The thermometer reading of 98.6°F has been a gold standard for a century and a half, ever since a German doctor laid it down as the “normal” human body temperature.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/explained-why-986%C2%B0f-no-longer-%E2%80%98normal%E2%80%99-body
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/indian-express-new-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/medical-research
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/united-states-america-us
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-care