SENSE OF LOCALITY. 541 



sensory nerves convey tactile impressions, and, speaking generally, 

 the parts of the outer skin which have the keenest tactile sense 

 are also the most ready to excite feelings of pain. 



The intensity of the stimulation for the sense of touch must 

 be kept within certain limits in order that it be adequate, i. e., 

 capable of exciting the specific mental perceptions. If the 

 stimulus exceed these limits, only a general impression, namely, 

 that of pain, is produced. 



The power of forming judgments by feeling an object differs 

 very much in different parts of the body, being generally most 

 keen where the surface is richest in touch corpuscles, namely, the 

 palmar aspect of the hands and feet, and especially the finger 

 tips, the tongue, the lips, and the face. 



When we feel a thing in order to learn its properties, we make 

 use of all the qualities of which our sense of touch is made up. 

 We estimate the number of points at which it impinges on our 

 finger tip, we rub it to judge of smoothness, we press it to find 

 out its hardness, and at the same time we gain some knowledge of 

 its temperature and power of absorbing heat. 



To get a clear idea of our complex sense of touch we must 

 consider each of the different kinds of impressions separately. 



SENSE OF LOCALITY. 



By this is meant our power of judging the exact position of 

 any point or points of contact which may be applied to the skin. 

 Thus, if the point of a pin be gently laid on a sensitive part of 

 the skin, we know at once when we are touched, and, if a second 

 pin be applied in the same neighborhood, we feel the two points 

 of contact, and can judge of their distance from one another and 

 their relative position. When we feel a body, we receive impulses 

 from many points of contact bearing varied relationships to each 

 other, and thus we become conscious of a rough or a smooth 

 surface. 



The delicacy of the sense of locality differs very much in dif- 

 ferent parts of the skin. It is most accurate in those parts which 

 have been used as touch organs during the slow evolution of the 

 animal kingdom. 



