Like many people, historian A. Roger Ekirch thought that sleep was a biological constant -- that eight hours of rest a night never really varied over time and place.
원문출처 : https://www.cnn.com/2022/01/09/health/sleep-history-wellness-scn/index.html
원문출처 : https://www.cnn.com/2022/01/09/health/sleep-history-wellness-scn/index.html