III. 1. _Other muscular motions are associated with the sensitive
ones._ 2. _And other sensual motions._

I. 1. Many of the motions of our muscles, that are excited into action by
irritation, are at the same time accompanied with painful or pleasurable
sensations; and at length become by habit causable by the sensations. Thus
the motions of the sphincters of the bladder and anus were originally
excited into action by irritation; for young children give no attention to
these evacuations; but as soon as they become sensible of the inconvenience
of obeying these irritations, they suffer the water or excrement to
accumulate, till it disagreeably affects them; and the action of those
sphincters is then in consequence of this disagreeable sensation. So the
secretion of saliva, which in young children is copiously produced by
irritation, and drops from their mouths, is frequently attended with the
agreeable sensation produced by the mastication of tasteful food;, till at
length the sight of such food to a hungry person excites into action these
salival glands; as is seen in the slavering of hungry dogs.

The motions of those muscles, which are affected by lascivious ideas, and
those which are exerted in smiling, weeping, starting from fear, and
winking at the approach of danger to the eye, and at times the actions of
every large muscle of the body become causable by our sensations. And all
these motions are performed with strength and velocity in proportion to the
energy of the sensation that excites them, and the quantity of sensorial
power.

2. Many of the motions of our organs of sense, or ideas, that were
originally excited into action by irritation, become in like manner more
frequently causable by our sensations of pleasure or pain. These motions
are then termed the ideas of imagination, and make up all the scenery and