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.