290 



ELEMENTS OF PHYSIOLOGY 



531, Temperature. This part of the sense of touch is 

 located only in certain points or spots, called heat spots 



and cold spots, situated a 

 small fraction of an inch 

 apart (Fig. 198). Some 

 spots give a sensation of 

 heat only, and some of 

 cold only. The sense is 

 so delicate that a differ- 

 ence of \ of a degree of 



FIG. 197. Four Papillae of the True Skin, 



magnified. The epidermis has been re- temperature between two 

 moved. Most papillae contain touch cor- objects Can be detected. 



Extremely hot and cold 



objects injure the tissues and do not give sensations of 

 temperature, but only of pain. 



532. Pain. A sensation 

 greatly increased or often re- 

 peated becomes unpleasant 

 and is called pain. The same 

 physical influence may be 

 felt at one time as a pleasant 

 touch, and at another time as 

 a pain, depending upon the 

 state of the nerve tissue. 

 When an influence is becom- 

 ing strong enough to endan- 

 ger the body, the simple 

 sensation of touch becomes 

 changed into one of pain 

 and warns us to avoid the 

 danger. When a nerve is 

 laid bare and touched, or cut 

 midway in its course, the feel- 

 ing is not one of touch, but of pain. Pain is a protection, 

 and therefore more of a good than an evil. In many 



FIG. 198. Cutaneous "Cold" Spots 

 (light shading) and "Hot" Spots 

 (dark shading) ; Anterior Surface of 

 the Thigh. 



