SKIN-SENSATIONS 425 



side of the forearm and hand to be cut in his own arm, in order 

 that he might study carefully the revival of sensations. He 

 found that he never lost his ability to recognize displace- 

 ments of the tissues beneath the skin. Pacinian bodies and 

 other end-organs of deep-lying nerves recorded pressure and 

 tension caused by pushing or rubbing with a blunt instrument. 

 Seven weeks after the injury he began to recognize stimuli that 

 do harm hot things, cold things, pricking with a pin 

 although his power of localizing the spot injured was extremely 

 vague. In seven weeks, that is to say, the protopathic nerves, 

 which do not follow the same definite lines as the nerves of the 

 special senses, but form open networks with many alternative 

 paths, had re-established their skin connections. Only gradu- 

 ally and very slowly did critical sensations return the ability 

 to distinguish degrees of warmth, to recognize as separate two 

 points of a pair of compasses, to feel a touch with cotton- 

 wool. 



According to a theory set forth in this book (p. 312), pain 

 is not a set of sensations, but a condition of the central nervous 

 system which renders it unduly excitable, or excitable in a 

 particular manner, to impulses which have the same local 

 origin as the nerve-current which sets up the condition of 

 pain. When a nerve of the skin has been cut, the epithelial 

 ramifications are renewed before any specialized tactile or 

 other sense-organs have regained their nervous connections. 

 When the area which has regained its surface ramifications, but 

 has not regained its sense-organs, is injured, no localization of 

 pain results. Indeed, the obscure sensations which are then 

 experienced if the skin be injured can hardly be described as 

 painful. The ramified nerves pour their agitation into the 

 grey matter of the spinal cord ; but it is not the agitation per se 

 which causes pain. It is the passage of impulses through the 

 agitated area that gives to them, when they reach conscious- 

 ness, not only a topographical meaning, but also a distressful 

 feeling. Until the specialized organs of the skin have been 

 restored to working order, there are no impulses to pass through 

 the agitated grey matter, and therefore no feelings of pain. 

 According to this view there are two systems of afferent nerves, 

 the protopathic and the specialized or critical. The former 

 is very widely and very abundantly distributed to the surface 



