rner the height of a woman,
with a gown like a woman's. You approach it, speak to it and get no
reply, and you find you can walk directly through it, for it is a
shadow. Perhaps you were frightened. Perhaps you imagined she was a
thief. Your first judgment was wrong and you correct it. The insane
person, however, has defective mental processes. He cannot group
together his perceptions and form proper conceptions. His imagination
runs riot. His emotions of fear or anger are not easily limited. He
has to some extent lost the control over his mental actions that you
and other people possess if your brains are normal. The insane man
will insist that there is a woman there, and not a shadow, and to his
mind it is not absurd to walk directly through this person. He cannot
correct the wrong idea. Such a wrongly interpreted sense perception is
called an illusion. Another example of illusion is the mistaking the
whistle of a locomotive for the shriek of a pursuing assassin.

_What Hallucinations Are_

The insane man may also suffer from hallucinations. A hallucination is
a false perception arising without external sensory experience. In a
hallucination of sight, the disease in the brain causes irritation to
be carried to the sight-centers of the brain, with a result that is
similar to the impression carried to the same centers by the optic
nerves when light is reflected into the eyes from some object. An
insane man may be deluded with the belief that he sees a face against
the wall where there is nothing at all. When the air is pure and sweet
and no odor is discoverable, he may smell feathers burning, and thus
reveal his hallucination of smell.

_Delusions Common to Insanity_

The insane man may have wrong ideas without logical reason for them.
Thus, an insane man may declare that a beautiful actress is in love
with him, when there is absolutely no foundation for such an idea. Or,
he may believe that he can lift 500 pounds and run faster than a
locomotive can go, while in reality he is so feeble as scarcely to be
able to walk, and unable to dress himself. Such ideas are delusions.
Sane people may be mistaken; they may have hallucinations, illusions
and delusions; but they abandon their mistaken notions and correct
their judgment at once, on being shown their errors. Sane people see
the force of logical argument, and act upon it, abandoning all
irrational ideas. The insane person, on the other hand, cannot see the
force