INSOMNIA, OR WAKEFULNESS.

We have seen that the condition of normal sleep is determined by a peculiar molecular state of the substance of the brain—a modification regularly alternating with that by means of which the condition of wakefulness is sustained. We have also seen that sleep is liable to variations in its intensity, and that its course may be partially interrupted by dreams, or even by a more or less complete resumption of the movements of locomotion, constituting the different varieties of somnambulism. Our attention must now be directed to the consideration of those greater disturbances of sleep which either serve to prevent its full development, or else to actually interrupt its course, rendering it incomplete and fragmentary, or even abolishing it altogether. But, inasmuch as the healthy brain, when associated with a healthy body, can only by an extraordinary effort of the will be kept awake beyond a certain period, and then only for a short time beyond the ordinary interval of wakefulness, it follows that the study of the usual causes of insomnia must be an investigation of morbid conditions of the bodily functions. Sleeplessness, therefore, must result, 1st, from a disturbance of the peripheral sensory organs of the nervous system; 2nd, from disordered conditions of the sensory nerves and nerve tracts; 3rd, from morbid states of the brain; 4th, from any or all of these conditions operating in association with each other. We may, therefore, consider, I, Insomnia caused by irritation of the peripheral portions of the sensory apparatus; and, II, Insomnia caused by morbid states of the central nervous organs.

I. Insomnia caused by irritation of the peripheral portions of the sensory apparatus.

Irritation of the sensory apparatus may be ranked in three classes:

1. Affections of the organs of special sense.—Prominent among these is the effect of light upon the eye. The darkness of night favors sleep; the presence of light hinders its incidence and renders it less profound. During the gloom of a total eclipse animals seek their shelter; birds hide themselves in their nests; domestic fowls arrange themselves upon the roost, and seem quite disconcerted by the speedy return of sunlight. Children often find it difficult to sleep in an illuminated room. I have known nurses who would sit with a wakeful infant under a powerful gaslight till after midnight, and then would express their surprise that the baby persisted in gazing at the flame instead of going quietly to sleep. The inhabitants of Northern Europe find it necessary to darken their sleeping rooms during the long polar day; and travelers in such regions often suffer for want of the natural sleep which only darkness affords. Judge Caton, writing of his travels in Norway[28] says: “We longed for darkness and for night. Do what we could to darken the windows to keep out the light, still it was not night as nature makes it, and which the habit of a lifetime had rendered necessary to sound repose. Artificial darkness, especially when incomplete, is as far from night as artificial light is from day.... These sunny nights can hardly conduce to health, they steal away so much of sleep. One does not readily get sleepy in the sunshine, and then we are so apt to forget to look at the watch to see if it is time to retire.”

In the tropical regions of the world it is usual for the inhabitants to sleep during the middle of the day; but they take great pains to exclude the light from their houses during the hours of sleep. The Pacific Islanders cover their faces with the bed clothes for the purpose of excluding the light while attempting to sleep. Repose thus obtained in the daytime often serves to convert the night into a season of wakefulness. The Africans sleep and dream away the heated hours of the day, and give up considerable portions of the night to festivity in the open air—a practice which undoubtedly contributes to the permanence of an inferior grade of social life.

Sudden illumination of the sleeping room will frequently awaken the sleeper. During the great fire in Chicago, A. D. 1871, many persons were thus aroused from their slumbers as the flames lighted up the streets adjoining their houses. One of my acquaintances was awakened one night by a flash of light from the lantern of a burglar who was moving noiselessly about her chamber. The experience of almost every one will testify to the effects of sheet-lightning silently illuminating the sky by night. Dreams, also, are not unfrequently excited by the incidence of light upon the closed eyelids.[29]

The sense of hearing is one of the most persistent of the special senses during the incidence of sleep. It is perhaps the most excitable of these senses during the period of repose. Long after the subject has become immersed in sleep his auditory apparatus remains sensitive to sounds. Dreams are often produced by impressions upon the ear. Often in sleep it seems as if the sense of hearing remained wakeful and watchful for expected signals, as when an alarm clock serves to arouse the sleeper at an appointed hour. Sometimes the sleeper may be shaken and tumbled about in his bed without waking, but if he be addressed by name he will usually reply. It is scarcely probable that the auditory apparatus is any more wakeful than other portions of the nervous system, but its external portions remain during sleep more completely exposed and adapted to the reception of impressions than is possible for the eye and for the organs of touch and taste.

