8 
CURT P. RICHTER 
periodic. The interval between the periods in the adult is how¬ 
ever considerably longer than in the infant, usually about one and 
one half to two hours. 
Experiments are now being carried on by Mr. Ging Wang in 
the Hopkins Laboratory on the activity of the newly born rat 
before it has had any contacts with the environment, before it has . 
ever nursed, in order to establish whether the periods are present 
at birth or dependent on later environmental influences. The 
results obtained so far seem to indicate that the activity at 
birth is continuous and uninterrupted by regular intervals of 
quiescence. 
The probable relation of these activity periods to certain en¬ 
vironmental influences (the hunger reactions) as well as to the 
rest of the behavior of the organism will be discussed in detail 
in the last two chapters. 
II. RELATION OF SPONTANEOUS ACTIVITY TO FOOD 
It was found at the beginning of this work that the spontaneous 
activity of the rat is very intimately related to the food habits 
of the animal. This relation will now be examined in some detail 
from the following points of view; (1) what happens to spon¬ 
taneous activity (simply the amount of activity, disregarding for 
the moment the periods of activity) when the animal is deprived 
of all food, when it is starved; (2) how spontaneous activity is 
distributed over the day with relation to the last feeding periods 
and also with relation to the time of next feeding (anticipation of 
feeding). 
The general conditions were maintained practically the same as 
above. The laboratory was kept constantly either illuminated 
or darkened over longer periods of time. The temperature was 
kept constant at 23°C. All noises and odors were eliminated. 
The animals were fed punctually at a certain time each day 
(in most of the experiments at twelve noon). Food was placed 
in each cage in specially arranged receptacles and left there for 
twenty-five minutes. Then all of the remaining food was care¬ 
fully removed. This method of feeding gave each animal plenty 
of time to satisfy its hunger under fairly natural conditions. It 
