NERVE OVERLAP — PAIN SENSE — PERIPHERAL NERVES 363 



pressure with a blunt object, care being taken to obtain from the 

 patient responses only to pain from prick of a sharp point. I 

 believe pressure of even 35 grams to be permissible to map out 

 the overlap of sense of prick pain. No exact measurements of 

 threshold to prick pain were made and in the majority of cases 

 pressure did not exceed 30 grams. 



1. USUAL AREA IN WHICH SENSATION TO PIN PRICK RETURNED 

 BEFORE TACTILE SENSIBILITY 



For the purpose of this investigation only such cases were 

 selected to illustrate the dissociated return of sensibility to pin 

 prick as were not instances of regenerating nerves. To insure 

 this one of two conditions were insisted on : first the presence of 

 pam sense having been demonstrated within the area of the 

 nerve's supposed anatomic supply, that nerve is found, at opera- 

 tion, to be divided and the ends separated. Second, the nerve 

 having been seen to be divided at operation, presence of pain 

 sense was demonstrated in its distribution within the length of 

 time given for the return of protopathic sensibility as the result 

 of regeneration (Head, Rivers and Sherren, 43 days). In my 

 cases under the second condition 28 days was the limit with the 

 exception of lesions of the radial nerve in which the limit was 37 

 da3^s. 



The areas in which sensibihty to pain returns before tactile 

 sensibility are the same under both conditions. It is unneces- 

 sary to describe them and they will only be illustrated (figs 

 1, 2, 3, 4). 



A few conclusions may be drawn from these observations: 

 1. Following section of a mixed nerve the complete loss of 

 sensibility to pain is far less than the loss of tactile sensibility, 

 which corresponds to the accepted sensory distribution of a 

 nerve. 2. The early and dissociated return of sensibility to 

 pain occurs in certain areas specifically constant for each indi- 

 vidual nerve. Inasmuch as in the cases above illustrated, this 

 return of sensation could not have resulted from nerve regen- 

 eration it follows that these areas are regions of nerve overlap. 

 3. The areas in which early return of prick pain was observed 



THE JOURNAL OP COMPARATIVE NEUROLOGY, VOL. 32, NO. 3 



