lead armies to victory, and
kingdoms to prosperity; or discover and improve the sciences, which
meliorate and adorn the condition of humanity.

* * * * *

SECT. XI.

ADDITIONAL OBSERVATIONS ON THE SENSORIAL POWERS.

I. _Stimulation is of various kinds adapted to the organs of sense, to
the muscles, to hollow membranes, and glands. Some objects irritate our
senses by repeated impulses._ II. 1. _Sensation and volition frequently
affect the whole sensorium._ 2. _Emotions, passions, appetites._ 3.
_Origin of desire and aversion. Criterion of voluntary actions,
difference of brutes and men._ 4. _Sensibility and voluntarity._ III.
_Associations formed before nativity, irritative motions mistaken for
officiated ones._

_Irritation._

I. The various organs of sense require various kinds of stimulation to
excite them into action; the particles of light penetrate the cornea and
humours of the eye, and then irritate the naked retina; rapid particles,
dissolved or diffused in water or saliva, and odorous ones, mixed or
combined with the air, irritate the extremities of the nerves of taste and
smell; which either penetrate, or are expanded on the membranes of the
tongue and nostrils; the auditory nerves are stimulated by the vibrations
of the atmosphere communicated by means of the tympanum and of the fluid,
whether of air or of water, behind it; and the nerves of touch by the
hardness of surrounding bodies, though the cuticle is interposed between
these bodies and the medulla of the nerve.

As the nerves of the senses have each their appropriated objects, which
stimulate them into activity; so the muscular fibres, which are the
terminations of other sets of nerves, have their peculiar objects, which
excite them into action; the longitudinal muscles are stimulated into
contraction by extension, whence the stretching or pandiculation after a
long continued posture, during which they have been kept in a state of
extension; and the hollow muscles are excited into action by distention, as
those of the rectum and bladder are induced to protrude their contents from
their sense of the distention rather than of the acrimony of those
contents.

There are other objects adapted to stimulate the nerves, which terminate in
variety of membranes, and those especially which form the terminations of
canals; thus the preparations of mercury particularly affect the salivary
gland