refluctuations of the spirit of animation; nor are they supposed to be
vibrations or revibrations, nor condensations or equilibrations of it; but
to be changes or motions of it peculiar to life.

* * * * *

SECT. VI.

OF THE FOUR CLASSES OF FIBROUS MOTIONS.

I. _Origin of fibrous contractions._ II. _Distribution of them into
four classes, irritative motions, sensitive motions, voluntary motions,
and associate motions, defined._

I. All the fibrous contractions of animal bodies originate from the
sensorium, and resolve themselves into four classes, correspondent with the
four powers or motions of the sensorium above described, and from which
they have their causation.

1. These fibrous contractions were originally caused by the irritations
excited by objects, which are external to the moving organ. As the
pulsations of the heart are owing to the irritations excited by the
stimulus of the blood; and the ideas of perception are owing to the
irritations excited by external bodies.

2. But as painful or pleasurable sensations frequently accompanied those
irritations, by habit these fibrous contractions became causeable by the
sensations, and the irritations ceased to be necessary to their production.
As the secretion of tears in grief is caused by the sensation of pain; and
the ideas of imagination, as in dreams or delirium, are excited by the