SLEEP. 67 



Yet, if we look a little deeper into the matter, 

 the question " Why do almost all animals require 

 this nightly period of rest and unconsciousness'. " 

 is surely one that calls for a rational and compre- 

 hensive answer. It is easy enough to say glibly, 

 " Of course we need repose " ; but, after all, this 

 merely appears to be a sufficient reply because we 

 are so accustomed to the fact itself ; it is no 

 explanation — it is simply a re-statement of the 

 original problem. Stones do not require a special 

 period of repose, nor do plants, nor even some of 

 the lowest animals. Nay, in the human body itself 

 there are two important sets of organs which work 

 on ceaselessly, night and day, never pausing or 

 resting, — the heart and the breathing apparatus, — 

 and tlicre is at first sight no apparent reason why 

 one part of our frame should need such extended 

 repose, while another goes on moving and Jicting 

 with unfailing freshness from year's end to year's 

 end. However deep our slumber may be, the 

 blood is still being pumped up vigorously through 

 its channels by the i)owerful muscles of the heart, 

 and the breath is still being regularly drawn in 

 and out by the slow and even movements of the 

 gently rising and falling chest. Some sufficient 

 reason must certainly exist why heart and lungs 

 should difler so cons[)icuously in this respect from 

 brain and limbs. If we consider the true nature 

 and meaning of sleep, we shall se<i that such a 



