The afferent nerves are images, the brain is an image, the disturbance travelling through the sensory nerves and propagated in the brain is an image too. If the image which I term cerebral disturbance really begot external images, it would contain them in one way or another, and the representation of the whole material universe would be implied in that of this molecular movement. Now to state this proposition is enough to show its absurdity. The brain is part of the material world; the material world is not part of the brain. Eliminate the image which bears the name material world, and you destroy at the same time the brain and the cerebral disturbance which are parts of it. Suppose, on the contrary, that these two images, the brain and the cerebral disturbance, vanish : ex hypothesi you efface only these, that is to say very little, an insignificant detail from an immense picture. The picture in its totality, that is to say the whole universe, remains. To make of the brain the condition on which the whole image depends is in truth a contradiction in terms, since the brain is by hypothesis a part of this image. Neither nerves nor nerve centres can, then, condition the image of the universe.