H. Bretzl, Botamsche Forschungen des Alexanderzuges (Leipzig: B. G. Teubner, 1903); процитировано в книге Martin C. Moore-Ede, Frank M. Suizman, and Charles A. Fuller, The Clocks That Time Us; Physiology of the Human Circadian Timing System (Cambridge, Massachusetts: Harvard University Press, 1982), p. 5.
