SLEEP 167 



ably schoolboys and schoolgirls (under our present 

 conditions of life and work) ought to be given ten hours 

 or more. Whilst adult men sleep from six to eight or 

 nine hours, it is a curious fact that old people not very 

 old people, but those of sixty-five or thereabouts often 

 find themselves unable to sleep more than four hours at 

 night, and take an hour or two in the daytime to make 

 up for the deficiency. I remember hearing Mr. Darwin 

 state this as to himself to his physician, Sir Andrew 

 Clarke, who said it was very usual at his age, and diffi- 

 cult to explain, since at a greater age, when a man is 

 called " very old," a more or less continuous somnolent 

 condition sets in. The father of a great judicial dignitary 

 of these days, himself a barrister in large practice, when 

 he was sixty years old would snatch fifteen or twenty 

 minutes' sleep at any and every opportunity throughout 

 the day, even at the midday meal sometimes, so as 

 altogether to disconcert those who were with him, and 

 he told me that he never slept more than four hours at 

 night, but got up and commenced work at four in the 

 morning. The cessation in early old age of the desire 

 for more than half the amount of sleep taken by younger 

 men suggests that the regulating cause of the number 

 of hours which are needed for sleep may be simply and 

 directly the actual amount of work done by body and 

 mind. This imperceptibly becomes less as men grow 

 older, and so less recuperative sleep is necessary, though 

 what work they do may be more effective and better 

 adjusted to its purpose when they have arrived at the 

 condition which is called " old age." 



We have seen that sleep in its widest sense comprises 

 the simple condition of quiescence brought about in 

 even the minutest living things by the recurring night, 

 as well as the strangely elaborated varieties of cessation 

 of activity in the whole or parts of the brain of man 



