PREFACE
That it may well be difficult to explain the nature, differences, causes, and importance of sleep and waking, I think is made clear enough by the fact that concerning them there is great doubt and dissension among the highest philosophers and physicians. For Galen, when he questioned what sleep was, and what waking, decided at length that he could not be certain in what order of phenomena to classify them. Aristotle indeed, in his definitions of sleep and waking, arranges them in different places. Judging from selected books of all authors, no one, in my opinion, has been able to enumerate the general differences of sleep and waking by any certain method. Alcmœn thinks sleep is produced when the blood in the veins flows back and becomes congested. Empedocles believes it to arise from the chilling of heat in the blood. Diogenes states that sleep is induced by the blood pushing to the inner cavities of the body the air that is introduced into bodies. Plato and the Stoics taught that it arose of itself by the letting go of the spirit (or the releasing of the breath) and the consequent relaxation.
It is needless to refute the cause which Aristotle gives for sleep, and Galen for waking. They do not accord. The one thinks the true cause arises and has its seat in the heart,—the other in the brain. On account of which disagreement, great contention has been excited among more recent philosophers and physicians, as to which view to adhere to. Some attribute one significance, others another to these things. And so, because of the great difficulty introduced, there is nothing relative to the matter which is not in the deepest obscurity and doubt. A knowledge of this thing is, nevertheless, most useful, even if come upon by any other fortunate means, and not only through the knowledge of the doctors; by such means, for instance, as through the study of the general arts; for if it is joyful to philosophize, and to happen upon the hidden and abstruse things in the secret places of nature,—who would not find great pleasure in learning the causes of the sleeping and waking of creatures, why now they take long, now short sleeps; why at one time it is difficult to capture sleep,—at another time impossible to dispel it?
We wonder how at one moment sleep leads to waking; how waking and sleeping mutually succeed each other; why diverse things serve to explain each other, as sleep, waking,—and waking, sleep.
Sometimes these, sleep and waking, are injurious,—at other times beneficial. For sleep and also waking bring forth diseases, intensify them; both equally drive them away, soothe sorrows and likewise intensify them; by one and the other alike, morbid causes are often destroyed more effectually than by any other remedy; indeed, in conjunction with the benefit of these (sleep and waking), concoctions, food, purgatives, and finally all the functions of the different parts of the body may be exercised to the best advantage; nor is it possible, indeed, for a creature to live, or to maintain his life, without sleep and waking.
There is no action of the body or mind which has greater values to the body, nothing which supplies more reliable signs for discerning bodily ills, and showing how to be rid of them.
Of which things, indeed, the investigation and knowledge is most useful, and not without pleasure to those who delight in the understanding of things; that is what Aristotle, prince of philosophers, notices, when he writes his whole book concerning sleep and waking,—and often elsewhere at random in his writings. Not the less does Hippocrates notice them in his citations, for he wrote most sayings on the subject, so many that I omit them; and there are many in other books, of which a definite impression does not remain in my memory. But as I have said, when all, or certainly most writers on this subject may be perplexed with regard to these things, and involved in many difficulties, no one ought to condemn me, if, after them, and many men, I presume to write on this subject.
CHAPTER I
BY WHAT CAUSES AND MEANS SLEEP AND WAKING ARE PRODUCED, ACCORDING TO THE OPINION OF ARISTOTLE
To refute the opinion of the philosophers concerning the causes of sleep and waking, I think superfluous; because, with Aristotle’s views surviving now many centuries, no authority among these other writers may be greater than his; and because the ignorant premises of the others makes all discussion of them become inane.