Throughout the first series, Sobke worked hard, but with evidently increasing dissatisfaction.  He clung persistently to his acquired tendency to choose the end boxes, and after each trial he returned less willingly to the starting point.  Up to this time his attitude toward the experimenter had been perfectly friendly, if not wholly trustful.  But when on July 21 he was brought into the apparatus for the second series, he exhibited a wholly new form of behavior, for instead of attending diligently to the open doors and devoting his energies to trying to find the right box, he instead, after gazing at them for a few seconds, turned toward the experimenter and jumped for him savagely, throwing himself against the wire netting with great force.  This was repeated a number of times during the first two or three trials, and it occurred less frequently later in the series.  Since nothing unusual had happened outside of the experiment room, the suggested explanation of this sudden change in attitude and behavior is that the monkey resented and blamed on the experimenter the difficulty which he was having in obtaining food.

From this time on until the end of my work, Sobke was always savage and both in and out of the apparatus he was constantly on the watch for an opportunity to spring upon me.  Previously, it had been possible for me to coax him into the apparatus by offering him food and to return him to his cage by walking after him.  But on and after the twenty-first of July, it was impossible for me to approach him without extreme risk of being bitten.

Doctor Hamilton when told of this behavior, reported that several times monkeys have shown resentment toward him when they were having trouble in the experiment.  I therefore feel fairly confident that I have not misinterpreted Sobke’s behavior.  When on July 22 I gave Sobke an opportunity to enter the apparatus, he refused, and it was impossible to lure him in with food.  Two hours later, having waited meantime for his breakfast, he entered readily and worked steadily and persistently through his third series of trials, but in no one of these trials did he choose correctly.  Neither on this day nor the following did he exhibit resentment while at work.  He apparently had regained his affective poise and was able to attend as formerly to the task of locating his rewards.

During these first three series, although the ratio of right to wrong choices stood 0 to 10, there occurred a marked reduction in the number of trials in which aid was necessary as well as in the total number of choices, and on July 23 correct reactions began to appear.  Improvement during the next hundred trials was steady and fairly rapid, and on July 31, a record of seven right to three wrong trials was obtained.  This was surprising to the experimenter, as well as gratifying, since he was eager to have the animal complete this problem before work should have to be discontinued.