CHAPTER XIV 



SLEEP 



ABOUT one-third of an average human life is passed in 

 the familiar and yet mysterious state which we call sleep. 

 From one point of view this seems a large inroad upon the 

 period in which our consciousness has its exercise: a sub- 

 traction of twenty-five years from the life of one who 

 lives to be seventy-five. Yet we know that the efficiency 

 and comfort of the individual demand the surrender of all 

 this precious time. It has often been said that sleep is a 

 more imperative necessity than food, and the claim seems 

 to be well founded. 



The writer once asked a psychologist how he would 

 define sleep, and received the answer, "Why, it is nothing 

 at all." It has been simply described as inattention. 

 Both these characterizations turn upon the idea that sleep 

 is a suspension of consciousness and ignore its physiologic 

 features. Our own judgment as to whether we have been 

 asleep or not is evidently based upon the same concep- 

 tion. If this is the whole story, no animal can be said to 

 sleep unless we grant that it is conscious at other times. 

 We readily recognize that sleep is more clearly a part of the 

 lives of the higher animals than of those below them in the 

 scale, but it is hard to set limits to its occurrence. All 

 mammals and birds are assumed to sleep; probably the 

 reptiles do, but we do not feel so sure about the frog or the 

 fish. 



It might be more rational to reverse the order of inquiry 

 and, instead of asking how far down in the scale there is 

 sleep, we might ask, at what level, as we ascend the scale, 

 do we find animals awake? Is not all life, below a certain 

 stratum, somnambulistic? An idea much like this has 



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