Conceive, then, of this interlaced physical structure extending throughout the whole organism as a kind of circular mechanism, having its periphery at the surface of the body and limbs, ramifying among and into the internal organs, with various nerve-centers distributed through the interior mechanism, and the one great nerve-center in the brain. Conceive of this structure, further, as fed continually by the blood-vessels, which repair its waste of tissue and keep it in proper tone and activity. Then imagine it as first put in operation in some animal in whom it has become developed as we now know it in ourselves, and let that animal stand as the primeval man, who has become, by inherited transmission of gradual accumulations, possessed of this consummate development of nervous organization. You can then observe the method of its action, and can perceive how mind became developed, and what it is. What I have now given you is only a general description of the structure of the nervous mechanism, and in order to understand its functions, we may take it up, in an individual, at a point of time when it had not experienced a single movement or change from a state of rest, but when it was completely fitted to act. Observe, then, that its action will consist in the origination and accomplishment of motion; or, in other words, in molecular change of the substance composing the nerves, which, for illustration only, may be likened to the conductor through which the molecular disturbance passes which is popularly, but not scientifically, called the electric fluid. At the surface of the body and limbs, the external termini of the nerves are exposed to disturbance by contact with an external object. Along the highly sensitive and minute conductor, the nerve which has by contact with an external object at its outer extremity received a slight shock, there passes through the fluid or semi-fluid substance of the nerve a wave of disturbance, or a succession of such waves. This disturbance reaches the brain, the great nerve-center, where it becomes a feeling. In this way is generated the feeling of contact with an external object, and this is what is commonly called the sense of touch, which is simply a feeling produced in the great nerve-center of the brain. Now, to reverse the process, let us suppose that this feeling, caused by touching an external object, provokes or excites a desire to remove that object, or to get rid of the continuance of the feeling, and to be without the irritation or pain which it is causing. From the central seat of nervous action, the brain, along another nerve, there proceeds a wave, or a series of waves, in the fluid or semi-fluid substance of which the conductor of that nerve is composed, and motion is communicated to some muscle or set of muscles, which need to be put in motion in order to break the contact with the external object. In like manner, all internal organs of the body, the viscera, are supplied