Page:The New International Encyclopædia 1st ed. v. 18.djvu/284

* SLEEP. 238 SLEEPING SICKNESS. slower and weaker pulse ; and lessened arterial pressure. There are three main types of sleep theory, the circulalory, the chemical, and the histological. The first circulatory theory was that of con- gestion. Sleep was the result of pressure upon the brain due to venous congestion. The evidence for this view came from the analogy between the condition of sleep and that produced by apoplexy, opiates, and the lethargy caused bj' pressure on the brain in cases of fractured skull. The second theory turns to amc-iiiia. the e.xact opposite of congestion. A large number of well-attested facts prove the existence of a cortical ansemia during sleep. Pressure upon the carotid arteries will produce a dream-like state of consciousness. In several instances of fractured skull direct me- chanical measurements have demonstrated the anc-emia of sleep. The chemical theories are of two types, accord- ing as they are based on ( 1 ) combustion or ( 2 ) .auto-intoxication. The combustion theories, all of which are concerned with the use of oxygen or carbonic-acid gas, may be represented by Pflii- ger's idea that the stored up intra-molecular oxygen is exhausted by activity (vibration and explosion) of nerve cells, and each cell finally becomes saturated with carbonic acid. The ex- plosions of the cells become less numerous, and the condition of relative cerebral inactivity, sleep, thus results. This theory is not buttressed by sufficient experimental evidence, nor does our recent knowledge of the function of oxygen in the body warrant us in attributing sleep to its lack. In the auto-intoxicatioji theories it is as- serted that certain products of decomposition of DIAGRAM SHOWING THE DEPTH OF SLEEP AS THE NIGHT ADVANCES. The abscissje (0. 1...7) represent the hours elapsed since the oncoming of sleep: the ordinates (0, 5. ..25) show the re- lative intensit.v of stimulus necessary to arouse the sleeper in any given hour. living substance influence the continuance of cell activity; in the older form of this theory the products mentioned were chiefly lactic acid and creatine; in the recent theories the influence of modern bacteriology' has led to the substitution of certain poisons, such as the ptomaines and the leucomaines, which are formed more rapidly than they can be oxidized during active labor of the day. During sleep these poisons are gradu- ally oxidized and removed from the blood. An excessive quantity of these substances produces insomnia, which, as we all know, is often char- acteristic of extreme fatigue. Tlic rapid advance in histological technique within the last few .years has led to certain dis- coveries concerning the nature of the nerve cell and its processes, or the neurone, which shed some light upon the conditions of sleep. Of special interest are the results of investigations upon the connection of neurone to neurone. We know that each nerve element is structurally inde- pendent, but functionally interdependent. Mi- croscopic examination has shown that the nerve cell possesses dili'ercnt chemical properties when in a waking or a sleeping or fatigued condition, and that the disposition of the 'contact gran- ules' or 'gemmules,' which some authorities deem the structural means for the interconnection of neurones, while functioning, varies according to the condition of activity or rest in the nervous system. Upon these facts various theories have been advanced, which find the cause of sleep in dissociations of the neurones. These theories have taken three principal forms: Dissociation through amceboid movements of cell p-rocesses, dissociation through interposition of neuroglia (non-nervous) cells, and profuse connection through torpor of processes. But no single theory, whether vaso-motor, chemical, or histological, is adequate for a com- plete explanation of sleep. Recent observations of the daily life of protozoa and other simple forms show that such organisms never sleej), and, of course, never exhibit phenomena of fatigue. Somewhere in the line of evolution the phenome- na of fatigue and sleep must make their ap|)ear- ance. It seems likely, therefore, that ])rofitable work upon the proldem of sleep is to be expected in the future from the side of comparative physi- ology and psychology. BiBLioc.K.piiY. Donaldson. The Grouth of the Brain (New York. 1.S07); American Text Book of Physiology (Philadelphia, 1896) : Errera, Snr le mccanisme du sommeil (Brussels, 189.5) ; Manaceine, Hleep. Its Physiology, Pathology. Hy- giene, and Psychology ( Eng. trans., New York, 1897) ; Michaelis, Der Hchlaf nach. seiner Bedeu- tung fiir den gesnndcn und kranken ilenschen (Leipzig, 1894), For detailed bibliography, con- sult i'oster or Manaceine. See Dbeamino : Somnambulism. SLEEPER SHARK, or Xurse Shark. One of the large .rctic sliarUs of the family Scym- nidiP, closely allied to the dogfishes (Squalidae), especially Somniosis mierocephahis, which reaches a length of ir> feet and is renowned as an enemy of whales, biting large pieces out of their bodies. SLEEPING BEAUTY, The. The fairytale of a jirincpss who falls into an enchanted sleep for a hundred years and is awakened by a prince, who penetrates the dense wood which grew up about her castle. It is told by Charles Perrault in "La Belle au Bois Dormant." in Contes du temps passe (1697). translated by Grimm as Dornrosehen. and versified by Tennyson in "The Day Dream." The legend in varying forms is very old, found even in Egyptian and Hindu tales and paralleled in the magic sleep of Brunhilda. SLEEPING SICKNESS, or Negro Lethargy. An epidemic disease occurring among the inhab- itants of tropical West .frica, characterized by periods of sleep recurring at short intervals. The course of the disease is from four months to