32 
CURT P. RICHTER 
The records for the two animals are shown in figures 17 and 18. 
In these figures the time of the day is indicated on the abscissae, 
the amount of activity during each hour on the ordinates. A 
record of normal activity was taken on the day preceding the 
experiment, that is on the day before the animals were deprived 
of food. The record of the distribution of activity on this day 
is shown in the top curves marked ‘normal’. The shape of these 
curves corresponds in general outline to the composite distribution 
curve in figure 6. The records for the following days of starvation 
show that the general shape of this distribution curve is main¬ 
tained for three to four days after the removal of food. The 
curve becomes more and more flattened out with each day of 
starvation until on the fifth day it is practically a straight line. 
In the second experiment similar evidence was obtained. It 
was shown earlier that the rat is more active in the dark than in 
the light—and that progressively with age it becomes more and 
more active in the dark. The spontaneous activity then of 
animals that live in the open places where they are subjected 
to the daily changes of light and darkness of the day and night 
•will not be evenly distributed over the twenty-four hours, but 
will be confined for the greater part to the night hours. This will 
depend partly of course on the time the animals are fed. When 
however the food factor is eliminated by leaving the food in the 
cage all the time, then the activity should be limited even to a 
greater extent to the night hours. An animal in the open then 
is alternately active approximately for a period of twelve hours 
and then inactive for a period of twelve hours throughout its 
entire life. What happens to these alternating periods of activity 
and inactivity when the animals are placed in an environment 
of constant darkness? 
This was tried out in the following way. An animal was chosen 
for the experiment that was fairly old, 650 days, and which was 
still quite active,.and which also had been subjected to the daily 
change of light and darkness throughout its entire life. This 
animal was placed in the laboratory in complete darkness. There 
it was confined in a cage which was somewhat larger than the 
ordinary triangular cages. This cage had two small exits, one 
