to a projection of mental images
which have, owing to certain circumstances, gained a preternatural
persistence and vividness. Sometimes it is the images that have been
dwelt on with passionate longing before the disease, sometimes those
which have grown most habitual through the mode of daily
occupation,[63] and sometimes those connected with some incident at or
near the time of the commencement of the disease.

In mental disease, auditory hallucinations play a part no less
conspicuous than visual.[64] Patients frequently complain of having
their thoughts spoken to them, and it is not uncommon for them to
imagine that they are addressed by a number of voices at the same
time.[65]

These auditory hallucinations offer a good opportunity for studying the
gradual growth of centrally originating hallucinations. In the early
stages of the disease, the patient partly distinguishes his
representative from his preservative sounds. Thus, he talks of sermons
being composed to him _in his head_. He calls these "internal voices,"
or "voices of the soul." It is only when the disease gains ground and
the central irritability increases that these audible thoughts become
distinctly projected as external sounds into more or less definite
regions of the environment. And it is exceedingly curious to notice the
different directions which patients give to these sounds, referring them
now to a quarter above the head, now to a region below the floor, and so
on.[66]

_Range of Sense-Illusions._

And now let us glance back to see the path we have traversed. We set out
with an account of perfectly normal perception, and found, even here, in
the projection of our sensations of colour, sound, etc., into the
environment or to the extremities of the organism, something which, from
the point of view of physical science, easily wears the appearance of an
ingredient of illusion.

Waiving this, however, and taking the word illusion as commonly
understood, we find that it begins when the element of imagination no
longer answers to a present reality or external fact in any sense of
this expression. In its lowest stages illusion closely counterfeits
correct perception in the balance of the direct factor, sensation, and
the indirect factor, mental reproduction or imagination. The degree of
illusion increases in proportion as the imaginative element gains in
force relatively to the present impression; till, in the wild illusions
of the insane, the a