logi 



The work of Head, who was the pioneer in this method of investiga- 

 tion, must also be mentioned. He found that when the median nerve 

 was divided in his own arm, recovery of sensation began with the 

 restoration of sensibility to pain and to extreme degrees of heat and 

 cold ; but the hand still remained for a time as insensitive as before to 

 such stimuli as slight touch. In the parts which had regained their 

 sensibility to severe stimuli, like pricking and extremes of heat and cold, 

 the sensation radiated widely, was referred to remote parts, and could not 

 be accurately localized. This form of sensibility Head calls protopathic. 

 As the nerve recovered further, a second form of sensibility appeared, 

 associated with accurate localization of cutaneous stimuli and dis- 

 crimination of two compass points. Light touch and moderate degrees 

 of heat and cold could now be again appreciated. This form of sensi- 

 bility he terms epicritic. A third form of sensibility (deep sensibility} 

 was investigated after complete division of the radial and external 

 cutaneous nerves at the elbow. The radial half of the arm and back 

 of the hand became totally insensitive to cutaneous stimuli, but re- 

 tained their sensibility to pressure or to any stimulus which deformed 

 the subcutaneous structures, as well as their power of localization of 

 such stimuli. The afferent fibres upon which this deep sensibility 

 depends must run with the motor nerves. According to Head, the 

 other two forms of sensibility (protopathic and epicritic) also depend 

 on two separate systems of nerves, of which the protopathic is the older 

 in the phylogenetic sense, and has a wider distribution. It is assumed 

 that the protopathic fibres regenerate more easily and speedily than the 

 epicritic or than the motor nerves of voluntary muscle. The proto- 

 pathic fibres are supposed by Head to exert a trophic influence. A 

 part deprived of its nerve-supply is liable to injuries, and the sores so 

 produced heal slowly. But as soon as ' protopathic ' sensibility returns 

 to the part, they heal rapidly, even in the absence of all epicritic sensa- 

 tion. The intestine is described as possessing 'protopathic,' but not 

 'epicritic,' sensibility i.e., it reacts to extremes of heat and cold, but 

 not to moderate heat and cold or light touch. 



Quite recently an elaborate study of the loss and return of the 

 skin sensations after section of a cutaneous nerve has been made by 

 Boring. His work is distinguished from that of all previous ob- 

 servers by the fact that he brought to his task the training of a 

 professional psychologist, and that he studied in detail for fifteen 

 months the area of skin with whose innervation he intended to 

 interfere. Section of the nerve chosen (the anterior branch of the 

 internal cutaneous nerve in the forearm) caused anaesthesia and 

 hypoaesthesia of a relatively small area of skin (on the volar aspect 

 of the forearm near the wrist), so that it was possible to make an 

 intensive study of it, and the observations were continued for more 

 than 1,000 days after the operation. Points on the affected area 

 were identified by reference to a series of points tattooed on the 

 skin represented by crosses in Fig. 466. 



The sensations studied, in addition to those of warmth and cold, 

 were the four qualities which appear upon mechanical stimulation 

 of the skin: Contact, cutaneous pressure, subcutaneous or deep 

 pressure and pain. Boring uses the terms ' tickle-contact/ ' pene- 

 trating pressure,' ' dull pressure/ and ' sharpness ' for these quali- 



