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rently, but soon without control; the brain- disturb his contemplated enjoyment. An matter wastes too rapidly, and delirium en- after-dinner sleeper temporarily resembles sues. During this time the volatile alcohol the permanent condition of a pig fattened is diffusing itself through the system, con- for the butcher. In its case, fat accumuverting arterial into venous blood, and load-lated round the viscera pushes up the diaing that fluid with a spirit which has a ten-phragm against the lungs, and compels them dency to prevent change in the tissues, so to play in a contracted space. When the that the drunkard gradually becomes stupid, animal further distends its stomach with falls off his chair in the stupor of sleep, or, food, it gives a few grunts as an ineffectual if too far gone, dies of venous apoplexy. attempt at a more active respiration, and is In a like way intoxicating gas, the nitrous in a deep sleep in a few minutes. Obese oxide of Davy, acts upon its inhaler. The men, from a similar cause, are also prone first effect is to produce rapid arterializa- to sleep. tion of the blood, so that the inhaler has an ardent desire for activity. mount up into the air like a bird, or he be- in inverse proportion to the amount of oxygen He tries to "The tendency to sleep in different animals is comes combative, and knocks down persons bonic acid produced. Thus reptiles and the nain his vicinity, while his ideas become won-ked amphibia produce, relatively to their weight, consumed by them, and to the amount of carderfully rapid, though incoherent. During this time carbonic acid is being abundantly formed, and its depressing effect soon ends the period of exhilaration. Under the influence of chloroform the period of exhilaration is usually momentary, for the vapour acts quickly on the blood, and soon changes that in the brain from a red to a purple hue. As the anesthetic influence passes away, the purple hue fades, and numerous vessels filled with red blood again become apparent. Harley, in his experiments with blood, found that a small portion of chloroform added to it prevents transformation, and therefore yields the condition for sleep. The cases now cited show clearly that any cause which increases the flow of arterial blood in the brain produces cerebral excitement; while any cause which diminishes the action of oxygen produces depression, sleep, or torpor, according to its degree of action. The known tendency to sleep after dinner may be given as another illustration. When the stomach is distended with food, the diaphragm is made to encroach on the lungs, and diminishes their play, or, in other words, prevents the full access of oxygen to the blood. At the same time the stomach becomes charged with arterial blood, and the vessels of the intestines also are
according to the experiments of Müller, onetenth the amount of carbonic acid evolved by mammalia and one-nineteenth that of birds. We have no numbers to express the tendency to sleep of these animals, but it is known that reptiles are peculiarly liable to be in a state of torpor or sleep, while birds are, on the contrary, wakeful animals. A reptile, such as a frog, will exist in a state of torpor for hours in an atmosphere of hydrogen, while birds die in a few seconds with the ordinary symptoms of asphyxia. The same circumstance of a diminished supply of oxygen, which induces sleep in reptiles, acts also in different mammalia in the promotion of this state, according to the relative size or activity of their lungs. It also operates in a like way with different men.
erably conclusive that sleep is due to a diminished supply of arterial blood in the Having now seen that the proofs are tolbrain, or, in other words, to the inability of itself to the world, we now proceed to conthe brain-matter to undergo those changes sider more in detail than we have yet done, through which the mind can alone manifest the objects and purposes of sleep. These are mainly
1. The restoration of wasted organs.
unusually full. If an animal in the act of which we can ascertain to what extent the digestion be killed, the vessels of the aliWe have as yet no exact measure by mentary canal and of the liver are found to day are repaired during the night, though be gorged, while those of the brain, spinal doubtless much is done in this way. As general tissues of the body wasted in the marrow, and even of the muscles, are contracted and comparatively bloodless. Here, then, we have all the conditions of sleep. urea is the chief representative of waste, The postprandial sleeper now draws his upon the subject by ascertaining how much we might expect some light to be thrown chair close to the fire, in order that his nap twenty-four hours. A man who spent two may be undisturbed. There are two physi- days, one at rest, chiefly in reading novels, passes away at the different periods of the ological reasons for this act. Less oxygen the other at work with a turning lathe, is entering the body to burn the food, and he feels cold; but this cold would excite the passed in the first day 58 per cent. of the respiratory organs to increased activity, and
* Dr. Lyon Playfair.
