some of the extremities of it. This appears, first, because our desires and
aversions always terminate in recollecting and comparing our ideas, or in
exerting our muscles; which are the motions of the extremities of the
sensorium. And, secondly, because desire or aversion begins, and frequently
continues for a time in the central parts of the sensorium, before it is
peculiarly exerted at the extremities of it; for we sometimes feel desire
or aversion without immediately knowing their objects, and in consequence
without immediately exerting any of our muscular or sensual motions to
attain them: as in the beginning of the passion of love, and perhaps of
hunger, or in the ennui of indolent people.

Though sensation and volition begin or terminate at the extremities or
central parts of the sensorium, yet the whole of it is frequently
influenced by the exertion of these faculties, as appears from their
effects on the external habit: for the whole skin is reddened by shame, and
an universal trembling is produced by fear: and every muscle of the body is
agitated in angry people by the desire of revenge.

There is another very curious circumstance, which shews that sensation and
volition are movements of the sensorium in contrary directions; that is,
that volition begins at the central parts of it, and proceeds to the
extremities; and that sensation begins at the extremities, and proceeds to
the central parts: I mean that these two sensorial faculties cannot be
strongly exerted at the same time; for when we exert our volition strongly,
we do not attend to pleasure or pain; and conversely, when we are strongly
affected with the sensation of pleasure or pain, we use no volition. As
will be further explained in Section XVIII. on sleep, and Section XXXIV. on
volition.

2. All our emotions and passions seem to arise out of the exertions of