332 THE HUMAN BODY. 



tion; touch proper, heat and cold, and pain; and we can 

 with more or less accuracy localize them on the surface of 

 the body. The interior of the mouth possesses also these 

 sensibilities. Through touch proper we recognize pressure 

 or traction exerted on the skin, and the force of the pres- 

 sure; the softness or hardness, roughness or smoothness, of 

 the body producing it; and the form of this, when not too 

 large to be felt all over. 



The delicacy of the tactile sense varies on different parts 

 of the skin; it is greatest on the forehead and temples, 

 where a weight of y^ of a grain can be felt. 



The Localization of Skin Sensations. When the eyes are 

 closed and a point of the skin is touched we can with some 

 accuracy indicate the region stimulated; although tactile 

 feelings are alike in general characters, they differ in some- 

 thing (local sign) besides intensity by which we can distin- 

 guish them as originated on different parts of the skin. 

 The accuracy of the localizing power varies widely in dif- 

 ferent skin regions, and is measured by observing the least 

 distance which must separate two objects (as the blunted 

 points of a pair of compasses) in order that they may be 

 felt as two. The following table illustrates some of the 

 differences observed: 



Tongue-tip 04 inch 



Palm side of last phalanx of finger 08 " 



Red part of lips 16 " 



Tip of nose 24 " 



Back of second phalanx of finger 44 " 



Heel 88 



What sensations do we get through the skin? Name another part 

 of the body which also gives rise to these sensations. What do we 

 recognize by means of the sense of touch? 



Where is the tactile sense most acute? 



What is meant by the localization of skin sensations? Does the ac- 

 curacy of localization differ in different regions of the skin? Illustrate, 



