THE PROBLEM OF LEARNING 1 87 



All that was necessary usually was to remove the 

 wooden cover from the entrance tube (Fig. 55), 

 and the worm would begin to crawl forward. As 

 it entered the exit tube, it found relief from the 

 annoying stimulus of the bright light. 



Suspended hairy caterpillars swinging just in 

 front of the nose of a hungry frog furnished a 

 tempting satisfaction to the hunger urge. But 

 the hairs evidently irritated the tongue and the 

 reactions to this stimulus after a few trials made 

 the frog prefer going hungry to trying to eat the 

 hairy caterpillars. The earthworm was punished 

 by exposing its body to a bright light and the frog 

 was punished by tempting it to eat something that 

 would at least be unpleasant if not actually 

 painful. 



The hungry racoons were allowed a drink of 

 milk or a reward of sugar for successfully 

 executing their "lesson." After they had eaten, 

 their time in performing an experiment was slower 

 "due to approaching satiety" writes Cole. When 

 the animals were too hungry, they were so eager 

 to secure food that it invariably prolonged the 

 time of escape from the experiment box. The 

 racoons were rewarded by food for their success. 



How natural it all sounds to read "There ap- 

 pear to be 'good' and 'bad' days for the earth- 

 worm. When it does what the teacher (experi- 

 menter) wishes, the worm has a good day, when 



