ABSTRACT
Now it hath already been made manifest that all the operations of the body may be divided into two divisions, namely those which appertain to the spirit (or, soul) and those which appertain to nature. Those which appertain to the spirit may be divided into [three classes, namely], those which appertain to the mind, and those which appertain to the senses, and those which appertain to motion. It hath, moreover, been said that it is the brain itself which performeth the operations of the mind, some by means of other members, and some, that is to say, those which belong to the mind, it performeth itself. Now in this Chapter we are about to teach concerning the injuries which happen to the operations of the mind, that is to say, those which are caused by the three cavities of the brain. The first is that which imagineth things and is called "phantasy" 1 (or, "imagination"); the second is that which thinketh out things and is named "intelligence" (or, "understanding"); and the third is that which remembereth and is called "memory". Now the brain itself was not constituted by nature to be an organ of perception only, but it hath been the chief of the senses from the beginning. The brain itself by means of nerves sendeth the power to feel• into all the members of the body. And this is exceedingly well known from the fact that, if any nerve whatsoever be severed, straightway that
member which it serveth becometh without feeling, because that power, which came down into it from the brain and was distributed throughout it, hath been withdrawn from it. And this is also exceedingly well known from the fact that in sleep the senses either are wholly idle, or they work obscurely; in the latter case it is well known that the power which cometh
Page 2 down from the head to the members descendeth in I a small quantity. It is customary to describe these two kinds of sleep by the words "deep sleep" and "light sleep". The soundness of sleep varieth in proportion to the amount of power which cometh down [from the head]. And thus it happeneth that according as the power which cometh down and descendeth [is great or little] even so is the depth of the sleep. Therefore it seemeth that during the whole period of sleep the power of the spirit (or, soul) is at rest, and that the natural
Fol. 211. force worketh I vigorously. And this fact is well known. When this power is weary so soon as a man lieth down it is straightway made strong again, more especially if the man lieth down after [partaking of] a moderate portion of food. Moreover, during ·the time of sleep, digestion taketh place satisfactorily throughout the whole body, and not in the belly only; and, moreover, very properly, that member also in which [is seated) the principle of the rational soul is rested. Now it seemeth that the heart worketh slowly 1 [during sleep], since it hath not need of a lengthy period of rest; with the brain, however, such is not the case, for it worketh without cessation always during sleep. For this reason deep sleep falleth upon those who toil excessively, inasmuch as power hath descended in abundance and flowed from the head h1to them whilst they were toiling. Because, then, of the emptying out (or, exhaustion) of that power which was emitted by the brain, and because of the fatigue caused by [his] excessive exertions, he who is tired hath need both of rest and strength. Therefore men fall asleep easily after exertion and sleep heavily, and they do so also after they have partaken of food whensoever it hath [much] moisture in its composition. And they likewise sleep much
when they drink large quantities of wine, and they also sleep to excess when they bathe in very hot water, which they pour on their heads .. For all these things appear to fill the brain, and the brain hath need of the fullness whensoever I it is over-Page 3 worked and dried up through over-exertion. And from all these things it is well known that, when the brain hath worked very much and is disposed to rest, it causeth itself to fall asleep naturally, and especially if it hath within itself the power which feedeth it. If it hath anointed itself with moisture, or hath become cold through excessive cold, then [its] sleep is that which ariseth from absolute stupor and deathlike senselessness. And thus is it with all the [other) senses.
