nations of the first order,
whereas the complete hallucinations of the second order are
comparatively rare. The first I shall call rudimentary, the second
developed, hallucinations.

Rudimentary hallucinations may have either a peripheral or a central
origin. They may first of all have their starting-point in those
subjective sensations which, as we have seen, are connected with certain
processes set up in the peripheral regions of the nervous system. Or,
secondly, they may originate in a certain preternatural activity of the
sensory centres, or "sensorium," in what has been called by German
physiologists an automatic excitation of the central structures, which
activity may probably diffuse itself downwards to the peripheral regions
of the nerves. Baillarger would call hallucinations of the former class
"psycho-sensorial," those of the latter class purely "psychical,"
hallucinations.[57]

It is often a matter of great difficulty to determine which part of the
nervous system is originally concerned in these rudimentary
hallucinations. It is probable that in normal life they are most
frequently due to peripheral disturbance. And it seems reasonable to
suppose that where the hallucination remains in this initial stage of a
very incompletely interpreted visual or auditory impression, whether in
normal or abnormal life, its real physiological source is the periphery.
For the automatic excitation of the centres would pretty certainly issue
in the semblance of some definite, familiar variety of sense-impression
which, moreover, as a part of a complex state known as a percept, would
instantly present itself as a completely formed quasi-percept. In truth,
we may pretty safely argue that if it is the centre which is directly
thrown into a state of activity, it will be thrown into the usual
complex, that is to say, _perceptional_, mode of activity.

Let us now turn to hallucinations properly so called, that is to say,
completely developed quasi-percepts. These commonly assume the form of
visual or auditory hallucinations. Like the incomplete hallucinations,
they may have their starting-point either in some disturbance in the
peripheral regions of the nervous system or in the automatic activity of
the central structures: or, to use the language of Baillarger, we may
say that they are either "psycho-sensorial" or purely "psychical." A
subjective visual sensation, arising from certain conditions in the
retina and connected portion