SOI 



SLEAFOKD 



SLEEP 



song*. These are scanty in Bohemian, and almost 



entirely wanting in Polish. Old Bulgarian liteia 

 ture, such as it has come down to us, consists 

 mainly of religious works, original and translated. 



Sec Pypin ami Spasovich, fttnrim SlariniukH/i Lit-ni- 

 (ur (' History of Slavonic Literature,' in Russian, 1.-7' 1 : 

 there iii a (ierman translation ) ; Miklosich, Vtnjleichtnde 

 liriitnmtitik tlrr Stttriwhtn Sprackfn (4 vola. Vienna, 

 1879); Leskien, Altbuhiaritchet Lcteburk (3d ed. ls-r, .. 

 For grammar:! of special languages, aee under respective 

 headings. And see Talvi (Mrs Robinson), Literature 

 oftht Slaric Xationt (New York, 1850) ; Slavonic Litrra- 

 tun, by tlie present writer, W. R. Morfill (Lond. 1883). 



Slenfbrd, a town of Lincolnshire, on the right 

 bank of the Slea, a branch of the Wit ham, 17 miles 

 SSK. of Lincoln. It has a fine church (built in 

 1271 ). a grammar-school ( 1624), and a monumental 

 cross ( 1850). Here King John fell sick after cross- 

 ing the Wash, and whilst spending the night in 

 the old castle (now almost wholly disappeared). 

 Pop. 4965. 



Sledges. See SLEIGHS. 



Sleep is symptomatic of repose in the hrain 

 and nervous system ; in those who are awake 

 cerehral activity is unceasing. Potential energy 

 is being constantly expended in mental opera- 

 tions, vital processes, muscular movements, \c. ; 

 also in the perception of impressions that stream 

 towards the brain incessantly from every part 

 of the economy and of the environment. This 

 is attended by wear and tear of the nervous 

 textures, and by the deposition in them of waste- 

 products pro|K>rtionate to the work effected. 

 Waking is therefore a positive condition one in 

 which energy is consumed more quickly than it is 

 restored, and than the waste-products are elimin- 

 ated. It is a state that entails a full working 

 blood supply to the brain. After a time, longer or 

 shorter, a sense of fatigue suggestive of repose 

 supervenes that is only relieved by sleep. Sleep, 

 on the contrary, is a negative state one in which 

 these processes are reversed. The brain is inactive ; 

 consciousness and volition are in abeyance; co- 

 incident ly the central blood-supply is diminished, 

 the brain is smaller in size, and its temperature is 

 lowered. Expenditure of energy is curtailed to the 

 greatest extent compatible with life. Recupera- 

 tive processes continue, and predominate over the 

 destructive ; the nervous structures are depurated, 

 and potential energy is accumulated. When 



recuperation is c pined awaking occur-, and is 



accompanied by feelings of invigoration. Waking 

 and sleep, therefore, are indicative of cerebral 

 activity and of cerebral rest ; they are both 

 physiological functions of a healthy nervous system. 

 NV'lien either is unduly prolonged, curtailed, or 

 modified it gives evidence of a departure from 

 health. 



The brain is a composite organ. It contains 

 innumerable centres which dominate an equally 

 vast variety and number of functions ; and these 

 require ami obtain sleep in varying degrees accord- 

 ing to (heir functions. The supreme ( psychical) 

 centres which are constantly alert during waking 

 need more sleep than some of the subordinate 

 centres. These latter rest partially by day, so that 

 the complete abdication of their functions at night 

 IS less urgently required. 



