AND PHYSIOLOGY. 



345 



615. Preventives of SI eep — Any unusual noise or place 

 of sleeping will prevent or disturb the sleep of many persons. 

 Thus the singing of a mosquito keeps many a man awake a 

 long time. But if a noise be repeated often, it will have 

 no effect of this kind. The college Freshman for the few first 

 mornings is readily awaked by the first stroke of the early 

 prayer-bell, but in a short time it has no effect whatever. 

 " A gentleman who had taken his passage on board a man of 

 w r ar, was aroused on the first morning by the report of the 

 morning gun, which chanced to be fired just above his head; 

 the shock was so violent as to cause him to jump out of bed. 

 On the second morning he was again awakened, but this time 

 he merely started and sat up in bed ; on the third morning 

 the report had simply the effect of causing him to open his 

 eyes for a moment and turn in his bed ; on the fourth morn- 

 ing it ceased to affect him at all, and his slumbers continued 

 to be undisturbed so long as he remained on board. :) 



616. An Absence of Accustomed Sounds prevents 

 Sleep. — The reverse of this sometimes happens, if there be a 

 cessation of monotonous and unaccustomed sound, by which 

 sleep was induced. Thus a person who has boon read or 

 preached to sleep, will awake if the reader or preacher pause 

 or stop, before any disturbance is made, and a person asleep 

 in a railway train, will often awake on the stopping, or even 

 on the slackening of the train. 



617. Amount of Sleep. — The amount of sleep necessary 

 for man, varies exceedingly, being affected by the conditions 

 of age, temperament, habit, and exhaustion. Infants and 

 very old people sleep the most. The former require it that 

 the constructive process may go on as uninterruptedly as 

 possible, and they generally sleep three fourths of the time. 

 The latter need a large amount of sleep, because the vital 

 energies are so feeble. 



615. What will often easily prevent sleep? Instance the college Freshman and the 

 gentleman on the man of war. 616. How does an absence of accustomed sounds affect 

 sleep ? 617. What amount of sleep is necessary ? What ages sleep the most ? 



