PERIODICITY IN HUMAN BEINGS AND MICE 



811 



-p 1.05 



.00 



a. 



E 



0) 



095 



^ 0.90 

 o 



c 0,8 5 

 o 



o 



E 



■^ 080 

 o 



k- 



Q. 

 O. 

 < 



0.75 



0.00 i-it- 



.^* 





X 



90-rnmufe interval 

 o 180-minufe interval 



_L 



_L 



I 



_L 



22 



23 24 25 



Estimate of period (hours)!; 



26 



Fig. 6. Two periodograms computed from the same data on mean rectal 

 temperature of a group of male institutionalized patients. All the data 

 were used in one case (Ar = 90'), while every second group mean of the 

 time series was omitted in the other case (Af = 180') (1 = 97.5 hr). 



divert our attention away from the mathematical description of a 

 periodicity to some experimental findings which concern the underly- 

 ing mechanisms. 



ANALYSIS OF MECHANISMS 



Circadian Periods in the Mammal at Several Levels 

 of Physiologic Organization 



As a first approximation to analyses of the mechanisms involved in 

 certain mammalian physiologic 24-hr periodicities, we shall herein 

 distinguish those factors which maintain a rhythm from those that 

 synchronize it with its environment. We are attempting this distinction, 

 since as we shall see, a physiologic rhythm can run independently of 

 the 24-hr clock and thus can exhibit phase differences with respect to 



