1898] ANIMAL INTELLIGENCE 267 
will probably claw the string or loop or button so as to open the door. And 
gradually all the other non-successful impulses will be stamped out and the 
particular impulse leading to the successful act will be stamped in by the result- 
ing pleasure, until, after many trials, the cat will, when put in the box, 
immediately claw the button or loop in adefinite way. . . . Starting, then, with 
its store of instinctive impulses, the cat hits upon the successful movement, and 
gradually associates it with the sense-impression of the interior of the box until 
-the connection is perfect, so that it performs the act as soon as confronted with 
the sense-impression. . . . Previous experience makes a difference in the quickness 
with which the cat forms the associations. After getting out of six or eight 
boxes by different sorts of acts the cat’s general tendency to claw at loose objects 
within the box is strengthened and its tendency to squeeze through holes and 
bite bars is weakened ; accordingly it will learn associations along the general 
line of the old more quickly. Associations between licking or scratching and 
escape are similarly established, and there was a noticeable tendency to diminish the 
act until it becomes a mere vestige of a lick or scratch. After the cat gets so that 
it performs the act soon after being put in, it begins to do it less and less 
vigorously. The licking degenerates into a mere quick turn of the head with one 
or two motions up and down with tongue extended. Instead of a hearty scratch, 
the cat waves its paw up and down rapidly for an instant.” 
These experiments confirm the conclusion to which I have been 
led by my own observations that the method of animal intelligence 
is to profit by chance success and to build upon fortunate items of 
experience casually hit upon and not foreseen. I need not here 
repeat cases already published, such as the opening of a gate on the 
part of my fox terrier by lifting the latch, a trick he certainly learnt 
by this method; but I may very briefly describe one or two further 
observations not yet recorded. I have watched my dog’s behaviour 
when a solid indiarubber ball was thrown towards a wall standing 
at right angles to its course. At first he followed it right up to the 
wall and then back as it rebounded. So long as it travelled with 
such velocity as to be only just ahead of him he pursued the same 
course. But when it was thrown more violently, so as to meet, him 
on the rebound as he ran towards the wall, he learnt that he was 
thus able to seize it as it came towards him. And, profiting by the 
incidental experience thus gained, he acquired the habit—though 
for long with some uncertainty of reaction—by slowing off when the 
object of his pursuit reached the wall so as to wait its rebound. 
Again, when the ball was thrown so as to rebound at a wide angle 
from a surface, at first,—when the velocity was such as to keep it 
just ahead of him,—he followed its course. But when the velocity 
was increased he learnt to take a short cut along the third side of a 
triangle, so as to catch the object at some distance from the wall. 
A third series of experiments were made where an angle was 
formed by the meeting of two surfaces at right angles. One side of 
the angle, the left, was dealt with for a day or two. At first the 
ball was directly followed. Then a short cut was taken to meet its 
deflected course. On the fourth day this method was well estab- 
