686 



SLEEP. 



passionless people, who may be said to live 

 very slowly, are usually great sleepers ; but 

 this rather because, through the dullness of 

 their perceptions, they are less easily kept 

 awake by sensorial or mental excitement, than 

 because they really require a prolonged cessa- 

 tion of activity. As they are half asleep 

 during the waking state, so would it appeal- 

 that the constructive operations must be far 

 from active while they are asleep, so little 

 do they seem restored by the repose. 



The amount of sleep, cceteris paribus, re- 

 quired by individuals, is very greatly influenced 

 by habit ; and, contrary to what we might 

 anticipate, we find that the briefest sleepers 

 have usually been men of the greatest mental 

 activity. Thus Frederick the Great and John 

 Hunter are said to have only required five hours' 

 sleep out of the twenty-four. General Elliot, 

 celebrated for his defence of Gibraltar, is re- 

 corded not to have slept more than four hours 

 out of the twenty-four.* Sir Gilbert Blane 

 states f that General Pichegru informed him 

 that, " in the course of his active campaigns, 

 he had for a whole year not more than one 

 hour of sleep, on an average, in twenty-four 

 hours." We suspect that if he had said " one 

 hour of sleep at a time," he would have been 

 nearer the truth. This we believe to have 

 been the case with regard to the Duke of 

 Wellington during the Peninsular campaigns. 

 Dr. Elliotson saysj, " I heard Baxter, the 

 coachmaker, declare that he never took more 

 than three hours' sleep during the most 

 active period of his life." We doubt if it 

 would be possible for any one to sustain a 

 life of vigorous exertion with a smaller allow- 

 ance than this. 



The influence of habit is further shown 

 in producing an aptitude for repose, or a 

 readiness to wake, at particular periods. 

 Thus, if a man is accustomed to go to rest at 

 ten o'clock, and to rise at six, he will pro- 

 bably awake at six, even if he have not fallen 

 asleep until twelve. And in like manner, 

 if the morning sleep have been unusually 

 protracted, the desire for sleep will probably 

 return at the accustomed hour in the evening. 

 The influence of habit is further exerted in 

 producing an aptitude for sleep whenever the 

 opportunity is afforded. Thus, the celebrated 

 pedestrian Capt. Barclay, when accomplishing 

 his extraordinary feat of walking 1000 miles in 

 as many successive hours, obtained at last 

 such a mastery over himself that he fell asleep 

 the instant he lay down. And the sleep of 

 soldiers, sailors, and others, who may be pre- 

 vented from obtaining regular periods of re- 

 pose, but are obliged to take their rest at 

 short intervals, may be almost said to come 

 at command ; nothing more being necessary 

 to induce it than the placing the body in an 

 easy position, and the closure of the eyes. 

 On the other hand, habit favors the protrac- 

 tion of sleep. This was the case with Quin, 

 the celebrated actor, who could slumber for 



* Macnish, op. cit. p. 34. 

 t Medical Logic, p. 83. 

 j Physiology, p. 001. 



twenty-four hours successively; and with Dr. 

 lleid, the metaphysician, who could take as 

 much food, and afterwards as much sleep, as 

 were sufficient for two days. 



It is needless to dwell upon the obvious 

 fact, that, other things being equal, the amount 

 of sleep required by man is proportional to 

 the amount of mental exertion put forth during 

 the waking hours ; since this is an obvious 

 result of what has been laid down as the 

 cause of the demand for sleep. It may be 

 remarked, however, that we must not measure 

 the amount of sleep by its duration alone ; 

 since its intensity is a matter of equal import- 

 ance. The light slumber which is disturbed 

 by the slightest sounds, cannot be as reno- 

 vating as the profound sopor of those whom 

 no ordinary noise will awake. 



There are certain states of the nervous 

 system in which there is an entire absence of 

 sleep ; and this may continue for many days, 

 or even weeks or months. Insomnia is, for 

 instance, one of the characteristics of acute 

 mania, and may also exist in various forms of 

 monomania. It is usually, also, one of the 

 symptoms of incipient meningeal inflammation. 

 And it may constitute a specific disease in 

 itself. In all these cases, however, the pre- 

 ponderance of the destructive processes over 

 the constructive manifests itself, sooner or 

 later, in the exhaustion of the mental and 

 bodily powers. Thus mania, when prolonged 

 or frequently occurring, subsides into de- 

 mentia. When meningitis (or rather inflam- 

 mation of the surface of the hemispheric gan- 

 glia) is fully developed, a rapid disintegration 

 of nervous matter takes place, as indicated 

 by the large amount of alkaline phosphates in 

 the urine.* The same would probably be 

 detected in cases of idiopathic insomnia; which 

 state, if it continue for any length of time, is 

 sure to be followed by a great sense of 

 wretchedness and prostration, frequently ac- 

 companied by continual restlessness. Such 

 effects, too, in a less aggravated degree, result 

 from habitual deficiency of sleep; whether 

 this results from emotional excitement, which 

 keeps repose at bay, or from a voluntary de- 

 termination to keep the intellect in activity. 

 This is a very common occurrence among 

 industrious students, who, with a laudable 

 desire for distinction, allow themselves less 

 than the needed quantum of repose. Head- 

 ache, tension, heat, throbbing, and various 

 other unpleasant sensations in the head, give 

 warning that the brain is being overtasked ; 

 and if this warning be not taken, sleep, which 

 it was at first difficult to resist, becomes even 

 more difficult to obtain ; a state of general 

 restlessness and feverish excitement are in- 

 duced ; and if, in spite of this, the effort be 

 continued, serious consequences, in the form 

 of cerebral inflammation, apoplexy, paralysis, 

 fever, insanity, or loss of mental power, more 

 or less complete, are nearly certain to be 

 induced. Some individuals can sustain such 

 an effort much longer than others, but it is a 

 great mistake to suppose that they are not 

 * See Dr. Bence Jones in Phil. Trans. 1846. 



