68 Dr Graves on the Sense of Touch. 



skin, these two points excite but one sensation, and are by the 

 touch erroneously judged to be but one. Thus the tips of the 

 fingers and the point of the tongue were found to possess the 

 most accurate sense of touch, for when the points were dis- 

 tant but half a Parisian line from each other (counting from the 

 inner surface of each point), the feeling of the two distant points 

 existed, and when they were within two-fifths of a line, although 

 the person seemed to feel but one body, he nevertheless felt it 

 to be longer in one direction than in another. The dorsum of 

 the tongue was remarkably less sensible, for if the points placed 

 m a line parallel to the median were less distant than three lines 

 from each other, they were not felt to be distant. Few persons 

 who have not tried similar experiments will he prepared to credit 

 the announcement of the very great difference which exists hetzveen 

 the tactile accuracy of different portions of the shifi. On this sub- 

 ject the observations of Weber are quite novel, and open a new 

 field for inquiry, not only to the physiologist, but to the practi- 

 cal physician and surgeon ; for it is obvious that injuries or re- 

 medies applied to the skin must act with very different degrees 

 of energy on parts so widely different in tactile sensibility from 

 each other. I have repeated many of Weber's experiments, and 

 confirmed his results. A little practice is necessary in order to 

 accustom ourselves to judge concerning the sensation, compared 

 as the points of the compass approach each other, and come 

 within the limits of confusion (a term I have adopted to express 

 the distance at which they produce the feeling of but one bod}-, 

 longer, however, in one direction than another). The sensation 

 imparted is most curious. A few instances will suffice to prove the 

 extent of the scale through which this limit of confusion ranges, 

 when the points are placed on the same horizontal line. 



Tip of the tongue 1 line. Margin of tongue, one inch from 

 its tip, 2 hues. Skin on the zygomatic bone, 6 lines. Forehead, 

 6 lines. Hairy scalp, 8 lines. Middle of back, 12 lines. Near 

 the upper border of the scapula, 18 lines. Inferior angle of the 

 scapula, 24} lines. On the loins, 12 fines. Side of abdomen, 12 

 lines. Anterior surface of arm, 10 lines. Posterior do. 14. 

 lines. Tips of the fingers, 1 fine. Do. of toes, 3 lines. 



The above results were obtained in examining the skin of 

 others. The followinor, which Weber has arranged in the ascend- 



