The brain is an organ. The student will acquire a solid principle if he grasps this idea firmly: that the nervous organism is homogeneous in its center and in its ramifications, and that its function is simply such as its mechanical efficiency determines. Nothing justifies the excessive belief which imputes to the “white” or “gray” matter (accessory to sensory and motor activity) the function of secreting the intelligence and the will, as the liver does bile. A confusion in terms seems to imply it. The brain is an organ, like the stomach and the heart; and, just as the digestive or circulatory systems have their precise function, the nervous system has its own, which is the production of sensation and movement. I use the word “production” designedly. It would be inexact to see in the nerves simply threads bound together, agents inert in themselves, of a double transmission; “afferent” (as they say) here; “efferent” there; ready indifferently to telegraph a noise, a shock, or an order of the inner mind. The apparatus assures the opening of a cerebral wave, constant as a pulse, to all the body. Sensation is not a passive phenomenon; it is a special state of activity. I compare it to a vibrating cord, on which the note is formed by the correct position of the fingers. By sensation, I verify facts; by movement, I control action. But the vibration is constant. And this view permits us to advance our investigation further. All vibration implies a source, as all circles have a center. The source of nerve vibration resides in the brain, which, separated from all the other organs, fills the entire cavity of the sealed skull. The rule of analogy, at the outset, forbids seeing in it anything but the agent of reception, of transformation, and of digestion (so to speak) of the initial commotion. One can imagine that this duty has devolved especially on the peripheric matter which the white substratum forms, as an agency of amplification and of composition; and finally, that the complicated organs of the base of the brain are so many laboratories, setting the scene for distribution, arranging keyboards, installing the apparatus of substitution and of regulation. We must now consider the vibration itself. By this I mean a double movement,--one by which a body proceeds from a point to return to it. Here is the element we seek,--the symbol which constitutes essentially all life. The vibration of our brain is the agitation of the source of life, the emotion of matter in contact with that Divine Unity whose possession constitutes our typical personality. This is the umbilical cord of our dependence. The nerves, and the contact that they give us with the exterior world, are but the instruments of our knowledge; and it is in this sense alone that they are the conditions of it. As one makes trial of a tool, so we fashion the education of our senses. We learn to know the world through its contact with our intimate identity.