40 Foster, Physical Basis of Psychical Events, 



analogous to that between electric induction and con- 

 duction. But this, it must be remembered, is nothing 

 more than a vague illustration. 



I have alluded to this bridge because, recently, great 

 importance has been attached to the possibility of the 

 transference of one unit to another being directly and 

 boldly modified through the bridge being made longer or 

 shorter by the physiological processes of contraction and 

 relaxation of the nervous material. In the case of many 

 cells, notably the pyramidal cells of the cortex, the den- 

 drites are furnished with minute, rod-like appendages, 

 sometimes spoken of as "thorns." Now, making every 

 allowance for changes in appearance being simply 

 the result of differences in the mode of preparation of 

 microscopical specimens (and the technique of the micros- 

 copical study of nervous structures is undoubtedly com- 

 plex and uncertain), it seems to be established that these 

 minute appendages while at one time conspicuous, may 

 be at other times inconspicuous, as if they had been with- 

 drawn or retracted. And it is maintained that the retracted 

 condition may be brought about by influences, generally 

 rough and powerful ones, such as electric shocks or poisons 

 brought to bear on the nervous system, or even on the 

 organism as a whole. The retraction of such an 

 appendage will increase the length of the bridge spoken 

 of above, or will establish a bridge where no obvious one 

 existed before, and hence may be supposed largely to 

 modify, or even to abolish altogether the transference 

 of neural events from one unit to another. And, indeed, 

 some writers have boldly used this phenomenon as a 

 mechanical explanation of neural, and so, of psychical 

 events. It has been suggested, for instance, that, as the 

 result of fatigue, these appendages to the dendrites of a 

 cortical cell are retracted after prolonged activity of the 

 cell, that the transference of neural changes from the 



