Finally, it follows that we do not see bodies in themselves, and that if, through the flow of animal spirits or otherwise, there were excited in the brain disturbances like those we now have with open eyes, and should all external bodies be annihilated and hence be absolutely invisible in themselves, we would still see what we now see, as a result of the general laws concerning the union of soul and body; and this is what happens during sleep, in those in a high fever, and in madmen.