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[[FILE:Ivan-Pavlov06.jpg|border|right|thumb| [https://en.wikipedia.org/wiki/Ivan_Pavlov Pavlov] in his laboratory <ref>[https://en.wikipedia.org/wiki/Ivan_Pavlov Pavlov] in his laboratory, Image by [https://en.wikipedia.org/wiki/Karl_Bulla Karl Bulla], [https://enhistory-foto.wikipedialivejournal.orgcom/wiki/Iskra_(magazine) Iskra magazine] 268684.html ИСКРЫ, No. 12, March 24, 1913], [https://en.wikipedia.org/wiki/Wikimedia_Commons Wikimedia Commons]</ref> ]]