THE PHYSICAL PHENOMENA OF SLEEP.
The approach of sleep is characterized by a languor which is agreeable
when it can be yielded to, but which, when circumstances prevent this, is
far from being pleasant. Many persons are rendered irritable as soon as
they become sleepy, and children are especially liable to manifest ill
temper under the uncomfortable feelings they experience when unable to
indulge the inclination to sleep. It is somewhat difficult to analyze the
various phenomena which go to make up the condition called sleepiness. The
most prominent feelings are an impression of weight in the upper eyelids,
and of a general relaxation of the muscles of the body, but there is
besides an internal sensation of supineness, enervation, and torpor, to
describe which is by no means easy. This sluggishness is closely allied in
character if not altogether identical with that experienced before an
attack of fainting, and is doubtless due to a like cause--a deficient
quantity of blood in the brain. Along with this languor there is a general
obtuseness of all the senses, which increases the separation of the mind
from the external world, already initiated by the physical condition of
the brain. The liveliest scenes cease to engage the attention, and the
most exciting conversation no longer interests. For a time, indeed, such
circumstances may dissipate the inclination for sleep, but eventually
nature obtains the ascendency and consciousness is lost. Before this event
there is usually yawning--a phenomenon strongly indicative of a wearied
attention; the head nods and droops upon the breast, and the body assumes
that position which is most conducive to ease, comfort, and entire
muscular inactivity.
The order in which the muscles lose their power is in general well marked,
and bears a distinct relation, as Cabanis[30] has pointed out, to the
importance of their functions. Thus, the muscles which move the arms and
legs become relaxed before those which support the head, and the latter
before those which maintain the erectness of the back. This, however, is
not always the case, for, as we have already seen, individuals will
occasionally walk, and keep their position on horseback, while in a sound
sleep, and all of us have seen persons slumbering in church, their heads
dropping on their breasts, but yet firmly holding their prayer-books in
their hands under the pretense of going through the services.
As regards the senses, the sight is of course the first to be lost in
ordinary cases--the closure of the eyelids interposing a physical
obstruction to the entrance of light. Even when the eyelids have been
removed, or from disease cannot be closed, the sight, nevertheless, is the
first of the special senses to be abolished. Some animals, as the hare for
example, do not shut the eyes when asleep; but even in them the ability to
see disappears before the action of the other senses is suspended.
These latter are not altogether abolished during sleep; their acuteness is
simply lessened. Taste is the first to fade, and then the smell; hearing
follows, and touch yields last of all, and is most readily re-excited. To
awake a sleeping person, impressions made upon the sense of touch are more
effectual than attempts to arouse through any of the other senses; the
hearing comes next in order, smell next, then taste, and the sight is the
last of all in capacity for excitation.
During sleep the respiration is slower, deeper, and usually more regular
than during wakefulness. The vigor of the process is lessened, and
therefore there is a diminution of the pulmonary exhalations. In all
probability, also, the ciliated epithelium which lines the air-passages
functionates with reduced activity. Owing to this circumstance and to the
general muscular torpor which prevails, mucus accumulates in the bronchial
tubes and requires to be expectorated on awaking.
The circulation of the blood is rendered slower. The heart beats with more
regularity, but with diminished force and frequency. As a consequence the
blood is not distributed to distant parts of the body so thoroughly and
rapidly as during wakefulness, and accordingly the extremities readily
lose their heat. Owing to the reduction in the activity of the respiratory
and circulatory functions, the temperature of the whole body falls, and
coldness of the atmosphere is less easily resisted.
The functions of the several organs concerned in digestion have their
activity increased by sleep. The blood which leaves the brain, goes, as
Durham has shown, to the stomach and other abdominal viscera, and hence
the quantities of the digestive juices are augmented, and the absorption
of the nutritious elements of the food is promoted.
The urine is excreted in less quantity during sleep than when the
individual is awake and engaged in mental or physical employment, because
the wear and tear of the system is at its minimum.
The perspiration is likewise reduced in amount by sleep. In warm weather,
however, the effort to go to sleep often causes an increase in the
quantity of this excretion, just as would any other mental or bodily
exertion. This circumstance has led some writers to a conclusion the
reverse of that just expressed. Others, again, have accepted the doctrine
of Sanctorius on this point without stopping to inquire into its
correctness. This author,[31] among other aphorisms relating to sleep,
gives the following:
“Undisturbed sleep is so great a promoter of perspiration, that in the
space of seven hours, fifty ounces of the concocted perspirable matter do
commonly exhale out of strong bodies.
“A man sleeping the space of seven hours is wont, insensibly, healthfully,
and without any violence, to perspire twice as much as one awake.”
The observations of Sanctorius with his weighing chair led to a good many
important results, but they were inexact so far as the function of the
skin was concerned, in that they made no division between the loss by this
channel and that which takes place through the lungs, for by perspiration
in the above quotations he means not only the exhalation from the skin,
but the products of respiration--aqueous vapor, carbonic acid, etc. His
apparatus was, besides, very imperfect, and could not possibly have given
the delicate indications which the subject requires.
