DISCOVERY 



239 



of a boy who was abandoned in the streets of Nurem- 

 berg at the age of seventeen. His childhood had been 

 spent " in absolute solitude, having no knowledge of 

 men, animals, or plants." He alwaj's went to sleep as 

 soon as the sun had set. 



There is no doubt that man is "intended" to rest 

 his brain and his mind for about one-third of his life ; 

 and animals which hibernate or sleep during the winter 

 spend one-half of their lives in repose. ^ 



The Physiological Purpose of Sleep 



Going to sleep is not a matter of choice ; we i/iiisi 

 sleep just as we must eat to live ; and in reality loss 

 of sleep is more damaging than loss of food. This has 

 been borne out by experiments and by the effects, 

 both on men and animals, of periods either of starva- 

 tion or of lack of sleep. Soldiers in the late war 

 found lack of sleep more trying than lack of food. 

 Sleep is therefore equivalent to some food ; a person 

 after the abstention from food of the eight hours' 

 sleep is not nearly so hungry as a person who, awake, 

 has not had food for eight hours. 



In sleep not only is the grey matter of the highest 

 part of the brain resting, but all the sj'stems of the body 

 are also relatively inactive. Thus the muscles are 

 rela.xed, the breathing is slower and shallower, the heart 

 beats more slowly and less forcibly, the blood-pressure 

 is reduced, the digestion is less active. Of course all 

 this is relative ; the centre for breathing in the 

 highest part of the spinal cord cannot stop, nor can the 

 kidneys or the liver — they are only less active than 

 during waking ; the complete cessation of their activitj' 

 would mean death. 



Young, immature animals sleep a very great deal ; 

 this is probably due to the fact that in immature 

 organisms upbuilding of the tissues must prevail over 

 disintegration, and this upbuilding in the brain has as 

 its correlative the state of unconsciousness. Processes 

 of repair, rest, restoration after fatigue in the central 

 nervous system are related to sleep, so that we can 

 understand how damaging to the nervous system must 

 prolonged sleeplessness be. 



Sleep and Death 



Physiologically speaking, sleep is sharply contrasted 

 with death. Sleep is restorative of vitality, death 

 the extinguishing of it. We sleep to wake ; we 

 slumber in repose to work better on waking. And yet 

 the poets see close resemblances between sleep and 

 death, as is very well known. 



Thus we have in Macbeth (Act II, sc. 3) ; " Shake 



1 Very interesting examples of this were given by Sir 

 Arthur Shipley in recent articles in Discovery (vide the 

 June and July issues). 



off this downy sleep, death's counterfeit " ; and again 

 in Cymbeline (Act II, sc. 2) : " Sleep, thou ape of 

 death." 



"How wonderful is death, 

 Death and his brother Sleep " — 



says Shelley in " Queen Mab." Tennyson, in " In 

 Memoriam," calls sleep " death's twin brother." And 

 Phineas Fletcher long before had said : " Sleep's but 

 a short death, death's but a longer sleep," all follow- 

 ing much more ancient writers. Far nearer the truth 

 are the beautiful words of Jesus : " She is not dead 

 but sleepeth." 



Sleep is deepest in the first hour, somewhat less so 

 in the second, and normally much lighter in all the 

 others. This has been investigated by physiologists, 

 who have measured the intensity of sound or of 

 electrical shock necessary to awake a sleeper. 



The Causes of Sleep : (1) Fatigue 



As regards the causes operative in bringing on sleep, 

 the first that would occur to us is fatigue. We cannot 

 sleep if we are not tired in some degree. Sleep due to 

 a healthy degree of fatigue is pleasant, as we are told 

 in Ecclesiastes (ch. v, 12) : " The sleep of a labouring 

 man is sweet." In exactly the same strain speaks 

 Belarius in Cymbeline (Act III, sc. 6) : " Weariness 

 can snore upon the flint, when resty sloth finds the down 

 pillow hard." Fatigue is, on its material (objective) 

 side, a mild blood-poisoning (toxaemia). During the 

 waking hours certain soluble substances produced by 

 the muscles, the nervous system, and other tissues 

 get into the blood, and in traversing the grey matter 

 of the brain greatly reduce its activity. These 

 chemical fatigue- poisons are supposed to raise the 

 resistance to the flow of impulses over the ceils of the 

 grey matter of the brain (cortex cerebri) to such an 

 extent that the cells cease to be active, and therefore 

 unconsciousness supervenes. Whatever be the exact 

 mode of action of those poisons, there is no doubt 

 at all that extreme fatigue can bring on the most 

 profound kind of sleep known. 



We may call this factor in sleep or type of sleep 

 the chemical. As has been said, " we stifle our brain 

 cells with the ashes of our waking fires." 



There are manj' examples of sleep of chemical origin 

 through great fatigue. Thus in the good old days of 

 muzzle-loaders in the " wooden walls," some of the 

 gun crew would, through sheer exhaustion, lie down 

 beside the guns which continued the cannonade at their 

 very ears. 



Philip Gibbs, in his account of the retreat from 

 Mons, thus describes this sort of thing: "Being 

 attacked was the only thing that kept them awake. 

 Towards the end of this fighting they had a drunken 



