SELF-PRESERVATION AND THE MENTAL LIFE 151 



muscles, and the internal organs. Existing physio- 

 logical knowledge of this subject was materially 

 deepened by studies made, not long ago, by Dr. 

 Head of London, who, in order to investigate the 

 sensations from the skin, caused certain nerves 

 near his own hand to be cut, and afterwards examined 

 his arm and hand systematically. In this way he 

 discovered three distinct forms of sensibility. One 

 of these Head calls deep sensibility, supplied to the 

 deeper structures by nerves running in company with 

 the motor nerves. The skin itself was found to 

 have two distinct forms of sensibility, one (the 

 epicritic) by which it is possible to detect light 

 touches and impressions of warmth and coolness; 

 a second (the protopathic) which is not evoked by 

 light touches, but by comparatively deep pin pricks, 

 or by heat or cold, or by touching or pulling hairs. 

 The protopathic sensibility has the peculiarity that 

 an intense stimulation gives a distinct, though not 

 usually localized, pain of widespread and radiating 

 character. When located, it may not be at the point 

 stimulated, but at a considerable distance. The 

 two systems, the epicritic and the protopathic, 

 though largely distinct, show intimate relationships. 

 There appears, moreover, to be a distinct analogy 

 between the sensibility of the viscera and that sub- 

 served by the protopathic system, and, indeed, their 

 nerve supply is part of the same mechanism. Head 

 found that heat and cold applied within the walls of 

 the intestines were referred by patients not to the 



