rval of relaxation the muscle regains
its power of voluntary contraction; which is probably occasioned by a new
supply of the spirit of animation. In weaker people these contractions
cease sooner, and therefore recur more frequently, and are attended with
shorter intervals of relaxation, as exemplified in the quickness of the
pulse in fevers with debility, and in the tremors of the hands of aged or
feeble people.

After a common degree of exhaustion of the sensorial power in a muscle, it
becomes again gradually restored by the rest of the muscle; and even
accumulated in those muscles, which are most frequently used; as in those
which constitute the capillaries of the skin after having been rendered
torpid by cold. But in those muscles, which are generally obedient to
volition, as those of locomotion, though their usual quantity of sensorial
power is restored by their quiescence, or in sleep (for sleep affects these
parts of the system only), yet but little accumulation of it succeeds. And
this want of accumulation of the sensorial power in these muscles, which
are chiefly subservient to volition, explains to us one cause of their
greater tendency to paralytic affection.

It must be observed, that those parts of the system, which have been for a
time quiescent from want of stimulus, as the vessels of the skin, when
exposed to cold, acquire an accumulation of sensorial power during their
inactivity; but this does not happen at all, or in much less quantity, from
their quiescence after great expenditure of sensorial power by a previous
excessive stimulus, as after intoxication. In this case the muscles or
organs of sense gradually acquire their natural quantity of sensorial
power, as after sleep; but not an accumulation or superabundance of it. And
by frequent repetitions of exhaustion by great stimulus, these vessels
cease to acquire their whole natural quantity of sensorial power; as in the
schirrous stomach, and schirrous liver, occasioned by the great and
frequent stimulus of vinous spirit; which may properly be termed irritative
paralysis of those parts of the system.

In the same manner in common palsies the inaction of the paralytic muscle
seems not to be owing to defect of the stimulus of the will, but to
exhaustion of sensorial power. Whence it frequently follows great exertion,
as in Sect. XXXIV. 1. 7. Thus some parts of the system may cease to obey
the will, as in common paralysis; others may cease to be obedie