The persistent sensitiveness of the ear during sleep is not so much a capacity for noticing sounds as a sensibility to variations in sonorous impressions. Thus a steady and monotonous noise may, if long continued, serve to render one sleepy; but the sudden cessation of the same sound will awaken every one. Slowly lulled to sleep by the incessant rumble of the engine upon one of the old-fashioned Long Island Sound steamboats, how immediate the awakening of a whole cabin full of people, when the wheels were suddenly stopped! A recent traveler in Guiana[30] relates a curious experience with an Indian magician who undertook to cure him of a slight headache and fever. The method of cure consisted in placing the patient at night in his hammock, while the magician kept up a hideous succession of yells and shouts, shaking the walls and roof of the house with an uproar which never ceased for six hours. Before long the patient passed into a kind of fitful sleep or stupor, during which he seemed to be suspended in a surging ocean of sound. When the noise died away, as if growing fainter in the distance, he would rouse up into a semi-conscious state, but when it again increased he would fall back into stupor. At last, when the noise finally ceased, he awoke completely, but without the slightest relief from headache—an experience quite illustrative of the manner in which the brain may be affected by sound.

It is not often that the sense of smell becomes the avenue of impressions that interfere with sleep. So different are the capacities of individuals in this particular that an odor which might severely annoy one person, would pass almost unnoticed by another. Large cities are sometimes invaded by overwhelming stenches from the various factories which spring up in their neighborhood. While it is seldom true that the vapors discharged by such establishments are directly deleterious to health, they may become indirectly a cause of ill-health through the wakefulness occasioned by them among weakly invalids. The smell of smoke in a bed-chamber sometimes serves to awaken a sleeper, giving warning of the outbreak of a fire in the building. Less energetic odors may disturb the depth of sleep without actually waking the patient. Thus Maury records[31] that when he was made to inhale the vapor of cologne water while asleep, he dreamed of being in the shop of a perfumer.

Excitement of the sense of taste would, doubtless, operate in a similar manner; but it is so difficult to arouse this sense without at the same time irritating the nerves of common sensation about the mouth, that very little can be said regarding the matter. Dreams of gustatory sensations are usually of subjective origin, dependent upon some reflex movement, or upon some agitation of the organ of memory, within the brain.

If, with Sir William Thompson,[32] we recognize a sixth sense—the sense of temperature—it must be admitted that through the varying sensations of heat and cold, sleep can be greatly disturbed. Every one will recall to mind the story told by Dugald Stewart, of a gentleman who dreamed of walking over heated lava on Mt. Ætna when a bottle of hot water was placed against his feet, in bed, on account of some slight indisposition. The temperature of the air is one of the most important factors in the determination of sleep. A high temperature keeps every one awake—a fact well known among the unfortunate denizens of the garrets in our great cities. Not only is wakefulness the direct result of heat, but it is aggravated and embittered by the accompaniments of a torrid climate—insects, foul air, and cutaneous disorders. In the East Indies, so difficult is sleep under such conditions that the wealthy inhabitants compel their servants to cool them all night with the punkah, a large, swinging fan, suspended above the bed, and kept in motion by means of a cord leading outside of the bed-room to the verandah, where the punkah-wallah sits and pulls the string while his master sleeps. So powerful is the force of habit in the organization of the automatic apparatus of the body that, though these punkah-pullers often fall asleep, they still continue, without interruption, the successive movements by which the fan is kept in operation.

The evil effects of a high temperature are greatly aggravated by the presence of humidity in the atmosphere. Dampness interferes with the process of exhalation from the surface of the body, which, consequently, tends to become overheated. The tissues, under such circumstances, are imperfectly defecated, and rapidly pass into a condition of imperfect nutrition. This depresses all the functions of the body, and renders the nervous system inordinately irritable. Sleep cannot be profound and refreshing, because of the over-excitable state of the brain. During the long, hot season in tropical countries, it often becomes necessary to seek a temporary retreat among the highlands and mountains, in order to find a climate sufficiently dry and cool to furnish the condition for refreshing sleep. For the same reason many of the inhabitants of the Southern United States are forced to spend the summer months in the invigorating atmosphere of Minnesota and Northern Michigan. One of the most delightful of experiences may be procured on any warm day in summer by embarking, at Chicago, upon one of the steamboats bound to Mackinac. At the wharf, in the hottest and dirtiest part of the city, all is dust, perspiration, and discomfort. The wide cabins are filled with people who are tired, thirsty, and discouraged. Sickly, squalling babies swarm in numbers sufficient to drive one mad. As the sun goes down, the signal-whistle sounds, head-lines and stern-lines are quickly cast off, the propeller churns the mire behind the boat. Slowly swings the huge fabric away from the shore, gliding between the walls of sun-scorched brick that line the stream on either side. At last the light-house at the mouth of the river is passed, and we are out upon the blue waves of Lake Michigan, with a heavenly breeze searching every crack and cranny of the hull. New life animates every form, and presently a great silence pervades the brilliant cabins. The children have left their woes behind, and, for the first time, in many weeks, perhaps, they and their weary mothers sleep the sleep of innocence and peace.

