CUTANEOUS SENSATION AFTER NERVE‐DIVISION

1. Section of the anterior branch of the internal cutaneous nerve in the forearm resulted in anaesthesia and hypoaesthesia of a small area of skin on the volar aspect near the wrist and slightly to the ulnar side. 2. All forms of sensibility tended to return gradually to normal. Recovery was from anaesthesia or hypoaesthesia through decreasing degrees of hypoaesthesia to normal; warmth and cold, however, passed through an intermediate stage of hyperaesthesia. 3. Pain, pressure, and cold became normal at about the same rate; warmth was relatively very much delayed. 4. Distribution of sensitivity over the skin was always irregular and patchy. 5. In initial stages there were two zones of sensory defect: an inner zone of anaesthesia and an outer zone of hypoaesthesia, which shaded off from normal sensitivity at its outer edge to extreme deficiency at its inner boundary. 6. The course of recovery for the two zones was similar. The outer zone always preceded the inner in recovery, and never showed so extreme a degree of abnormality as the inner. 7. The regions of sensory loss were approximately the same for all forms of sensibility. 8. Sensibility returned to the outer parts of the affected region first. There was no evidence that it followed the course of the nerve. 9. During recovery warmths and colds were frequently experienced as intense and diffuse. Pressures and pains were often remotely referred. Sometimes remote reference and immediate reference occurred together and a sensation was felt as ‘double.’ 10. Deep sensibility to pressure and pain was not altered. 11. Localisation of pressures of 20 grms. and discrimination of two pressures applied at 20 grms. remained unaffected. 12. No new qualities of sensation were experienced at any time. Many unique experiences were found to be merely unusual combinations of familiar qualities. 13. The hypothesis of Head and others, which assumes that cutaneous sensibility may be divided into “protopathic” and “epicritic” groups, is open to criticism (a) because it is inconsistent in its evolutionary aspect with the hypotheses of development of other modes of sensation; (b) because it cannot replace other hypotheses of cutaneous sensibility, since it is applicable only to a particular group of facts; (c) because it is not sufficiently thoroughgoing to constitute a true theoretical formulation; and (d) because it indicates generalities which admit of exceptions or are of doubtful status. 14. A more satisfactory theory is one which assumes that single sensory spots are innervated by more than one nerve fibre, that the multiple innervation is projected upon the central nervous system as multiple excitations which depend for their degree upon their relative strengths, their separations in the region of projection, and a limitation of the available amount of central energy. Under these conditions, multiple innervation may be effective as summation or as inhibition of the excitations involved. The division of inhibiting fibres may result in hyperaesthesia or in abnormal localisation; the gradual appearance of these forms of abnormality is due to the gradual effect of practice in the assumption of vicarious function.