EXPERIMENTAL PSYCHOLOGY 



known diseases of the spinal cord, with resulting paral- 

 ysis, it is the ganglion cells themselves that are found 

 to be destroyed. Similarly, in the case of sufferers 

 from chronic insanities, with marked dementia, the 

 ganglion cells of the cortex of the brain are found to 

 have undergone degeneration. The brains of pare tics 

 in particular show such degeneration, in striking corre- 

 spondence with their mental decadence. The position 

 of the ganglion cell as the ultimate centre of nervous 

 activities was thus placed beyond dispute. 



Meantime, general acceptance being given the histo- 

 logical scheme of Gerlach, according to which the mass 

 of the white substance of the brain is a mesh-work of 

 intercellular fibrils, a proximal idea seemed attainable 

 of the way in which the ganglionic activities are corre- 

 lated, and, through association, built up, so to speak, 

 into the higher mental processes. Such a conception 

 accorded beautifully with the ideas of the association- 

 ists, who had now become dominant in psychology. 

 But one standing puzzle attended this otherwise satis- 

 factory correlation of anatomical observations and 

 psychic analyses. It was this : Since, according to the 

 histologist, the intercellular fibres, along which im- 

 pulses are conveyed, connect each brain cell, directly or 

 indirectly, with every other brain cell in an endless 

 mesh- work, how is it possible that various sets of cells 

 may at times be shut off from one another? Such 

 isolation must take place, for all normal ideation de- 

 pends for its integrity quite as much upon the shutting- 

 out of the great mass of associations as upon the in- 

 clusion of certain other associations. For rx.miple, a 

 student in solving a mathematical problem must for 



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