The dependence of a high atmospheric temperature upon the direction of the wind renders the course of the aerial currents a matter of great importance in relation to sleep. The southerly winds which, in the northern hemisphere, are hot and enervating, always produce an increase of wakefulness. The winds that blow from the heated deserts of Africa, Arabia, and Australia, are greatly dreaded upon this account, as well as for the other numerous discomforts which fly in their train. Their cessation, and their replacement by a cool, polar current brings relief at once. The changes thus produced in the electrical condition of the atmosphere doubtless contribute more than is usually known to these results. A cloudless sky gives evidence of positive electricity, which is much stronger in winter than in summer.[33] Clouds are sometimes positive and sometimes negative. According to Fonssagrives[34] the atmospheric electricity is positive during northerly winds, and negative during the prevalence of winds from the southerly quarters of the horizon. Great disturbances of the electrical condition of bodies is often observed during the occurrence of the sirocco in North Africa. Arago has related the case of an officer in the French army[35] who saw sparks of electricity leaping from his epaulettes at every blast of the sirocco encountered on a march in the neighborhood of Algiers. Such atmospheric disturbances often produce very disagreeable effects upon persons of a nervous temperament. According to Fonssagrives (loc. cit.) such patients frequently experience, during the prevalence of storms which traverse great distances, a high degree of insomnia, together with headache, pains in the limbs, joints, and old injuries, and a general indefinable sensation of discomfort. S. Weir Mitchell has carefully traced the connection between these phenomena and the variations of barometric pressure which accompany the revolving storms that cross the continent in a northeasterly direction.[36]

Though the effect of a high atmospheric temperature is unfavorable to sleep, an excessive temperature produces the opposite condition. Stupor rather than sleep is the consequence of insolation and of exposure to great heat from artificial sources. This is a pathological process, and, therefore, must not be mistaken for natural sleep. It may result either from cerebral congestion, or from cardiac exhaustion, and is characterized by an extraordinary bodily temperature and a high rate of mortality.[37] So elaborate are the arrangements for the preservation of a uniform temperature throughout the body that it is practically impossible for a sunstroke to occur unless the regulative apparatus has been previously deranged by ill-health.

Excessive cold operates in like manner to produce a condition of stupor that tends to a fatal termination. But moderate degrees of cold act as excitants of wakefulness. By effecting a contraction of the vessels of the skin cutaneous circulation is impeded. The venous side of the circulatory apparatus becomes overloaded with blood; the exhalation of carbonic acid and the production of heat are reduced. The discomfort that results from this disturbance of the natural functions of the tissues is sufficient to arouse the brain to wakefulness, just as an imperfect oxidation of the blood serves to excite the respiratory centre in the medulla oblongata. It is hardly necessary to allude in this connection to the increased flow of blood through the brain occasioned by this as by every other excitement of the sensorium. Local refrigeration of any portion of the body thus acts as a painful excitant of the cerebrum, and produces wakefulness, very much as distention of the intestines with gas will keep one awake. It is for this reason almost impossible to sleep with cold feet. Conditions of this sort are pathological, and are far in excess of the agreeable coolness which favors sleep. The effects of progressive diminution of the temperature of the air are well illustrated by the hibernation of animals.[38] As the temperature of the air diminishes, in winter, animals like the marmot fall into a species of sleep. Their movements of respiration and circulation are greatly reduced, and their bodily temperature falls, though it always remains several degrees above the temperature of the surrounding air. So long as the average degree of cold is maintained, the little creature sleeps naturally; but, if the air becomes extraordinarily cold, the physiological repose of the animal is disturbed. It becomes uneasy, wakes up, and seeks a warmer retreat. Too great a degree of cold thus becomes a cause of wakefulness. If the animal under these circumstances fails to secure protection against a falling temperature, it passes into a state of lethargy that is often fatal—a pathological condition being substituted for the physiological sleep of ordinary hibernation. In like manner the human animal may experience the threefold effects of refrigeration: first a pleasing coolness that favors sleep; then an uneasy sensation of cold which causes wakefulness; and, finally, a lethargy that paralyzes all the functions of the body and terminates in death.

