VALUE OF SLEEP 243 



enough ; at twenty years, from nine to nine and a half ; 

 and in adult life, from eight to nine. 



Habits of sleep. The nervous system tends to adapt 

 itself to whatever habits of sleep one acquires. Persons 

 who have accustomed themselves to short sleeping hours 

 are apt to feel that they are exceptions to the general 

 rule in that they require less sleep than the majority 

 of persons. It is, however, a matter of fact that those 

 who have regularly eight or more hours of sleep out of 

 the twenty-four rarely break down nervously, whereas 

 those who get less than eight hours, and especially those 

 who get less than seven, are very apt to break down 

 under mental strain. The safe rule, therefore, is not 

 to stint the nervous system in the hours of repair and 

 recuperation. 



Nervous breakdown. Curiously enough, one of the 

 early symptoms of the failing strength of the nervous 

 system is its apparent ability to do hard brain work on 

 but little sleep. Soon, however, as the habit of sleep- 

 ing less and less increases, the ability to work hard de- 

 creases. Finally, sleeplessness becomes so marked that, 

 in order to avoid a complete breakdown, a rest of months 

 and even of years may be necessary. The nervous sys- 

 tem has made a brave attempt to adapt itself to the 

 hardship of too much work and too little rest and has 

 failed. 



Value of work. Next to sleep, the most important 

 condition for the health of the nervous system is good 

 wholesome work. Like all the tissues of the body, the nerv- 

 ous system is developed by exercise, without .jvhich its 

 growth and power are stunted. To this exercise, all the 

 activity of the body contributes. Even the higher cen- 

 tres of the cortex, which are concerned with the more 

 purely intellectual forms of our activity, with our will- 