urea in the day-time, and 42 per cent. during | for which physiologists are anxiously waitthe night; while in the day of work 54 per ing, prove that night is the chief period for cent. were eliminated during waking and storing up oxygen in the blood, to be used 46 after sleep. As about 20 per cent. of during the day in the production of work, the total quantity would have amply sufficed when volition finds it ready at hand to exefor the waste of the involuntary organs, cute the voluntary motions, and to enable which are still active during sleep, the fig- the mind to make its manifestations through ures show that the renewal of tissues and changes in brain-matter. If it be estabthe removal of wasted matter are actively lished that night is the time for storing up proceeding during the night. The cells, in oxygen, the importance of sleeping in wellwhich all organized tissues originate, have ventilated rooms cannot be too strongly an independent vitality, and are not influ- insisted on. The workman has to store up enced in the performance of their duties by his force during the night, and should take the sleep of the brain, so that nutrition still every precaution to assist Nature in fulfillcontinues to be active, probably more active ing this important function. Pettenkoffer than at any period of the day, for construc- has compared this storing up of oxygen in tion is now the chief work of the body, the the circulating blood to a mill-stream, which animal, during sleep, having chiefly a vege- the miller can turn on one, one-half, or tative existence. The quiescence of the three-fourths, in exact proportion as the brain, and its inability to receive impres- work requires. The will uses the bloodsions or to send forth the commands of stream in the same way, having it always volition, permit a complete restoration of available for work. The miller has his millparts by delivering over the body to the pond as a reservoir of force to supply the entire control of constructive nutrition. stream; while the will has its reservoir of Sleep, in this sense, is not the brother of force filled during the night, and amply sufdeath (consanguineus leti), but rather the ficient to meet the wants of the day. But preserver of life. Somnus was very proba- another analogy may perhaps explain the bly the son of Nox, for she gave birth to process still better, and serve to fix it in our the day as well as to sleep; but the ancients minds. The little blood-disks sailing along may have been mistaken in making Erebus, in the stream of blood, with a vitality and a deity of hell, his father, for his birth be- motion of their own, may be likened to a tokens rather a celestial than an infernal fleet of tiny vessels in incessant activity. influence. During the night they take in a cargo of During sleep force is stored up in the oxygen in the lungs, and sail away with it body in a remarkable manner, as has been to every part of the system. Some of them shown by the experiments of Pettenkoffer. part with their cargo even during the night, At Munich, the King of Bavaria has erected and, laden with a return cargo of carbonic a chamber, supplied with every appliance acid, sail back to the lungs, where they disfor measuring the air which enters it and charge it by exchanging it for a new supply for ascertaining the composition of the air of oxygen. But the greater number of our that passes from it. This chamber is suffi-fleet are less active, and only discharge ciently large to enable persons to live com- their oxygen during the day, waiting till fortably in it during the time that they are made the subjects of experiments. Among other remarkable results which have flowed from the enlightened liberality of the Bava- What we have now stated as to the rich rian King, we have a series of experiments store of oxygen laid up in the blood during made on various individuals during their sleep, may appear to be inconsistent with waking and sleeping state. A healthy man the theory that it is due to a diminished was put into this chamber, with the light oxidation of brain-matter. A little considoccupation of taking to pieces the work of eration will show that there is no inconsista watch. Of the total quantity of oxygen ency. Sleep arises when work has dimininhaled by him 33 per cent. only were ab- ished the oxidation of the blood, and sorbed during the day, and about double, increased the amount of carbonic acid in or 67 per cent., during the night; while the the system, or, in other words, the quantity exhaled carbonic acid, the gaseous product of venous blood. It is not improbable that of transformation, was 58 per cent. during the excess of carbonic acid in the blood has the day and 42 per cent. during the night. a direct influence in the result, for the In the day of mechanical labour, the differ-experiments of Liston have shown that this ence between day and night was still more substance has a positive sedative effect upon striking. These remarkable results, if they the elements of the tissue, paralysing for the are confirmed by subsequent experiments, time their vital energies. The brain has
night before they take up again a new cargo of this gas, which has so many important functions to perform.
