792 PERIODIC FUNCTIONS IN MAMMALS 



and water, and an ambient temperature constant within ±2°C and 

 without daily fluctuations. The running wheel operates an electric 

 switch which, through a counting circuit, moves a penpoint on the 

 recording paper. The pen is reset to the base line every minute; so the 

 envelope of the solid graph represents the rate of turning of the wheel 

 in revolutions per minute. 



HAR. 29 



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APR. 19 



24 HOURS 



Fig. 1. Twenty-two-day records of running activity of a female adult 

 Peromyscus in constant darkness. Abscissa, 24-hr time span running 

 from left to right. Ordinate, successive days from top to bottom. Ordinate 

 of each daily record, number of revolutions of running wheel per minute. 

 Maximum rate shown about 125 rev/min. Period of rhythm, 23 hr 10 

 min. 



