80 Can Science Explain Life? 



perceptions last only a small fraction of a second 

 but nevertheless make a permanent impression on 

 our memory, whereas to build up nerve fibrils of 

 any length by endwise growth of the spirazines 

 would require a considerable period of time. The 

 immediate effects of such sense perceptions on the 

 cerebral cortex must therefore consist of altera- 

 tions in the chemical structures of the fibrils 

 already present and not in the formation of new 

 fibrils. Since impulses which enter the brain can 

 only be in the form of electric currents, it is not 

 unlikely that they may effect some sort of activa- 

 tion of the associative fibrils, as a result of which 

 the latter may continue to generate similar poten- 

 tials in the future. Thus, when an electric impulse 

 from a sense-perception enters the cerebral cortex 

 the ions may force their way through the dormant 

 chemical structures which form the walls of the 

 fibrils of the gray matter and leave open but re- 

 stricted passageways in their wake which may 

 permit the subsequent migration of similar ions 

 in the same direction. Kecurrent impulses simi- 

 lar to those of the original sense-impression may 

 therefore be generated and will manifest them- 

 selves as thought or memory, unless they find an 

 outlet through the motor nerves in which case 

 they will manifest themselves as acts of volition. 



