The Mental Life of the Monkeys 203 
‘no’ signal the act of holding the food six inches above the 
box instead of a quarter or a half an inch. The progress is 
shown in Fig. 31, Z and £,. I then tried taking the food 
from a saucer off the front of the box for the ‘yes’ signal and 
from a small box at the back for the ‘no’ signal. ‘Yes’ was 
perfect from the start (10 trials given). ‘No’ was right 
once, then wrong once, then right for the remaining eight. 
EXPERIMENTS WITH No. 3 
No. 3 was kept in a cage not half so big as those of 1 and 2. 
Perhaps because of the hindrance this fact offered to forming 
the habit of reacting in some definite way to ‘yes’ signals, 
perhaps because of the fact that I did not try hand move- 
ments as signals, there was no successful discrimination by 
No. 3 of the yellow from the black diamond or of a card with 
YES from a card with a circle onit. I tried climbing up to 
a particular spot as the response to the ‘ yes’ signal and stay- 
ing still as the response to the ‘no’ signal. I also tried in- 
stead of the latter a different act, in which case the animal 
was fed after both signals but in different places. In the 
latter case No. 3 made some progress, but for practical 
reasons I postponed experiments with him. Circumstances 
have made it necessary to postpone such experiments in- 
definitely. 
PERMANENCE OF THE ABILITY TO DISCRIMINATE 
No. 1 and No. 2 were tried again after intervals of 33 to 48 
days. The results of these trials are shown in Fig. 32. Here 
every millimeter along the base line represents one trial with 
the ‘no’ signal (the ‘yes’ signals were practically perfect), 
and failure is represented by a column 10 mm. high while 
