_I._ It is a texture, or web of fibres, which lines all cavities exposed to the atmosphere--for instance, the mouth, windpipe and stomach. It is the seat of the senses of taste and smell. _E._ And the nerves are the little witches that inform the brain how one thing is sweet, another bitter; one fragrant, another nauseous. Alimentiveness ever after frowns or smiles accordingly. So it seems that the actions of the brain, and of the external senses, are reciprocated by the nerves, or something of this sort. How is it, Isabel? Oh, I see! You say sensibility belongs to the nerves. So sights by means of--of what? _I._ Of the optical nerves. _E._ Yes; and sounds by means of the-- _I._ Auditory nerves. _E._ Yes; convey impressions of externals to the brain. And "Upon this hint" the brain acts in its consequent reflections, and in the nervous impulses which induce muscular contractibility. And this muscular contractibility is a contraction of the fibres of the muscles. This contraction, of course, shortens them, and this latter _must_ result in the bending of the arm. I think I understand it. What are the brain and spine, Isabel? How are they connected? _I._ You will get correct ideas of the texture of the brain by observing that of animals. It occupies the whole cavity of the skull, is rounded and irregular in its form, full of prominences, _alias_ bumps. These appear to fit themselves to the skull; but doubtless the bone is moulded by the brain. The brain is divided into two parts; the upper and frontal part is called the _cerebrum_, the other the _cerebellum_. The former is the larger division, and is the seat of the moral sentiments and intellectual faculties. The latter is the seat of the propensities, domestic and selfish. _A._ I thank you, Isabel. Now, what is this spine, of which there is so much "complaint" now-a-days? _I._ I will answer you from Paley: "The spine, or backbone, is a chain of joints of very wonderful construction. It was to be firm, yet flexible; _firm_, to support the erect position of the body; _flexible_, to allow of the bending of the the trunk in all degrees of curvature. It was further, also, to become a pipe or conduit for the safe conveyance from the brain of the most important fluid of the animal frame, that, namely, upon which _all voluntary motion depends, the spinal marrow_; a substance not only of the first necessity to action, if not to life, but of a nature so delicate and tender, so susceptible and impatient of injury, that any unusual pressure upon it, or any considerable obstruction of its course, is followed by paralysis or death. Now, the spine was not only to furnish the main trunk for the passage of the medullary substance from the brain, but to give out, in the course of its progress, small pipes therefrom, which, being afterwards indefinitely subdivided, might, under the name of nerves, distribute this exquisite supply to every part of the body."