SLEEP (p. 206).--_Some Curiosities of Sleep_.--One of the most refined and exquisite methods of torture is long continued deprivation of sleep. The demand for unconscious rest is so imperious that nature will accommodate itself to the most unfavorable surrounding conditions. Thus, in forced marches, regiments have been known to sleep while walking; men have slept soundly in the saddle; and persons will sometimes sleep during the din of battle. It is remarkable how noises to which we have been accustomed will fail to disturb our natural rest. Those who have been long habituated to the endless noise of a crowded city frequently find difficulty in sleeping in the oppressive stillness of the country. Prolonged exposure to intense cold induces excessive somnolence, and if this be induced, the sleep passes into stupor, the power of resistance to cold becomes rapidly diminished, and death is the inevitable result. Intense heat often produces drowsiness, but, as is well known, is not favorable to natural sleep....It is difficult to determine with exactness the phenomena of sleep that are absolutely physiological, and to separate those that are slightly abnormal. We can not assert, for example, that a dreamless sleep is the only normal condition of repose of the system; nor can we determine what dreams are due to previous trains of thought, or to such impressions from the external world received during sleep as are purely physiological, and what are due to abnormal nervous influence, disordered digestion, etc. The most remarkable experiments upon the production of dreams of a definite character, by subjecting a person during sleep to peculiar influences, are those of Maury. The hallucinations produced in this way are called hypnagogic (from its derivation this term is properly applied only to phenomena observed at the instant when we fall asleep, or when we are imperfectly awakened, and not to the period of most perfect repose), and they occur when the subject is not in a condition favorable to sound sleep. The experiments made by Maury upon himself are so curious and interesting that we quote the most striking of them in full. _First Observation_.--I am tickled with a feather successively on the lips and inside of the nostrils. I dream that I am subjected to a horrible punishment, that a mask of pitch is applied to my face, and then roughly torn off, tearing the skin of the lip, the nose, and the face. _Second Observation_.--A pair of pincers is held at a little distance from my ear, and rubbed with steel scissors. I dream that I hear the ringing of bells; this soon becomes a tocsin, and I imagine myself in the days of June, 1848. (The time of the French Revolution.) _Third Observation_.--I am caused to inhale Cologne water. I dream I am in a perfumer's shop; the idea of perfumes doubtless awakens the idea of the East; I am in Cairo, in the shop of Jean Farina....