SLEEP. 71 



and nervous system as well as legs and arms and 

 muscles. After a certain length of exercise, our 

 eyes, our ears, our tongues, and our nerves grow 

 tired and used up — they need rest as well as our 

 larger members. Above all, the brain itself has 

 then grown dull and used up — all its active parts 

 liave become quite literally worked out, and re- 

 quire to be once more rebuilt and restored, just as 

 the legs do after a long day's walk. Sleep, then, 

 is essentially the time when repair predominates 

 over waste, as in waking life waste predomi- 

 nates over repair. And it Is more especially the 

 time when rei)air takes place in the brain and the 

 great organs connected with it. We may rest our 

 legs or arms by lying down on a sofa; but we 

 cannot rest our brain except by sleeping. To lie 

 awake all night, however soft our couch, and to 

 sleep soundly are two very different things. Lying 

 awake, we may rest and restore our limbs, but we 

 are not restori' our brain and nerves. At last, 

 however, in ordinary cases, the brain ceases to 

 work — we think no longer, we are asleep. Then 

 the task of restoration begins apace ; the blood 

 quickly builds up the wasted organs of the various 

 faculties, and next morning, as soon as the work 

 of repair is completed, we wake up again fresh 

 and vigorous. 



It is clear, then, why, in most cases, night has 

 become the time for sleep. Since the brain, even 



