THE TEMPERATURE SENSE. 283 



then, no certainty of getting rid of a corn by ampu- 

 tating a toe. 



The Temperature Sense. Many cases are on record 

 in which, from accident or disease, the pressure sense was 

 lost and the temperature sense retained, or vice versa. 

 Such facts have led to the belief that the temperature 

 sense is distinct from that of touch, and has its own nerve 

 fibers and nerve endings. 



Two Sets of Nerve Fibers for Distinguishing Heat and 

 Cold. Since heat and cold are only differences in the 

 degree of heat, we would expect both of these kinds of 

 impressions to be received through one set of nerves. 

 There seems, however, to be good evidence of two sets of 

 nerve fibers, one for heat and the other for cold. In the com- 

 mon experience of the foot " going to sleep" by pressure 

 on the sciatic nerve, or the arm from compression of the 

 brachial nerve, the skin may be found, at a certain stage, 

 to be only slightly sensitive to warmth, while distinctly 

 sensitive to cold. In some diseases of the spinal cord the 

 skin may be affected by warmth, but not by cold. The 

 sensations of cold and pressure seem to be usually lost 

 or retained together, while those of warmth and pain 

 have a similar connection. But more accurate results are 

 obtained by touching the skin with a blunt metal pencil, 

 warmed or cooled. 



Warm Spots and Cold Spots. If this be applied at 

 regular close intervals, it is found that some places feel the 

 warm point, while others feel the cold. In this way the 

 skin has been mapped out into "warm spots" (warmth- 

 perceiving spots) and "cold spots" (cold-perceiving spots), 

 and still other areas seem not sensitive to temperature. 



