AND PHYSIOLOGY. 



343 



which there is a more or less perfect suspension of the activ- 

 ity of the brain. The functions of digestion, secretion, and 

 respiration, proceed during the soundest sleep, though with 

 less activity than during the wakeful state. In many cases, 

 however, the functions of the brain do not entirely cease, as 

 is seen in the phenomena of dreaming, where the brain seems 

 to be actively at work, but the senses and animal functions 

 are quiescent. Sleep is demanded by all animals to procure 

 rest to the different organs of the body, and in health it comes 

 to all, though in different degrees of soundness, but generally 

 the greater the exhaustion, the more complete the sleep. 



612. Periodical Tendency of Sleep— The Will can 

 for some Time overcome Sleep— The tendency to sleep 

 is periodical. All persons feel an inclination to sleep during 

 some portion of the twenty-four hours, and during the night, 

 if health be good and nature not perverted. Some strong 

 intellectual effort, however, or some powerful emotion, will 

 overcome drowsiness for a long time, as in the case of the 

 student working out a difficult problem, or a mother watching 

 her sick child. But when the problem is mastered, and the 

 child has safely passed the crisis, sleep comes on with irresist- 

 ible force. Cases occur constantly to show that the brain 

 must have its repose in spite of intellectual effort or danger. 

 It is related that boys wearied out with continued labor in the 

 battle of the Nile, slept during a part of the action, and in 

 another naval engagement, a captain slept two hours within a 

 yard of his largest gun, which was kept in action during the 

 whole time. Indians at the stake of torture will sleep on the 

 least remission of agony, but awake as soon as it is renewed 

 again. And we learn that a most barbarous punishment is 

 still practiced in China, that of keeping a victim awake until 

 he dies of sheer exhaustion. The distress of it is said to be 

 terrible. 



611. What is sleep ? What powers are inactive during sleep, and what processes are 

 carried on daring it? What is sleep necessary for? 612. State the fact of a periodical 

 tendency to sleep. Can the will overcome sleep ? For how long a time can it do it ? 

 lielate the facts mentioned. 



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