THE NERVOUS SYSTEM 355 



" impulse " is too heavily weighted by its association with the 

 idea of currents which are strong enough to prove effective 

 without the intervention of consciousness ; but no other is 

 available. They ring the bell of consciousness, however little 

 may be the attention which their summons secures. Atten- 

 tion cannot be directed to two things simultaneously. It 

 moves, as it were, on a succession of points. On some it rests 

 longer than on others. They make an impression which can 

 be recalled ; the rest being passed by so rapidly that they are 

 not remembered, it is as if they had never been perceived. 

 They blend, as a succession of moving lights blend, in pro- 

 ducing a background to consciousness. Not recognizing their 

 separateness, we interpret them as fused. A good deal of 

 misleading metaphor has been used, as it seems to the writer, 

 in accounting for the effect upon the mind of impressions 

 which make but a weak demand upon attention. They are 

 spoken of as " marginal " perceptions, from the analogy of the 

 ineffectiveness of impulses generated at the periphery of the 

 retina, as compared with those which give rise to direct vision. 

 A " subconscious," or even " unconscious," self is evoked. The 

 self cannot be less than conscious. Self is the passage of atten- 

 tion from sensation to sensation. Its relation to the not-self 

 is temporal, not spatial. 



Every sensation which is called up into consciousness, though 

 it occupy attention for the shortest possible time, tends to give 

 rise to movement is, indeed, in its very nature an impulse 

 flowing through a sensori-motor arc. The circuit for the 

 voluntary execution of a movement is represented as flowing 

 through kin aesthetic-movement arcs. This may be necessary 

 for volitional actions, but it is not essential for reflex actions. A 

 spinal frog will remove an irritant from its back with its hind- 

 leg, after the roots of all the afferent nerves of the hind-leg 

 have been cut. In this case the reflex is direct, from injured 

 skin to muscles of the leg. It is not double muscular sensa- 

 tions from the leg, liberated into efferent leg-muscle-nerves by 

 skin-sensations originated simultaneously in a part anterior 

 to the segments in which the roots have been cut. 



The unit of sensation to which attention can be directed has 

 yet to be defined. Like sensations sensations which are 

 correlated in experience, that is to say seem to fuse in con- 



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