62 THE SPEECH OF MONKEYS. 



nized it as the same sentence or combination of 

 sounds, and gave it the same reply each time. 

 I concluded that he had been taught to associate 

 this sign with some sound — for instance, "bed" 

 or "go;" but since that time I have found the 

 sign to be almost universal with this species of 

 monkey, and they use the sign to express ne- 

 gation. I have seen them use the sign in re- 

 sponse to certain things which were wholly new 

 to them, but where the idea was clear to them 

 and they desired to express dissent. The fact 

 that this sign is common to both man and sim- 

 ian I regard as more than a mere coincidence, 

 and I believe that in this sign I have found the 

 psycho-physical basis of expression. 



I have made scores of experiments on this 

 subject, and I find this sign a fixed factor of ex- 

 pression. In one case where I tried to induce a 

 monkey to allow me to take him into my hands 

 from the hand of his master, he would shake his 

 head each time, and make a peculiar sound some- 

 what like a suppressed cluck. I would try to 

 coax him with nuts, in response to which he 

 would make the same sound and sign each time, 

 and his actions showed beyond all controversy 

 his intention. I had taught a monkey to drink 



