12 MATHEMATICAL BIOPHYSICS OF THE CENTRAL NERVOUS SYSTEM 



S , coming, perhaps, from self-exciting circuits (chap, iv), is applied 

 to each of the intermediate neurons of the chain, and if the linear 

 representation is adequate the properties of the chain can be made ex- 

 actly the same as those of an individual neuron. Thus it is legitimate to 

 speak of two centers as connected by a single neuron even when it 

 would be more plausible on anatomical grounds to suppose that an 

 entire chain is required. On the other hand, chains can exhibit prop- 

 erties quite different from those of a single neuron, since, in particu- 

 lar, more variables enter, as is clear from equations (9) and (10). 



The utility of the notion of accessibility will become more appar- 

 ent when the general net is discussed in chapter v, but it is perhaps 

 sufficiently evident already that the properties of very complicated 

 nets might in special cases turn out to be very simple because of the 

 inaccessibility of certain centers to certain others. It is evident, too, 

 that whereas we have discussed accessibility only in connection with 

 the linear representation of <j>(S), very similar results must hold 

 in general. 



