Editing Robert Koch (section)

===Techniques in bacteria study===
Robert Koch made two important developments in microscopy; he was the first to use an [[oil immersion lens]] and a [[Condenser (optics)|condenser]] that enabled smaller objects to be seen.<ref name=":0" /> In addition, he was also the first to effectively use photography ([[microphotograph]]y) for microscopic observation. He introduced the "bedrock methods" of bacterial staining using [[methylene blue]] and [[Bismarck brown Y|Bismarck (Vesuvin) brown dye]].<ref name=":16" /> In an attempt to grow bacteria, Koch began to use solid nutrients such as [[potato]] slices.<ref name="Brock Biology of Microorganisms"/> Through these initial experiments, Koch observed individual colonies of identical, pure cells.<ref name="Brock Biology of Microorganisms"/> He found that potato slices were not suitable media for all organisms, and later began to use nutrient solutions with [[gelatin]].<ref name="Brock Biology of Microorganisms"/> However, he soon realized that gelatin, like potato slices, was not the optimal medium for bacterial growth, as it did not remain solid at 37&nbsp;°C, the ideal temperature for growth of most human pathogens.<ref name="Brock Biology of Microorganisms"/> Furthermore, many bacteria can hydrolyze gelatin, making it a liquid. As suggested to him by his post-doctoral assistant [[Walther Hesse]], who got the idea from his wife [[Fanny Hesse]], in 1881, Koch started using [[agar]] to grow and isolate pure cultures.<ref name=":7">{{Cite journal|last=Hufford|first=David C.|date=1988-03-01|title=A Minor Modification by R. J. Petri|url=https://academic.oup.com/labmed/article-lookup/doi/10.1093/labmed/19.3.169|journal=Laboratory Medicine|language=en|volume=19|issue=3|pages=169–170|doi=10.1093/labmed/19.3.169|issn=0007-5027}}</ref> Agar is a [[polysaccharide]] that remains solid at 37&nbsp;°C, is not degraded by most bacteria, and results in a stable transparent medium.<ref name="Brock Biology of Microorganisms"/><ref name=":5">{{cite book|author=Koch|first=Robert|title=Robert Koch |chapter=Die Ätiologie der Tuberkulose (1882) |series=Klassische Texte der Wissenschaft |date=24 March 1882|trans-title=The Etiology of Tuberculosis|chapter-url=http://edoc.rki.de/docviews/abstract.php?id=610|journal=Physiologische Gesellschaft zu Berlin/Berliner Klinische Wochenschrift|volume=19|pages=221–30|publisher=Springer |location=Berlin, Heidelberg |doi=10.1007/978-3-662-56454-7_4|isbn=978-3-662-56454-7|quote=From page 225: ''"{{lang|de|Die Tuberkelbacillen lassen sich auch noch auf anderen Nährsubstraten kultivieren, wenn letztere ähnliche Eigenschaften wie das erstarrte Blutserum besitzen. So wachsen sie beispielsweise auf einer mit Agar-Agar bereiteten, bei Blutwärme hart bleibenden Gallerte, welche einen Zusatz von Fleischinfus und Pepton erhalten hat.}}"'' (The tubercule bacilli can also be cultivated on other media, if the latter have properties similar to those of congealed [[blood serum]].  Thus they grow, for example, on a gelatinous mass prepared with [[agar-agar]], which remains solid at blood temperature, and which has received a supplement of meat [[broth]] and [[peptone]].)}}</ref>

==== Development of Petri dish ====
Koch's booklet published in 1881 titled "''Zur Untersuchung von Pathogenen Organismen''" (''Methods for the Study of Pathogenic Organisms'')<ref>{{Cite book|last=Koch|first=Robert|url=https://edoc.rki.de/handle/176904/5146|title=Zur Untersuchung von Pathogenen Organismen|publisher=Robert Koch-Institut|year=2010|location=Berlin|doi=10.25646/5071|orig-year=1881}}</ref> has been known as the "Bible of Bacteriology."<ref>{{Citation|last1=Booss|first1=John|date=2014|url=https://linkinghub.elsevier.com/retrieve/pii/B9780444534880000018|series=Handbook of Clinical Neurology|volume=123|pages=3–44|publisher=Elsevier|language=en|doi=10.1016/b978-0-444-53488-0.00001-8|isbn=978-0-444-53488-0|access-date=2021-04-15|last2=Tselis|first2=Alex C.|title=Neurovirology |chapter=A history of viral infections of the central nervous system |pmid=25015479}}</ref><ref>{{Cite journal|last=Hurt|first=Leslie|date=2003|title=Dr. Robert Koch:: a founding father of biology|url=https://linkinghub.elsevier.com/retrieve/pii/S1068607X02001671|journal=Primary Care Update for OB/GYNS|language=en|volume=10|issue=2|pages=73–74|doi=10.1016/S1068-607X(02)00167-1}}</ref> 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.<ref name=":8">{{Cite journal|last=Shama|first=Gilbert|date=2019|title=The "Petri" Dish: A Case of Simultaneous Invention in Bacteriology|url=https://pubmed.ncbi.nlm.nih.gov/31030894|journal=Endeavour|volume=43|issue=1–2|pages=11–16|doi=10.1016/j.endeavour.2019.04.001|pmid=31030894|s2cid=139105012}}</ref>

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!")<ref name=":2" /> 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.<ref name=":6" /> 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).<ref>{{Cite journal|last=Petri|first=Julius Richard|date=1887|title=Eine kleine Modification des Koch'schen Plattenverfahrens|url=https://archive.org/details/1887-petri-eine-kleine-modification-des-koch-schen-plattenverfahrens-2020-braus-|journal=Centralblatt für Bacteriologie und Parasitenkunde|volume=1|pages=279–280}}</ref> The culture plate was given an eponymous name [[Petri dish]].<ref>{{Cite journal|last=Mahajan|first=Monika|date=2021|title=Etymologia: Petri Dish|journal=Emerging Infectious Diseases|volume=27|issue=1|pages=261|doi=10.3201/eid2701.ET2701|pmc=7774570}}</ref> It is often asserted that Petri developed a new culture plate,<ref name=":0" /><ref>{{Cite journal|last=Zhang|first=Shuguang|date=2004|title=Beyond the Petri dish|url=https://pubmed.ncbi.nlm.nih.gov/14755282|journal=Nature Biotechnology|volume=22|issue=2|pages=151–152|doi=10.1038/nbt0204-151|pmid=14755282|s2cid=36391864}}</ref><ref>{{Cite journal|last1=Grzybowski|first1=Andrzej|last2=Pietrzak|first2=Krzysztof|date=2014|title=Robert Koch (1843-1910) and dermatology on his 171st birthday|url=https://pubmed.ncbi.nlm.nih.gov/24887990|journal=Clinics in Dermatology|volume=32|issue=3|pages=448–450|doi=10.1016/j.clindermatol.2013.10.005|pmid=24887990}}</ref> 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.<ref name=":7" /> It would also have been appropriate if the name "Koch dish" had been given.<ref name=":8" />