De somno et vigilia theses ad disputandum propositae

VII.
Proper causes are the sensory organs, the nerves produced to them, the objects, and in some, a defined interval. It is necessary that all these causes behave in a certain way so that sensation may occur.

VIII.
I call the common faculty that which flows from the principle of the senses, that is, primarily from the anterior ventricles of the brain, into each individual sensory organ, and which apprehends sensations; it is capable of this when it is neither corrupted, nor occupied in another work, nor weakened excessively, nor finally hindered in any other way.

IX.
The animal spirits are then suitable for effecting sensation when, with their quantity and quality, etc., correctly maintained, their motion necessary for this function is not hindered.

X.
The innate heat performs its ministry to the senses when it moves freely and in sufficient quantity to the ventricles of the brain and to any sensory organs.

XI.
For the motion of both (that is, of the heat and the spirits), cavities and pathways are required that are not closed, but unobstructed.

XII.
Now indeed, since sleep and waking are affections common to all the senses, and the peculiar causes of sensations can remain the same whether we sleep or wake (such as unobstructed nerves, the natural structure of the sensory organs, objects moved at the due interval), just as we ascribe waking as the commensurate effect to the common causes acting, so we believe that sleep should be ascribed to the same causes, either all or some, being deficient.