_Secretion._--The functions of the numerous glands throughout the body are diminished during sleep. The tears dry up, and the cornea receives less moisture. Hence the stickiness of the margins of the eyelids during the sleep of a patient suffering with conjunctivitis. He can open his eyes, on awaking, only after sufficient time has elapsed to revive the lachrymal flow. Exner[12] remarks the diminution of pathological secretion in nasal catarrh during the hours of sleep. The mouth in like manner ceases to receive its full quota of saliva, and its cavity quickly dries if the lips remain open. The secretions of the gastro-intestinal glands vary with the contents of the alimentary canal; but in general they are considerably diminished, and digestion is correspondingly retarded during the hours of sleep. The quantity of urine is lessened during sleep.[13] The elimination of urea and of other excrementitious matters is less during the night than by day.[14] Unless increased by disease, or by accidental circumstances connected with atmospheric temperature and unnecessary clothing, the perspiration is also diminished. _Nutrition._--All the molecular processes of nutrition are reduced by sleep. The lowering of the bodily temperature has been already indicated. The observations of Helmholtz[15] indicate that the actual liberation of heat in the tissues is but little more than one-third of the amount set free in an equal period of time during the waking hours. The numerous experiments[16] of Boussingault, Henneberg, Scharling, E. Smith, Liebermeister, Pettenkofer, Voit, and Lewin, clearly indicate the fact that during sleep less oxygen is absorbed, and less carbonic acid gas is discharged, by the tissues. Voit found that while, during the daytime, 435 grammes of oxygen were taken in by a working man, only 326 grammes were needed by the same individual during the nocturnal half of the day. Artificial sleep occasioned by chloral hydrate produced a similar reduction in the consumption of oxygen and in the formation of carbonic acid gas. Under the influence of morphine the reduction of CO_{2.} reached 27 per cent., and the diminution of oxygen amounted to 34 per cent. of the quantities furnished during wakeful activity. The comparatively small reduction (only 6 per cent.) in the decomposition of the nitrogenous elements of the body during the same period, exhibits the close relation between the metamorphosis of the non-nitrogenous elements of the tissues and the amount of bodily activity.