SPINAL COED AND NERVES 



309 



the arm in various places lightly with a pin a subject of ordinary 

 intelligence is able to indicate accurately that in certain lines 

 and areas the painful sensation is felt far more acutely than in 

 adjacent regions. This cannot depend on differences of pressure 

 in the pricking, for if the experiment be repeated at different 



FIG. 183. Hyperalgesic bands and areas in skin of upper limb 

 (A), lower limb (B), and thorax (C) of a normal individual. 

 (Langelaan.) 



times and on various subjects, the hyper- 

 algesic points are found fixed and well 

 denned. On tracing the hyperalgesic 

 points with a dermographic pencil upon 

 the skin of his subjects, Langelaan found 

 that they combined into definite fields 

 and lines, which coincide with the limit- 

 ing lines of Bolk's dermatomes (Fig. 

 183, A, B, C). 



The hyperalgesic lines seem to corre- 

 spond with those points at which the 

 dermatomes overlap; on the back of the c 



hand and the palm where some of the 



dermatomes (6, 7, 80, ID) fuse they form a definite area, not a 

 line, as seen at A in the above figure. 



It is worth noting that under certain pathological conditions, 

 e.g. in Tabes dorsalis, these hyperalgesic lines and fields become 

 pronounced and more easy to demonstrate than under normal 

 conditions. 



