r.

But if this vertigo becomes much greater in degree or duration, the first
link of this train of associated irritative motions expends too much of the
sensorial power, which was usually employed on the whole train; and the
motions of the stomach become in consequence exerted with less energy. This
appears, because in this degree of vertigo sickness supervenes, as in
sea-sickness, which has been shewn to be owing to less energetic action of
the stomach. And the motions of the heart and arteries then become weaker,
and in consequence more frequent, by their direct sympathy with the
lessened actions of the stomach. See Supplement, I. 12. and Class II. 1. 6.
7. The general weakness from fatigue is owing to a similar cause, that is,
to the too great expenditure of sensorial power in the increased actions of
one part of the system, and the consequent deficiency of it in other parts,
or in the whole.

The abatement of the heat of the skin in hectic fever by swinging, is not
only owing to the increased ventilation of cool air, but to the reverse
sympathy of the motions of the cutaneous capillaries with those of the
heart and arteries; which occurs in all fevers with arterial debility, and
a hot or dry skin. Hence during moderate swinging the action of the heart
and arteries becomes stronger and slower, and the action of the
capillaries, which was before too great, as appeared by the heat of the
skin, now is lessened by their reverse sympathy with that of the heart and
arteries. See Supplement, I. 8.

11. _Vertigo visualis._ Visual vertigo. The vertigo rotatoria described
above, was induced by the rotation or undulation of external objects, and
was attended with increased action of the primary link of the associated
motions belonging to vision, and with consequent pleasure. The vertigo
visualis is owing to less perfect vision, and is not accompanied with
pleasurable sensation. This frequently occurs in strokes of the palsy, and
is then succeeded by vomiting; it sometimes precedes epileptic fits, and
often attends those, whose sight begins to be impaired by age.

In this vertigo the irritative ideas of the apparent motions of objects are
less distinct, and on that account are not succeeded by their usual
irritative associations of motion; but excite our attention. Whence the
objects appear to librate or circulate according to the motions of our
heads, which is called dizziness; and we lose the means of balancing
ourselves,