before showed you. It is often also said to be a symptom of other
diseases, of parts remotely situated; as of the _stomach_, more
especially; whence the term _sick headach_, the stomach being supposed
to be the 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.