The nature and significance of the sensory phenomena resulting from cutaneous denervation have been subjects of much controversy among neurologists and psychologists. These phenomena—first studied systematically by Rivers and Head1—constitute the principal factual basis of Head's well known theory that the skin is innervated by two systems of afferent nerve fibers, called by him the protopathic and the epicritic. Head advanced this hypothesis in opposition to the traditional view which held that cutaneous sensitivity depends on the activities of four specific types of sensorineural mechanisms corresponding to the four psychologic "qualities" of touch, pain, cold and warmth. Head considered such a theory inadequate to account either for the patterns of dissociation produced by denervation or for the peculiar alterations in the character of the sensations elicited in such areas. Accordingly he proposed a dynamic theory patterned after Hughlings Jackson's doctrine of evolutionary levels of nervous organization. Two systems