g exhausted by fatigue,
and accumulated in rest, is now less expended, whilst one half of the body
is capable of receiving its usual proportion of it, and is hence derived
with greater ease or in greater abundance into the limbs, which remain
unaffected.

II. 1. The excess or defect of voluntary exertion produces similar effects
upon the sensual motions, or ideas of the mind, as those already mentioned
upon the muscular fibres. Thus when any violent pain, arising from the
defect of some peculiar stimulus, exists either in the muscular or sensual
systems of fibres, and which cannot be removed by acquiring the defective
stimulus; as in some constitutions convulsions of the muscles are produced
to procure a temporary relief, so in other constitutions vehement voluntary
exertions of the ideas of the mind are produced for the same purpose; for
during this exertion, like that of the muscles, the pain either vanishes or
is diminished: this violent exertion constitutes madness; and in many cases
I have seen the madness take place, and the convulsions cease, and
reciprocally the madness cease, and the convulsions supervene. See Section
III. 5. 8.

2. Madness is distinguishable from delirium, as in the latter the patient
knows not the place where he resides, nor the persons of his friends or
attendants, nor is conscious of any external objects, except when spoken to
with a louder voice, or stimulated with unusual force, and even then he
soon relapses into a state of inattention to every thing about him. Whilst
in the former he is perfectly sensible to every thing external, but has the
voluntary powers of his mind intensely exerted on some particular object of
his desire or aversion, he harbours in his thoughts a suspicion of all
mankind, lest they should counteract his designs; and while he keeps his
intentions, and the motives of his actions profoundly secret; he is
perpetually studying the means of acquiring the object of his wish, or of
preventing or revenging the injuries he suspects.

3. A late French philosopher, Mr. Helvetius, has deduced almost all our
actions from this principle of their relieving us from the ennui or taedium
vitae; and true it is, that our desires or aversions are the motives of all
our voluntary actions; and human nature seems to excel other animals in the
more facil use of this voluntary power, and on that account is more liable
to insanity than other animals. But in mania this violent exertion of
v