The Mental Life of the Monkeys 197 



incorrect responses. Thus the first figure of the set, Left 

 hand, <z, presents the following record : First 10 trials, all 

 wrong ; of next 10, 7 wrong ; of next 10, 6 wrong ; of next 

 10, 7 ; of the next, 9 ; of the next, 9 ; of the next, 4 ; of 

 the next, none; of the next, 3; of the next, 2, and then 

 70 trials without an error. 



I will describe some of the experiments in detail and then 

 discuss the graphic presentation of them all. 



EXPERIMENTS WITH No. i 



Having developed in No. i the habit of coming down 

 to the bottom of his cage to get a bit of food when he saw 

 me reach out and take such a bit from my desk, I tested 

 his ability to discriminate by beginning to use now one hand, 

 now the other, feeding him only when I used the left. I 

 also used different sets of words, namely, 'I will give some 

 food' and 'They shall not have any.' It will be seen later 

 that he probably reacted only to the difference of the hands. 

 The experiment is similar to that described on pages 129 

 and 130 of Chapter II. At the beginning, it should be 

 remembered, No. i would come down whichever hand was 

 used, no matter what was said, except in the occasional 

 cases where he was so occupied with some other pursuit 

 as to be evidently inattentive. He did come to associate 

 the act of going down with the one signal and the act of 

 staying still or continuing his ordinary movements with 

 the other signal. His progress in learning to do so is best 

 seen in the curves of his errors. To the ' yes ' signal he re- 

 sponded correctly, except for the occasional lapses which I 

 just mentioned, from the start and throughout. With 

 the 'no' signal his errors were as shown in Fig. 30, a. The 

 break in the curve at no and 120 is probably not significant 



