RELATION OF PAIN SENSORY THRESHOLD TO FORM OF MECHANICAL STIMULATOR

Abstract

The mechanical excitability of arm skin pain spots was reexamined employing spherical stimulators of various sizes, as well as other forms, radius of curvature being taken as the most suitable measure of "sharpness." Below 0.1 mm. diam. of point the corneified layer of skin may be penetrated, introducing a complicating factor. Above 1.5 mm. deep pain is felt below the pressure required for prick. Between these values the plot of pressure per diam.2 at prick threshold is horizontal, except for a gradual rise at the small-diam. end due to the resistance of the skin to sharp bending, resulting in a depressed area larger than the stimulator. Threshold prick is attained along the flat region of the curve when the lower half of a given sphere makes contact with the skin surface, stretching it in each case to approx., twice the initial area. From such data it is inferred that the effective pain stimulus to mechanical distortion of the skin is lateral stretch of the subepithelial nerve network. Various less quantitative tests point to the same circumstance indicating that the mechanical resistance of the corneif ied layer to stretch is a major factor in determining pain irritability.