810 SLEEP.—ITS PHENOMENA. oro-ans of animal life are rendered capable of renewed action by the operations of the organising force, which proceed without the consciousness of the animal, though ac¬ cordant with a well-contrived plan and with reason. In consequence of all parts of the organism participating to a certain extent in the states of excitement which affect primarily only one part, the waking of the system of animal life, and its consequent increased excitement, must be gradually imparted to those organs which are under the influence of the organic nervous system; and any functions which these organs may perform, in addition to thamere process of organisa¬ tion, will be in some measure affected. Hence it is that the heart’s action becomes rather more frequent at the time of waking than it was during sleep. The radiation or extension of excitement from the animal system to the organic ceases during sleep, and so far the organic part of the body has at that time a remission of action, though in a less degree than the animal system. If the waking state of the animal system is maintained much longer than natural, this extension of excitement from it to the or¬ ganic system not merely becomes more manifest, (for instance, in the acceleration of the heart’s action,) but the great exhaustion of the organised material by continued action is imperfectly balanced by the organising process. Hence the signs of defective nutrition, which soon show themselves when watching is long protracted. Having considered thus far the nature of sleep generally, we will now study more minutely its phenomena. On the commencement of sleep the senses cease to per¬ ceive external impressions, and the play of ideas, and the emotions, are entirely or in greater part silenced. The will ceases to rule the muscles; the eyelids, which ex¬ perience the sensation of fatigue, are no longer under command; the head droops, and this state of inaction soon extends over the whole animal system of organs. When sleep is perfect there is generally a complete absence of voluntary motion; while the involuntary movements of the organic muscles, and those movements of certain animal muscles which are only in part under the influence of the will, such as the respiratory movements, continue; the movements last-mentioned merely ceasing to be influenced by volition. The movements of the heart, and the respiratory movements, are somewhat less frequent than in the waking state. The action of some animal muscles is increased during sleep, they being apparently released from some counter¬ acting force which opposed them in the waking state. Such is the case with some of the muscles of the eyes, as well as with the muscles of the extremities in birds which sleep standing on one or both legs. During sleep the eyes have a peculiar position. At that time, as well as in a state of mere sleepiness, both eyes are turned inwards and upwards. This movement is still more strongly displayed in disorders of the nervous system; for example, in epilepsy and catalepsy. This position of the eye during sleep also gives it a very different expression from that which it has in death. The iris is contracted in a person asleep, and the pupil consequently nar¬ rowed; but on his awakening the pupil always dilates, becoming first, indeed, very wide, and then undulating, until it acquires the mean size which it has in the waking state. (See page 535.) A greater amount of external warmth is required for the body during sleep than at other times; and immediately after the awakening from sleep there is frequently great sensibility to cold. W;hen, during sleep, the conception of ideas by the mind does not entirely cease, dreams arise. These are for the most part composed of simple ideas and emotions; but general notions sometimes come into play, and movements affected by the animal muscles may be combined with the ideas as in the waking state. This condition of the mind is “dreaming,” as long as the sensorium is disturbed by something which gives to the operations of the mind a character opposed to that of the ordinary con¬ ceptions and thoughts of the same person. The ideas conceived in dreams so far re¬ semble those of the waking state, that they may refer to any period of the past life; just as in our ordinary condition we may look back to all periods of our life, and think at one moment of yesterday, and the next of times years past. If the ideas which occupy the mind during the waking state have a certain degree of persistence, the same ideas will recur in dreams during sleep. The dreams of some persons, on the other hand, refer chiefly to times long past. Many blind people, after they have been some time deprived of sight, cease to dream of visible objects, but their dreams accord with their present mode of intercourse with the external world. Other indivi¬ duals, who have lost their sight, continue through their whole life to dream of visible objects. The important circumstance, therefore, regulating these dreams of visible