2. Affections of the nerves of common sensation.—Chief among the causes of sleeplessness thus produced is pain. This is a modification of feeling, caused by excessive or extraordinary excitement of the peripheral nerves of sensation. The seat of the excitement may be in the skin or in the deeper tissues of the body. Cutaneous pain may be caused by the activity of various insects, like flies, mosquitos, fleas and bedbugs, or by the presence of certain parasites, such as the itch-mite, or by ordinary diseases of the skin, of which notable examples are found in erysipelas, erythema, urticaria, lichen, prurigo, certain varieties of eczema and psoriasis. The troublesome forms of pruritus which accompany icterus, or which may occur without any clearly defined cause, are frequent causes of wakefulness. The last mentioned disorder must, however, be sometimes recognized as a consequence of central nervous disorder, rather than a result of peripheral disease. Witness the frightful itching sometimes experienced during the progress of chronic myelitis. All kinds of injuries, wounds, ulcers, and other local inflammations are common causes of insomnia by reason of the painful impressions transmitted from them to the brain. Hence the great importance of anodynes and hypnotic remedies in the course of surgical practice. Diseases or injuries of the various peripheral nerves are notable causes of sleeplessness. Witness the horrible wakefulness caused by neuritis and by neuralgia. The development of neuromata in the stumps of amputated limbs may thus become a most painful cause of insomnia. Inflammations which encroach upon sensitive nerves produce intense pain with consequent loss of sleep. Of this very conspicuous examples are furnished by spinal meningitis, and by the effects of local periostitis causing compression of the branches of the fifth pair of nerves.

3. Affections of the sympathetic nerves.—So much still remains to be learned concerning the pathological functions of the sympathetic nerves that it is impossible to assign with any great degree of precision the exact amount of interference with sleep that may depend upon disordered conditions of this portion of the nervous system. Since their principal functions consist in the regulation of the flow of blood and lymph throughout the body, and in the control of the processes of nutrition, calorification, secretion and excretion, it follows that any considerable derangement of their healthy action must be represented by a corresponding disturbance of the brain. This may reach the field of consciousness in the form of pain, and thus may become a cause of sleeplessness. In all the phenomena of inflammation sympathetic nerves play an active part. In certain portions of the body, as in the principal viscera, and in the periosteal covering of the bones, they are the interstitial nerves of the structures. When the body is in a healthy condition these nerves convey impulses of a sensory character which do not reach the cerebral organ of conscious sensation. But in certain morbid states they become inordinately sensitive, and they then serve to convey and probably also to magnify sensations to an extent that may cause exquisite pain with all its consequences. Witness the pain experienced during the various forms of colic. Rheumatic inflammations, pleurisy, pericarditis, peritonitis, cystitis, metritis, ovaritis, gastro-enteritis, and other similar diseases owe their principal suffering to the affection of the sympathetic nerves connected with the respective organs which become the seat of pain. Including with the sympathetic nerve the pneumogastric nerve, which occupies a functional position between the strictly peripheral and the ganglionic nerves, all the various forms of pain and uneasiness experienced in the region of the heart and of the lungs may be assigned to this system of nerves. Thus the various species of respiratory disturbance, such as asthma and dyspnoea from any cause, and the forms of palpitation and other cardiac disorder may become causes of wakefulness. In like manner the vague and uneasy sensations associated with certain varieties of dyspepsia are frequent sources of sleeplessness, not merely by reason of the pain which they occasion, but also because of the general disorders of nutrition with which they are associated.

