imagination, which compose our dreams. 3. When in the cold fit of an
intermittent fever some parts of the system have for a time continued
torpid, and have thus expended less than their usual expenditure of
sensorial power; a hot fit succeeds, with violent action of those vessels,
which had previously been quiescent. All these are explained from an
accumulation of sensorial power during the inactivity of some part of the
system.

Besides the very great quantity of sensorial power perpetually produced and
expended in moving the arterial, venous, and glandular systems, with the
various organs or digestion, as described in Section XXXII. 3. 2. there is
also a constant expenditure of it by the action of our locomotive muscles
and organs of sense. Thus the thickness of the optic nerves, where they
enter the eye, and the great expansion of the nerves of touch beneath the
whole of the cuticle, evince the great consumption of sensorial power by
these senses. And our perpetual muscular actions in the common offices of
life, and in constantly preserving the perpendicularity of our bodies
during the day, evince a considerable expenditure of the spirit of
animation by our locomotive muscles. It follows, that if the exertion of
these organs of sense and muscles be for a while intermitted, that some
quantity of sensorial power must be accumulated, and a propensity to
activity of some kind ensue from the increased excitability of the system.
Whence proceeds the irksomeness of a continued attitude, and of an indolent
life.

However small this hourly accumulation of the spirit of animation may be,
it produces a propensity to some kind of action; but it nevertheless
requires either desire or aversion, either pleasure or pain, or some
external stimulus, or a previous link of association, to excite the system
into activity; thus it frequently happens, when the mind and body are so
unemployed as not to possess any of the three first kinds of stimuli, that
the last takes place, and consumes the small but perpetual accumulation of
sensorial power. Whence some indolent people repeat the same verse for
hours together, or hum the same tune. Thus the poet:

Onward he trudged, not knowing what he sought,
And whistled, as he went, for want of thought.

II. The repetitions of motions may be at first produced either by volition,
or by sensation, or by irritation, but they soon become easier to perform
than any other kinds of action, because th