Whether the condition of sleep promotes the absorption of morbid growths
and accumulations of fluids is very doubtful. Macnish[32] contends that it
does, but _a priori_ reasoning would rather lead us to an opposite
conclusion. Deficiencies are probably more rapidly made up during sleep
than during wakefulness, and thus ulcers heal with more rapidity, owing to
the increased formation of granulations which takes place; but the
removal of tumors, etc. by natural process involves the operation of
forces the very opposite of those concerned in reparation, and observation
teaches us that sleep is a condition peculiarly favorable to the
deposition of the materials constituting morbid growths. Some writers have
alleged that sleep accelerates the absorption of dropsical effusions, but
the disappearance of such accumulations during the condition in question
is clearly due to the mechanical causes depending upon the position of the
body.
It has also been asserted that there is an exaltation of the sexual
feeling during sleep. It is difficult to arrive at any very definite
conclusion on this point, but it is probable that here again the position
of the body conjoined with the heat of the bed has much to do in producing
the erotic manifestations occasionally witnessed. Every physician who has
had much to do with cases of the kind knows that sleeping upon the back,
by which means the blood gravitates to the generative organs and to the
lower part of the spinal cord, will often give rise to seminal emissions
with or without erotic dreams, and that such occurrences may generally be
prevented by the individual avoiding the dorsal decubitus and resting upon
one side or the other while asleep. The erections which the generality of
healthy men experience in the morning before rising from bed are likewise
due to the fact that the recumbent posture favors the flow of blood to the
penis and testicles. Such erections are usually unaccompanied by venereal
desire.
The ganglionic nervous system and the spinal cord continue in action
during sleep, though generally with somewhat diminished power and
sensibility. The reflex faculty of the latter organ is still maintained,
and thus various movements are executed without the consciousness of the
brain being awakened. Somnambulism is clearly a condition of exaltation in
the functions of the spinal cord without the controlling influence of the
cerebrum being brought into action. But, aside from this rather abnormal
phenomenon, there are others which are entirely within the range of
health, and which show that the spinal cord is awake, even though the
sleep be most profound. Thus, for instance, if the position of the sleeper
becomes irksome, it is changed; if the feet become cold, they are drawn up
to a warmer part of the bed; and cases are recorded in which individuals
have risen from bed and emptied a distended bladder without awaking.
The instances brought forward in a previous chapter of persons riding on
horseback and walking during sleep show the activity of the spinal cord,
and not that the will is exercised; and Cabanis[33] is wrong in the view
which he gives of such phenomena in the following extract.
Speaking of cases like those just referred to, he says:
“These rare instances are not the only ones in which movements are
observed produced during sleep by that portion of the will which is awake;
for it is by virtue of certain direct sensations that a sleeping man moves
his arm to brush away the flies from his face, that he draws the cover
around him so as to envelop himself carefully, or that he turns in bed
till he has found a comfortable position. It is the will which during
sleep maintains the contraction of the sphincter of the bladder,
notwithstanding the effort of the urine to escape.”
Such examples as the above we now know to be instances of reflex action,
and as not, therefore, being due to the exercise of the will.
Sleep favors the occurrence of certain pathological phenomena. Thus
individuals affected with hæmorrhoids have the liability to hemorrhage
increased when they are asleep. Several instances of the kind have come
under my notice. In one the patient lost so large a quantity of blood that
syncope ensued and might have terminated fatally had not his condition
been accidentally discovered. Bleeding from the lungs is also more apt to
occur during sleep in those who are predisposed to it. Darwin states that
a man of about fifty years of age, subject to hæmorrhoids, was also
attacked with hæmoptysis three consecutive nights at about the same
hour--two o’clock--being awakened thereby from a state of very profound
sleep. He was advised to suffer himself to be roused at one o’clock, and
to leave his bed at that hour. He did so with the result not only of
entirely breaking up the hemorrhagic disposition, but also of curing
himself of very violent attacks of headache, to which he had been subject
for many years.
Epileptic fits are also more liable to occur during sleep than at other
times, a fact not always susceptible of easy explanation. In a case of
epilepsy now under my charge, this proclivity is so well marked that the
patient, a lady, scarcely ever goes to sleep without being attacked. Her
face becomes exceedingly pale just before the fit, and if then seen the
paroxysm can be entirely prevented by waking her. She is never attacked at
other times, and I am trying, with excellent results thus far, the plan of
making her sleep altogether during the day and of waking her as soon as
her face becomes pallid. It is probable that the fits in her case are due
to a diminished amount of blood in the brain, and this supposition is
strengthened by the additional fact that bromide of potassium--a substance
which, as I have shown, lessens the amount of intracranial
blood--invariably rendered her paroxysms more frequent and severe.
Sleep predisposes to attacks of gout in those who have the gouty
diathesis, and likewise favors exacerbations in several other diseases
which it is scarcely necessary to allude to specifically. The accession of
fever toward night, and the increase which takes place in pain due to
inflammation are generally associated with the approach of night, and have
no direct relation with sleep.
Certain other morbid phenomena, such as somnambulism and nightmare, which
have a necessary relation with sleep, will be more appropriately
considered in another place.
On the other hand, sleep controls the manifestations of several diseases,
especially those which are of a convulsive or spasmodic character. Thus
the paroxysms of chorea cease during sleep, as do likewise the spasms of
tetanus and hydrophobia. Headache is also generally relieved by sleep,
though occasionally it is aggravated.