II. Insomnia caused by morbid states of the central nervous organs.

So intimately connected are the spinal cord and the brain that their disorders may properly be considered together. These may be classified as:

Disorders of circulation and nutrition.—HyperÆmia of the brain is a frequent cause of wakefulness. This may be maintained by an unconscious effort of the organ of the will under the influence of any great and unusual excitement of the mind. So soon as the mental excitement is allayed, the excessive afflux of blood subsides, and the brain becomes fitted for sleep. But, if excitement be too far prolonged, the nutrition of the nervous centres suffers, and the regulative apparatus of the cerebral circulation becomes exhausted, so that the brain cannot rest, because its inhibitory centres have lost their power of control over the lower ganglia of the organ. The cerebro-spinal centres are then in a condition analogous to that of a locomotive engine on which the engineer can no longer regulate the production and distribution of steam. Such a condition is usually the result of numerous antecedent causes. Long hours of work, scanty or improper food, insufficient sleep, bad hygienic surroundings and habits, with indulgence in the use of narcotics and stimulants, are among the most common causes of the disorder.

Active hyperÆmia of the nervous centers has been above mentioned as the consequence of cerebral function under unfavorable conditions. But, as the disorder persists, its type undergoes a change. We still speak of the disorder as functional in its character, but it continually tends to become organic. No visible alterations, perhaps, can be detected, but, evidently, there are radical changes in the substance of the nervous tissue. Nutrition suffers throughout the body to a degree that attracts attention. The blood diminishes in quantity and quality, till the patient becomes notably anÆmic. In this condition the brain is inordinately excitable. It is incapable of sustained activity, and the patient may even be oppressed by an inclination to constant drowsiness; yet he will be unable to sleep soundly, and his sleep will be continually agitated by dreams. This state is one of the constant accompaniments of slow starvation. The molecular structure of the nervous organs seems to be so slightly constructed, under such circumstances, that its equilibrium is disturbed by the most trifling incidents. It may be likened to a lofty wall of bricks laid up without mortar—“if a fox go up,” the entire structure may be thrown down with a tremendous noise. Thus the anÆmic and irritable brain will react excessively under the slightest impression; consciousness is invaded by perceptions which would never arise under normal conditions of the nervous tissue; and the mind is continually aroused. This form of wakefulness is very frequent among women who have become anÆmic, and among patients who are slowly convalescing from exhausting diseases.

It is impossible in every instance to decide whether a given state of wakefulness is the result of cerebral hyperÆmia or anÆmia. In the one case the persistence of wakeful activity of the mind is due to excitement of the cerebral cells, accompanied by a lavish irrigation of their substance with the plasma of the blood. In the other case the excitement is occasioned, not so much by increased afflux of the blood, as by a morbid instability of the nervous substance. The outcome in both cases is very similar—mental excitement and wakefulness.

In a third class of cases the agitation of the brain is produced by the direct action of certain chemical agents upon the cortical substance. Tea and coffee are familiar examples of such agents. The caffeine, by virtue of which they produce their effect, when transported to the brain, enters into combination with its protoplasm in such a way as to stimulate molecular movement. Perception is thus quickened, and the mind is aroused. Sleep is postponed until the effect of the stimulant has subsided. This form of wakefulness is quite different from that produced by alcoholic drinks. These operate, when taken in small quantities, to favor cerebral equilibrium—and consequent equanimity—by producing a general dilatation of the smaller blood-vessels. Their anÆsthetic influence is favorable to sleep, under such circumstances. But, if frequently repeated, these doses of alcohol modify the nutrition of the nervous system until, at last, a condition of irritable weakness is reached, in which wakefulness of a most distressing character is experienced.

Inflammations, degenerations, and neoplasms.—The early stages of inflammation involving the central nervous organs are marked by that form of insomnia which is associated with active hyperÆmia. The headache and painful delirium which accompany the different varieties of meningitis, are causes of a wakefulness that persists until the brain is merged in the coma of compression. The interstitial changes which cause the various forms of insanity, are in like manner causes of wakefulness. Local injuries and degenerations of brain-substance, tubercular deposits upon the meningies, and all the different forms of intra-cranial tumor, are causes of wakefulness, both by reason of the direct irritation which they produce, and by reason of the circulatory disturbances which arise in their neighborhood.

Finally, it must be observed that wakefulness may result from excitement of the brain by irritating substances transported through the blood from distant centers of disease in remote organs of the body, or derived from articles that have been absorbed with the food and drink, or with the air that enters the lungs. Thus wakefulness may accompany cutaneous disorders that interfere with perspiration. Imperfect elimination through the liver, kidneys and intestines, leaves the blood charged with excrementitious substances which arouse the brain to wakefulness. In like manner, various poisons, like lead, arsenic, etc., different miasms of telluric origin, the products of putrefaction, and the various animal contagia, may produce insomnia by their prejudicial effect upon the nutrition of the nervous structures throughout the body.