248 THE SPECIAL SENSES 



touch corpuscles are found in such structures as the 

 muscles, tendons and internal organs, and serve the same 

 purpose. 



When pressure is applied, to the skin, the elastic touch 

 corpuscles are so pressed out of shape that they press 

 upon the nerve ends. Nervous impulses are thereby 

 started, which pass up the sensory neurons, until on 

 reaching the cortex they excite certain of its nerve cells, 

 and thus give rise to sensations of touch. 



Other dermal senses. Although we do not under- 

 stand the mechanisms by which sensations of heat, cold 

 and pain are produced, yet the sensations themselves 



are so definite as to leave no 

 doubt that each has a special 

 end organ which responds to 

 the application of heat or cold 

 or harmful contact. Distinct 

 points in the skin have been 

 found which, when touched with 



FIG. 133. Diagram of a piece n -, 



of skin showing arrangement a Cold object Or 6V6U when 







v* <> 



pressed, give a sensation of 

 cold. Others when touched 



with a warm object give a sensation of heat; and still 

 others when firmly pressed give a sensation of pain. So 

 definite and specific are these points that pressure by a 

 warm point upon a * ' cold spot ' ' will produce a sensation 

 of cold. 1 



Fatigue. As in all the special senses, these mechan- 

 isms are so delicate that they quickly get tired out and 

 do not respond to stimulation. For example, a feel- 

 ing of cold or chilliness may be experienced by one who 

 is constantly overclothed, apparently because the heat 



1 The heat spots are much more difficult to locate than the cold. 



