Significance of Pain

PAIN, SIGNIFICANCE OF. In health we are conscious of few bodily sensations other than a sense of well-being, of physical and mental comfort and accord with our surroundings, with the addition, at certain times, of such pleasant attributes as a glowing skin or a ready appetite. The normal interruptions to this state of physiological balance are the transitory discomforts of a too-insistent hunger or a full bowel or bladder, or due to fatigue and such external agencies as heat and cold. We are made aware of ill-health either by an indefinable malaise or by more localized and disagreeable sensations ; of such are nausea, itching, dizziness and shortness of breath, each of which proclaims a de rangement of function in certain organs or tissues. The purpose of these symptoms is regarded as protective, just as a flow of tears or a winking eye-lid in response to a speck of dust in the eye is protective. The pain which accompanies and would, indeed, seem to induce the weeping and spasmodic movements of the lid is, in the conscious state, an accompaniment of the protective reflex.

Biological Purpose.

Of all the sensory phenomena of dis ease pain in one form or another is the most frequent and fre quently the most urgent. It differs in kind from the types of discomfort already cited and is due to distinct causes, but the difference between many other discomforts and pain is merely a matter of degree. Thus the ache of a muscle employed in some unwonted effort is probably due to the same factors as those which induce an agonising cramp; it only differs from cramp subjectively in being much more bearable. In both states the muscle-fibres are much tautened, more than is usual at rest or after mild activity; but in cramp the tautening increases until painful spasm occurs. Similarly the physiological discomfort of hunger, which depends upon an exaggerated tonic and contractile activity of the muscular coat of the stomach, is only a little re moved from the hunger-pain accompanying duodenal ulcer, in which tonic and contractile activity are reflexly exaggerated in moments of approaching emptiness by impulses originating in the nerves exposed by the ulcer.

The biological purpose of pain, wherever it occurs, and even although this purpose may sometimes seem difficult of acceptance, is undoubtedly protective. When the hand is pricked by the hidden pin it is spontaneously withdrawn to prevent a deeper injury. We are careful not to bite upon the sensitive tooth. The

pain of a broken limb or of an inflamed joint compels disuse and an attitude of rest most favourable to healing. The pain of pleurisy compels restricted and shallow breathing to lessen the friction of the delicate lining membranes of the lung and chest wall which have been invaded by infective agents and roughened by inflammation. The pain of angina pectoris compels instant and complete physical immobility to give the heart the best possible chance of rest and recovery in a moment of circulatory stress dangerous alike to itself and life.

Thus, patently in some instances, obscurely in others, pain serves to inhibit actions which would otherwise add further injury to tissues already damaged by disease. The victim of tooth-ache or some more serious agony can scarcely be expected to appreciate the methods of nature or to accept suffering as beneficial; religious devotees of varying cults may persist in claiming pain as a punish ment or an expiation for sin ; but the medical sciences continue to accumulate evidence which establishes pain and the other symptoms of disease as the necessary sensory element of mechan isms physiologically valuable because they prepare the way for nature's healing endeavour by the process of rest.

Physiological Interpretation.

The foregoing statement seeks to explain the biological significance of pain, but it is neces sary also to consider the physiological significance of special pains and of pains felt in various organs and tissues of the body. From an appreciation of the physiological significance of pain is derived information of the greatest value in medical diagnosis and treatment. In the skin special nerve-endings, with appropriate paths in the spinal cord have been demonstrated whose service is to transmit painful sensations, which are referred to and ap preciated in consciousness at the site of the actual injury. The skin is also endowed with nerve-fibres for touch, heat and cold. If we except the delicate mucous-membranes of the bodily orifices with their special sensibilities, it is doubtful whether any other tissues possess such specialized powers of appreciation and dis crimination. Indeed it is clear that they have small need of them.