Zucker I
Hosp Pract. 1976 Oct;11(10):83-91. doi: 10.1080/21548331.1976.11707013.
The most potent environmental synchronizer of "biologic clocks" in mammals is the light-dark cycle. The author describes experiments that identify a particular pathway--a derect connection between retina and hypothalamus--as the main route by which such biologic rhythms as the daily activity cycle, the estrous cycle, and the annual reproductive cycle are entrained to the external environment.
