MENTAL LIFE OF MONKEYS AND APES 29 



these fifty open doors may be defined as right ones, the expected 

 ratio of right to wrong first choices in the absence of previous 

 training is 1 to 4. The actual ratio for the first series given in 

 problem 2 is 1 to 8, while in the second series it is to 10. 



On the morning of May 13, work was interrupted in the ninth 

 trial by what seemed at the moment a peculiarly unfortunate 

 accident, but in the light of later developments, an incident most 

 fruitful of valuable results. 



Skirrl, in trial 9, directly entered box 1. Since this was not 

 the right box, he was punished by being confined in it for ten 

 seconds. While in the box he howled and when the entrance 

 door was raised for him to retrace his steps, he came out with 

 a rush, showing extreme excitement and either rage or fear, I 

 could not be sure which. At intervals he. uttered loud cries, 

 which I am now able to identify as cries of alarm. Repeatedly 

 he went to the open door of box 1 and peered in, or peered down 

 through the hole in the floor which received the staple on the 

 door. He refused to enter any one of the open boxes and con- 

 tinued, at intervals of every half minute or so, his cries. For 

 thirty minutes I waited, hoping to be able to induce him to 

 complete the series of trials, but in vain. Although it was 

 obvious that he was eager to escape from the apparatus, he 

 would not enter any of the boxes even when the exit doors were 

 raised. Instead, he gnawed at the door (12 in fig. 17) to the- 

 alleyway D and attempted to force his way through, instead of 

 taking the easy and clear route to the alleys, through one of the 

 boxes. His behavior was most surprising and puzzling. Finally, 

 I gave up the attempt to complete the series and returned him 

 to his cage by way of the entrance door to the response-compart- 

 ment E. 



I then entered the apparatus to seek some explanation of the 

 animal's behavior, and my search was rewarded by the finding of 

 two sharp pointed nails which protruded for an inch or more 

 in the middle of the floor of box L My assistant, who had been 

 charged with the task of installing the locks for the several doors, 

 had used nails instead of screws for attaching staples underneath 

 the floor and had neglected to clinch the nails. Skirrl, in the 

 dim light of the box, doubtless stepped upon one of the nails 

 and inflicted a painful, although not serious, injury upon him- 

 self. It was impossible for him to see clearly the source of his 



