as those who live near a waterfall, or a
smith's forge, after a time, cease to hear them. And in those
infectious diseases which are attended with fever, as the small-pox
and measles, violent motions of the system are excited, which at
length cease, and cannot again be produced by application of the same
stimulating material; as when those are inoculated for the small-pox,
who have before undergone that malady. Hence the repetition, which
occasions animal actions for a time to be performed with greater
energy, occasions them at length to become feeble, or to cease
entirely.

To explain this difficult problem we must more minutely consider the
catenations of animal motions, as described in Zoonomia, Vol. I. Sect.
XVII. The vital motions, as suppose of the heart and arterial system,
commence from the irritation occasioned by the stimulus of the blood,
and then have this irritation assisted by the power of association; at
the same time an agreeable sensation is produced by the due actions of
the fibres, as in the secretions of the glands, which constitutes the
pleasure of existence; this agreeable sensation is intermixed between
every link of this diurnal chain of actions, and contributes to
produce it by what is termed animal causation. But there is also a
degree of the power of volition excited in consequence of this vital
pleasure, which is also intermixed between the links of the chain of
fibrous actions; and thus also contributes to its uniform easy and
perpetual production.

The effects of surprise and novelty must now be considered by the
patient reader, as they affect the catenations of action; and, I hope,
the curiosity of the subject will excuse the prolixity of this account
of it. When any violent stimulus breaks the passing current or
catenation of our ideas, surprise is produced, which is accompanied
with pain or pleasure, and consequent volition to examine the object
of it, as explained in Zoonomia, Vol. I. Sect. XVIII. 17, and which
never affects us in sleep. In our waking hours whenever an idea of
imagination occurs, which is incongruous to our former experience, we
feel another kind of surprise, and instantly dissever the train of
imagination by the power of volition, and compare the incongruous idea
with our previous knowledge of nature, and reject it by an act of
reasoning, of which we are unconscious, termed in Zoonomia, "Intuitive
Analogy," Vol. I Sect. XVII. 7.

The novelty of any idea may be con