diminished in volume by work, as a muscle its temperature being only half a degree does, and a flow of cerebro-spinal fluid above that of the air. The hedgehog, which takes place, helping at the same time to wakes every three or four days to get snails expel the blood from the cranium. The and worms for food, in its waking state has a brain no longer being in a condition to temperature of 95°, and in its sleeping conoxidise, rapidly falls into unconsciousness, dition only of 45o. and the mind sending no commands to the voluntary organs, enables the blood to devote "Perhaps I might venture to throw out an itself to constructive instead of destructive explanation of the winter sleep of animals. In summer they accumulate fat in their bodies, work, and to get rid of its excess of carbonic acid, renewing at the same time its probably from the very fact of the smallness of oxygen. The increased supply of the lat-sufficient supply of oxygen to convert the surtheir lungs, which prevents the entrance of a ter, however, finds only partial access to plus unazotised food into carbonic acid and wathe brain, from which it is shut out by the ter. This fat, accumulating around the caul cerebro-spinal fluid. As the blood, how- and loins, pushes forward the diaphragm against ever, becomes richer in oxygen during the the lungs. The fat also gathers round the edges progress of the night, it courses through the of the heart and lungs, and still further diminlarger arteries still open to it (for many of ishes the space in which the latter ought to play. the capillaries become, by their contraction, Thus respiration is greatly retarded, in consetoo small to admit the blood-disks, and pass quence of which the animal falls asleep. only liquor sanguinis), and the increasing explanation accords with the interesting experioxygen becomes the condition of a natural ments of Saissy, who has shown that hybernatawaking from sleep. This explains the ing animals decompose most when they are in a experiments of E. Smith, who found that state of the greatest activity, that they respire towards morning more carbonic acid is and that the respiration becomes extremely less during autumn, as their fat accumulates, evolved, even during sleep, than is the case feeble at the commencement of their winter's in the earlier hours of the night. As the sleep, and ceases when that sleep becomes prooxygen augments in the blood-vessels of the found. There is not continued cessation of rebrain wakefulness follows, because that ele-spiration, for during the long-continued sleep of ment acquires power to compel cerebral hybernating animals the lungs play slowly, sevchange, and the mind now finds the mate- eral minutes often elapsing between each respirrial, placed at its disposal for external man- ation; the diminished state of oxidation in their ifestations, renewed and invigorated by con- bodies is proved by their reduced temperature, structive nutrition during repose. which is generally not higher than 40 above that of the surrounding medium. In this state, they may be aptly compared to lamps slowly burning, their fat being the oil, and the lungs the wick of the lamp. If this view of hybernadisposition to sleep, and it is known that pigs in tion be correct, very fat animals should show a the last stage of fattening are rarely awake. Instances have occurred in which pigs, being placed in a favourable condition, have actually proved their capability of being in a state analogous to hybernation. Thus, Martell describes the case of a fat pig overwhelmed with a slip of earth; it lived 160 days without food, and diminished in weight 120 lbs."
