which adds an additional
stimulus to that already too great. After some hours the sensorial power
becomes diminished in quantity, expended by the great activity of the
system; and thence, when the stimulus of the opium is withdrawn, the fibres
will not obey their usual degree of natural stimulus, and a consequent
torpor or quiescence succeeds, as is experienced by drunkards, who on the
day after a great excess of spirituous potation feel indigestion, head-ach,
and general debility.

In this fit of torpor or quiescence of a part or of the whole of the
system, an accumulation of the sensorial power in the affected fibres is
formed, and occasions a second paroxysm of exertion by the application only
of the natural stimulus, and thus a libration of the sensorial exertion
between one excess and the other continues for two or three days, where the
stimulus was violent in degree; and for weeks in some fevers, from the
stimulus of contagious matter.

But if a second dose of opium be exhibited before the fibres have regained
their natural quantity of sensorial power, its effect will be much less
than the former, because the spirit of animation or sensorial power is in
part exhausted by the previous excess of exertion. Hence all medicines
repeated too frequently gradually lose their effect, as opium and wine.
Many things of disagreeable taste at first cease to be disagreeable by
frequent repetition, as tobacco; grief and pain gradually diminish, and at
length cease altogether, and hence life itself becomes tolerable.

Besides the temporary diminution of the spirit of animation or sensorial
power, which is naturally stationary or resident in every living fibre, by
a single exhibition of a powerful stimulus, the contractile fibres
themselves, by the perpetual application of a new quantity of stimulus,
before they have regained their natural quantity of sensorial power, appear
to suffer in their capability of receiving so much as the natural quantity
of sensorial power; and hence a permanent deficiency of spirit of animation
takes place, however long the stimulus may have been withdrawn. On this
cause depends the permanent debility of those, who have been addicted to
intoxication, the general weakness of old age, and the natural debility or
inirritability of those, who have pale skins and large pupils of their
eyes.

There is a curious phenomenon belongs to this place, which has always
appeared difficult of solution; and that is,