170 PSTCHOLOGT. 



I should have been willing some years ago to name with- 

 out hesitation a third condition of discrimination — saying it 

 would be most developed in that organ which is susceptible 

 of the most various qualities of feeling. The retina is un- 

 questionably such an organ. The colors and shades it 

 perceives are infinitely more numerous than the diversities 

 of skin -sensation. And it can feel at once white and black, 

 whilst the ear can in nowise so feel sound and silence. But 

 the late researches of Donaldson, Blix, and Goldscheider, * 

 on specific points for heat, cold, pressure, and pain in the 

 skin ; the older ones of Czermak (repeated later by Klug 

 in Ludwig's laboratory), showing that a hot and a cold 

 compass-point are no more easily discriminated as two than 

 two of equal temperature ; and some unpublished experi- 

 ments of my own — all disincline me to make much of this 

 condition now.f There is, however, one quality of sensa- 



this article than give up those principles for the sake of any hypothesis 

 hitherto published about either organs of Corti or basilar membrane." 

 Professor Rutherford's theory of hearing, advanced at the meeting of the 

 British Association for 1886, already furnishes an alternative view vrhich 

 would make hearing present no exception to the space-theory I defend- 

 and which, whether destined to be proved true or false, ought, at any rate 

 to make us feel that the Helmholtzian theory is probably not the last wora 

 in the physiology of hearing. Stepano, ff. (Hermann und Schwalbe's Jahres- 

 bericht, xv. 404, Literature 1886) reports a case in which more than the 

 upper half of one cochlea was lost without any such deafness to deep notes 

 on that side as Helmholtz's theory would require. 



* Donaldson, in Mind, x. 399, 577; Gold.scheider, in Arcbiv f. (Anat. u.) 

 Physiologic; Blix, in Zeitschrift fiir Biologic. A good resume may be 

 found in Ladd's Physiol. Psychology, part ii. chap. iv. §§ 21-23. 



f I tried on nine or ten people, making numerous observations on each, 

 what difference it made in the discrimination of two points to have them 

 alike or unlike. The points chosen were (1) two large needle-heads, (2) 

 two screw-heads, and (3) a needle-head and a screw-head. The distance 

 of the screw-heads was measured from their centres. I found that when 

 the points gave diverse qualities of feeling (as in 3), this facilitated the 

 discrimination, but much less strongly than I expected. The difference, 

 in fact, would often not be perceptible twenty times running. When, 

 however, one of the points was endowed with a rotary movement, the 

 other remaining still, the doubleness of the points became much more evi- 

 dent than before. To observe this I took an ordinary pair of compasses with 

 one point blunt, and the movable leg replaced by a metallic rod which could, 

 at any moment, be made to rotate in situ by a dentist's drilling-machine, to 

 which it was attached. The compass had then its points applied to the skin 

 at such a distance apart as to be felt as one impression. Suddenly rotating 

 the drill-apparatus then almost always made them seem as two. 



