Manchester Mevioirs, Vol. xlii. (1898), No. 1*^. 37 



by a distance at least not less than the distance between 

 two cones. Had the visual mechanism been such that 

 each chain of units, with a cone at one end and a receptive 

 cortical cell at the other, was quite separate from its 

 neighbours an anatomical explanation of separate sensa- 

 tions might have seemed possible. But such an explana- 

 tion, quite apart from all other objections, is rendered 

 impossible by the mingling just spoken of Obviously, 

 even supposing that a single cone can be stimulated 

 alone, all its neighbours remaining at rest, the effect will 

 become a diffuse one as it is propagated along the mecha- 

 nism ; and the effects of the simultaneous stimulation of 

 two cones, even at some distance apart, will overlap. I will 

 not attempt to discuss what are the conditions which really 

 determine that two sensations shall be distinct. I have 

 brought these matters forward because they seem to 

 further illustrate the incorrectness of the view, that a sen- 

 sation is brought about by nervous impulses reaching 

 some cortical station, and there becoming suddenly trans- 

 formed, as if there were a sort of mosaic of sensations 

 corresponding to the retinal mosaic. It would seem pro- 

 bable that, in the development of any visual sensation, 

 several elements, several units for example of the corpus 

 geniculatum are concerned. Further, the phenomena of 

 simultaneous contact shew that all those elements are not 

 concerned in the same way ; in some, effects are produced 

 which appear the very opposite to those produced in 

 others. And, indeed, there seem some reasons for 

 believing that no one spot of the retina can be affected by 

 light, without the whole mechanism, without the elements 

 connected with the whole retina, being also affected in 

 some way or other at the same time. 



Assuming the truth of the view which I put before you 

 at an early part of the lecture, that differentiation of action 

 takes place not in any part of a unit rather than in any 



