SLEEP ANT) DREAMS. 



63 



thoir natiiro, and therefore needs no fntnro investigation, 

 or on the other hand, to leave the whole question in the 

 hands of the poets. The fact that we lie down to sleep 

 every night does not make it any the less extraordinary ; 

 and on the other hand mci'O wonder will not help ns to 

 knowledge. 



It is impossible to understand the subject unless we 

 consider it in a wide sense, and include not merely the 

 alternations of mental rest and activity through which wc 

 pass, but also the hibernation of animals, the sleep of the 

 vegetable world, the rest of individual cells and organs, and 

 even, perhaps, the death-like trance of the seeds of plants 

 which has been known to extend over thousands of year's, 

 the germ of life being quieseont but not destroyed. This 

 is a wide range, and loads us into such far fields that 

 wo can only wander over a small pai't of the ground, 

 stopping when we come across facts or thoughts that bear 

 on the question, "What is sleep ? " 



Wo may first notice that in its broadest sense sleep, " the 

 wide blessing," is univoi'sal amongst organised beings ; it is 

 necessary for them at some period of their existence to 

 slacken their activities, and rest awhile to gather fi'esh 

 strength. Organisms whose existence is tranquil and 

 languid do not as a rule require such frequent and regular 

 intervals for repose as those who live fast(!i'. Creatures of a 

 sluggish nature, and plants whose growth is genei-ally slow 

 and careless, do not stand in such need of constant I'enova- 

 tion as animals with muscles that arc frequently on the move, 

 and nervous systems that see and hear and think and feel. 

 This may bo said to be the chief function of sleep — to allow 

 the used up force to be replaced. The repair is probably, 

 as Herbert Spencer points out, as rapid during the day as 

 during the night; but whilst awake tlu^ waste greatly 



