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Does the rhythmic cycle discernible in any biological function occur in response to some regular external stimulus, or does it result from the influence of some internal "biological clock" mechanism?
Moreover, is this rhythm in function physiologically necessary?
These questions are important in a world where men may spend long periods in an artificial or rapidly changing environment. The crews of nuclear submarines and missile sites must spend many hours isolated from possible geophysical triggers to these rhythmic cycles; astronauts and the crews of inter-continental jets must maintain their efficiency despite disruption of the normal day-night cycle.
To find out more about these rhythmic cycles, what causes them, and what role they play in the body, a series of controlled environment experiments are being conducted at Baylor University School of Medicine, Houston, with the support of the National Aeronautics and Space Administration. A somewhat related study of the effects on
The Search for a Cause Of the Body's Cyclic Rhythms. JAMA. 1965;193(5):28-30. doi:10.1001/jama.1965.03090050098058