the sanguineous current must be somewhat diminished. The latter, by being inert, also requires less vascular action, as is shown by the lower temperature of the surface which takes place during the slumbering state. At the same time, although there is no increase of heat on the surface, the perspiration is augmented. According to Sanctorius, a person sleeping some hours undisturbed, will perspire insensibly twice as much as one awake. This tendency of sleep to produce perspiration, is strikingly exhibited in diseases of debility, or where there is acid in the stomach; in which cases, it is particularly apt to ensue; whence the nocturnal sweats so prevailing, and so destructive in all cachectic affections. Sanctorius farther states that the insensible perspiration is not only more abundant, but less acrimonious during sleep than in the waking state; that if diminished during the day, the succeeding sleep is disturbed and broken; that the diminution in consequence of too short a sleep, disposes to fever, unless the equilibrium is established on the following day by a more copious perspiration. Owing to the nocturnal

*There is a case related by Blumenbach of a person who had been trepanned, and whose brain was observed to sink when he was asleep, and to swell out when he was awake-a proof of the diminished circulation in that organ during the sleeping state.

sweats, the body is always somewhat lighter when we get up in the morning than when we lie down at night.

M. Castel observes,* that the greater part of animals sleep longer in winter than in summer. This fact, founded upon nature, should be converted into a law of health for man. It is precisely on account of perspiration that in the first of these seasons sleep is more necessary than in the second. In the one season, the want of perspiration during day is furnished in sleep; in the other, the diurnal sweat supplies that of the night, and renders much sleep less necessary. In other words, during summer the perspiration is so much excited by atmospheric temperature, that a few hours are sufficient to give issue to the fluids which have to be expelled by this means. For the same reason, the inhabitants of very cold climates sleep more than those who live in the warmer latitudes.

Animals which prey by night, such as the cat, the owl, &c., pass the greater part of their time in sleep, while those that do not are longer awake than asleep. They slumber during a part of the night, and remain awake so long as the sun continues

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above the horizon. The propensity of the former class of animals to sleep in the day-time seems to proceed from the structure of their eyes, as they see much better in darkness than light, and consequently pass in slumber that period in which their vision is of least avail to them.

From the increased irritability of the frame, and relaxed state of the cutaneous vessels during sleep, the system is peculiarly liable to be acted upon by all impressions, especially of cold; and those who fall asleep exposed to a current of air, are far more liable to feel the bad consequences thereof, than if they were broad awake. By a law of nature, the sensibility of the system is increased by any suspension of the mental or voluntary powers, for the same reason that it is diminished so soon as these powers resume their actions.

On awaking from sleep, the secretions of the lungs, kidneys, and salivary glands are more viscid than during day. The cause of this is obvious; not being evacuated for several hours, their thinner portions are absorbed: hence, the urine is highcoloured and sedimentous, the saliva viscid, and the phlegm from the lungs and trachea thick and tough. All these secretions, in common with those of the nostrils, ears, eyes, &c., are more scanty during sleep than at other times. An exception, however, to this

remark, so far as the urinary secretion is concerned, sometimes occurs in the case of drunkards, who often make water much more copiously at night than in the day-time.

The stature of the body is greater when we awake in the morning than when we lie down at night. Mr. Wasse, Rector of Aynho, in Northamptonshire, having measured a great many sedentary people and labourers of all ages and shapes, found the difference in this respect to be nearly an inch. This circumstance is owing to the state of the interverbral cartilages, which yield in some measure to the weight of the body in the erect posture, and recover their elasticity during the period of repose when this pressure is taken off them.

A priori, we might expect that the pupil of the eye would be largely dilated during sleep, in consequence of the light being shut out, but the reverse is the case. On opening the eye-lid cautiously, it is seen to be contracted; it then quivers with an irregular motion, as if disposed to dilate, but at length ceases to move, and remains in a contracted state till the person awakes.

In talking of the influence of sleep upon the body, the circumstance of stertorous breathing, or snoring, to which some persons are addicted, is worthy of remark. It will be found that such individuals are

either of a stout apoplectic make; that they snuff excessively; or sleep with their mouths open. Stertor, or snoring, is a symptom of determination of blood to the head; and whenever there is a tendency to cerebral congestion, it will be found a pretty constant attendant. Snuffing, by obstructing the nasal passages, and compelling the person to breathe through the mouth, has often the same effect; and if he respires in the latter manner, whether he snuffs or not, more or less stertor generally ensues.

I have alluded to yawning as one of the symptoms which usher in sleep, but it follows as well as precedes this state. It seems an effort of nature to restore the just equilibrium between the flexor and extensor muscles. The former have a natural predominancy in the system; and on being fatigued, we, by an effort of the will, or rather by a species of instinct, put the latter into action for the purpose of redressing the balance and poising the respective muscular powers. We do the same thing on awaking, or even on getting up from a recumbent posturethe flexors in such circumstances having prevailed over the extensors, which were in a great measure inert.

The degree of profoundness of sleep differs greatly in different individuals. The repose of some is extremely deep; that of others quite the reverse. The