SLEEP. 607 



horseback, and coachmen on their coaches."? " Nay, silence 

 itself may become a stimulus, while sound ceases to be so. Thus 

 a miller being very ill, his mill was stopped that he might not be 

 disturbed by its noise ; but this, so far from inducing sleep, pre- 

 vented it altogether; and it did not take place till the mill was 

 set a-going again. For the same reason, the manager of some 

 vast iron-works, who slept close to them, amid the incessant din 

 of hammers, forges, and blast furnaces, would awake if there was 

 any cessation of the noise during the night.'* " A person who 

 falls asleep near a church, the bell of which is ringing, may hear 

 the sound during the whole of his slumber, and be nevertheless 

 aroused by its sudden cessation <i :" and a person, sent to sleep 

 in a church by a stupid sermon, generally awakes as soon as the 

 preacher's humdrum is at an end. 



The ordinary cause of sleep is fatigue. The activity of the 

 day exhausts the powers of the brain feeling, understanding, and 

 will, and the brain sleeps. The greater, in point of duration or 

 intensity, the activity, the greater the disposition to sleep, unless 

 the exhaustion has produced aching or irritation, morbid con- 

 ditions, which, destroying the course of health, may prevent sleep. 

 It matters not whether the activity has been volition, passion, 

 sensation, or reflection. Exhaustion of one part of the encephalo- 

 spinal system exhausts the rest ; nay, so bound up together are 

 all parts of the body, the brain and the rest, that fatigue of the 

 brain exhausts all other parts, and fatigue of any part will impair 

 the powers of the brain, and great muscular exertion therefore 

 of any voluntary part exhausts the vigour of the mind. No one 

 thinks well who is fatigued by exercise, and nothing causes sleep 

 at night more than good exercise in the day. All studious men, 

 who are real thinkers, require a large allowance of sleep ; and find 

 a great difference in the soundness and urgency of sleep after a 

 day of intellectual labour, and a day accidentally spent in the 

 shallow prattling and reading common to the greater part of the 

 more expensively, but not better, educated persons who fancy 

 themselves to possess cultivated understandings ; or in the per- 

 formance of what is the daily routine of the majority of popular, 

 and probably fashionable, practitioners, who are destitute of sound 

 knowledge and strangers to reflection and study, and yet impu- 



p Dr. Macnish. q Dr. Macnish. 



s s 



