THE DISPLAY OF ENERGY 387 



fruit, but finding this did not work, approached the l)ox and gave it 

 a push toward the food, looking meanwhile at the banana. Dr. Kohler 

 then made the goal more interesting by adding a piece of an orange. 

 After a brief pause, Koko went back to the box, pushed it vigorously 

 until it was directly under the fruit, then climbed up on the box and 

 got his reward. The same problem was given Chica, another ape. 

 This was solved successfully several times until one day her com- 

 panion Teserca was resting on the box. While this was happening 

 Chica jumped in vain for the fruit, finally giving up in despair though 

 not attempting to use the box. Presently Teserca got down from the 

 box. At once Chica dragged the box under the fruit, climbed up, and 

 got her reward. Evidently the box on which Teserca was resting 

 meant to Chica something to "rest on" and not until the box alone 

 was seen with the fruit did it mean "something with which to get the 

 fruit." This simple problem was made more difficult by raising the 

 fruit to a greater height and adding three boxes which had to be piled 

 one on the other before the fruit could be reached. Such a problem 

 was solved by Sultan, an ape of unusual intelligence. Yerkes ^ made 

 a similar experiment with the gorilla Kongo in which three boxes had 

 to be stacked in order to reach food. K year after the successful 

 solution of this problem, the gorilla was furnished with a similar 

 problem, the three boxes being of slightly different size. The problem 

 was solved immediately, thus showing evidences of memory. 



The most difficult problem of all was solved by Dr. Kohler's ape 

 Sultan. Food was placed just out of reach outside the bars of the 

 cage and Sultan was given two sticks, one of which would fit into the 

 other. Sultan made a good many useless and rather stupid move- 

 ments before he finally "got the idea" with the aid of the experi- 

 menter, who had put one finger into the hole of one stick while holding 

 the stick close to the animal. Sultan, after playing with the sticks, 

 got the two sticks in a straight line and at once pushed the thinner one 

 into the opening of the thicker one. Once having made a long pole 

 with the two sticks, he immediately drew the banana into the cage 

 and was so well pleased with his performance that, without waiting to 

 eat the fruit, he proceeded by means of the double stick to pull in 

 other pieces of fruit. The second time the experiment was tried 

 Sultan almost immediately stuck one stick into the other and got 

 the fruit. In a later experiment he was given two similar sticks the 

 smaller of which was a little too large to go into the hole of the latter. 



1 Yerkes, R. M., " The Mind of the Gorilla." Comp. Psy. Mon., 1928, Vol. V, No. 2. 



