THE STORY OF NINETEENTH-CENTURY SCIENCE 



discovery lie, deraonstrably, in the gray cortex of the 

 brain, not in the white matter. But the full proof came 

 from pathology. At the hands of a multitude of ob- 

 servers it was shown that in certain well-known diseases 

 of the spinal cord, with resulting paralysis, it is the 

 ganglion cells themselves that are found to be destroyed. 

 Similarly, in the case of sufferers from chronic insani- 

 ties, with marked dementia, the ganglion cells of the 

 cortex of the brain are found to have undergone degen- 

 eration. The brains of paretics in particular show such 

 degeneration, in striking correspondence with their men- 

 tal decadence. The position of the ganglion cell as the 

 ultimate centre of nervous activities was thus placed be- 

 yond 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 ganglion ic activities are corre- 

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

 into the higher mental processes. Such a conception ac- 

 corded beautifully with the ideas of the association ists, 

 who had now become dominant in psychology. But 

 one standing puzzle attended this otherwise satisfactory 

 correlation of anatomical observations and psychic anal- 

 yses. It was this: Since, according to the histologist, 

 the intercellular fibres, along which impulses are con- 

 veyed, 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 depends for its integ- 

 rity quite as much upon the shutting out of the givnt 



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