SPACE II 



ordinarily sensitive to touch, and by its agency we test not 

 so much the nature of the external resistance (for that we 

 use in preference the ball of the finger) as its position in space. 

 In so doing, we ignore what the local signs have to tell us 

 about the place of our body ; to give us that, the inner 

 direction-signs link up directly with the sensations of touch, 

 and the sensation of " pressure there " no longer means 

 pressure on the forefinger, but pressure at that point in space. 



NATURE OF THE DIRECTION-SIGNS 



It can easily be shown that the determination of the point 

 in space depends simply on the voluntary direction-signs, 

 i.e. on the direction-signs connected with muscular activity 

 called forth by our nerve impulses; The proof of this is as 

 follows. Make the little finger bend itself over to the inner 

 side of the adjacent ring-finger ; then shut your eyes and 

 press the edge of a card on the balls of both fingers ; you 

 will feel one straight edge. Now with the other hand move 

 the same finger across the ring-finger (scarcely further than it 

 was able to go unaided), hold it firmly in this position with 

 the ring-finger, and now press the same card on the balls 

 of the fingers : if your eyes are shut, you will this time feel 

 two cards. The illusion disappears when the eyes are opened, 

 because the eye at once makes ^the correction. 



To the same cause is referable the well-known experiment 

 of transforming one ball into two by touching it simul- 

 taneously with the index- and middle-fingers crossed over 

 one another. 



From all of which it may confidently be inferred that the 

 very definite sensations coming from the joints and their 

 ligaments, although themselves localised, have no direction- 

 signs to inform us as to the position of the finger. The 



