Slonaker, Activity of the Rat. 349 



of Figs. 3 and 4. Fig. 3 represents the curves of total activity 

 from the beginning of this experiment, March 13, to the end, May 

 9, a period of 57 days. Fig. 4 represents the curves of daily 

 activity. For simplicity the curves pass through the ordinates 

 erected on each fifth day of the experiment, each representing the 

 average of the number of revolutions for the preceding five days. 



By comparing the curves of Fig. 3 and those of Fig. i a marked 

 difference is noticed. No. 3 was the most active in Experiment I, 

 but now it occupies third place. No. i, whose position was second 

 in the former experiment, now far surpasses all the others. 



When we compare the ages of these individuals at which they 

 were the most active we find that No. 3 did the most work when it 

 was between 85 and 95 days old. No. i (Fig. 4) at the age of no 

 to 127 days. No. 2 somewhere between 100 and 120 days, while 

 No. 4 never seemed to show much change from day to day. In 

 other words. No. 4 had passed the age of greatest activity before 

 the beginning of Experiment L Individual variation no doubt 

 accounts for these differences in the age of greatest activity. If 

 the average were taken it would bring the most active period as 

 indicated by greatest number of revolutions, at about theageof 105 

 days. 



Taking the data we now have, a hypothetical curve representing 

 the curve of activity from birth to death from old age could be 

 constructed. Such a curve would show a gradual increase in 

 activity to about the age of 100 days after which it would begin to 

 fall and would finally reach the base line at death. ^ But owing 

 to the individual variation manifested in these experiments, such 

 a curve could not be relied upon as being correct. In order to 

 construct such a curve Experiment III was begun. 



EXPERIMENT III. 



The foregoing experiments show the need of a curve represent- 

 ing the average of a number of individuals subjected to the same 

 conditions. That this might prove successful the rats should be 

 the same age, as closely related as possible, and all subjected to 

 the same food and environment. Accordingly, a litter of eight 

 rats was selected. At the age of 25 days they were practically 



^ The age which rats living in the above conditions would attain has not yet been ascertained. 