Hybernation is that state of winter sleep to which certain animals are subject. Among the most distinct winter sleepers are the bat, hedgehog, the marmot, the hamster, and the dormouse. The bear and beaver pass their winter in lethargy, but may be active enough if aroused. Cold-blooded animals, including the chelonian, saurian, ophidian, and batrachian tribes, have a winter of lethargic apathy, as also have some kinds of fishes. Diurnal and winter sleep are periodical phenomena differing only in degree. A bat sleeping during the day sinks in temperature just as it does in its long winter sleep. Hybernating animals have a ject without alluding to the phenomena of We can scarcely take leave of our subdegree of muscular irritability inversely pro- dreams and wakefulness, although we now portionate to the activity of their respiration. leave the region of science for that of specThus reptiles, with a sluggish respiration, ulation. Wakefulness, more or less in dehave a high degree of muscular irritability, while birds, with active respiration, are gree, is the experience of every one under much inferior in that respect. This provi- certain conditions, such as overwork of the sion is requisite during a long sleep to brain, mental excitement, or the stimulus allow the low arterialized blood to stimu- of tea or coffee. In certain forms of insanlate the heart to action, otherwise the animal must die of asphyxia. In full hybernation very little respiration goes on at all. A bat during its sleep took sixty-six hours to produce 34 cubic inches of carbonic acid,
ity this insomnia becomes protracted; and, dementia, because the destructive processes as a result, mania passes by subsidence into in the brain overpower the constructive nuDr. Lyon Playfair, p. 6.
extensive hemorrhage; they are probably an exaggerated expression of the nocturnal starts in sleep.
trition, which is allowed no repose of cere-over certain portions of the brain. During bral functions to enable it to repair the dreaming the face usually becomes flushed, wasted parts. When we work too hard or from a greater access of arterialized blood. too late, all of us feel that the brain has A phlegmatic person, whose heart beats been put into too active combustion by the slowly and whose lungs are inactive, rarely increased flow of blood, so that we have dreams. The greatest dreamer is the man not the power to quell the changes, and of nervous temperament, whose heart and permit the brain to seek repose. Tossing lungs do not move with the steadfastness of uneasily on the bed, our efforts are to draw the pendulum of a clock. The states of the blood to some other part of the brain, dreaming may be likened to, possibly are, so as to give rest to the affected part. If local states of brain-inflammation proceedour work has been such as to demand our ing from a determination of blood to particreasoning powers, we excite the imagina- ular parts, but which, like the tissues in intion, or we seek a monotonous mental occu- cipient inflammations described by Liston, pation by counting a certain number, or go have an intrinsic power of recovery from through the dreary task of reciting the list irritation when it has not been carried beof kings and queens of England. All this yond a certain point." In fever, the rapidly is for the purpose of directing the blood- circulating blood, propelled with unequal current to some other part of the brain, and velocity, produces a tendency to delirious to extinguish the fire which burns in the ex-dreaming. The convulsive starts which cited region. If all these efforts fail, we take place in sleep, often accompanied by place our feet, and in extreme cases our oppression, are perhaps occasioned not by whole body, in a warm bath, which, deter- an excess, but by a temporary deficiency of mining a flow of blood to the surface, re- blood in the brain, produced by some obmoves it from the brain, and enables us struction arising from inconvenience of posoften, with magical effect, to secure the ture or other cause. Epileptic convulsions coveted repose. Narcotics, as Harley Has are suspected to be due to a bloodless conshown, have a wonderful effect in prevent-dition of the brain, and generally arise after ing the oxygen in the blood from transforming organic substances, and in extreme cases are used by the physician to combat cases of insomnia. Wakefulness in health is the Aristotle's treatise on Sleep contains many result of excessive transformation of brain- errors and some truths. Among the latter substance, induced by the activity of mind we class, though Lewes does not, his asserwhich compels the change to enable it to tion that sleep is the period in which nutrimanifest itself to the external world. In tion is most active. We do not understand disease, this transformation, proceeding as that Aristotle limited the period of nutritive a primary part of the phenomenon, induces construction to sleep, but merely that then the mental manifestations without balance it was dominant. Undoubtedly nutrition or order, and results in delirium or insanity. proceeds all through the twenty-four hours Dreaming appears to be simply