LOCAL SIGN. 289 



thus projected, as it were, on the cortex of the brain, tactile 

 centers for the hind leg, fore leg, neck, eye, ear, trunk, etc. ; 

 and it follows that each point of the skin has a corresponding 

 point in the cerebral cortex. Thus for each stimulation of a 

 point of the cerebral cortex there is a Local Sign, and thus we 

 localize tactile impressions." The accuracy varies, and is 

 ordinarily keenest where the nerves are most numerous. 

 Where the sense of locality seems to be improved by cultiva- 

 tion, this appears to be due to keener discrimination in the 

 brain-cells, and not to changes in the nerves or nerve endings. 

 This is indicated in the fact that if the fingers of one hand 

 become more discriminating by practice, it will be found that 

 the fingers of the other hand, without special training, are also 

 improved. 



The delicacy of localizing touch is usually tested in this 

 way. The blunted points of a light pair of compasses are 

 allowed to rest gently on the skin of various parts of the 

 body. If the two points are very close together they will be 

 felt as one pressure. That part which can best distinguish, as 

 two points of touch, these blunt points, is considered the 

 most sensitive. By this test the tip of the tongue is the 

 most sensitive, being able to distinguish, as two separate 

 points of contact, the tips of the compasses when only one 

 twenty-fifth part of an inch apart. Following is the order of 

 degrees of sensitiveness : tip of tongue, tips of fingers, lip, tip 

 of nose, eyelid, cheek, forehead, knee, neck ; while the middle 

 of the back seems least sensitive, the two points not produ- 

 cing two distinct sensations until they are more than two and 

 a half inches apart. In general those parts which are most 

 used, and those parts which are more freely movable, are most 

 sensitive ; for instance, the knee is much more sensitive than 

 the middle of the thigh or the middle of the leg, and the 

 elbow than the middle of the arm or forearm. If the compass 