The incursion of sleep is gradual. It is syn- 

 chronous with the subsidence of activity in the 

 brain and nervous -y-iem. and it is best studied in 

 thi- connection. Molecular activity does not cease 

 in the whole brain instantly, but in one portion 

 after another until the whole organ become- 

 tranquil. It is suspended lir-t in the centres 

 situated highest in the cerebrum, and afterwards 

 in those at Tower levels, till the medulla oblongata 

 and spinal cord are included. It consequently 



atlccts the motor centres of the hrain first. The- 

 earliest symptom of sleep is the weakening of th& 

 voluntary muscles; iclaxation takes place in one- 

 set after another until the Ixwly iu-sumes the hori- 

 /ontal |M>sture. The sphincter muscles arc excep- 

 tional ; they remain contracted. During deep sleep- 

 true slackening occurs in the muscular liluc-. even 

 in diseases like tetanus and hydrophobia. A man 

 may fall asleep in motion, its in walking or 

 riding, and maintain his equilibrium ; a certain 

 amount of activity being sustained in the motor 

 centres enable- him to do so. If he yields to sleep 

 in a stationary attitude, the motor centres lieing 

 quiescent, he tends to sink into the recumbent 

 posture. Activity next wanes in the psychical 

 centres of the brain. The will ceases to control 

 the working of the intellectual faculties, and the 

 perceptive powers are lessened. The mind, no 

 longer inhibited from within nor corrected from 

 without, revels in ab-mditic- until mental o|>era- 

 tions cease, or, at least, till they are wrapped 

 in oblivion. The centres of the special sen-e- 

 ta the brain are next involved, and usually in the 

 following order ; they fail to perceive slight 

 or ordinary impressions, while their s|>ecial nci\c- 

 transmit them in a slow and imperfect manner, 

 (n) Vision: The eyelids close; the eyeballs turn 

 upwards and inwards in the orbits. The eye 

 balls occasionally, if rarely, move inde|>endent]\ , 

 and not in unison, during sleep. The pupils con- 

 tract the contraction being in ratio to the depth 

 of sleep ; they dilate widely in the act of 

 awaking. (6) Hearing: Loud noises interrupt 

 sleep, though an expected noise does so more 

 readily. Monotonous sounds do not prevent "i 

 interrupt sleep ; their cessation may terminate 

 it. (c) Smell : Slight odour- may prevent the 

 onset of sleep; but very pronounced smells are 

 required to disturb it. ((**) Taste: It is difficult 

 to determine the condition of this sense during 

 sleep, the sense of touch being apt to vitiate the 

 conclusion, (e) Touch: This is the most sen-i 

 the sense during sleep. It is chiefly through 

 it that man is warned of danger, and that his 

 safety is secured. Heflex acts can always be 

 elicited, their vigour depending on the strength of 

 the stimulus, the degree of sensitiveness of the 

 part to which it is applied, and the depth of sleep. 

 The centres in the medulla oblongata then become 

 less active. They chiefly dominate the heart, the 

 lungs, and arterial pressure. The heart beats from 

 ten to twenty times less per minute, and the blood 

 pressure is diminished. The respirations are about 

 four fewer per minute. The inspirations are 

 shallower and chiefly thoracic. The pause between 

 inspiration and expiration is practically absent. 

 Pettenkofer and Voit stated that of the total car- 

 iKinic acid eliminated in twenty-four hours 58 per 

 cent, is given off during the twelve hours of day 

 and 42 per cent, during the twelve hours of night ; 

 whilst 67 per cent, of the oxygen taken in i- 

 alworbed during the twelve hours of night and .S.'f 

 per cent, during the day. The centre- that domin- 

 ate the various secretions only respond to suitable 

 stimuli, and as these are wanting during sleep the 

 secretory organs are less active. The digestive 

 juices are not formed, and if the gast ro intestinal 

 movements do not cease entirely, they are greatly 

 lessened. The urine is secreted in one-fourth the- 

 quantity. The quantity of sodium chloride, sul- 

 phates, and urea it contains is smaller ; the latter 

 is decreased one half. The secretion of sweat is 

 increased, and that of milk is continued. 



In consequence mainly of the inactivity of the 

 Ixxlily functions the bodily temperature falls as 

 much as from 0"'5 to 2 F. , chiefly for some hours 

 after midnight: it l>eing lowest about 4 A.M. It 

 falls similarly by day in those who work by night 



