Petri dish

A Petri dish (alternatively known as a Petri plate or cell-culture dish) is a shallow transparent lidded dish that biologists use to hold growth medium in which cells can be cultured, originally, cells of bacteria, fungi and small mosses. The container is named after its inventor, German bacteriologist Julius Richard Petri. It is the most common type of culture plate. The Petri dish is one of the most common items in biology laboratories and has entered popular culture. The term is sometimes written in lower case, especially in non-technical literature. What was later called Petri dish was originally developed by German physician Robert Koch in his private laboratory in 1881, as a precursor method. Petri, as assistant to Koch, at Berlin University made the final modifications in 1887 as used today. Penicillin, the first antibiotic, was discovered in 1929 when Alexander Fleming noticed that penicillium mold contaminating a bacterial culture in a Petri dish had killed the bacteria around it. Petri dishes are usually cylindrical, mostly with diameters ranging from , and a height to diameter ratio ranging from 1:10 to 1:4. Squarish versions are also available. Petri dishes were traditionally reusable and made of glass; often of heat-resistant borosilicate glass for proper sterilization at 120–160 °C. Since the 1960s, plastic dishes, usually disposable, are also common. The dishes are often covered with a shallow transparent lid, resembling a slightly wider version of the dish itself. The lids of glass dishes are usually loose-fitting. Plastic dishes may have close-fitting covers that delay the drying of the contents. Alternatively, some glass or plastic versions may have small holes around the rim, or ribs on the underside of the cover, to allow for air flow over the culture and prevent water condensation. Some Petri dishes, especially plastic ones, usually feature rings and/or slots on their lids and bases so that they are less prone to sliding off one another when stacked or sticking to a smooth surface by suction.