INSOMNIA, OR WAKEFULNESS.
Sleep, gentle sleep,
Nature’s soft nurse, how have I frighted thee
That thou no more wilt weigh mine eyelids down
And steep my senses in forgetfulness?
--KING HENRY IV, SECOND PART.
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.
2. Affections of the nerves of common sensation.
3. Affections of the sympathetic nerves.
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 dyspnœa 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:
1. Disorders of circulation and nutrition.
2. Inflammations and degenerations.
3. Neoplastic encroachments.
_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.