De somno et vigilia theses ad disputandum propositae

XVII.

It remains, therefore, that we conclude the primary and per se cause of all sleep is the impediment of the common sense, and that this happens because the animal spirits are kept at rest in the source of all senses.

XVIII.

With these foundations laid, it will be possible to construct complete definitions of waking and sleep in this manner without labor.

XIX.

Waking is an affection of the animal by which all sensations can be exercised, arising from the free motion of the animal spirits in the anterior ventricles of the brain, as well as the motion of the sensitive faculty toward the sensory organs.

XX.

Sleep is an affection by which all sensations cease, with the common faculty frustrated, because of the rest of the animal spirits contained in the ventricles of the brain, especially the anterior ones.

XXI.

Nor will it be difficult to ascend from here to the antecedent and evident causes of sleep and waking. For just as those things which in any way resist the motion of the spirits are established as causes of sleep, so those which are the cause that they are agitated more vehemently are correctly thought to effect waking. Whence it is consistent that all causes consist either in the mobile itself, that is, the spirits, or in the mover, or in the pathways or cavities through which the motion occurs.

XXII.

To these heads must be referred entirely those things which are taken, performed, elicited, and retained, and are applied from without, provided they contribute anything to conciliating sleep, or can rouse the sleeper.