gradual descent of the curve indicates the gradual decrease in
time required, and thus pictures the progress of the animals in
learning the maze.]

The combination of steps into larger units is shown also by certain
variations of the experiment. It is known that the rat makes little
use of the sense of sight in learning the maze, guiding himself mostly
by the muscle sense. Now if the maze, after being well learned, is
altered by shortening one of the straight passages, the rat runs full
tilt against the new end of the passage, showing clearly that he was
proceeding, not step by step, but by _runs_ of some length. Another
variation of the experiment is to place a rat that has learned a maze
down in the midst of it, instead of at {308} the usual starting point.
At first he is lost, and begins exploring, but, hitting on a section
of the right path, he gets his cue from the "feel" of it, and races
off at full speed to the food box. Now his cue could not have been any
single step or turn, for these would all be too much alike; his cue
must have been a familiar _sequence_ of movements, and that sequence
functions as a unit in calling out the rest of the habitual movement.

[Illustration: Fig. 49.--(From Watson.) A puzzle box. The animal must
here reach his paw out between the bars and raise the latch, _L_. A
spring then gently opens the door.]

In short, the rat learns the path by _elimination_ of false reactions
and by _combination_ of single steps and turns into larger
reaction-units.

The puzzle-box experiment.

Place a hungry young cat in a strange cage, with a bit of fish lying
just outside, and you are sure to get action. The cat extends his paw
between the slats but cannot reach the fish; he pushes his nose
between the slats but cannot get through; he bites the slats, claws at
anything small, shakes anything loose, and tries every part of the
cage. Coming to the button that fastens {309} the door, he attacks
that also, and sooner or later turns the button, gets out, and eats
the fish. The experimenter, having noted the time occupied in this
first trial, replaces the cat, still hungry, in the cage, and another
bit of fish outside. Same business, but perhaps somewhat quicker
escape. More trials, perhaps on a series of days, give gradually
decreasing times of escape. The useless reactions are gradually
eliminated, till finally the cat, on being placed in the cage, goes
instantly to the door, turns the b