Pain is one of the most common of all the symptoms manifested by the nervous system; yet it is impossible to frame a definition which will exactly describe it. Indeed, it is impossible to formulate a definition of pain which will distinguish it from pleasure, the opposite condition. Numerous attempts have been made by philosophers as well as physicians to describe this most common of all symptoms, but without success. Notwithstanding, this need not be considered so great a misfortune, since every one knows what it is, making a description unnecessary. We shall under this head, too, point out some of the principal kinds of pain, their significance, and the best methods of treatment to adopt for their relief. Pain has been classified as follows:

Inflammatory Pain

This is the pain of inflammation, but varies in character, according to the part affected and the intensity of morbid action, being sometimes sharp and lancinating, as in the pain of pleurisy, at other times throbbing, as in an abscess in which pus is forming, or dull and continuous, when inflammation is only moderate in intensity and considerable in extent.

Irritative Pain

This is a pain which arises from some sort of irritation of a nerve. The irritation may be mechanical or chemical, or it may be due to causes too subtle to be discovered.

Reflex Pain

This variety of pain is felt at some point remote from the location of the morbid condition which gives rise to it. We see illustrations of it in cases of headache, neuralgia, and tenderness of the spine which arises from disease of the uterus and ovaries in women, and in cases in which pain in various organs is excited by the irritation of worms in the intestinal canal.

Pain Originating in Nerve Centers

This variety of pain is best illustrated by hysteria, a disease in which the difficulty undoubtedly exists chiefly in the nerve centers, although the exact nature of the diseased condition has not yet been fully made out. Neuralgia of the various parts of the body arising from tumors in the brain is also an example of this kind of pain.

Numerous kinds of pain have been described by various authors, as tingling pain, often referred to as "pins and needles," aching, smarting, burning, gnawing, rasping, throbbing, lancinating, dull, heavy, etc., and various other modifications of pain. It is hardly possible to attach to each of these different kinds of pain a definite significance. It may be remarked that, in general, acute smarting or lancinating pain is indicative of active congestion or inflammation, while a dull, heavy, continuous pain indicates passive congestion.

The Causes of Pain - Diseases Of The Nervous System

Romberg has very well said, that pain is "the prayer of the nerve for healthy blood." Defective nutrition is undoubtedly the most common cause of pain. We often have very acute pain arising in consequence of a deficient supply of blood to the affected nerve. Congestion is also a frequent cause of pain, the distended blood-vessels subjecting the sensitive nerve fibres to an abnormal amount of pressure.