great a quantity of volition.

After every exertion of our fibres a temporary paralysis succeeds, whence
the intervals of all muscular contractions, as mentioned in No. 3 and 4 of
this Section; the immediate cause of these more permanent kinds of
paralysis is probably owing in the same manner to the too great exhaustion
of the spirit of animation in the affected part; so that a stronger
stimulus is required, or one of a different kind from that, which
occasioned those too violent contractions, to again excite the affected
organ into activity; and if a stronger stimulus could be applied, it must
again induce paralysis.

For these powerful stimuli excite pain at the same time, that they produce
irritation; and this pain not only excites fibrous motions by its stimulus,
but it also produces volition; and thus all these stimuli acting at the
same time, and sometimes with the addition of their associations, produce
so great exertion as to expend the whole of the sensorial power in the
affected fibres.

V. _Of Stimulus less than natural._

1. A quantity of stimulus less than natural, producing a decreased exertion
of sensorial power, occasions an accumulation of the general quantity of
it. This circumstance is observable in the hemiplagia, in which the
patients are perpetually moving the muscles, which are unaffected. On this
account we awake with greater vigour after sleep, because during so many
hours, the great usual expenditure of sensorial power in the performance of
voluntary actions, and in the exertions of our organs of sense, in
consequence of the irritations occasioned by external objects had been
suspended, and a consequent accumulation had taken place.

In like manner the exertion of the sensorial power less than natural in one
part of the system, is liable to produce an increase of the exertion of it
in some other part. Thus by the action of vomiting, in which the natural
exertion of the motions of the stomach are destroyed or diminished, an
increased absorption of the pulmonary and cellular lymphatics is produced,
as is known by the increased absorption of the fluid deposited in them in
dropsical cases. But these partial quiescences of sensorial power are also
sometimes attended with other partial quiescences, which sympathize with
them, as cold and pale extremities from hunger. These therefore are to be
ascribed to the associations of sympathy explained in Sect. XXXV. and not
to the general accumulation of