356 "Journal of Comparative Neurology and Psychology. 



These figures are the averages of the four rats. SHght fluctua- 

 tions in the averages occur. I can not give the cause of this 

 difference. It certainly cannot be due to their food, for they were 

 fed the same during the time represented in this table. The 

 fluctuations might be due to changes in barometric pressure. I 

 have not as yet demonstrated this. The cause, therefore, cannot 

 at present be given. 



It is very noticeable that in general when there is a great reduc- 

 tion in the average amount of work during the night the following 

 day shows a marked increase. In other words, they seem to 

 prefer to do about so much work each 24 hours and if this amount 

 is not done during the night they are more active the following day. 



A better idea of the amount of work may be gotten if the num- 

 ber of revolutions is converted into distance. A little less than 1 1 75 

 revolutions of each cage are equal to one mile. From this we see 

 that the average nightly run at the age of 70 days is about 

 five miles. The average number of revolutions during the day 

 time at the same age is only about one-tenth of a mile. Many 

 individual cases far surpass this average amount of work. The 

 greatest run which I have observed for a single night (14 hours 

 and 45 minutes) was 16,516 revolutions, or a distance of fourteen 

 and one-tenth miles. Such a run is usually followed by a notice- 

 able reduction in activity the following day. 



By close and quiet observation one could see that activity was 

 apparently performed from the mere love of it. The rats would 

 frisk about, jump and play, then start the wheel going and run it 

 for a number of turns without a stop. After a few seconds, or 

 minutes' rest they would start it again with renewed vigor. This 

 playful attitude was especially noticeable at the age of 50 days. 

 As they grow older this activity which was displayed in frolicking 

 and investigation gradually assumed the form of turning the 

 wheel. So that by the time the rat reached the age of 80 days 

 most of its spontaneous activity was manifested in revolutions 

 of the cage. I have seen them run as many as 100 revolu- 

 tions in a minute without a single stop. This is equivalent to a 

 twelfth of a mile The records in Fig. 6 show that in many 

 cases if periods of rest occurred they were extremely short. In one 

 case (No. 4, last record) there appears to be continuous activity 

 for two and a half hours before a rest. This appearance, I think, 

 is due to the slow movement of the paper. I have never yet seen 



