30 DEVELOPMENT AND PURPOSE CHAP. 



cesses of neighbouring cells. 1 We explore the brain fruit- 

 lessly for any one centre to which all things are brought and 

 from which all start anew. What we find is myriad on 

 myriad of ramifications so arranged that any disturbance 

 may propagate itself through the whole area and awake 

 response from any cell whose stored-up energies are sensi- 

 tive to its stimulus. Undoubtedly there must be precise 

 conditions determining which cells will respond to a given 

 stimulus and in what way. But as to this we know only 

 the broad empirical fact that the response is in general one 

 that is suitable or at least relevant to the situation, and that 

 the effectiveness of the response depends on the main- 

 tenance of functional continuity between the nerve fibres 

 which constitute the paths of communication. The central 

 system appears in short as an exceedingly complex system 

 of intercommunication, by means of which, to put the 

 matter in very general terms, any element in our experience 

 may be brought into relation with the whole mass of our 

 stored-up energies in such a way as to facilitate orderly and 

 consecutive action. 



The matter may be made a little clearer by reverting to 

 the scheme of reflex action and its inhibition as ordinarily 

 described. If I withdraw my hand sharply from contact 

 with a hot object the process is explained physically as a 

 reflex. The contact with the skin is held to send a nerve 

 excitement to a c sensory ' cell, which again propagates it to 

 c motor ' cells, which in turn give rise to impulses descend- 

 ing the motor nerves and resulting in muscular contractions 

 of the hand and arm. But if it is a point of honour or of 

 safety not to flinch but to hold on, what happens physically, 

 it is conceived, is that the excitement in the sensory cell 

 passes along other fibres besides those which lead to the 

 motor area ; that it awakens in turn other cells in different 

 portions of the brain, and that these by one or other of the 



1 The available evidence goes to show that the processes of different 

 nerve-elements are not, in vertebrates, in actual contact. The point 

 of interconnection between them is called a synapse, and it is probable 

 that to pass the synapse the excitement has to overcome a certain 

 resistance, the strength of which, as compared with the resistance at 

 other synapses by which the excitement might find outlet, is probably of 

 high importance in determining its path. 



