f the two optic nerves, which are nearly the
size of a quill, or equal to some of the principal nerves, which serve the
limbs.

4. _Vomitio a calculo in uretere._ The action of vomiting in consequence of
the increased or decreased actions of the ureter, when a stone lodges in
it. The natural actions of the stomach, which consist of motions subject to
intermitted irritations from the fluids, which pass through it, are
associated with those of the ureter; and become torpid, and consequently
retrograde, by intervals, when the actions of the ureter becomes torpid
owing to previous great stimulus from the stone it contains; as appears
from the vomiting existing when the pain is least. When the motions of the
ureter are thus lessened, the sensorial power of association, which ought
to actuate the stomach along with the sensorial power of irritation, ceases
to be excited into action; and in consequence the actions of the stomach
become less energetic, and in consequence retrograde.

For as vomiting is a decreased action of the stomach, as explained in Sect.
XXXV. 1. 3. it cannot be supposed to be produced by the pain of gravel in
the ureter alone, as it should then be an increased action, not a decreased
one.

The perpetual vomiting in ileus is caused in like manner by the defective
excitement of the sensorial power of association by the bowel, which is
torpid during the intervals of pain; and the stomach sympathizes with it.
See Enteritis, Class II. 1. 2. 11. Does this symptom of vomiting indicate,
whether the disease be above or below the valve of the colon? Does not the
softer pulse in some kinds of enteritis depend on the sympathy of the heart
and arteries with the sickness of the stomach? See Ileus and Cholera.

Hence this sickness, as well as the sickness in some fevers, cannot be
esteemed an effort of nature to dislodge any offensive material; but like
the sea-sickness described above, and in Sect. XX. 4. is the consequence of
the associations of irritative or sensitive motions. See Class I. 1. 3. 9.

5. _Vomitio ab insultu paralytico._ Paralytic affections generally commence
with vomiting, the same frequently happens from a violent blow with a stick
on the head; this curious connection of the brain and stomach has not been
explained; as it resembles the sickness in consequence of vertigo at sea,
it would seem to arise from a similar cause, viz. from disturbed irritative
or sensitive associations.

6. _Vomitio a ti