358 LEWIS J. POLLOCK 



interrupted current, and to degrees of temperature between 

 22°C. and 40°C. In this area are felt only the stimuli affecting 

 the protopathic sensibility, such as the prick of a pin and tem- 

 peratures below 20°C. and above 40°C. 



This seeming dissociation of sensory loss which persists, 

 throughout the time of regeneration of an injured nerve, offers 

 among others two problems. First, the reason for the preser- 

 vation of certain sensibility in the intermediate zone or that 

 area between the borders of the loss to light touch and the loss 

 to pin prick, and, second, the reason for the increase in size of 

 this area of sensibility as time goes on. 



The preserva-tion of sensibility to any type of stimulation 

 within the sensory area usually assigned to a nerve immediately 

 following its section can be due to but one cause, nerve overlap. 



The further return of sensibility in the intermediate zone can 

 be due to but two conditions, nerve regeneration or the assump- 

 tion of function by adjacent nerves. Relative to the possibility 

 of nerve overlap, Head (2) and his co-workers state that ^'such 

 overlapping should lead to rapid restoration of sensibility to 

 prick, and in some cases possibly forms a factor when sensation 

 returns with unusual rapidity. Commonly no wide loss to 

 prick on the pahn follows division of the median nerve, because 

 the fibers which conduct this form of sensation are supplied from 

 both nerves. But supposing the nerve supply 'of the median 

 palm came overwhelmingly from the median, division of the 

 nerve would produce at first total analgesia. This might rapidly 

 pass away, to some extent, as soon as the few fibers of the ulnar 

 nerve to the median palm became capable of supplying sufficient 

 sensibility for the transmission of impulses." Again they say 

 (page 149) ''With so much overlapping of nerve supply, com- 

 plete recovery of sensibility to prick pain might occur without 

 union of the divided nerve, by a further development of those 

 fibers in the uninjured nerve which normally supply the affected 

 parts. In areas where sensation to prick is only partially lost, 

 such substitution undoubtedly occurs, .... But there is 

 no evidence to show that restoration of sensation can be pro- 

 duced in analgesic parts without union of a divided nerve." 



