CHAPTER XL VIII 

 THE SPECIAL SENSES 



General. It is quite essential that we receive some 

 very definite information in regard to the world out- 

 side of ourselves. For this we depend upon the so- 

 called special senses. Originally there were thought to 

 be just five of these, feeling, tasting, smelling, seeing, 

 and hearing. To these, however, we must add some 

 others, especially the sense of temperature and of pain. 

 For the purpose of receiving impressions from the out- 

 side world and then of converting them into nerve cur- 

 rents we have highly specialized organs, such as the eye 

 and the ear. 



Touch. The sense of touch is the most widely dis- 

 tributed of the special senses, for all parts of the skin, 

 the tongue, and the mucous membrane of the mouth 

 and nose are sensitive to touch. In the dermis of the 

 skin there are many minute elevations called papillae. 

 In some of these there are modified structures contain- 

 ing the ends of nerves of touch, called touch corpuscles. 



In some parts of the body these corpuscles are very 

 close together so that the sense of touch is keen. In 

 other parts they are far apart so that the sense of touch 

 is dull. The degree of sensitiveness of the various parts 



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