is defined to be that state wherein the body appearing perfectly at rest, external objects move the organs of sense as usual, without exciting the usual sensations.

Sleep is broken off unnaturally, when any of the organs of sensation is so briskly acted on, that the action is propagated to the brain.

Sleep being one of the non-naturals, it is not possible for those to preserve their health, who do not go to sleep in a regular manner: for sleep repairs the spirits, which are dissipated by watching; and consequently it restores the strength of those who are weak, indisposed, or labour much. It likewise promotes perspiration, contributes greatly to digestion, and more to nutrition. The night is the most proper for sleep; for the vigour of the mind and body are better restored in the night than in the day; thus nocturnal labour and lucubrations impair the health.