part first or principally affected, and the headach
symptomatic of this. I am confident, however, that in a majority of
instances the reverse is the case, the affection of the head being the
cause of the disorder of the stomach. It is no proof to the contrary,
that _vomiting_ often relieves the headach, for vomiting is capable of
relieving a great number of other diseases, as well as those of the
brain, upon the principle of _counter-irritation_. The stomach may be
disordered by nauseating medicines, up to the degree of full vomiting,
without any headach taking place; but the brain hardly ever suffers,
either from injury or disease, without the stomach having its functions
impaired, or in a greater or less degree disturbed: thus a blow on the
head immediately produces vomiting; and, at the outset of various
inflammatory affections of the brain, as _fever_ and _hydrocephalus_,
nausea and vomiting are almost never-failing symptoms. It is not denied,
that _headach_ may be produced through the medium of the stomach; but
seldom, unless there is previously disease in the head, or at least a
strong predisposition to it. In persons habitually subject to headach,
the arteries of the brain become so irritable, that the slightest cause
of disturbance, either _mental_ or _bodily_, will suffice to bring on a
paroxysm.

The _occasional_ or _exciting causes of headach_, then, are principally
these:--

1. _Emotions of mind_, as fear, terror, and agitation of spirits; yet
these will sometimes take off headach when present at the time.

2. Whatever either increases or disorders the general circulation, and
especially all causes that increase the action of the cerebral arteries,
or, as it is usually though improperly expressed, which occasion a
determination of blood to the head. Of the former kind are violent
exercise, and external heat applied to the surface generally, as by a
heated atmosphere or the _hot bath_; of the latter, the direct
application of heat to the head; falls or blows, occasioning a shock to
the brain; stooping; intense thinking; intoxicating drinks, and other
narcotic substances. These last, however, as well as _mental emotions_,
often relieve a paroxysm of headach, though they favour its return
afterwards.

3. A disordered state of the stomach, of which a vomiting of _bile_ may
be one symptom, is also to be ranked among the _occasional causes_ of
_headach_.

These _occasional causes_ do not in general produce