ne in their orgasm, or increased activity.

I. _Of the Action of Vomiting._

The manner, in which the stomach and the diaphragm and abdominal muscles
acquire their associate action in vomiting, requires some attention. It is
not probable, that this action of vomiting occurs before nativity; as the
uniform application of the nutritive liquor amnii to the mouth of the
foetus, and the uniform expenditure of its nourishment, would not seem to
give occasion to too great temporary repletion of the stomach; and would
preclude the deglutition of any improper material. After nativity the
stomach of the child may be occasionally too much distended with milk; as
previous hunger may induce it to overgorge itself; and by repeated efforts
the act of vomiting is learned, as a means of getting free from a
disagreeable sensation. Thus when any disgustful material, as a bitter
drug, is taken into the mouth; certain retrograde motions of the tongue and
lips are produced, for the purpose of putting the disagreeable material out
of the mouth again.

When the stomach is disagreeably stimulated by the distention or acrimony
of the aliment, a similar effort to regurgitate it must occur; and by
repeated trials the action of the diaphragm and abdominal muscles by
squeezing the stomach assists its retrograde exertion to disgorge its
contents. In the same manner when a piece of gravel is pushed into the
urethra, or a piece of indurated bile into the neck of the gall-bladder,
after they have been in vain pressed forward by the usual motions of those
ducts, they return into the bladders of gall and urine by the retrograde
motions of them.

That this is one mode, in which vomiting is induced, appears from the
instantaneous rejection from the stomach occasioned by some nauseous drug,
or from some nauseous idea; and lastly, from the voluntary power, which
some people have been said to have acquired, of emptying their stomachs,
much in the same manner as ruminating animals bring up the grass from their
first stomach.

There are nevertheless many modes by which these inverted motions of the
stomach and oesophagus are induced, and which it is of consequence to
distinguish from each other. The first is the mode above described, where
an effort is made to dislodge something, which stimulates the stomach into
disagreeable sensation; and which is returned by repeated exertions; as
when a nauseous drug is taken into the mouth, or a bit of sand falls into