22 ROBERT M. YERKES 



to observe the animal's movements, and when on April 12 Skirrl 

 was again introduced to it for further preliminary training, he 

 utterly refused to enter the boxes, giving every indication of 

 extreme fear of the white floors and even of the sides of the 

 boxes. Finally, the attempts to induce him to enter the boxes 

 had to be given up, and he was returned to his cage unfed. The 

 following day I was equally unsuccessful in either driving or 

 tempting him with food into the apparatus. But on April 14 

 he was so hungry that he was finally lured in by the use of food. 

 He cautiously approached the boxes and attempted to climb 

 through on the sides instead of walking on the floor. It was 

 perfectly evident that he had an instinctive or an acquired fear 

 of the white surfaces. As the matter was of prime importance 

 for the success of my work, I inquired of Doctor Hamilton, and 

 of the men in charge of the cages, for any incident which might 

 accotmt for this peculiar behavior, and I learned that some three 

 months earlier, while the animal cages were being whitewashed, 

 Skirrl had jumped at one of the laborers who was applying a 

 brush to the framework of one of the cages and had shaken 

 some lime into his eyes. He was greatly frightened and enraged. 

 Evidently he experienced extreme discomfort, if not acute pain, 

 and there resulted an association with whiteness which was , 

 quite sufficient to cause him to avoid the freshly painted 

 apparatus. 



Having obtained an adequate explanation of this monkey's 

 peculiar behavior, I proceeded with my efforts to induce him to 

 work smoothly and rapidly, and on April 15, by covering the 

 floor with sawdust, I so diminished the influence of the white- 

 ness as to render the preliminary training fairly satisfactory. 

 At the end of two more days everything was going so well that 

 it seemed desirable to begin the regular experiment. 



On the morning of April 19, Skirrl was introduced to the 

 apparatus and given his first series of ten trials on problem 1. 

 This problem demanded the selection of the first door at the 

 left in any group of open doors. The procedure was as pre- 

 viously described in that the experimenter raised the entrance 

 doors of a certain group of boxes, admitted the animal to the 

 reaction-chamber, punished incorrect choices by confining the 

 animal for thirty seconds, and rewarded correct choices by rais- 

 ing the exit door and thus permitting escape and the obtaining 



