This section is from the book "Health", by W. H. Coefield.
Supposing that, instead of cutting through the whole of the spinal cord, you cut through the front part of it, so as to cut right across the white matter of the front of the spinal cord, it is then found that the animal is no longer capable of moving any muscles on either side of the body supplied by nerves below that cut, so that this shows that the stimuli which cause the movement of the muscles of the body travel down through the white matter in the front part of the spinal cord.
If, on the other hand, one half of the cord be cut through-say on the right side-then it is found that the animal has lost all power of moving the muscles of the right side of the body supplied by nerves from below the cut, so that the stimuli which cause the movement of the muscles travel down the spinal cord upon the same side as the muscles which are to be moved. But he has lost sensation on the other side of the body in the parts of the body supplied with nerves below that cut, so that it is clear that the paths which convey sensation up the spinal cord travel up the opposite side of the cord,- the-paths which convey sensation from the left leg, for instance, up the spinal cord, travel up the right hand side of the spinal cord, and the paths which convey sensation from the right leg up the spinal cord travel up the left hand side of the spinal cord.
I have told you already, from the simple experiment of cutting through the white matter of the front part of the spinal cord, that the stimuli causing movement travel down the white matter of the cord. If you cut through the white matter of the front part of the cord in one place, and the white matter of the back part in another place, so that with the two cuts you have cut through the whole of the white matter, only in two different places, it is found that sensation is not interfered with; so that it is clear that the paths which convey sensation in the spinal cord travel in the grey matter in the spinal cord, which you have left untouched.
So we come to this, that the stimuli which cause movement and the stimuli of sensation are conveyed along the spinal cord. If you cut the spinal cord clean across, the conveyance of these stimuli is stopped altogether. That the stimuli which cause the movement of the muscles are conveyed in the white matter of the front part of the spinal cord towards the muscles that are going to be moved, and on the same side of the cord as the muscles are that are going to be moved; that the stimuli which pass from the different parts of the body up the spinal cord travel up in the grey matter of the spinal cord, and on the opposite side of it.
So we see that the spinal cord is a great conductor of impressions to and from the different parts of the body; but it is more than this. When you have cut through the spinal cord of an animal, I have said that he cannot feel anything in the parts to which the nerves below the cut go, and that he cannot move any of the muscles of his own" accord; but if you take that animal and tickle the soles of his feet, or irritate the skin in any way, he will kick out; if he does not feel how can he do that? It is not he who does it at all; it is not his will; the animal shows no sign of pain, and does not know anything that is happening to that part of his body, but still the muscles in that part of his body contract violently, and the parts are moved; and that shows a very remarkable thing, that the spinal cord itself is capable of originating movement, that it is capable in some way of itself interpreting sensation and of commanding movements independently of the will of the animal Now, movements of that kind, which are produced entirely without the will of the animal, go by the name of reflex movements; they are so called from the idea of reflection. It seems as if stimulus applied to the skin at a certain part of the body is conveyed through the posterior roots of the spinal nerves to the part of the spinal cord which is no longer in connection with the brain, and as if that part reflected it along the motor roots of the nerves to the muscles to be moved, and that is why such acts are called reflex acts.
Eeflectidn is not a very accurate simile, because if you irritate a part of the skin, however small, if you irritate a nerve, or a very small branch of a nerve, that irritation is transferred to the spinal cord along perhaps only one of these nerves; or if you irritate the posterior root of one of these nerves after it has been cut through, not only the muscles to which that nerve goes contract, as you would expect if it were merely a kind of reflection, but that stimulus is distributed in the grey matter of the spinal cord, and stimuli are sent along many motor roots on both sides of the cord, so that a large number of muscles are moved. The grey matter of the spinal cord, from being capable of originating such movements itself, is called a nervous centre. So you see the spinal cord has two different functions: it is a conductor of impressions, both of stimuli which produce movement and of those which cause sensation, and it is also an independent nervous centre; and, more than that, if you cut through the cord in two places, the part that is left between the two places is an independent nervous centre, capable of interpreting sensations that come to it, and sending messages along the anterior roots of the nerves connected with it to the muscles to which they go, and causing them to contract. Now you see what we mean when we speak of a nervous centre.
These nerves that I have been speaking about are made up of bundles of fibres, nerve fibres, and each of these nerve fibres can be shown to consist of a little tube with a little thin cord running down its centre inside of it. The nerves are made up of these bundles of nerve fibres, and you will see at once that these nerve fibres bear a strict analogy in their construction to the telegraph wires which are laid down under the streets, and consist of copper wire with a coating of gutta-percha. The white matter of the spinal cord is made up also of these nerve fibres running the whole length of the spinal cord. The grey matter is made up of large irregular star-shaped bodies, which go by the name of nerve cells. Now I have made a comparison with the electric telegraph, and you will see from what I have already told you, how far that comparison holds; it holds to a very large extent.