SENSE OF TOUCH. 2OQ 



Function. Governs all the movements of the tongue and influences the 

 functions of mastication, deglutition and articulation. 



THE SENSE OF TOUCH. 



The sense of touch is a modification of general sensibility, and is located 

 in the skin, which is especially adapted for this purpose on account of the 

 number of nerves and papillary elevations it possesses. The structures of the 

 skin and the modes of termination of the sensory nerves have already been 

 considered. 



The tactile sensibility varies in acuteness in different portions of the body, 

 being most marked in those regions in which the tactile corpuscles are most 

 abundant e. g., the palmar surface of the third phalanges of the fingers and 

 thumb. 



The relative sensibility of different portions of the body has been ascertained 

 by means of a pair of compasses: the points of the instrument being guarded 

 by cork, it was then determined how closely they could be brought together, 

 and yet be felt at two different points. The following are some of the measure- 

 ments: 



Point of tongue J of a line. 



Palmar surface of third phalanx i line. 



Red surface of lips 2 lines. 



Palmar surface of metacarpus 3 lines. 



Tip of the nose 3 lines. 



Part of lips covered by skin 4 lines. 



Palm of hand 5 lines. 



Lower part of forehead 10 lines. 



Back of hand 14 lines. 



Dorsum of foot 18 lines. 



Middle of the thigh 30 lines. 



The sense of touch communicates to the mind the idea of resistance only, 

 and the varying degrees of resistance offered to the sensory nerves enable ur 

 to estimate, with the aid of the muscular sense, the qualities of hardness so 

 softness of external objects. The idea of space or extension is obtained when 

 the sensory surface or the external object changes its place in regard to the 

 other; the character of the surface, its roughness or smoothness, is estimated 

 by the impressions made upon the tactile papillae. 



Appreciation of Temperature. The general surface of the body is more or 

 less sensitive to differences of temperature, though this sensation is separate 

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