BRAIN AND NERVOUS SYSTEM. 371 



thought or observation, he will yet read, perhaps only the 

 lightest books, such as require the least exertion of mind, 

 or he will talk, if of nothing more important, he will tell of 

 the news of his little neighborhood, or he will sit at his 

 window and watch the passengers in the highway. In some 

 way or other, the brain is frequently exercised, though often 

 m the gentlest way. There are few who sit long in entire 

 listlessness, without a thought or an emotion. This would 

 be as painful as to sit immovably still for any considerable 

 period, without moving a limb. 



860. The brain has the same liability to fatigue from 

 labor, and exhaustion from excess of exercise, as the mus- 

 cles. It has a definite power of exertion, beyond which it 

 cannot pass, without leaving it enfeebled. If its action is 

 confined within this due limit, and sufficient opportunity is 

 given, at proper intervals, for its recovery, it will never fall 

 below its average standard of effective labor, and it will be 

 able on each day to do a full day's work. But, if this limit is 

 exceeded, its strength is reduced so far below its own stand- 

 ard, that it is not recruited in the allotted time of rest, and 

 consequently is unable to perform even the usual work on 

 the following day. 



861. A gentleman in 1842 had occasion to write several 

 hundred letters, and wished to finish them as early as possi- 

 ble. With the average industry he could write thirty a day, 

 without being fatigued beyond the power of the night to 

 restore his mental energies. But, feeling over-anxious to 

 finish the work, he began one morning at six o'clock, and 

 sat at his desk until twelve at night. Within these eighteen 

 hours he wrote fifty letters, and then, exhausted in mind, he 

 retired to rest, but did not readily sleep the brain, being 

 much excited, was not easily quieted. The next day he 

 was too weary to write, and wrote none. That day was 

 entirely lost ; and even on the third day he fell short of his 

 thirty lettersij_consequently he lost more than he gained by 

 this vain attempt to overwork the brain. 



862. When the brain has thus been in long and active 



