Key points are not available for this paper at this time.
This series reports studies on circadian systems in insects and mammals.In constant darkness and temperature an organism may display one or more circadian rhythms in functions such as locomotion, drug sensitivity, or the specific activity of individual enzymes.The period, r, of such rhythms is about 24 hours; it is usually precise and always temperature-compensated.In discussing these phenomena we describe the whole cell or organism as a circadian system whose output manifests (a directly observable) circadian rhythm, which must, a priori, be the result of a periodicity in its physiological control systems.We restrict the term circadian oscillation to this periodic driving element in the system's controls.Clearly the total system comprises, in addition to the driving oscillation, a plethora of physio- logical subsystems driven by this pacemaker.These driven elements may or may not be themselves periodic; in either case they are not oscillations ultimately responsible for the total system's periodicity.The driving oscillation entrains to (locks onto) a restricted class of environmental cycles, principally that of light and, to a lesser extent, temperature.It is thus responsible for phasing the entire cir- cadian system to the daily cycle of change in the environment.Our interest is in the following general questions: (1) What is the nature of the driving oscillation?(2) What is the mechanism of its entrainment by environ- mental cycles?(3) How is it coupled to the peripheral subsystems which it drives?* This work was performed under contracts
Colin S. Pittendrigh (Sun,) studied this question.