28 .1 AMES ROLLIN SLONAKER 



amount of running activity during the lifetime. In order that 

 the figures representing the activity at a given age may not 

 represent a single day's run, but an average day's run at that 

 age the following scheme was used. The number of revolutions 

 for the five days preceding and the five days succeeding the 

 day representing the age desired were taken and from these 

 an average day's run was estimated. This eliminates the possible 

 effect of food, temperature, or other conditions which might 

 cause a sudden slump or increase in the activity of a given day. 

 Table I represents such averages and shows the average 

 number of revolutions made each day by each rat at the ages 

 indicated. Consulting this table it is readily seen that in each 

 case there is a rapid increase in average daily running. But 

 instead of its being a uniform increase it was rhythmic in char- 

 acter. There was a rapid increase in the amount of activity 

 for a month or so after which there was a decrease. This was 

 followed again by another increase and decrease. The rhythmic 

 effect is best shown in Fig. n. These curves show the average 

 daily running for each rat at the ages indicated. In other words 

 it is the data of Table I put in the form of curves. The differ- 

 ence in the average daily activity of the males and the females 

 is very noticeable. It is also interesting to note that the rhythmic 

 increase and decrease of activity of each of the males accords 

 very closely as to time, while that of the female does not cor- 

 respond so closely. So far I am not sure of the causes which 

 underlie this rhythmic variation. These changes correspond more 

 or less to the fluctuations in the weight of the rats as shown in 

 Fig. 13. The causes for the changes in weight will be discussed 

 later under the topic of growth. I will, however, state that 

 following an increase in the amount of protein food given there 

 was an increase in weight accompanied generally by a greater 

 or less increase in activity. But as the results are not always 

 constant there must be something else which influences and 

 causes these rhythmic fluctuations. If the changes in activity 

 of the female corresponded closely to those of the males or as 

 closely as the males do among themselves I would consider 

 they might be due to the periods of heat. At such times there 

 is a tendency in both sexes when near each other to excessive 

 running. The fact that No. 2 and No. 4 were situated one on 

 each side of No. 3 and that these two males did more running 



