SENSE OF LOCALITY. 539 



not tactile impressions, and that in the spinal cord the sensory and 

 tactile impulses pass along distinct tracts. Further, certain nar- 

 cotic poisons destroy ordinary sensation without removing the sense 

 of touch. This effect is also brought about by cold, when for in- 

 stance the fingers are benumbed, gentle contact excites tactile im- 

 pressions, while the ordinary sensations of pain can only be aroused 

 with difficulty even by severe pressure. 



However, most of the nerves we are in the habit of calling sen- 

 sory 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 con- 

 sider 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 



