148 INTELLIGENT BEHAVIOUR 
simple as it is, possesses several other marked advantages besides 
those which accompany experiment of any sort. It was merely to 
put animals when hungry in enclosures from which they could escape 
by some simple act, such as pulling at a loop of cord, pressing a lever, 
or stepping on a platform. The animal was put in the enclosure, food 
was left outside in sight, and his actions observed. Besides recording 
his general behaviour, special notice was taken of how he succeeded 
in doing the necessary act (in case he did succeed), ayd a record 
was kept of the time that he was in the box before performing the 
successful pull, or clawing, or bite. This was repeated until the 
animal had formed a perfect association between the sense-impression 
of the interior of that box and the impulse leading to the successful 
movement. When the association was thus perfect, the time taken 
to escape was, of course, practically constant and very short, 
Fie 22.—Cage used in Professor Thorndike’s experiments. 
“Tf, on the other hand, after a certain time the animal did not 
succeed, he was taken out, but not fed. If, after a sufficient number 
of trials, he failed to get out, the case was recorded as one of complete 
failure. Enough different sorts of methods of escape were tried to 
make it fairly sure that association in general, not association of a 
particular sort of impulse, was being studied. Enough animals were 
taken with each box or pen to make it sure that the results were not 
due to individual peculiarities. None of the animals used had any 
previous acquaintance with any of the mechanical contrivances by 
which the doors were opened, So far as possible the animals were 
kept in a uniform state of hunger, which was practically utter hunger.” 
