475 



the range of 3 to 5 /x in diameter. Moreover the 

 group responding tonically had a higher maximal 

 frequency of discharge than that responding in phasic 

 fashion. In line with Bullock's thought, however, 

 was the finding in both these groups of lower ma.xi- 

 mal frequency than in the large myelinated nocicep- 

 tive fibers 6 to 9 // in diameter. These generally gave 

 a phasic discharge to light pin prick, ending about 

 0.2 sec. after the onset of the stimulus. It is apparent 

 that useful generalizations from the welter of facts 

 before us regarding pain and impulses in nerve 

 fibers are difficult. 



P.'MN IN .'>iBNOR.M.-\L A.N.-\TO.MICAL STATES AT PERIPHERY 



Dtv 



oj Cutaneous Nerves 



Both the quality and the degree of pain sensi- 

 bility become altered following injury to nervous 

 pathways concerned with its conduction. The most 

 painstaking and best controlled studies of the changes 

 have been made by investigators who divided and 

 then sutured the cut ends of one or more cutaneous 

 nerves in themselves. They then followed the sensory 

 status during the period of recovery. These workers 

 included Rivers & Head (223), Trotter & Davies 

 (270), Boring (30), Sharpey-Schafer (245) and Lanier 

 et al. (157). AH but the first group tended to agree 

 with Trotter & Davies that "the changes consequent 

 upon depriving a piece of skin of its nerve supply 

 are distributed in a central area of absolute lo.ss, 

 surrounded by a zone of much less loss which is 

 slight toward the periphery and deepens toward the 

 center." They also observed that the "defect of sensi- 

 bility to pain is precisely similar in character and dis- 

 tribution to the defects in sensibility to cold, to heat 

 and to touch." In addition, Trotter & Davies found 

 that there was an altered quality to many sensory 

 stimuli on the tenth to twelfth postoperative day, 

 lasting up to the sixth or eighth week. This developed 

 in spotty, irregular fashion largely peripheral to the 

 analgesic zone in the previously hypalgesic or so- 

 called intermediate zone. Later a more extensive 

 area of altered quality of sensation came on when 

 regeneration began. 



In the first 'hyperalgesic' stage they found that 

 pain after pinprick has an abnormally unpleasant 

 quality, radiates diffusely, tends to provoke a motor 

 response, is poorly localized or may be a persistent 

 severe burning which may reappear spontaneously 

 afterwards. Two point discrimination is reduced in 



the area and touch, although evoked only by stimuli 

 normally above the threshold, may then have a pain- 

 ful quality. In the later stage of regeneration the same 

 qualitative abnormalities can be elicited from the 

 previously analgesic zone. These abnormal features 

 may persist for many months and then gradually 

 decline. In general these reports have been well con- 

 firmed but their significance remains widely debated 

 and the mechanisms of production obscure. The 

 names applied to the situation have been as varied as 

 the hypotheses; 'hyperpathia', 'intensification", 'dyes- 

 thesia', 'over-reaction' and 'paradoxical pain' have 

 been used. Hyperalgesia is probably the least appro- 

 priate term since it implies a lowered threshold to 

 pain which is in fact usually not the case in this 

 condition. 



The development of the early phase of hyperpathia 

 was correlated by Pollock (214) with the ingrowth 

 of fibers from the adjoining peripheral nerves for two 

 reasons: a) the early hyperpathia (and the other re- 

 covery of sensation) appears long before regenerating 

 fibers could reach the skin; and b) such .sensation 

 is not lost if the regenerating nerve trunk is cut a 

 second time. Weddell and as.sociates (285) have in fact 

 demonstrated unmyelinated fibers growing out from 

 the intermediate into the originally anesthetic zone 

 using methylene blue stain in man. More recently 

 Weddell and associates (personal communication) 

 have acquired evidence that a denervated sector of 

 the cornea is reinnervated from three sources of nerve 

 supply. 



Head & Sherren (122) hypothecated that the nor- 

 mal sensations were mediated by 'epicritic' groups of 

 nerves and that the abnormal qualities ensued only 

 when 'protopathic' fibers were excited. Their com- 

 plex formulation completely failed to fit the facts 

 brought out h\ each of the succeeding workers who 

 studied their own sensations before and after de- 

 liberate cutaneous nerve section. Cobb (46) in his 

 work on patients with peripheral nerve injuries after 

 World War I drew attention to the fact that Head's 

 alleged areas of dissociation of sensibilities arose 

 from comparing stimuli which were not quantita- 

 tively equivalent. He found, for example, that the 

 areas of sensory loss were coextensive if one used a 

 soft brush to test cutaneous touch and a needle point 

 at 15 gm pressure for pain. .Sufiice it to sav that 

 despite the cogency of the criticisms of all of these 

 workers it has required the devastating verbal scythe 

 of Waishe (282), giving incisiveness to his keen 

 critical powers, to .sweep from the literature favorable 

 reference to the 'protopathic' and 'epicritic' nervous 



