Yet it is my perception which has vanished. What does this mean, if not that my perception displays, in the midst of the image world, as would their outward reflexion or shadow, the eventual or possible actions of my body? Now the system of images in which the scalpel has effected only an insignificant change is what is generally called the material world; and, on the other hand, that which has just vanished is 'my perception' of matter. Whence, provisionally, these two definitions: I call matter the aggregate of images, and perception of matter these same images referred to the eventual action of one particular image, my body.
Let us go more deeply into this reference. I consider my body, with its centripetal and centrifugalThe brain is concerned with motor reaction, not with conscious perception. nerves, with its nerve centres. I know that external objects make in the afferent nerves a disturbance which passes onward to the centres, that the centres are the theatre of very varied molecular movements, and that these movements depend on the nature and position of the objects. Change the objects, or modify their relation to my body, and everything is changed in the interior movements of my perceptive centres. But everything is also changed in 'my perception.' My perception is, then, a function of these molecular movements; it depends upon them. But how does it depend upon them? It will perhaps be
