Sleep is one of the most important functions of the body. As the physiologist, Bunge,[324] remarks, “a man can live for a month without food, but he must succumb after only a few days if he fails to sleep.”
That sleeplessness leads to death has been proved by experiments on animals by Maria de Manasseine, who has demonstrated that animals from three to four months old invariably died if treated in such manner that they could not sleep at all. At the same time their temperature fell four to five degrees, and the number of their red blood-corpuscles decreased from five millions to two millions per cubic millimeter. Manasseine also discovered important changes in the brain of animals which had died from sleeplessness.
Before we get sleepy, as a rule, we feel tired and suffer from fatigue. Working from morning to night—for even idle persons work through the action of their organs—our muscles make numerous contractions, and it has been demonstrated by Weichardt[325] that toxic products are thus accumulated in them. This savant made animals perform very fatiguing movements for several consecutive hours; he then injected extracts from those muscles which had been subjected to such exercise, into other animals, which animals in turn exhibited symptoms of great fatigue; and he has gone so far as to show that such animals may even die during the next twenty to forty hours.
Similar conditions prevail in human beings to a greater or less degree. According to Prof. Obersteiner, of Vienna, and Binz, sleep is produced by an accumulation of the products of fatigue in the brain, and these substances are carried off during sleep. Thus sleep is similar to a condition of auto-intoxication caused by the accumulation of the products of work, be it muscular or mental, during the time that we are awake.
In the next chapter we shall show that sleeplessness occurs in all cases where the thyroid gland is degenerated. This gland, as we show in different parts of this book, destroys the toxic products formed in the body. When this gland is degenerated these products cannot be destroyed, and thus a condition of auto-intoxication will follow, as in myxœdema, which has sleeplessness as one of its most typical symptoms.
According to our present physiological knowledge the center of sleep is seated in the brain just as are other functions, such as intelligence, will-power, imagination, etc. As we have mentioned in the chapter on the agencies which control the condition of our nervous system and mentality, all these are changed when the thyroid is altered, for they suffer alteration after the thyroid is removed or destroyed by disease; and, on the other hand, they can be improved by thyroid treatment. Thus, sleep being one of these functions, it is only logical to assume that the thyroid controls sleep, which proposition we shall support with a mass of evidence in our next chapter; we will also mention there that after the injection of adrenalin, in the vicinity of the brain, Dr. Zeigan[326] has produced sleepiness in animals. Adrenalin produces an anæmic condition of the parts into which it is injected, caused by the contraction of the blood-vessels.
There has been a dispute on this question, whether it is hyperæmia of the brain, or its anæmic condition, which induces sleep.
In addition to the experiments of Dr. Zeigan, which we have referred to, and with which we will deal further in our next chapter, there are also other circumstances which support the idea that in sleep the brain must be in an anæmic condition.
We know that in order to fall asleep the brain must be at complete rest, for otherwise it is impossible to sleep; if the function of the brain is roused by any exciting influence, as for instance, if we ponder deeply over any scientific problem, sleep is out of the question. We think this can be amply proved by a very interesting experiment carried out by the physiologist, Mosso, in order to show that the process of thought produces a hyperæmia of the brain. Mosso made a man lie horizontally on a sort of scale, so that the balance was perfectly level. The subject was then told to think deeply, and upon so doing the head end became heavier, and the balance was depressed in that direction.
We can also note that any other agency which produces a greater flow of blood to the brain will be an impediment to sleep. For instance, many people are unable to sleep when they have taken a certain amount of alcohol, such as wine, just before going to bed; and this is more observable in those who are unaccustomed to alcohol, and who become flushed, feel hot in the head, and become mentally excited after taking even small quantities. On the other hand persons accustomed to spirit drinking, in whom no such symptoms are exhibited, may possibly be able to sleep; this demonstrates toxic action, which may be followed by deep sleep, by the action of alcohol on the thyroid gland. Taken in small quantities alcohol excites thyroid action, but taken in large quantities it causes its exhaustion as already previously mentioned.
Long ago it was accepted as a well-known fact that a hot head and flushed face prevent good sleep; but good regular sleep is obtained when the head is cold.
Sleepiness after dinner is attributed by Bunge to the accumulation of blood in the digestive organs, which produces an anæmia of the brain. As we show in the next chapter, the alteration in the thyroid by its destruction of toxic products from the intestine, may also in part do this.
Very interesting experiments have been carried out by Christern,[327] under the direction of Prof. Kreis, of Freiburg, who showed that the pressure of blood in the cavity of the skull of a boy decreased while he was asleep.
As we have already stated, sleep is attributed generally to a condition of auto-intoxication. When we rise in the morning, after having slept well and soundly during the night, we feel so fresh that these toxic products must assuredly have left the body during the night. On the other hand, after a sleepless night we feel so miserable and weak that the supposition is not unjustified that possibly we have not gotten rid of these harmful products. Professor Bouchard[328] has endeavored to show, by an examination of urine passed during the night, that this has a greater toxic action when injected into animals than has urine passed during the day.
As before mentioned, according to Obersteiner and Binz, during sleep the products of fatigue, which have accumulated in the brain during the day, are removed by the blood.
Everything points to the fact that through sleep we are getting rid of toxic products; and sleep is thus a function, the regularity of which is of the utmost importance for our prospects for a prolonged youth and healthy old age.