In all the varied motions of the body this double action of the nerves takes place. It is obvious that without an _outward_ impulse from the brain, upon which the desire of the mind first made an impression, no motion of the muscles of the arm and the hand could have taken place; and it is also obvious that without an _inward_ impulse from the nerves to the brain you would not have known that the muscles had fulfilled your instructions. The hand might have dropped by the side of the book, or have gone too far, or not far enough, and you would not have been aware of the result, but for an inward communication through the nerves. We are not now speaking of the nerves which endow us with the sense of _feeling_, because they are regarded as separate and distinct from those nerves that produce in us consciousness of muscular response. When we walk, rise, or sit, we are made conscious, without any special feeling being exerted, that the muscles have placed the limb, or the body, in the desired position, that it is set down safely and firmly, and that we may repose upon it securely without further attention. We refer the impressions made by the book upon the nerves of the hand, and which enable us to tell whether it feels hot or cold, whether its surface is rough or smooth, and so on, to the special sense of _feeling_. The consciousness of muscular action is a separate and distinct function; and it is generally believed that the same nerves that convey the command of the will outward, bringing back the intimation that the will has been obeyed, but that _different fibres_ of the nerves convey the _outward_ and the _inward_ impulses. A single nerve may therefore be likened to a _double wire_ connected with the electric telegraph: one transmitting despatches in one direction, and the other in the opposite direction. 961. _What are the nerves of special sense?_ The nerves of special sense are those through which we _hear_, _see_, _feel_, _smell_, and _taste_. [Verse: "For the Lord seeth not as man seeth; for man looketh on the outward appearance, but the Lord looketh on the heart."--SAMUEL XVI.] 962. _What are the nerves of sympathy?_ The nerves of sympathy, or the system of _sympathetic nerves_, are those which are distributed to the _internal organs_, and which are independent of the will. They regulate the motions of the heart, the lungs, the stomach, &c., and stimulate the organs of secretion, so that those organs _work in harmony with each other_.