362 THE BODY AT WORK 



affords no ground for the explanation of mental images, 

 hallucinations, dreams. A few lines may be spared to show 

 that this objection does not hold. We cannot attempt to 

 explain the conscious control of thought. It is a part of the 

 impenetrable mystery to which we have just referred. But, 

 granted that it obtains, the direction by the ego of afferent 

 nerve-currents through the same strands which formerly 

 vibrated to sensations which drew a picture, and hence the 

 revival of its image, is no more incomprehensible than the 

 liberation of afferent impulses from muscles into efferent 

 channels. Brain-chains are composed of many links. Their 

 interconnection is illimitable. When I recall the appearance 

 of the house in which I lived as a child, I throw into the chain 

 impulses (from somewhere) which traverse the final links, where 

 passage implies consciousness. At the edge of the lace-work of 

 linked threads the impulses light up a pattern which child- 

 hood's experience worked into the apparatus of thought. 



If we were to admire the perfection of any special aspect 

 of the brain's functioning, the rarity of hallucinations might 

 give us cause for wonder. That impulses so seldom leave their 

 own paths is more astonishing than that occasionally, when the 

 brain is excited and its nutritive conditions deranged, the 

 impulses which the ego can direct into channels where they 

 revive an image should sometimes, and with far greater force, 

 make their own way down well-worn paths, lighting up a 

 picture which deceives the ego. Dreams, by contrast, throw 

 up in a strong light the part played by attention in intelligent 

 life. The capacity for alertness is due to the favouring of one 

 set of impulses by suppressing others. The favoured impulses 

 hold the road. Concentration of attention is keeping thought 

 to one line by resisting all temptation to wander into by-paths. 

 The waking condition is the state in which all nerve-ways are 

 closed, with the exception of those which consciousness is 

 using. The more severe the closure, the more vivid is con- 

 sciousness. In sleep all paths are open. In none is the 

 potential acquired by impulses in the process of overcoming 

 resistance high enough to evoke consciousness. A burst of 

 impulses ascends from the stomach, set a-flowing by undigested 

 fragments of salmon and cucumber, or mounts from the arm on 

 which the sleeper has been lying until its circulation has been 



