muscles, as in those, who talk or struggle in their dreams; or in
those, who are affected with complete reverie (as described in the next
Section), great surprise is produced, when they awake; and these as well as
those, who are completely drunk or delirious, totally forget afterwards
their imaginations at those times.

20. As the immediate cause of sleep consists in the suspension of volition,
it follows, that whatever diminishes the general quantity of sensorial
power, or derives it from the faculty of volition, will constitute a remote
cause of sleep; such as fatigue from muscular or mental exertion, which
diminishes the general quantity of sensorial power; or an increase of the
sensitive motions, as by attending to soft music, which diverts the
sensorial power from the faculty of volition; or lastly, by increase of the
irritative motions, as by wine, or food; or warmth; which not only by their
expenditure of sensorial power diminish the quantity of volition; but also
by their producing pleasureable sensations (which occasion other muscular
or sensual motions in consequence), doubly decrease the voluntary power,
and thus more forcibly produce sleep. See Sect. XXXIV. 1. 4.

Another method of inducing sleep is delivered in a very ingenious work
lately published by Dr. Beddoes. Who, after lamenting that opium frequently
occasions restlessness, thinks, "that in most cases it would be better to
induce sleep by the abstraction of stimuli, than by exhausting the
excitability;" and adds, "upon this principle we could not have a better
soporific than an atmosphere with a diminished proportion of oxygene air,
and that common air might be admitted after the patient was asleep."
(Observ. on Calculus, &c. by Dr. Beddoes, Murray.) If it should be found to
be true, that the excitability of the system depends on the quantity of
oxygene absorbed by the lungs in respiration according to the theory of Dr.
Beddoes, and of M. Girtanner, this idea of sleeping in an atmosphere with
less oxygene in its composition might be of great service in epileptic
cases, and in cramp, and even in fits of the asthma, where their periods
commence from the increase of irritability during sleep.

Sleep is likewise said to be induced by mechanic pressure on the brain in
the cases of spina bifida. Where there has been a defect of one of the
vertebrae of the back, a tumour is protruded in consequence; and, whenever
this tumour has been compressed by the hand,