peripheral sense-organ, and
to an external force acting on this.

The most striking instances of these errors of localization are found in
abnormal circumstances. It is well known that a man who has lost a leg
refers all sensations arising from a stimulation of the truncated fibres
to his lost foot, and in some cases has even to convince himself of the
non-existence of his lost member by sight or touch. Patients often
describe these experiences in very odd language. "If," says one of Dr.
Weir Mitchell's patients, "I should say I am more sure of the leg which
ain't than the one which air, I guess I should be about correct."[30]

There is good reason for supposing that this source of error plays a
prominent part in the illusions of the insane. Diseased centres may be
accompanied by disordered peripheral structures, and so subjective
sensation may frequently be the starting-point of the wildest illusions.
Thus, a patient's horror of poison may have its first origin in some
subjective gustatory sensation. Similarly, subjective tactual sensations
may give rise to gross illusions, as when a patient "feels" his body
attacked by foul and destructive creatures.

It may be well to remark that this mistaken interpretation of the seat
or origin of subjective sensation is closely related to hallucination.
In so far as the error involves the ascription of the sensation to a
force external to the sense-organ, this part of the mental process must,
when there is no such force present, be viewed as hallucinatory. Thus,
the feeling of something creeping over the skin is an hallucination in
the sense that it implies the idea of an object external to the skin.
Similarly, the projection of an ocular impression due to retinal
disturbance into the external field of vision, may rightly be named an
hallucination. But the case is not always so clear as this. Thus, for
example, when a gustatory sensation is the result of an altered
condition of the saliva, it may be said that the error is as much an
illusion as an hallucination.[31]

In a wide sense, again, all errors connected with those subjective
sensations which arise from a stimulation of the peripheral regions of
the nerve may be called illusions rather than hallucinations. Or, if
they must be called hallucinations, they may be distinguished as
"peripheral" from those "central" hallucinations which arise through an
internal automatic excitation of the sensory centre. It is plain from
th