70 SLEEP. 



wasted organs. There is no reason wliy simple 

 lying-by sliould mend a wearied muscle any more 

 than it would mend a broken watch; there must 

 be a positive process of renewal in the expended 

 tissue. If, after our steep climb uphill, we sit 

 down upon a bench at the top, and rest our weary 

 limbs, then so long as we remain still the wasted 

 muscles are actually undergoing a rebuilding pro- 

 cess — they are being restored to their original 

 condition by taking up their proper material from 

 the blood tliat perpetually circuhites through 

 them. That is why, after a few minutes' rest, we 

 are able to go on again almost as fresh as ever; 

 the muscles aie once more put into working order, 

 and the machine is ready to begin operations again. 

 The longer the exercise, however, the longer must 

 be the period of rest and repair, and, after a 

 whole day's active employment, we need a whole 

 night's uninterrupted repose. 



Still, even this consideration does not sufficiently 

 explain wliy that needful rest should necessarily 

 take the form of sleep. It might reasonably be 

 asked, " Would not mere muscular repose do just as 

 well ? Why should we require slumber in addition 

 to inactivity? Why might we not just put our 

 legs up on a sofa, and read or talk the whole night 

 through ? " Everybody knows that such mere 

 muscular rest is not sufficient ; and the reason is 

 because we have a mind as well as a body, a brain 



