VTii TOUCH 353 



nerve, gives rise not to a sensation of heat or cold, but 

 simply to pain. Thus, if the elbow be dipped into a 

 mixture of ice and salt, the cold first affects the skin of 

 the elbow, giving rise to a sensation of cold at the elbow, 

 but afterwards attacks the trunk of the ulnar nerve, 

 which at the elbow lies not very far below the skin ; and 

 this latter effect is felt as a sensation, not of cold, but of 

 pain. The pain, moreover, thus caused is not felt in the 

 trunk of the nerve at the elbow, where the cold is acting, 

 but in the parts where the fibres of the nerve end, more 

 particularly in the little and ring fingers. 



Again, the sensation of heat, or cold, is relative rather 

 than absolute. Suppose three basins be prepared, one 

 filled with ice-cold water, one with water as hot as can 

 be borne, and the third with a mixture of the two. If 

 the hand be put into the hot-water basin, and then 

 transferred to the mixture, the latter will feel cold ; but 

 if the hand be kept a while in the ice-cold water, and 

 then transferred to the very same mixture, this will feel 

 warm. 



Like the sense of touch, the sense of warmth varies in 

 delicacy in different parts of the body. The cheeks are 

 very sensitive, more so than the lips ; the palms of the 

 hands are more sensitive to heat than their backs. Hence 

 a washerwoman holds her flat-iron to her cheek to test 

 the temperature, and one who is cold spreads the palms 

 of his hands to the fii'e. 



The differences in the sensitiveness of the skin to heat 

 and cold at various points may be readily determined by 

 touching the several points with the blunt end of a wire 

 whose temperatm-e can be kept constant at any desired 

 (Jewree. In this way it is found that some points respond 

 to heat but not to cold, others to cold but not to heat, 

 so that we meet with "heat spots" and "cold spots." 

 The accompanying figure shows the distribution of these 

 spots in a small area of the skin of the thigh. 



