XXXVI. THE SENSES 



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Nerves in the skin; a, nerve fiht-r ; b. tactile 

 papillae, containing a tactile corpuscle ; e, 

 papillae containing blood vessels. (After 

 Benda.) 



Touch. — In animals having a hard outside coverinpr, such as 

 certain worms, insects, and crustaceans, minute hairs, which are 

 sensitive to touch, are found growing out from the body covering. 

 At the base of these hairs are 

 found nerve cells which send 

 a nerve fiber inward to the 

 central nervous system. 



Organs of Touch. — In man, 

 the nervous mechanism which 

 governs touch, is located in 

 the folds of the dermis or in 

 the skin. Special nerve end- 

 ings, called the tactile corpus- 

 cles, are there found. They 

 are inclosed in a sheath, or 

 capsule, of connective tissue. 

 Inside is a complicated nerve ending, and ner\^e fibers are sent in- 

 ward to the central nervous system. The number of tactile cor- 

 puscles present in a given area of the skin determines the accuracy 

 and ease with which objects may be known by touch. 



If you test the different parts of the body, as the back of the liand. tho 

 neck, the skin of the arm, of the back, or the tip of the tonf^uc, witli a i)air 

 of open dividers, a vast difference in the accuracy with which tho two p(»ints 

 may be distinguished is noticed. On the tip of the tongue, tlio two points 

 need only be separated by 2V of an inch to be so distiiiKui.^hod. In the 

 small of the back, a distance of two inches may be reached before the 

 dividers feel like two points. 



Temperature, Pressure, Pain. — The feeling of temperature, 

 pressure, and pain, the latter only in part, are determined by organs 

 in the skin. Physiologists believe, however, that these organs are 

 distinct from the apparatus which distinguishes touch. 



Taste Organs. — The surface of the tongue is folded into a num- 

 ber of little projections known as papilhe. These may be more 



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