a wake--perhaps, in absolute quantity, in as great a fulness of one portion of a nervous centre, ratio in the day as in the night. But we have while the other portions, and most proba- explained that the manifestation of force bly the other centres, are in a state of sleep. is always accompanied by a degradation Hence particular feeling or special kinds of of tissue, and that, while activity continues, ideas may be called into action by the trans- its waste must be at a greater rate than its formation of one region of brain-substance, reparation. If the destruction were exactly while other feelings or ideas are asleep, and balanced by the construction, there need are thus prevented by comparison and re- not arise fatigue or inability of tissues to flection from modifying those which are continue their work; we see this exempliawake. Milton clearly sees this in a fine fied in the heart and lungs, which have no passage in which he writes of dreams when cessation from labour, from the birth to the Reason is asleep:death of the individual. The period of repose is required for the completion of such repairs as the nutritive process, though always at work, was unable to overtake during the period of activity, and for a thorough overhauling, as it were, of the whole animal machine, so that it may be in perfect order for the next day's labour. It is this which, in the language of Shakespeare, makes life "rounded by a sleep." Lewes
"Oft in her absence mimic Fancy wakes
It has already been mentioned that when a trephined animal is asleep, and appears to be disturbed by dreams, a blush starts
in his work on Aristotle objects to this view | antly manifested by the physical and mental
"Were it true, the longest sleepers should be the strongest animals, since their repair of waste would be most effectual. Were it true, many dreadful cases of slow atrophy might be cured by opiates. Were it true, the sleepless maniacs, and men who sleep but little, would show rapid destruction of substance. To admit that muscular and nervous tissue require intervals of repose is not equivalent to admitting that their nutrition is only, or even mainly, effected during sleep." P. 260.
We have written on the subject of sleep with a freedom which is justified by the present state of scientific inquiry. Though the mind acts through matter, the metaphysical writers on the insensative state of the mind, with the exceptions of such men as Bain, Laycock, Spencer, Maudsley, and Carpenter, dared not discuss the changes which notoriously influence its manifestations; and to say the truth, our feet have not yet crossed beyond the mere threshold These objections do not appear to have of the inquiry. Birth and death are the much weight. It depends upon the activity Alpha and Omega of man's earthly existwith which nutrition is carried on in an in- ence, which begins and ends with sleep. dividual, whether he may require a long or Even the foetus in the womb of its mother short sleep for the purposes of repair. reposes in a state of continued sleep, proJeremy Taylor, John Hunter, Frederic of duced by the arterial blood with which it is Prussia, Napoleon, Wellington, Humboldt, supplied being adulterated with venous and the elder Descrozilles, could rise re- blood before it reaches the growing brain. freshed after two or three hours of sleep, After birth, the infant spends much of its while the average time required by mankind time in the vegetative state of existence is eight hours. Long sleepers need not be most favourable to its growth, for in its case strong men, as asserted in the above pas- the conditions of waste are subordinate to sage, even if nutrition is fairly active, for those of supply. In middle life these are when the sleep is in excess of the require- balanced, the experience of mankind showments, as in the case of indolent and luxu- ing that one-third of an active existence is rious men who pass an inert life, the nutri- still required to keep the body in a state of tive functions having done their work sink repair through the constructive processes into abeyance, as there is no muscular or dominant during sleep. In the old man the mental activity to cause further waste or to nutritive processes of the body are less acnecessitate new construction. Nor would tive than the causes of waste, and he thereopiates in atrophy suffice to remove, though fore sleeps frequently in order to favour the they might lessen, a disease which consists action of the former. At last the destructin the nutritive functions themselves being ive action seizes upon some vital organ, unable to fulfil their purpose. The pro- and the old man takes his last sleep in death. tracted cases of wakefulness in persons The sleep of death, from which there is no afflicted with acute mania merely prove waking on this side of the grave, differs that nutrition still proceeds in that state; from the sleep of life by passing over existthis no physiologist would deny, but the ence at a period when the nutritive proevidence that the destructive processes pre-cesses are not in a position to repair that ponderate over the constructive is abund- which has been wasted.