1 66 SCIENCE FROM AN EASY CHAIR 



slowed down, and the body temperature falls. The 

 scattered fat of the body, and fatty matter and other 

 material stored in special structures called " hibernating 

 glands," are oxidised and slowly consumed during this 

 period, which may last for three or even four months. 

 The animal on waking is often in a very emaciated 

 condition. 



It is undoubtedly the case that the human natives of 

 high latitudes (such as the Norwegians), where there is 

 no night in full summer, and where there is prolonged 

 darkness in winter, have acquired the habit of keeping 

 awake for many days in succession in summer, whilst 

 making up for the loss of sleep by excessive indulgence 

 in it during the winter. It is by no means clear how 

 far man is capable of resisting the demand for recurrent 

 daily sleep without injury to health. Undoubtedly many 

 men are compelled by their avocations to sleep by day 

 and wake by night. The length and duration of " spells 

 of sleep " and the power to sleep little or not at all at 

 one season, and almost uninterruptedly at another, with- 

 out injury to health, are matters of habit, occupation, 

 and circumstance. We have no ground for saying that 

 every man "ought" to sleep eight hours or more per 

 diem, or, on the contrary, for insisting that he should 

 only sleep five or less. All depends on what he is 

 doing when he is awake, and what other people are 

 doing (so as to disburb him) when he is asleep ; and we 

 do not even know whether ten or twelve hours' sleep 

 would injure a man, were he able to take it, nor can we 

 suggest how it would injure him supposing it did not 

 interfere with his feeding and exercise. 



As to quantities of sleep, there is the curious fact that 

 the amount habitually taken in the civilised communities 

 of this part of the world differs at different ages. Babies 

 sleep a good part of the twenty-four hours, and prob- 



