itation, electricity, magnetism, and perhaps of other ethereal fluids
yet unknown.

* * * * *

ORDO II.

_Decreased Associate Motions._

GENUS I.

_Catenated with Irritative Motions._

As irritative muscular motions are attended with pain, when they are
exerted too weakly, as well as when they are exerted too strongly; so
irritative ideas become attended with sensation, when they are exerted too
weakly, as well as when they are exerted too strongly. Which accounts for
these ideas being attended with sensation in the various kinds of vertigo
described below.

There is great difficulty in tracing the immediate cause of the deficiences
of action of some links of the associations of irritative motions; first,
because the trains and tribes of motions, which compose these links, are so
widely extended as to embrace almost the whole animal system; and secondly,
because when the first link of an associated train of actions is exerted
with too great energy, the second link by reverse sympathy may be affected
with torpor. And then this second link may transmit, as it were, this
torpor to a third link, and at the same time regain its own energy of
action; and it is possible this third link may in like manner transmit its
torpor to a fourth, and thus regain its own natural quantity of motion.

I shall endeavour to explain this by an example taken from sensitive
associated motions, as the origin of their disturbed actions is more easily
detected. This morning I saw an elderly person, who had gradually lost all
the teeth in his upper jaw, and all of the under except three of the
molares; the last of these was now loose, and occasionally painful; the
fangs of which were almost naked, the gums being much wasted both within
and without the jaw. He is a man of attentive observation, and assured me,
that he had again and again noticed, that, when a pain commenced in the
membranes of the alveolar process of the upper jaw opposite to the loose
tooth in the under one (which had frequently occurred for several days
past), the pain of the loose tooth ceased. And that, when the pain
afterwards extended to the ear and temple on that side, the pain in the
membranes of the upper jaw ceased. In this case the membranes of the
alveolar process of the upper jaw became torpid, and consequently painful,
by their reverse sympathy with the too violent actions of the inflamed
membranes of the loose tooth; and then by