SLEEP. 



683 



respect 1 , then, even the ordinary sleep of the 

 warm-blooded animal may be regarded as an 

 incipient hibernation. Some writers have 

 spoken of the organic functions as performed 

 with increased activity during sleep ; a doc- 

 trine so inconsistent with obvious facts, that 

 it could never have been sustained except on 

 the basis of a preconceived idea with regard 

 to the antagonism between the relative ac- 

 tivity of the functions of organic and animal 

 life, which idea is in itself fallacious. The 

 actual renovation of the nervous and mus- 

 cular tissues by the nutritive processes, pro- 

 bably takes place with peculiar energy during 

 the functional inactivity of those parts ; but 

 the preparation of the nutritive materials, 

 which is the office of the digestive and as- 

 similative apparatus, seems to go on more 

 slowly during sleep ; and it is quite certain 

 that less oxygen is then taken into the sys- 

 tem, and less carbonic acid generated and set 

 free. 



The access of sleep is sometimes quite 

 sudden ; the individual passing at once from 

 a state of mental activity to one of complete 

 torpor. More generally, however, it is gradual; 

 and is marked by phenomena which are par- 

 ticularly worthy of attention. "While the 

 mind remains poised, as it were, between sleep 

 and the opposite condition," says Dr. Macnish*, 

 " it is pervaded by a strange confusion, which 

 almost amounts to wild delirium ; the ideas 

 dissolve their connection from it, one by one ; 

 those which remain longest behind are faint, 

 visionary, and indistinct; and its own essence 

 becomes so vague and diluted, that it melts 

 away in the nothingness of slumber; as the 

 morning vapours are blended with the sur- 

 rounding air by the solar heat." In this passage 

 there is an attempt made to depict the result 

 of the loss of that power of voluntary control 

 over the current of thought, the possession of 

 which is the especial characteristic of the 

 human mind in its state of normal activity. 

 It is the complete suspension of this power, 

 as we shall presently see, which, taken in 

 connection with the entire want of sensibility 

 to external objects, constitutes the state of 

 dreaming ; and the same suspension, occurring 

 before the mind is altogether withdrawn from 

 connection with the external world, constitutes 

 that curious intermediate state betwixt sleeping 

 and waking, which may readily pass into either 

 condition. Thus, if the torpor of the sen- 

 sorial centres be allowed to increase, sleep is 

 produced ; but if it be dissipated by some sen- 

 sory impression of unusual strength, wakeful- 

 ness is brought back again, a dreamy impression 

 remaining, both of what had been passing in 

 the mind itself, and of that which had been 

 taking place around. Now, it appears to be 

 by suspending the mind's attention to its own 

 proceedings, and by drawing off the attention 

 of the sensorium from all other impressions 

 upon the organs of sense, that the monoto* 

 nous sensations already referred to favour 

 the access of sleep. And it may be further 

 affirmed that all the successful plans for vo- 

 * Philosophy of Sleep, p. 21. 



luntarily producing sleep have some such 

 modus operandi ; their success being dependent 

 upon the intentional fixation of the thoughts 

 upon some one class of sensory impressions 

 (as in the method of Mr. Gardner), or upon 

 some very simple and uniform mental process 

 (such as counting, repeating a French or Greek 

 verb, &c.); and when the attention has been 

 once thus fixed, the monotony of the impression 

 serves to retain it there, so that it abandons, as it 

 were, all control over its operations, and allows 

 itself to be gradually wrapped in repose under 

 the influence of that continued recurrence of 

 similar impressions, which seems even more 

 potent as a soporific than the suspension of 

 all sensational stimuli. 



The gradual loss of consciousness and of 

 voluntary control over the muscular system 

 during the invasion of sleep is thus described 

 by Dr. Macnish : " Previous to the acces- 

 sion of sleep, a feeling of universal lassitude 

 prevails; this sensation heralds in the phe- 

 nomena of slumber, and exhibits itself in 

 yawning, heaviness of the eyes, indifference to 

 surrounding objects, and all the characteristics 

 of fatigue. If the person be seated, his head 

 nods and droops, and, in all cases, the muscles 

 become relaxed, and the limbs thrown into 

 that state most favourable for complete mus- 

 cular inaction. The lying position is, con- 

 sequently, the best adapted for sleep, and the 

 one which is intuitively adopted for the pur- 

 pose. The organs of the senses do not re- 

 lapse into simultaneous repose, but suspend 

 their respective functions gradually and suc- 

 cessively ; sight, taste, smell, hearing, and 

 touch, parting with sensation in the order in 

 which they here stand, and gliding insensibly 

 away. In the same manner the muscles do 

 not become simultaneously relaxed ; those of 

 the limbs giving way first, then those of the 

 neck, and lastly the muscles of the spine. 

 Nor do the external senses, on awaking, re- 

 cover all at once their usual vigour ; we, for 

 some seconds, neither hear, nor see, nor smell, 

 nor taste, nor touch, with our usual acuteness. 

 Ordinary sights dazzle our eyes; ordinary 

 sounds confuse our ears; ordinary odours, 

 tastes, and sensations, our nose, our tongue, 

 and our touch : they awake successively, one 

 after another, and not in the same instant." * 



The power of being aroused by impressions 

 made upon the organs of sense, is, as already 

 remarked, one of the chief distinctions be- 

 tween sleep and stupor. The strength of the 

 impression requisite to produce this effect 

 depends upon two circumstances, which re- 

 quire separate consideration : first, the pro- 

 foundness of the slumber; and, second, the 

 relation of the impression to the habitual 

 condition of the mind. It is a familiar fact 

 that most persons are much more easily 

 aroused towards the morning, when the slum- 

 bers are lighter, than they are during the early 

 part of the night, when the sleep is more 

 profound. In fact, the spontaneous awaken- 

 ing which takes place when our repose has 

 been sufficient for the restoration of mental 

 * Op. cit. p. 22. 



