CHAP, in.] THE PHASES OF LIFE. 1551 



awake, as we say, the sleeper. It would seem as if the afferent 

 impulses met in their course with an unwonted resistance to their 

 progress, as if the wheels of the cerebral machinery worked stiffly 

 so that the lesser shocks of molecular change which otherwise 

 would have moved them, were broken and wasted upon them. 

 Corresponding to this block or lessened inroad of afferent impulses, 

 the outflow of efferent impulses is stopped or largely diminished ; 

 the body gives no sign of the working of a conscious will, the 

 eyelids drop and the head nods, and the various actions by which 

 the erect posture is maintained are let go for lack of the govern- 

 ing motor impulses. And psychological self-inquiry tells us that 

 in complete sleep this absence of outward signs of cerebral activity 

 has its fellow in the absence of inward marks ; the interval between 

 falling asleep and awakening is a blank and gap in the history of 

 the mind. 



We say ' complete sleep ' since there are many degrees of sleep, 

 the state which we call that of dreaming being one of them ; and 

 between the most perfect wide-awakefulness and that deepest 

 slumber which refuses for a long time to give way before even the 

 strongest stimuli, no clear line of demarcation can be drawn. 

 When we fall asleep the tie between ' ourselves ' and the external 

 w^orld is not suddenly snapped, we do not by one step pass from 

 consciousness to unconsciousness ; and the same when conversely 

 we awake ; as the world vanishes from us or comes back to us, the 

 afferent impulses of sight, of sound and of other kinds, for a 

 period which may be brief but always exists, produce, before they 

 cease or begin appreciably to affect us at all, effects in ascending or 

 descending scale which we call unreal. And the outward signs of 

 sleep may vary from one in which volition is present and even 

 dominant, to one in which even the simplest reflex movements 

 of the skeletal muscles are with difficulty evoked, and the mainte- 

 nance of some skeletal tone ( 597) and of breathing afford, so far 

 as the skeletal muscles are concerned, almost the only token that 

 the central nervous system is alive. But we cannot enter here 

 into the psychology of sleep and dreams. 



Though the phenomena of sleep are largely confined to the 

 central nervous system and especially to the cerebral hemispheres, 

 the whole body shares in the condition. The pulse and breathing 

 are slower, the intestine, the bladder, and other internal muscular 

 mechanisms are more or less at rest, and the secreting organs are 

 less active, some apparently being wholly quiescent ; the secretion 

 of mucus attending a nasal catarrh is largely diminished during 

 slumber, and the sleeper on waking rubs his eyes to bring back to 

 his conjunctiva its needed moisture. The output of carbonic acid, 

 and the intake of oxygen, especially the former, is lessened ; the 

 urine is less abundant, and the urea falls. Indeed the whole 

 metabolism and the dependent temperature of the body are 

 lowered ; but we cannot say at present how far these are the 



