Page:Popular Science Monthly Volume 76.djvu/440

436 nerves." When a viscus is the seat of origin of pain the impulses which ascend its sympathetic nerves excite the centers of sensory nerves in the spinal cord.

The theory which I have attempted to outline in this article is laid on the same basis, somewhat broadened. All pain is "referred"—to the right spot, if its source be in the skin; because the skin is elaborately supplied with place-defining nerves—to an organ or part, skin, muscle, joint, which the ego, during the progress of self-investigation, has discovered in the same segment of the body, if its source be in a viscus.

The body is permeated with a felt-work of nerves, unprovided with specialized nerve-endings, conveying no definite information, and in consequence without precise distribution in the seat of consciousness. This non-specialized system which binds the various parts of the body together is the mechanism through which the caliber of blood-vessels, erection of hairs, secretion of glands, contraction of the walls of ducts and of the intestines, and many other domestic adjustments are effected. It is also the medium through which the gray matter of the cerebrospinal axis is affected sympathetically with damage to the tissues. The resultant altered conductivity of the gray matter leads to modification •of the only kind of impulses with which consciousness is concerned—impulses which inform. We infer that the damage which is giving:rise to a feeling of pain is in the part from which the modified impulses 'come.

When attempting to formulate the theory of pain it is necessary to discard the prejudice that there need be a proportional relation between the intensity of pain and the magnitude of the physiological changes which condition it. A heavy blow hurts more than a light one. Yet a change which could not be detected by any piece of apparatus in use in a physiological laboratory, if it affect the nerve-tissue of a tooth, may give rise to more pain than is caused by a crushed limb.

Another prejudice, from which it is difficult to shake free, attributes to the mind an innate knowledge of the topography of the body; an innate knowledge, that is to say, of the distribution of its news-agents, the sensory endings of nerves.

Thirdly, it is necessary to remember, when investigating the machine, that the machine is the man. It is not sufficient to design a scheme of telephone wires requiring for its use a listening ear at its center, the brain. The ear is a part of the machine. There is no need to picture a system of pain nerves, carrying news of damage to an attentive mind. A departure from the normal in the functioning of the sensory apparatus is pain.