The nervous system puts the body into relation with the external world as a whole, but for convenience it is subdivided into the afferent system, by which impressions come in, and the efferent system, by which the muscles are set in motion. Of the two halves, the afferent system has a just right to priority, for the efferent system is merely its consequence. Sights, sounds, smells, etc., reach the brain by afferent paths from the external world, and are there moulded into thoughts. Their effects we see in poetry, architecture, sculpture, or laundry work, according to the method of the brain in treating the raw material it receives, and of a quality corresponding to the fineness with which the brain examines them, and can control the motor organs of the body. Whatever goes in at the afferent door, and some people’s sensory apparatus is much more easily affected than others, produces its effect within. Sometimes the energy is expended in thought, sometimes in action; sometimes it trickles away as laughter. But all these phenomena have a material basis: matter producing changes in matter. ‘Those delicate tissues wherein the soul transacts its earthly business,’ as Stevenson so picturesquely describes the brain, stick to their earthly business. There is no astral department opened yet. A man may evolve a great idea from the data he receives, but he must give it a material coefficient if he does not wish it to be lost to his earth-bound brothers. He may write it in a book, or he may sculpture it in marble; but the most convenient means of communicating with his fellows is by sound, which he can command by expelling the air in his lungs over vibrating cords in his throat. These cords are adjusted at the position and tension to give a desired note; and the cavities of the chest, throat and mouth acting as resonators, a noise is produced, which is shaped by the tongue, lips and teeth into words. By means of language the human body is enabled to co-operate with others of its kind for the development of the resources of the earth, the shaping of society, and the forming of individual character. But here physiology ends and other sciences begin. ESSAY V. THE BODY. I. Such, as far as it can be compressed into four short essays, is the nature of protoplasm. We have sketched out its powers; described how it exists only in the form of a cell; and shown how cells, by forming a community and sharing the work, simplify the business of living, and secure great advantages for themselves individually. But now we have something fresh—the body.