Circadian rhythm

“ The only time that one could get a breath was about five o’clock in the morning; in the middle of the day the sun’s rays are white-hot needles,—this is the only way that I can express it; and even if one carries an umbrella, the heat pierces directly through. ”

“ Every hour differs from the last. There is a time just between three o’clock and five when all the vibrations of the earth change. It seems the good-bye of the night and the awakening of the day. Day holds night in some subtle, lingering embrace that will not let go until the very gray of the dawn drives the reluctant darkness from the earth. ”

“ During sleep, moreover, when the vital forces are being renewed, the functions of the body go on more slowly than while we are awake, the heart beats less quickly, and less heat is evolved, as may easily be seen by taking the temperature of a sleeper with a clinical thermometer. The temperature of the atmosphere also falls at night, and sometimes very suddenly and considerably, so that even greater care is required as to night clothing than as to that worn during the day. ”

“ Once the sun is well up our sleep—supposing our life fairly normal—is no longer truly sleep. When the sun comes up the centers of active dynamic upper consciousness begin to wake. The blood changes its vibration and even its chemical constitution. And then we too ought to wake. We do ourselves great damage by sleeping too long into the day. The half-hour's sleep after midday meal is a readjustment. But the long hours of morning sleep are just a damage. We submit our now active centers of upper consciousness to the dominion of the blood-automatic flow. ”

“ You think you will enjoy the evening twilight an hour or two before going to bed, and lo! the morning begins to dawn. It seems absurd to turn in and sleep by daylight, but you sleep, nevertheless, until eight or nine o'clock, and get up but little refreshed with your repose. You miss the grateful covering of darkness, the sweet, welcome gloom, which shuts your senses, one after one, like the closing petals of a flower, in the restoring trance of the night. The light comes through your eyelids as you sleep, and a certain nervous life of the body that should sleep too keeps awake and active. ”

“ Probably each hour in the day has for most of us some outer or inner sign associated with it as closely as these signs with the days of the week. It must be admitted, after all, however, that the great improvement of the time-perception during sleep and trance is a mystery not as yet cleared up. All my life I have been struck by the accuracy with which I will wake at the same exact minute night after night and morning after morning, if only the habit fortuitously begins. ”

“ Natural sleep is that condition of physiological repose in which the molecular movements of the brain are no longer fully and clearly projected upon the field of consciousness. This condition is universally observed in all healthy animals; and its recurrence is intimately associated with the diurnal revolution of the earth, and the succession of day and night. The disappearance of daylight is, for the majority of living creatures, the signal for cessation of active life. ”

“ When we rise in the morning, the contractibility being abundant, the stimulus of the blood produces a greater effect, the pulse becomes slow, and the contractions strong; it becomes more frequent, however, till dinner time, from a diminished contractibility; after dinner, from the addition of the stimulus of food and chyle, it again decreases in frequency, and becomes slow till the evening, when its frequency returns, because the contractibility becomes exhausted: and this frequency continues till the vital power have been recruited by sleep. ”

“ It is generally observed, that the pulse is slower in the morning, that it increases in frequency till noon, after dinner it again becomes slow, and in the evening its frequency returns, which increases till midnight. ”

“ During the prevalence of high temperatures the blood flows in increased proportion to the surface of the body and to the extremities, and consequently the quantity in the brain is diminished. Sleep accordingly results unless the irritation induced by the heat is so great as to excite the nervous system. Heat applied directly to the head exerts, of course, a directly contrary effect upon the cerebral circulation, as we see in sun-stroke. Here there is internal cerebral congestion, loss of consciousness, stupor, etc. ”

“ Whatever be the explanation, it is an undoubted fact that day and night cannot be properly exchanged. About one or two o’clock in the morning the heart’s action sinks, and nature points to the necessity for rest. Sleep in the day time does not compensate for the loss of that at proper time, and slumbers prolonged to a late hour do not refresh the mind or body as does sleep between the hours of eleven and six or seven, the normal period for rest. ”

“ The clock strikes with a steady pulse, though sometimes it seems in a fever—sometimes in a fit. At any rate we have some fixed standard to correct the calculation of our waking time; but in dreams the standard itself is visionary. ”

“ In some cases even a few moments of sleep will give the recuperative powers an opportunity to reassert themselves and regain the ground that they have lost, thus restoring the balance sufficiently to enable the machine to go on working.
Students often ask what is the best time for sleep. Unquestionably the rule of nature is that the day is for work and the night is for rest, and no infringement of nature's laws can ever be a good thing. One of the serious evils of our modern unnatural life is that noon is no longer, as it should be, the centre of the day. ”

“ But that during the day does not agree with all, because the time spent in sleep is not sufficient for the complete digestion of the food; and, when the digestion is interrupted unseasonably, those who rise from sleep at noon are often troubled with acidity and flatulence, and sometimes even with a gurgling noise in their bowels, unless from habit or sufficient rest these bad effects be obviated. The best season for sleep is the night, for the humidity and drowsy stillness of night contribute to perfect digestion. Wherefore after these nocturnal slumbers we feel the most desire for evacuation. ”

