BEHAVIORISTIC STUDY OF THE RAT 
53 
during different parts of the contraction period. If the animal 
happens to find the teats during the part of its activity which is 
caused by the milder contractions it will nurse just as at any 
other time; but the changes that take place within the organism 
when milk or food is taken during this part of the contraction 
period are so slight that no definite associations can be built up 
between them and the sucking at the teats and the taking of 
food. When however, the animal happens to find the teats 
during the period of main stomach contractions things are quite 
different. Now the changes resulting from the taking of the milk 
are strong enough to become associated with the stomach activity, 
and form the basis of the cycle: stomach contractions—going- 
out to teats—nursing—inhibition of contractions—relief. There 
are further reasons why these reactions become associated more 
readily during the period of strong contraction: first the fact that 
during the period of strong contractions the animals are more ac¬ 
tive and vigorous than during the period of milder contractions; 
secondly chances and the frequency on a simple trial and error 
basis of finding the teats during the former period will be much 
greater. Then also for the reason that milder contractions are 
more easily stopped the animal will nurse for a shorter time during 
this part of the period. Besides these simple factors of frequency, 
duration, recency of stimulation, there will be other rather more 
situational factors which will help to build up the association; 
such things as odor of the teats, the warmth of the mother’s 
body, etc., and, of course, the encouraging reaction of the mother 
herself. 
Gradually the main stomach contractions and the sucking of 
the teats become permanently associated and there is less tend¬ 
ency for the animal to suck at the teats during the period of weaker 
contractions. The onset of the main stomach contractions comes 
to serve as a signal for the taking of food and the animal no longer 
hesitates but goes directly to the teats. Later on, after the 
animals are weaned, as was the case in the double cage, the onset 
of the main contractions served as a signal for the animal to go 
to the food box. 
