378 MAUEY OX SLEEP AND DREAMS. 



what seem its anomalies, have all reference, more or 

 less direct, to this great function of repair a function 

 fulfilled, it may be, simply by suspension or modifica- 

 tion of those actions which exhaust the nervous power, 

 while reproduction of this force is going on or pos- 

 sibly by changes in the brain itself, an effect of the 

 conditions to which it is submitted in sleep. 



For it must be remembered that sleep repairs not 

 the vital functions only, but simultaneously those func- 

 tions which we distinctively describe as mental attributes, 

 and of which the brain is, to our present limited com- 

 prehension, the organic instrument. The intellectual 

 part of our nature, taking the phrase in its largest 

 sense, is exhausted by its continued exercise, in like 

 manner as the bodily organs, and requires the same in- 

 termittent periods of repose and repair. 



If other proof were needed of the great function 

 which sleep fulfils in the economy of life, it may at 

 once be found in the effects which follow the privation 

 of this repair. A single sleepless night tells its tale, 

 even to the most careless observer. A long series of 

 such nights, resulting, as often happens, from an over- 

 taxed and anxious brain, may often warrant serious 

 "apprehension, as an index of mischief already existing, 

 or the cause of evil at hand. Instances of this kind, 

 we believe, are familiar to the experience of every 

 physician. 



But here, as in so many other cases, the evil of 

 deficiency has its counterpart in the evil of excess. 

 Sleep protracted beyond the need of repair, and en- 

 croaching habitually upon the hours of waking action, 



