BEHAVIORISTIC STUDY OF THE RAT 
11 
marks on the kymograph paper) on the ordinates. The average 
daily activity for the five days preceding the experiment is given 
on the first ordinate. 
In the next experiment on the distribution of activity with 
relation to the time of feeding it was first undertaken to determine 
simply how the amount of activity of the first half of the day 
(the first twelve hours after the feeding period) compares with 
the activity during the second half. It was found that the activity 
during the first twelve hours is very much greater than during 
the second twelve. But the ratio of the amount of activity 
during the first twelve hours to the activity during the second 
was found to depend on the age of the animal. This is shown in 
figure 5 where the age in days is given on the abscissae and the 
ratio of the amount of activity during the first and second halves 
of the day are given on the ordinates. It is seen that the very 
young animals are almost twice as active during the twelve hours 
immediately following the daily meal than during the next twelve. 
In the very old animals the amount of activity during these two 
periods is almost evened out. This curve is based on records 
from thirty-five animals of three different ages. 
When instead of dividing the twenty-four hours following the 
time of feeding into two twelve-hour periods they are divided into 
one hour periods, the curve of the distribution of activity has a 
very characteristic form. Such a curve is shown in figure 6. 
This curve is based on the records obtained from forty animals 
250 days old. In this figure the time of the day is indicated on 
the abscissae in hours, while the amount of activity per hour is 
indicated on the ordinates. The animals were fed at 12 o’clock 
noon. The room was kept in constant illumination. It is seen 
that immediately following the daily feeding period there is a 
period of relative inactivity lasting from four to five hours. Then 
there follows a period of very intense activity for eight to ten 
hours. This is followed in turn by a period, lasting from five to 
seven hours, of almost complete inactivity. During the last 
two to three hours of the twenty-four the activity increases very 
rapidly again right up to the time of the next feeding period. 
