SLEEP 



505 



and sleep by day. According to Helmholtz, a 

 man gives off about three times more heat when 

 he is awake than he does when he is asleep. Dur- 

 ing sleep the economy is more vulnerable to the 

 influence of deleterious surroundings ; it lias less 

 resisting power. Hence it is that infectious and 

 malarial diseases are so readily contracted by sleep- 

 ing in places in which these poisons abound ; hence 

 also the liability to catch cold from sleeping in a 

 draught. Briefly summarised, during sleep the 

 brain, ganglia, medulla oblongata, and spinal cord 

 are in a state of repose. And the extent to which 

 they are involved may be inferred from the fact 

 that sleeping persons suffer little, if any, from 

 shock in accidents which affect those who are 

 awake most injuriously. 



Sleep varies in depth in persons of different ages. 

 It is usually profound in the young, and light in 

 the aged. The depth bears some relation to its 

 duration. Natural sleep varies from time to time 

 during the same night. The observations of Kohl- 

 schutter, of Rumnio and Ferrannini, and of Mon- 

 ninghoff and Piesbergen showed that it was 

 deepest an hour after its onset, when its intensity 

 decreases quickly, then more slowly, and again it 

 becomes more profound a second time after tour to 

 five hours. This is important in sleep-disturbance, 

 for excitations will act more powerfully when it is 

 lightest. On the other hand, when it is deepest 

 the lowest centres are least inhibited, and the 

 blood is less thoroughly oxygenated. It is then 

 that epileptic, convulsive, spasmodic, and such-like 

 seizures are most apt to occur. Cases of sleep 

 lasting for weeks and months have been recorded 

 ( that of Johann Latus in the hospital of Myslowitz 

 in Silesia in 1891-92 lasted 11 months) ; in Britain 

 it occurs in neurotic patients, and sometimes is 

 called trance. It is pathological and not natural 

 sleep. In western Africa 'sleeping sickness" is 

 a well-known fatal disease. 



Cause of Sleep. For upwards of two thousand 

 years continuous attempts have been made to 

 elucidate the cause of sleep without success ; many 

 theories have been promulgated, but they have 

 fallen short of explaining it. 



Of circulatory theories the one that prevailed 

 daring many centuries attributed sleep to a deter- 

 mination of blood to the head ; and much evidence 

 was adduced in its support. Nevertheless, con- 

 gestion of the brain is incompatible in health with 

 good and refreshing sleep. This hypothesis was 

 replaced by the aniemic theory. From the obser- 

 vations of Don.lere (1854), Durham (1860), Reg- 

 nar.1 (1868), Hammond and Weir- Mitchell (1869), 

 and Ehrmann, Salathe, and F. Frauck (1877), it 

 would seem to be conclusively demonstrated that 

 the blood-supply of the brain is lessened during 

 sleep. Whether this is causative, concomitant, or 

 consequent is still open to conjecture. Patho- 

 logical aim'mia is a well-recognised source of wake- 

 fulnfss. It appears certain that a blood-supply 

 sufficient for nutritive purposes, but insufficient for 

 mental activity, is an essential factor in natural 

 sleep. The brain, like all other organs, governs 

 and is not governed by its vascular supply. 



Hiimboldt suggested one of several chemical 

 theories that sleep was due to the want of oxygen ; 

 and many have since urged that everything that 

 deprives the brain of oxygen conduces to sleep. 

 An atmosphere deficient in oxygen, or one contain- 

 ing an excess of carbonic acid, induces drowsiness 

 and sleep, but it is poisoned, and not healthy sleep. 

 Pfliigger lielieved that activity of the psychical 

 cells depends on the quantity of intra-molecular 

 oxygen they contain, and that all function is 

 attended (particularly in the gray matter) by ex- 

 plosive movements in the cells, caused by the com- 

 bination of oxygen with the tissue-elements, in 



which oxygen is consumed and carbonic acid is 

 formed. He thought that these movements used 

 up the oxygen at a greater speed than the circula- 

 tion could replace, and that a time arrived when 

 the lack of oxygen and an excess of carbonic acid 

 caused drowsiness and sleep. Again, it has been 

 urged that the waste-products (resulting fron* 

 mental operations) in the nervous textures occa- 

 sioned sleep. Preyer believed that the accumula- 

 tion of these (ponogenes) at first caused fatigue, 

 then sleep, and that waking occurred when they 

 were eliminated in sleep. This doubtless is a. 

 factor in the causation of sleep, but it does not 

 explain it. 



The absence of external stimuli, such as occurs in 

 the darkness and quietness of night, has been 

 credited with causing sleep. It is a desirable aid 

 to sleep, but, in health, sleep ensues despite all 

 disturbing agencies even on the torture-rack. 

 Sleep has been ascribed to the law of periodicity 

 that governs all organised things. The study of 

 the l>odily functions shows that rest and activity 

 alternate even the heart gets about ten to twelve 

 hours rest in the pauses between its contractions. 

 Of other numerous theories, it will suffice to say 

 that no one of them can be accepted as fully 

 explaining and finally settling the subtle problem. 

 It may be that the mystery will never be solved 

 until a deeper insight into the working of the mind 

 itself is acquired. 



How long should one sleep ? is a question that must 

 be answered generally. No hard and fast law can 

 be laid down ; every man must be a rule to him- 

 self. It is quite clear that nature intends every- 

 one to sleep until the effects of waking are dissi- 

 pated, and until the bodily energy is renovated. 

 In childhood, when the constructive processes of 

 growth involve large expenditure of energy, sleep 

 is long and profound. In youth much sleep is still 

 needed. In middle age, when decay and repair 

 alone require to l>e balanced, less sleep is required. 

 In old age, when repair is slowly and imperfectly 

 effected, more sleep is desirable. The duration of 

 sleep is also largely influenced by sex, tempera- 

 ment, occupation, habit of sleep, season, climate, 

 &c. The true guide is the recuperation of the 

 energies ; that is indicated by a feeling of well- 

 being on awakening. Some persons awake, after 

 sleeping for an apparently sufficient number of 

 hours, worn, jaded, and exhausted. That is an 

 indication of disease, pointing to an inability on 

 the part of their textures to accomplish their 

 reparation. 



Sleeplessness. The effects of curtailed sleep are 

 very marked. The loss of a single night's sleep is 

 attended by symptoms of enervation ; that of several 

 nights' sleep, by serious consequences. In many 

 diseases the lack of sleep determines a fatal issue ; 

 conversely, sleep often determines recovery. Few 

 persons appreciate the fact that the voluntary cur- 

 tailment of sleep for an hour every night for a year 

 is equivalent to the loss of forty-four nights' sleep of 

 eight hours' duration. That represents an enormous 

 expenditure of energy e.g. during that time the 

 cardiac pulsations are approximately 210,000 and 

 the respirations about 90,000 more frequent than 

 they would have been during sleep. Lndue cur- 

 tailment of sleep is attended by loss of flesh, the 

 essence of emaciation being the preponderance of 

 decay over repair. The skin becomes dry, and it 

 loses its suppleness and translucency. All the 

 bodily textures are badly nourished, and the 

 organs suffer from lack of innervation. When 

 sleep has been limited unduly, inability to sleep 

 ensues and becomes the bane of existence. Ex- 

 haustion of the cerebral structures leads to still 

 graver symptoms, such as insanity. Indeed, 

 insomnia preludes or enters to a greater or less 



