74 PSYCHOLOGY. 



Now if we admit that sensation and imagination are due 

 to the activity of the same centres in the cortex, we can see a 

 very good teleological reason why they should correspond 

 to discrete kinds of process in these centres, and why the 

 process which gives the sense that the object is really there 

 ought normally to be arousable only by currents entering 

 from the periphery and not by currents from the neighbor- 

 ing cortical parts. We can see, in short, why tlie sensational 

 process ought to be discontinuous with all normal ideational 

 processes, hoivever intense. For, as Dr. Mlinsterberg justly 

 observes : 



" Were there not this peculiar arrangement we should not distinguish 

 reality and fantasy, our conduct would not be accommodated to the 

 facts about us, but would be inappropriate and senseless, and we could 

 not keep ourselves alive. . . . That our thoughts and memories should 

 be copies of sensations with their intensity greatly reduced is thus a 

 consequence deducible logically from the natural adaptation of the 

 cerebral mechanism to its environment."* 



Mechanically the discontinuity between the ideational 

 and the sensational kinds of process must mean that when 

 the greatest ideational intensity has been reached, an order 

 of resistance presents itself which only a new order of force 

 can break through. The current from the periphery is the 

 new order of force required ; and what happens after the 

 resistance is overcome is the sensational process. We may 

 suppose that the latter consists in some new and more vio- 

 lent sort of disintegration of the neural matter, which now 

 explodes at a deeper level than at other times. 



Now how shall we conceive of the ' resistance ' which 

 prevents this sort of disintegration from taking place, this 

 sort of intensity in the process from being attained, so 

 much of the time ? It must be either an intrinsic resist- 

 ance, some force of cohesion in the neural molecules them- 

 selves ; or an extrinsic influence, due to other cortical cells. 

 When we come to study the process of hallucination we 

 shall see that both factors must be taken into account. 

 There is a degree of inward molecular cohesion in our 

 brain-cells which it probably takes a sudden inrush of 



*Die Willenshandhing (1888), pp. 129-40. 



