Petri Dish This is a Petri dish, made in England by Pyrex (as stamped in white). It consists of a clear glass circular tray with a fitting lid, used to hold growth medium for cell culture. The Petri dish was originally developed by Robert Koch (1843–1910) in his private laboratory in 1881. He initially used horizontally leveled pouring apparatus to prepare gelatin plates, which were stacked in large bell jars for cultivation. To simplify the process and reduce the need for additional equipment, he later adopted the use of flat double dishes (10–11 cm in diameter, 1–1.5 cm high), where the upper dish acted as a lid. These dishes allowed gelatin mixed with inoculation material to solidify in a thin, protective layer, reducing contamination from airborne germs. Julius Richard Petri (1852–1921), while working as Koch's assistant at Berlin University, refined this design in 1887, resulting in the modern Petri dish. This item, suitable for sterilisation, remains a standard laboratory tool for microbiological studies today. 1900-1949