“ The observations of Hohl and Allix [8] indicate that among very young children the difference between the pulse of sleep and the pulse of wakefulness may equal forty beats. According to [Pg 7] Guy (loc. cit.) the pulse is more variable in the morning than during the afternoon or evening.
Temperature.—Aside from the almost hourly fluctuations of the bodily temperature, a noticeable sinking of the temperature-curve is observed during the hours of sleep. This alone is sufficient to indicate a diminished rate of combustion in the tissues. ”

“ But it has been shewn, that those motions, which are perpetually excited, as those of the arterial system by the stimulus of the blood, are attended by a great accumulation of sensorial power, after they have been for a time suspended; as the hot-fit of fever is the consequence of the cold one. Now as these trains of ideas caused by sensation are perpetually excited during our waking hours, if they were to be suspended in sleep like the voluntary motions, (which are exerted only by intervals during our waking hours,) an accumulation of sensorial power would follow ”

“ Under favorable conditions eight hours of undisturbed sleep would almost suffice to counteract the physiological mischief of the sixteen waking hours. During sleep the organ of consciousness is at rest, and the energies of the system seem to be concentrated on the function of nutrition and the renewal of the vital energy in general; sleep promotes digestion, repairs the waste of the muscular tissue, favors the process of cutaneous excretion, and renews the vigor of the mental faculties. ”

“ 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. ”

“ Another curious thing, friends tell me, affects them in this winter night-time, and that is the disposition of men to hibernate. Fifteen and sixteen hours of sleep are commonly required, while in the nightless summer-time three and four and five hours satisfy all the demands nature seems to make—thus the long sleeps of winter compensate for the lack of rest taken during the summer-time. ”

“ A change in the time of her diurnal rotation, as affecting the length of the day and night, must at once be followed by a corresponding modification of the periodicities of the nervous system of animals; a change in her orbitual translation round the sun, as determining the duration of the year, would, in like manner, give rise to a marked effect. If the year were shorter, we should live faster and die sooner. ”

“ Whatever increases the activity of the [Pg 36] cerebral circulation tends to preserve wakefulness; and whatever decreases the activity of the cerebral circulation, and, at the same time, is not inconsistent with the general health of the body, tends to induce and favor sleep. Such circumstances may act primarily through the nervous or through the vascular system. Among those which act through the nervous system, may be instanced the presence or absence of impressions upon the senses, and the presence or absence of exciting ideas. ”

“ The coincidence of the time of sleep with the occurrence of the great terrestrial phenomena that cause night is more apparent than real. The oscillations of vital activity are not correlated to the terrestrial revolutions as effect and cause, but the occurrence of sleep, in the majority of cases, on the advent of night is largely the result of habit. Whilst the darkness and stillness of night are favourable to sleep, the state of physiological repose is determined more by the condition of the body itself. Fatigue will normally cause sleep at any time of the twenty-four hours. ”

“ Those animals which are nocturnal feeders are diurnal sleepers, while those which are crepuscular, sleep partly in the night and partly in the day; but in all, the complete period of these functions is twenty-four hours. Man, in like manner, in all nations and ages, takes his principal rest once in twenty-four hours; and the regularity of this practice seems most suitable to his health, though the duration of the time allotted to repose is extremely different in different cases. ”

“ A similar nap in the afternoon is not so good, but is better than nothing. The tepid sitz-bath on going to bed will often produce sleep, and so will gentle percussion given by an attendant with palms of the hand over the back for a few minutes on retiring. To secure sound sleep do not read, write or severely tax the mind in the evening. ”

“ This is without counting the seven nights of the last week, during which there were observers for longer or shorter periods in the house, none of whom recorded any sight or sound of a supernormal kind, unless it were the percussive or detonating noise heard by Mr. "Etienne."
The term "night" is here understood to cover the period between the hour of going to rest at night, to that of leaving one's room next morning, even if the phenomena occurred in the daylight hours of the early morning. The term "day" is used to cover the hours of active, waking life, from breakfast to bedtime. ”

“ Sleep intensifies and grows deeper until the second quarter of the second hour. In the second and third quarters of that hour, the intensification is rapid and significant, and then it decreases just as rapidly, until the second quarter of the third hour. At that point sleep becomes less and less profound until morning, in the second half of the fifth hour. At this moment the intensity of sleep begins again to increase, but in contrast with the first increase is very light and takes a long time. ”

“ Before leaving the subject of sleep, we should note the benefit to be derived from regularity in sleep. All Nature seems to move rhythmically and sleep is no exception. Insomnia may be treated by means of habituating one's self to get sleepy at a certain time, and there is no question that the rising process may be made easier if one forms the habit of arising at the same time every morning. To rhythmize this important function is a long step towards the efficient life. ”

“ Going to bed before the usual hour is a frequent cause of Night-Mare, as it either occasions the patient to sleep too long, or to lie awake in the night. Passing a whole night, or part of a night, without rest, likewise gives birth to the disease, as it occasions the patient on the succeeding night to sleep too sound. Indulging in sleep too late in the morning is an almost certain method to bring on the paroxysm ”

“ To emphasise what we have just said, punctuality in going to bed is the most important point of all. The brain, like the digestion, has a marked tendency to get into habits, either bad or good. And if anyone goes to bed at different times, later on some evenings than others, the brain is liable to select the latter hour as the one for falling asleep. This means that even on the nights when people go to bed in good time they cannot get to sleep for the next hour or two. If they would stick to the one hour regularly, the brain would soon learn to do the same. ”