514 PSYCHOLOOT. 



oue of tliese spots and ah, and the other and ef. Volkmann'8 

 experiments show this. He and Fechner, prompted by 

 Czermak's observation that the skin of the blind was twice 

 as discriminative as that of seeing folks, sought by experi- 

 ment to shoAv the eftects of practice ujDon themselves. They 

 discovered that even within the limits of a single sitting 

 the distances at which points were felt double might fall 

 at the end to considerably less than half of their magnitude 

 at the beginning ; and that some, though not all, of this 

 improved sensibility was retained next day. But they 

 also found that exercising one part of the skin in this way 

 improved the discrimination not only of the corresponding 

 part of the opposite side of the body, but of the neighbor- 

 ing parts as well. Thus, at the beginning of an experimen- 

 tal sitting, the compass-points had to be a Paris line asun- 

 der, in order to be distinguished by the little-finger-tip. 

 But after exercising the other fingers, it was 'found that the 

 little-finger-tip could discriminate points only half a line 

 apart.* The same relation existed betwixt divers points of 

 the arm and hand.f 



Here it is clear that the cause which I first suggested 

 fails to apply, and that we must invoke another. 



What are the exact experimental i3lienomena? The 

 spots, as such, are not distinctly located, and the difference, 

 as such, between their feelings, is not distinctly felt, until 

 the interval is greater than the minimum required for the 

 mere perception of their douhleness. "What we first feel is a 

 bluntness, then a suspicion of doubleness, which presently 

 becomes a distinct doubleness, and at last two different- 

 feeling and differently placed spots with a definite tract of 

 space between them. Some of the places we try give us 

 this latest stage of the perception immediately ; some only 

 give us the earliest ; and between them are intermediary 

 places. But as soon as the image of the doubleness as it is 

 felt in the more discriminative places gets lodged in our 

 memory, it helps us to find its like in places where other- 

 wise we might have missed it, much as the recent hearing of 



* A. W. Volkmann : Ueber den Einfluss der Uebung, etc., Leipzig Be- 

 nch te, Math.-pbys. Classe, x, 1858, p. 67. 

 \lbid., Tabellel.p. 43. 



