30 ROBERT M. YERKES 



injury. He was greatly frightened and expressed the emotion 

 most vigorously. His behavior strongly suggested a super- 

 stitious dread of some unseen danger. It may be that the in- 

 stinctive fear of snakes, so strong in monkeys, was partly respon- 

 sible for his response. 



The first result of this accident was that more than two weeks 

 were lost, for it was impossible, during the next few days, to 

 induce the animal to enter any of the multiple-choice boxes 

 voluntarily. From May 14 to May 24, I labored daily to over- 

 come his newly acquired fear. The usual procedure was to 

 coax him through one box after another by standing at the exit 

 door with some tempting morsel of food. After several days 

 of this treatment, he again trusted himself to the boxes, although 

 very circumspectly and only when both entrance and exit 

 doors were raised. Not until May 24 was it possible to resume 

 regular experimentation, and on that day it was found necessary 

 to indicate the right box by raising the exit door slightly and 

 then immediately lowering it. Trials in which this form of aid 

 was given are indicated in table 2 by a star following the last 

 choice. 



Gradually, Skirrl regained his confidence in the apparatus 

 and began to work more naturally. For a long time he would 

 not stand punishment, and it was necessary for the experimenter 

 to be very careful in locking the doors, since the sound of the 

 bar sliding beneath the floor often frightened and caused him to 

 qtiit work. Day after day the tendency to peer through the 

 'holes in the floor at the entrance to the boxes rendered it clear 

 that the animal feared some danger from beneath the floor. 

 This behavior was so persistent that much time was wasted in 

 the experiments. 



On the last day of May, punishment by confinement for ten 

 seconds in wrong boxes was introduced, but since this tended 

 to discourage the monkey, there was substituted for it on June 

 1 the punishment of forcing him to work his way out of each 

 wrong box by raising the entrance door which had been closed 

 behind him. This he could fairly readily do, and his stay in 

 a box rarely measured more than ten seconds. 



As a variation in "the mode of procedure, confinement for 

 thirty seconds was tried on June 5, but it worked unsatisfactorily 

 and had to be abandoned. During this series, the animal was 



