816 



PERIODIC FUNCTIONS IN MAMMALS 



4 th Day in Constant Darkness 



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140 



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60 



05:oo 



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Time (hours) 



05:00 



Fig. 11. Circadian periods of body activity in mice kept at different 

 temperatures. Data suggest operation of some mechanisms of temperature 

 compensation for maintenance of circadian periods in gross motor activity. 



period. Figure 3 shows, in turn, periodograms computed for data on 

 individual mice. It may be seen, first, that five of the six periodograms 

 exhibit periods shorter than 24 hr. Second, this shortening in period 

 (after blinding) is not the same in all the animals constituting the 

 group. Third, it is pertinent that, at later time points after blinding, 

 there is a tendency toward a resynchronization of the rhythms in 

 Winded and in sham-operated mice. During the third month after 

 blinding, this tendency comes clearly to the fore in the periodogram 

 (Fig. 4) ; a visual inspection of the plot of mean temperatures, in turn, 

 reveals the tendency toward resynchronization quite clearly at 5 

 months after blinding but less clearly at 3 months after blinding. In 

 this case, the periodogram detected what the inspection of the data 

 may have missed, and, what is more important, the inference made 

 from the periodogram on data obtained at 3 months after blinding was 

 confirmed by the data obtained another 2 months later. 



The above data suggest that stimuli received by the eye can syn- 

 chronize the 24-hr rhythm in rectal temperature with the environ- 

 mental time scale, since upon removal of the eyes a dissociation of the 

 rhythm from the environment is seen (Halberg, Visscher, and Bittner, 

 1954). These data also suggest that stimuli other than those received 



