Sleep
2 of the 6 encyclopedias on this shelf carry an entry for Sleep. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a condition of the body in which the nerves rest and cease to carry impressions to the brain or to convey orders. One who is soundly asleep neither sees, hears, tastes, nor feels. If a sensation be violent enough to set the nerves in action, the sleeper is awakened. During sleep, the mind is not conscious. Any action of the body is involuntary. The heart continues to beat, for its action is involuntary-not dependent on the will of the owner. Any circumstance that tends to lessen the sense impressions induces slumber. A slight monotonous circumstance, such as the faint chirp-chirp of a cricket, that attracts the attention and causes the mind to leave other matters and forget its problems, leads to slumber. Cases are on record of prisoners lulling their guards to sleep by some such device. The lullaby song and the slow swing of the cradle act on this principle. Artificial sleep may be caused by certain drugs. The poppy is the plant of sleep. All animals having nervous systems require sleep. Most flesh-eating animals sleep in the daytime and prowl at night. Moths fly abroad at night and rest in the daytime. Man sleeps naturally at night. Those whose occupations require night work testify that sleep in the daytime, even under the most favorable conditions, is not so refreshing. Children require more sleep than adults; fleshy people more than slender people. Outdoor employment and exercise in cold air lead to drowsiness. Adults require to sleep rather less than a third of their time. Sleep has not failed to attract the notice of poets: Tired nature's sweet restorer, balmy sleep!-Young. Poor labour sweet in sleep was locked.-Burns. Blessings light on him who first invented sleep.-Cervantes. Our birth is but a sleep and a forgetting.-Wordsworth. Sleep that knits up the ravel'd sleave of care, The death of each day's life, sore labour's bath, Balm of hurt minds, great nature's second course, Chief nourisher in life's feast.-Shakespeare. Death is an eternal sleep.-Inscription on the gate of a French cemetery.
Collier's New Encyclopedia (1921)
that natural state or condition of unconsciousness in animals which alternates with a period of activity. In this state the involuntary functions, such as those of nutrition, secretion, etc., go on as usual, but the voluntary powers are quiescent.
What Has Changed in the Last Century
Aiton's in 1910 described sleep as a state in which "the nerves rest and cease to carry impressions to the brain" and "the mind is not conscious," and Collier's in 1921 likewise called it simple unconsciousness with the voluntary powers quiescent. Both accounts were written before the electroencephalogram (Hans Berger, 1924) made it possible to record the sleeping brain, which turned out to be busy rather than idle: in 1953 Eugene Aserinsky and Nathaniel Kleitman at Chicago identified rapid-eye-movement sleep, the phase in which most vivid dreaming occurs, and sleep is now mapped as a cycle of distinct stages repeating roughly every 90 minutes through the night. The old note that daytime sleep "is not so refreshing" anticipated the modern account of the circadian clock, traced in the 1970s to the suprachiasmatic nucleus of the hypothalamus and to the hormone melatonin. Sleep medicine is now a clinical speciality in its own right, treating disorders such as obstructive sleep apnoea and narcolepsy that neither entry mentions, and sleep is understood to play an active role in memory consolidation rather than being mere rest.
Written for this edition, 2026.