass or plastic cylindrical dish that biologists use to culture cells. It was named after the German bacteriologist Julius Richard Petri (1852–1921) who invented it in 1887 when working as an assistant to Robert Koch. Glass Petri dishes can be re-used by sterilization (for example, dry heating in a hot air oven at 160 °C for one hour); plastic Petri dishes must be disposed of after use.