STUDIES ON PAIN. A NEW METHOD FOR MEASURING PAIN THRESHOLD: OBSERVATIONS ON SPATIAL SUMMATION OF PAIN

Abstract

The purpose of these studies has been to present a new method for measuring pain thresholds, together with experimental observations on the physiology of pain and on the effect of various chemical agents upon pain thresholds. Methods for estimating the intensity of the stimulus required to evoke a painful sensation in the skin may be classified under the headings: mechanical, chemical, electrical, and thermal. The mechanical devices as used by von Frey (1) and by Eddy (2), involving production of pain by pressure, empirically correlated the amount of pressure and the pain threshold. The deformation and internal stresses in the tissues responsible for the sensation were not investigated, and it may not be assumed that there is a simple proportion-ality between the pressure and the intensity of the sensory stimulus. The chemical methods of irritating the skin have not been thoroughly explored. The thermal methods of producing pain are among the oldest and were introduced as a method of study by Goldscheider (3) in 1884. These methods, involving application of hot objects to the skin or immersion of a member in hot water, have added little of a quantitative nature to the study of pain sense. The only method of study for which the relation of the stimulus to its physi-ologic and sensory effects has been investigated, is the electrical method of stimulating with Faradic current, introduced by Helmholtz (4) and studied carefully by Martin (5). This method has been widely used, largely in the study of the action of analgesics by Martin and his co-workers and by Macht and his associates (6). Recently, Hauck and Neuert (7) have used high frequency currents in the study of pain thresholds. Valuable work has been done with the above methods but none of them combines the flexibility and precision necessary for some investigations.