84 ROBERT M. YERKES 



to compel the animal's attention to the problem and to lead him 

 to work without discouragement. There were, it is true, days 

 on which it seemed practically certain that the problem would 

 be solved, but as it turned out, Julius never succeeded in choos- 

 ing correctly throughout a series of ten trials. 



As a last resort, in order to make perfectly sure that the orang 

 utan was doing his best, I decided to introduce corporal punish- 

 ment in a mild form. For this purpose, I placed my assistant 

 in charge of the apparatus and the series of trials, and stationed 

 myself in one corner of the reaction-chamber with a whip in 

 my hand. Whenever Julius entered a wrong box, I approached 

 him with the whip and struck at him, being careful not to injure 

 him and rarely striking him at all, for the threat was more effec- 

 tive than a blow. He was extremely afraid of the whip and 

 would begin to whine and attempt to get out of the way as soon 

 as he saw it. 



This method was introduced on August 10, but no improve- 

 ment resulted, and in the end there was no reason to consider 

 it more satisfactory than the other procedures. I am now 

 wholly convinced that Julius did his best to choose correctly 

 in the majority of the numerous series which were given him in 

 connection with problem 2. 



From trials 1001 to 1100, a radical departure from the pre- 

 vious methods was introduced in that the right box was indi- 

 cated to the animal by the slight and momentary raising of its 

 exit door. Of course no records of the choices for this group 

 ,of one hundred trials appear in table 9, for the simple reason 

 that the animal inevitably and immediately entered the right 

 box. It was thought that this method might serve to break 

 up the previously developed tendencies toward inadequate 

 forms of response and so encourage the animal that he would 

 later solve the problem when given opportunity to select the 

 right box without aid from the experimenter. But as a matter 

 of fact, while the ratio of right to wrong first choices was 1 to 

 .67 in the series preceding this change of method, it was 1 to 1.50 

 in the first series following its use. There is no satisfactory 

 evidence that Julius profited by this experience, though as a 

 matter of fact he did succeed in making his best daily record, 

 eight right to two wrong choices, on August 4, after 1190 trials. 



The curve of learning for this problem has been plotted and 



