MENTAL LIFE OF MONKEYS AND APES 81 



wholly different method. Even over night a new method might 

 develop. In the monkeys, although there was occasionally 

 something comparable with this, it was by no means so evident. 



After two hundred and fifty trials on problem 2 had been given 

 Julius, it seemed desirable to introduce a radical change in method 

 in order to stimulate him to maximal effort. It was therefore 

 decided to force him to make a round trip through the apparatus 

 in connection with each choice, and to let this forced labor serve, 

 in the place of confinement, as punishment for mistakes. This 

 new method yielded peculiar and characteristic results. They 

 differ from those previously obtained largely because of the 

 orang utan's remarkably strong tendency to reenter the box 

 through which he had just passed. This occurred so persist- 

 ently, as may be seen in table 9 (June 17, second series, June 

 18, etc.), that a further modification of method was introduced 

 in that after the same wrong box had been entered five times 

 in succession, the experimenter on the next choice of the box 

 confined the animal for a stated interval, say sixty seconds, in 

 it, and then allowed it to escape by way of the exit door and 

 choose repeatedly until it finally located the right box. Were 

 it not for this particular feature of the method, the number of 

 choices recorded after June 17 would unquestionably be very 

 much greater than the table indicates. 



The new method proved a severe test of the orang utan's 

 patience and perseverance, for he had to work much harder 

 than formerly for his reward, and often became much fatigued 

 before completing the regular series of ten trials. Early in the 

 use of this method, he developed the habit of rolling around 

 from exit door to starting point by a series of somersaults. When 

 especially discouraged he would often bump his head against 

 the floor so hard that I could hear the dull thud. As has been 

 noted, I found it desirable to vary the procedure repeatedly. 

 It proved especially interesting to give one series per day with 

 the round trip as punishment and another series with confine- 

 ment as punishment. 



Day after day, as the experiment progressed, slight or great 

 fluctuations of the ratios of right to wrong choices appeared, 

 but without consistent improvement. There was, to be sure, 

 as the last column of table 9 shows, a radical improvement 

 during the first six hundred and fifty trials, for the number of 



