The Mental Life of the Monkeys 197 
incorrect responses. Thus the first figure of the set, Left 
hand, a, 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, g; 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. 1 
Having developed in No. 1 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. 1 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 110 and 120 is probably not significant 
