122 L. W. COLE 



received in the first fifty trials 30 such stimuli. These additional 

 stimuli seemed to inhibit completely the impulse to enter the 

 electric passageways. In the case of chicks 56-60, inclusive, 

 only the average number of pain stimuli received during the 

 first forty trials can be considered as chick 5 6 would not attempt 

 to escape after the fortieth trial. In the first forty trials chicks 

 57, 58, and 59, which succeeded, each received an average of 

 15.3 pain stimuli. Chicks 56 and 60 received an average of 

 20.5 such stimuli and failed, while chick 55, which went to the 

 wrong passageway in nine of the first ten trials, flew from the 

 door of escape with such violence that he was injured in alight- 

 ing. Those chicks failed, therefore, which made more wrong choices 

 in their early trials and consequently received more pain stimuli 

 than their successfid companions. The additional repetitions of 

 the stimulus seem to have stamped in the impression of the 

 pain and to have caused the failures rather than a native differ- 

 ence of brain plasticity as I had supposed on observing the 

 marked difference of behavior between successful and unsuc- 

 cessful chicks. Here, as elsew^here, repetition seems to be pre- 

 potent in determining memory, if these smooth brained and 

 extremely stupid creatures may be said to have memory. The 

 difference betw^een arousing extremely slow and cautious dis- 

 crimination and inhibiting all efforts to escape lies, I believe, 

 in the added number of pain stimuli given in early trials to 

 the chicks which failed. 



Records were kept of the sex of all the chicks used in the 

 experiments but they revealed no correlation between sex and 

 rate of learning. In fact the slow and rapid learners were dis- 

 tributed rather evenly between the two sexes. 



Under the conditions of the experiments, it seemed probable 

 that the heavier chicks received stronger electric stimuli than 

 the lighter ones and therefore learned the more rapidly. But 

 the weights of the chicks of several groups were recorded every 

 three days during the period of experimentation without reveal- 

 ing differences between the heavier and the lighter individuals 

 either in behavior or rate of learning. Again, there was no 

 correlation between weight and sensitiveness to the current in 

 the chicks whose threshold of sensitiveness was determined 

 before training them. 



I have shown that, for easy discrimination, increase of the inten- 



