84 INTRODUCTION TO NEUROLOGY 



of cutaneous nerves in their own bodies by Head, Trotter, and Davies for 

 the purpose of studying more critically the distribution of the various 

 sensory functions in and around the anesthetic areas produced by the 

 injuries and the phenomena accompanying the restoration of these functions 

 during the regeneration of the nerves. But general agreement has not yet 

 been reached on all questions. 



Head and his colleagues are of the opinion that all forms of cutaneous 

 sensibility (touch, temperature, and pain) are grouped in two series, each 

 served by different nerve-fibers and end-organs; these he terms "proto- 

 pathic" and "epicritic" sensibility. Protopathic sensibility is subjectively 

 general diffuse sensibility of a primitive form. Its sense organs are arranged 

 in definite spots, and yet these sensations have no clear local reference or 

 sign; that is, the spot stimulated cannot be accurately localized. There are 

 separate spots for touch, heat, cold, and pain; these spots being generally 

 grouped near the hair bulbs. In fact, the hairs are the most important 

 tactile organs of this system and the other sense qualities belonging here are 

 intimately associated with the roots of the hairs. Epicritic sensibility is 



Fig. 27. End-bulb of Krause from the conjunctiva of man. The 

 nerve-ending forms a globular skein within a delicate connective-tissue 

 cansulp,. (After Dncnpl.^ 



capsule. (After Dogiel.) 



a more refined sort of discrimination, and is regarded as a later evolutionary 

 type. It includes light touch, on the hairless parts of the body particularly, 

 and the discrimination of the intermediate degrees of temperature. Cuta- 

 neous localization and the discrimination of the distance between two points 

 simultaneously stimulated (the "compass test") are functions of this sys- 

 tem; but pain sensibility is not included, this being wholly protopathic. 



Trotter and Davies repeated some of Head's experiments and, while 

 confirming most of his observations, they were led to somewhat different 

 conclusions. They do not regard the protopathic and epicritic series as 

 served by distinct systems of nerves, but as different physiological phases of 

 the same systems of nerve-fibers and end-organs. 



2. End-organs for Sensibility to Cold. 



3. End-organs for Sensibility to Heat. Physiological experiment 

 shows that warmth and cold are sensed by different parts of the skin (the 

 warm spots and the cold spots respectively), and Head is of the opinion that 

 each of these types of sensibility may be present in an epicritic and a proto- 

 pathic form. What end-organs are involved here is by no means certain. 

 The margin of the cornea was found by von Frey to be sensitive to pain and 



