BEHAVIORISTIC STUDY OF THE RAT 
25 
These determinations were made in three different ways: (1) 
On the basis of the spontaneous activity in the simple stationary 
cages, described above. (2) On the basis of the amount of work 
done in the revolving drums, the total number of revolutions made 
at different ages. (3) On the basis of the readiness and com¬ 
pleteness with which nests are built under normal conditions. 
The technique employed in the first method was essentially 
the same as that described in the experiments above. For the 
reason that it was not possible to obtain continuous uninterrupted 
records on a group of rats throughout the entire period of their 
lives records were taken instead at frequent intervals for fifteen 
months on a very large group (40) of animals of all different ages 
(26 to 700 days). Records were taken for five to eight days at 
frequent intervals. In this way a sufficiently large number of 
records were obtained for all stages in the development of the 
rat. Before each series of experiments the animals were given two 
to three days time or longer in which to accustom themselves 
to the cages. Twelve of the animals of the group were left in 
stationary cages all the time in order to eliminate the effects on 
the activity which might be caused by frequent changes back and 
forth from the activity cages to the ordinary cages. The effects 
of these changes on the rest of the group did not prove to be very 
great. Records were taken always under the same conditions 
of temperature and illumination. 
‘ The relation of activity to age determined by this first method 
is shown in figure 14, in the curve marked “Stationary Activity 
Cages. ” In this curve the age of the animals is shown on the 
abscissae in days, while the average amount of activity per day 
in activity units is given on the ordinates in the second column 
labelled “Activity Units/’ In this curve it may be seen that at 
25 days the rat is quite inactive. From this age to the age of its 
maximum activity, 175 days, its activity increases very rapidly. 
After 175 days its activity begins to fall off, slightly at first, then 
fairly rapidly until at 600 days it reaches the original level of 
inactivity from which it started. 
In the second method ordinary revolving drums were used. 
They were 12 inches in diameter and 10 inches wide, and revolved 
