INTRODUCTION 15 



that area, the spot, though unaffected by the operation in 

 any direct way, will give rise to no further sensations even 

 when it is severely injured. Hence, it is clear that the 

 pain does not reside simply in the skin. But not only may 

 pain thus be absent from a given area of skin ; it may be 

 present when the skin with which it is supposed to be 

 associated is absent. Persons who by accident or other- 

 wise have lost an arm or a leg often experience long after 

 the loss vivid and intense sensations from definite parts 

 of the missing member. So precise and sharp are these 

 sensations and so certainly do they seem to be associated 

 with the lost part that some of the less knowing of these 

 unfortunates have attempted to exhume or otherwise get 

 possession of the lost member in an endeavor to alleviate 

 their unpleasant sensations. 



These misunderstandings, for such they are, can be 

 swept away at once and the matter put in its true light 

 when we recognize that our sensations are not located in 

 the peripheral parts affected, but in the central nervous 

 system, and within that portion of it known as the cere- 

 bral cortex. As long as this organ is intact, sensations 

 may arise, and, though these are usually due to nervous 

 impulses from the sensory surfaces, they may be called 

 forth by an internal stimulus as well. Thus it is that a 

 missing arm may be represented by sensations years 

 after it has been severed from the body. With a loss of 

 an appropriate part of the cerebral cortex, however, 

 comes a loss of sensation that is absolute and final. From 

 this there is no recovery (Parker, 1916 b). 



This modern view of the relation of sensation to the 

 nervous system was initiated by the anatomists and 

 physiologists of the Renaissance. Thus, Vesalius taught, 

 in the sixteenth century, that the chief soul was engen- 



