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Development of Petri dish

Koch's booklet published in 1881 titled " Zur Untersuchung von Pathogenen Organismen " (Methods for the Study of Pathogenic Organisms) has been known as the "Bible of Bacteriology." In it he described a novel method of using glass slide with agar to grow bacteria. The method involved pouring a liquid agar onto the glass slide and then spreading a thin layer of gelatin over it. The gelatin made the culture medium solidify, in which bacterial samples could be spread uniformly. The whole bacterial culture was then put on a glass plate together with a small wet paper. Koch named this container as feuchte Kammer (moist chamber). The typical chamber was a circular glass dish 20 cm in diameter and 5 cm in height and had a lid to prevent contamination. The glass plate and the transparent culture media made observation of the bacterial growth easy.

Koch publicly demonstrated his plating method at the Seventh International Medical Congress in London in August 1881. There, Louis Pasteur exclaimed, "C'est un grand progrès, Monsieur !" ("What a great progress, Sir!") It was using Koch's microscopy and agar-plate culture method that his students discovered new bacteria. Friedrich Loeffler discovered the bacteria of glanders (Burkholderia mallei) in 1882 and diphtheria (Corynebacterium diphtheriae) in 1884; and Georg Theodor August Gaffky, the bacterium of typhoid (Salmonella enterica) in 1884. Koch's assistant Julius Richard Petri developed an improved method and published it in 1887 as " Eine kleine Modification des Koch’schen Plattenverfahrens " (A minor modification of the plating technique of Koch). The culture plate was given an eponymous name Petri dish. It is often asserted that Petri developed a new culture plate, but this was not so. He simply discarded the use of glass plate and instead used the circular glass dish directly, not just as a moist chamber, but as the main culture container. This further reduced the chances of contaminations. It would also have been appropriate if the name "Koch dish" had been given.