796 PERIODIC FUNCTIONS IN MAMMALS 







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Fig. 4. Twenty-three-day record of running activity of a young female 

 Peromyscus with a period length in constant darkness of 24 hr 40 min. 

 Light cycle of 2 hr light per day presented for 9 days (short horizontal 

 lines under daily record). Coordinates as in Fig. 1. 



synchronized to a 24-hr cycle of 12 hr Hght per day. This animal was 

 then subjected to constant light and showed a daily delay in the onset 

 of activity of about 30 min. In constant darkness it again showed a 

 period of about 24 hr 10 min. Similar observations with Peromyscus 

 have been made (Pittendrigh, personal communication). Apparently 

 light presented at the end of the period of activity has a different effect 



