or preserving our perpendicularity, by vision. So that in this
vertigo the motions of the associated organs are decreased by direct
sympathy with their primary link of irritation; as in the preceding case of
sea-sickness they are decreased by reverse sympathy.

When vertigo affects people about fifty years of age, their sight has
generally been suddenly impaired; and from their less accurate vision they
do not soon enough perceive the apparent motions of objects; like a person
in a room, the walls of which are stained with the uniform figures of
lozenges, explained in Sect. XX. 1. This is generally ascribed to
indigestion; but it ceases spontaneously, as the patient acquires the habit
of balancing himself by less distinct objects.

A gentleman about 50 was seized with an uncommon degree of vertigo, so as
to fall on the ground, and not to be able to turn his head, as he sat up
either in his chair or in his bed, and this continued eight or ten weeks.
As he had many decayed teeth in his mouth, and the vertigo was preceded and
sometimes accompanied by pains on one side of his head, the disease of a
tooth was suspected to be the cause. And as his timidity was too great to
admit the extraction of those which were decayed; after the trial of
cupping repeatedly, fomentations on his head, repeated blisters, with
valerian, Peruvian bark, musk, opium, and variety of other medicines;
mercurials were used, both externally and internally, with design to
inflame the membranes of the teeth, and by that means to prevent the torpor
of the action of the membranes about the temple, and parietal bone; which
are catenated with the membranes of the teeth by irritative association,
but not by sensitive association. The event was, that as soon as the gums
became sore with a slight ptyalism, the pains about the head and vertigo
gradually diminished, and during the soreness of his gums entirely ceased;
but I believe recurred afterwards, though in less degree.

The idea of inflaming the membranes of the teeth to produce increased
sensation in them, and thus to prevent their irritative connection with
those of the cranium, was taken from the treatment of trismus, or locked
jaw, by endeavouring to inflame the injured tendon; which is said to
prevent or to remove the spasm of the muscles of the jaw. See Class III. 1.
1. 13. and 15.

M. M. Emetics. Blisters. Issues about the head. Extraction of decayed
teeth. Slight salivation. Sorbentia. Incitantia